support for water sector plan development
TRANSCRIPT
Support for water sector plan
development – Garissa County Assessment of the water availability and demand
Kenya RAPID Program
Oct 12, 2017
Draft report
ii
Draft report
Colophon
Document title . Support for water sector plan development
Client . Millennium Water Alliance
Status . Draft report
Datum . Oct 12, 2017
Project number . 611
Author(s) . S. Burger, D. Benedicto van Dalen, S. de Wildt,
R.C. van der Meulen
Executive summary
This report is established to support informed decision making and strategies for
sustainable development and use of water sources and infrastructure for multiple users
in Garissa County. It is based on the principles of Integrated Water Resources
Management (IWRM), taking into account all main elements determining the water
availability in the current situation and in the future. It will support decisions on which
kind of resource (e.g. groundwater abstraction or rainwater harvesting) can best be
developed for which kind of specific use in time and space.
The water demand analysis for Garissa County shows that the total water demand is very
small (less than 1%) compared to the three months with rainwater surplus in an average
rainfall year (April, May and November). To meet the water demand necessities, decision
makers need to face the challenge of planning and developing infrastructure based on
the principles of IWRM. The different demands need to be met not only in terms of
quantity and quality, but also in terms of time and space. Rainwater harvesting is
therefore the most sustainable way, since it is the largest water input and recharged
every year. Other opportunities can be found in the use of river discharge and the
groundwater resources. Both need to be evaluated carefully to be developed in a
sustainable way to avoid overexploitation and generate conflict among the different
users group.
The biophysical landscape of Garissa County also provides very effective, low-cost
alternatives for the harvesting and buffering of (rain) water through 3R measures,
especially for times of high needs (droughts). In Garissa County storage of rainwater
mainly on the ground, and in some parts also in the ground shows a lot of potential for
interventions such as road water harvesting, water pans and sand dams.
Support for water sector plan development - iii -
Table of contents
1 Introduction ..................................................................................................................... 1
2 Biophysical landscape................................................................................................... 2
Topography .................................................................................................................................... 2
Soils .................................................................................................................................................. 4
Land use .......................................................................................................................................... 6
Vegetation Index ........................................................................................................................... 6
Nature reserves ............................................................................................................................. 9
Geology ............................................................................................................................................ 9
3 Water availability .......................................................................................................... 11
Introduction ................................................................................................................................ 11
Precipitation ................................................................................................................................ 11
Evapotranspiration .................................................................................................................... 13
Net precipitation ........................................................................................................................ 14
River in & outflow ...................................................................................................................... 16
Groundwater resources ........................................................................................................... 18
Water quality ............................................................................................................................... 21
Water budget ............................................................................................................................... 23
4 Demand for multiple uses ............................................................................................ 24
Introduction ................................................................................................................................ 24
Domestic water demand .......................................................................................................... 24
Livestock drinking water demand ........................................................................................ 25
Rangeland water demand ........................................................................................................ 26
Agricultural water demand ..................................................................................................... 26
Wildlife drinking water ............................................................................................................ 27
Industrial water demand ......................................................................................................... 27
Conclusions on demand .......................................................................................................... 28
5 Integrating water availability and demand .............................................................. 30
Introduction ................................................................................................................................ 30
County scale balances .............................................................................................................. 30
Requirements, opportunities and challenges for meeting the water needs ............. 31
Linking water resources to demand ..................................................................................... 34
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Draft report
3R potential (landscape approach) ....................................................................................... 36
Deep groundwater potential .................................................................................................. 38
Grazing area potential map .................................................................................................... 40
6 Conclusions and recommendations .......................................................................... 44
Water demand and availability .............................................................................................. 44
Development of water use ...................................................................................................... 44
Water potential ........................................................................................................................... 46
Stakeholder engagement and policy integration .............................................................. 47
7 Literature ........................................................................................................................ 48
Annex 1: Calculation Water Need Tool ............................................................................. 50
Annex 2: 3R potential map .................................................................................................. 55
Annex 3: Background information BGS groundwater potential maps........................... 57
Annex 4: Sustainable agriculture in arid land ................................................................... 59
Support for water sector plan development - 1 -
1 Introduction
The goal of the Acacia Water part of the Kenya RAPID program is to support informed
decision making for policy development, and to support strategies for responsible
development and use of water sources for multiple uses. Our vision is that it will be an
integral approach, taking into account all main elements of the water demand now and
in the future and all main resources of water, so that well informed decisions for a
sustainable water supply can be made. For this an assessment framework is required to
support decisions on which kind of resource (e.g. groundwater abstraction, or rainwater
harvesting) can best be developed for which kind of use. An order of magnitude
methodology, rather than a detailed study of one of the elements, provides insight in the
full range of available resources and the natural capacity for development in the region.
Approach
The role of Acacia Water in the Kenya RAPID program is the expert partner on
biophysical and hydrogeological data requirements and information collection. Acacia
Water will assist counties to interpret the data into knowledge to support informed
decision making for policy development, and to responsibly develop and utilize existing
water sources for multiple uses through locally appropriate technologies. Existing data
available will be combined to support improved decision-making on integrated water
management of the counties.
The methodology presented in this report provides insight in the balance between the
multiple demands and supplies, the potential and the difficulties to fulfil the demand
with existing resources, the feasible infrastructure, and the potential for growth based
on the availability of the natural resources.
In line with the current livelihoods, we focus on the domestic and livestock demand and
provide additionally an indication of the possibilities for agricultural development.
Water requests from other sectors (such as industrial water demand and mining) are
mostly not available, and should be estimated based on the known data in Garissa
County.
How to read this report
Chapter 2 presents all data collected and analysed which is the base for understanding
the hydrology and hydrogeology of Garissa County in order to analyse the potential for
3R interventions. Chapter 3 presents an overview of the water resources availability,
from precipitation to surface water, from shallow to deep groundwater. In chapter 4 we
make an assessment of the demand, current and future for the different uses: domestic,
agriculture, livestock and wild life. In chapters 5 and 6 an analyses is carried out on the
opportunities and challenges to increase water availability through the potential for 3R
interventions and conclusion and recommendations are given.
- 2 - Draft report
2 Biophysical landscape
Topography
General
Garissa County borders Wajir County to the North, Isiolo County to the West, Ethiopia in
the East, and Tana River, and Lamu Counties to the South. The county covers an area of
approximately 44,459 km².
Altitude variation
Garissa County is located at the coastal plains of Kenya. Altitude variations in the
county are limited, ranging from sea level in the south eastern coastal strip to nearly
500 m a.s.l. in the north west of the county.
Figure 1: Altitude variation in the north of Kenya (based on 90m DEM – SRTM)
Slopes
The slope is an important factor for intervention suitability studies as it influences the
potential of runoff. Moreover, slope is one of the major factors determining the
potential for in-stream riverbed storage methods, as well as determining erosion control
measures.
Support for water sector plan development - 3 -
Figure 2 provides a map of the project area with the slope classes. As the figure shows,
the slopes in Garissa County are all very low, due to the fact that the county is located in
the coastal plain and contains sedimentary formations. Only in the west of Garissa
County slightly higher slopes are present (up to 10%).
Figure 2: Slope categories (based on 90m DEM – SRTM)
- 4 - Draft report
Soils
Both intervention suitability and groundwater potential are very dependent on soil -
many interventions use infiltration of surface runoff as a method of winning water,
while groundwater recharge is also directly dependent on infiltration capacity.
Infiltration capacity is very dependent on soil type. Moreover, some soils are associated
with high salinity of groundwater. Suitability for agriculture and sensitivity to land
degradation is related to soil type as well, both dependent on soil structure and texture.
Box 1 explains how soil degradation and salinization happens.
Box 1: Irrigated agriculture in arid lands: salinization will eventually
happen
All soils contain and different water sources contain a certain amount of dissolved
minerals (e.g. salts). The concentration of these minerals can change due to
evaporation of water (rise in concentration) or rainfall (lowering of the concentration).
In case of irrigated agriculture, the constant shortage of water for the plants is solved
by adding additional water from boreholes, reservoirs or rivers. This is brought to the
fields via irrigation channels and brought to the plants via flush irrigation, sprinklers
or drip irrigation.
All surplus water is lost to the ground, and will eventually evaporate into the sky.
This upward flow of water transports minerals to the surface, where only the water
evaporates and the minerals remain in the soil. The longer this upward flow occurs,
the more the salt concentration will rise.
When the concentrations of salt reach levels of 0,5 to 1,0 % the concentration becomes
toxic for most plants. When these levels are reached, soils become unfertile and can no
longer be used for cultivation. When soils have become salinized, it is very difficult
(and sometimes impossible) to reverse: it has to be flushed out to drainage channels or
to deeper layers (if groundwater levels are deep). This process however can also cause
contamination of the shallow groundwater.
In order to prevent salinization of lands, dryland farming offers good opportunities.
Worldwide more and more experience is gained in making dryland farming a profitable
business, while at the same time salinization of soils is prevented and even reduced
(due to healthy soil life).
A soil map of the project area is shown in Figure 3. Due to the constant larger
evapotranspiration than the precipitation in arid lands, soils can become saline. In the
ASAL’s in the North of Kenya contain quite some saline soils can be found (Agro-
Climatic Zones V – VII; Sombroek et al, 1982), mainly at Vertisols, Fluvisols, Solonchacks,
Solonetz, Gleysoils, Regosols, Planosols and Luvisols (Gijsbertsen, 2007).
Garissa County contains large areas with solonetz (SN), soils that can be very saline. For
these areas it is important to take soil salinity into consideration when evaluating 3R
and groundwater potential. However, a saline soil does not automatically mean that the
runoff will be saline as well. This is something that has to be evaluated during
catchment or micro-catchment assessments and when planning possible interventions.
The other main soils in Garissa County are
Support for water sector plan development - 5 -
- Planosols (PL) - poor properties, waterlogging can occur, the soils are chemically
degraded and the surface can have become acid
- Lixisols (LX) – strongly weathered soils, which clay has washed-out down to an
subsurface horizon that has low activity clays and a high base saturation level.
- Arenosols (AR) – soils developed in residual sands with at least 35% rock or
coarse fragments
The minor spread out soils in Garissa County are:
- Gleysols (GL) - soils that are often saturated for a long time
- Vertisols (VR) - clay rich soils that develop wide cracks when drying. These soils
can be relatively saline.
- Cambisols (CM) – Soils without a layer of accumulated clay, humus, soluble salts
or iron, generally well drained.
If the soil map is compared with the slope and geology map, it can be seen that
the Cambisols are on top and downhill of the Gneisses, migmatides, quartzites
and granitoids formations
Figure 3: Soil map of Garissa County (adapted from: Sombroek et al, 1982)
- 6 - Draft report
Land use
As can be seen from Figure 4 the land use in Garissa County is mainly characterized by
rangelands (light yellow), which are being used by pastoralist communities and flood
plains. The white indicated areas are predominantly barren plains and bare rock
mountain ranges. In the South of Garissa County, between Masalani and Hulugho there
are some arable lands.
Figure 4: Interpreted land use map of Garissa County
Vegetation Index
The Normalized Difference Vegetation Index (NDVI) is a remote sensing based indicator
of greenness of an area. Tiles are available for every month. NDVI data is available since
2000. Spatial resolution of the NDVI tiles is 250 m. This NDVI is closely related to
vegetation cover and soil moisture. Values range from zero to one, representing bare
areas with no vegetation (0) to areas fully covered with vegetation (1).
All the NDVI tiles for Garissa County have been analysed. For every pixel over this whole
period of 15 year statistics have been calculated. Two images with some results of this
Support for water sector plan development - 7 -
analysis are shown in Figure 5. On the left is the average NDVI shown for Garissa County
over the period 2000 till 2015. On the right is the variance of the NDVI in Garissa County
shown; the variance is the square of the standard deviation. This NDVI variance is a
statistical parameter that shows how strong each NDVI pixel varies in time. For example,
when the NDVI variance value is low, it means that there is limited fluctuation in the
vegetation cover. If the average NDVI is high and the variance is low, this area is always
green, while if the average NDVI is high and the variance is high, it means that some
parts of the year it is very green, while other parts of the year it is poorly vegetated.
The higher the average NDVI, the greener the colour in Figure 5 left; the lower the NDVI,
the more red. The higher the variance of the NDVI, the greener; the lower the variance of
the NDVI, the more red (Figure 5 right).
The general vegetation pattern in Garissa County is: the further from the coast, so the
dryer Garissa County becomes. This results in a NDVI that is reducing towards the North
West. Most parts not only have a low NDVI, the variance is also low, which means that it
remains poorly vegetated for most of the year. Some riverbeds have a relatively low
mean NDVI but with a NDVI variance that is a bit higher, which means that some parts
of the year, water is available for vegetation. In the south-southeast of the county
average NDVI is relatively good, but this is with a high variance; this means that these
areas are green part of the year, but lose their greenness during the dry season.
Figure 5: Average NDVI (left) and variance of NDVI (right) of Garissa County, based on MODIS
satellite data (2000-2015)
A different analysis that has been carried out is the determination of the change in the
NDVI over the period of 15 years. This is shown in Figure 6. A positive slope (green)
means that the NDVI value has increase over the years. A negative slope (red) means that
he NDVI value has decreased over the years. The unit of the change showed is NDVI
values /10,000 per year.
- 8 - Draft report
This shows that in large parts of Garissa County the vegetation cover is reducing over
the last 15 years. In some parts for example in the North of Bura the vegetation cover is
improving.
One of the reasons for this reduction of vegetation cover is the production of charcoal,
which has become quite an issue in Garissa County. Other causes are possible as well.
The actual cause of the change at a certain location has to be determined on the ground.
It can be that external causes such as a change in rainfall resulting in a change of
vegetation cover. Or it is cause by local causes, such as human induced vegetation cover
reduction due to for example overgrazing or (as mentioned already) tree cutting for
charcoal production.
The reduction of vegetation however is worrying, since vegetation cover is an important
aspect in relation to erosion prevention, water retention, grazing grounds but also local
and regional water recycling: vegetation plays a key role in making water available
further downwind e.g. the more vegetation will be removed in Garissa County, the dryer
the North of Kenya becomes.
Figure 6: Annual change in the NDVI between 2000 and 2015 in Garissa County (source: MODIS)
Support for water sector plan development - 9 -
Nature reserves
As Figure 7 shows, there are a couple of small protected areas in the county. The Rahole
National Reserve on the border with Isiolo County is a vast stretch of thorny bushland,
with dryland species of flora and fauna. Two other reserves are locates along the Tana
river, Tana River reserve being home to two endangered primate species and the
Arawale being one of the last stronghold of the critically endangered Hirola antelope.
The last protected area is the Boni National Reserve, covering some of Kenya’s unique
coastal forests.
Figure 7: Protected areas of Garissa County
Geology
Geology is very important when determining both intervention suitability and
groundwater potential. It directly influences both soil and slope, and infiltration is very
dependent on the kind of rocks. Moreover, some chemicals, fluorides for instance, are
associated with rock type.
- 10 - Draft report
The geological map of Garissa County is shown in Fout! Verwijzingsbron niet
gevonden.. Garissa County has quite a uniform geology. In the west is a small part with
Gneisses, migmatides, quartzites and granitoids. The rest of the county is all
sedimentary formations, sandstones and recent sand deposits (Quaternary).
Figure 8: Detailed geological map of Garissa County (data source: OneGeology)
Support for water sector plan development - 11 -
3 Water availability
Introduction
Looking at the water resources, should be the first step in knowing if and how much
water is available. The different sources for Garissa County are: precipitation in
combination with evaporation, river water and groundwater. Data on the water sources
are scarce. All available information combined, however, makes that it is possible to say
something about the water situation in Garissa County.
This can be data from rain gauges, river discharge measurements, groundwater
abstraction data, (ground)water level data, or remote sensing data based on what is
measured with satellites. In Garissa County some data on river discharges is available;
regarding the other water sources for the whole county however, only remote sensing
data is available. Remote sensing data needs to be validated with on the ground
measurements. This, however, is not possible, due to the lack of field measurements.
Consequently, data has a lower accuracy.
So the data presented in this chapter is a good estimation of the water resources
situation in Garissa County, but has a limited accuracy, because of the lack of on the
ground measurements. Having access to less accurate data, is however, a huge step
forward compared to having no data at all.
Precipitation
Mean precipitation in Garissa County is low, with an average of about 366 mm/year.
Variation can be quite high, with an especially high peak in 1997 where estimated
precipitation reached over 1,000 mm (Figure 9, left). Precipitation shows a bimodal
pattern throughout the year, with wet season peaks in April and in November. In the dry
seasons, precipitation is very low, especially in July and August where it is practically
absent (Figure 9, right). Precipitation is highly variable in the wet seasons though. This
erratic pattern, that is expected to increase due to climate change, can create flash
floods flowing through seasonal rivers, exacerbating the prevailing drought and food
insecurity in Garissa County.
Figure 10 illustrates spatial variation of precipitation in Garissa County. Throughout the
county, precipitation is low, especially in the interior, resulting in a similar vegetation
pattern as was shown in Figure 5. Low coastal precipitation rates are expected to be an
error in the remote sensing data, because if it was this dry in these regions, NDVI values
would probably be much lower. At the hills slightly inland, precipitation rates are
reaching over 500 mm/y on average in some places.
- 12 - Draft report
Figure 9: Annual precipitation of Garissa County (left) and mean monthly precipitation with its 20th
and 80th percentile (right) based on ARC2 data.
Figure 10: Average annual precipitation in Garissa County (source: ARC2)
Garissa County receives rain twice a year, around April and around November. Between
April and November is the main long dry season. The dry season (see Figure 11)
normally lasts around 140 to 175 days, half a year. In extreme cases one rainy season
fails and the dry season lasts for more than 300 days.
Support for water sector plan development - 13 -
Figure 11: Length of the dry season per year in Garissa County (Source: NOAA ARC2)
Evapotranspiration
Evapotranspiration is dependent on the availability of soil moisture and surface water.
Therefore it is closely linked to both precipitation (section 3.2) and NDVI (section 2.4).
Evapotranspiration in Garissa County is on average 558 mm/y, with moderate variation
between years (350-600 mm/y) (
Figure 12, left). Throughout the year, wet season peaks are clearly visible, with highest values in May
and in November/December, and lowest values in February and September (
Figure 12, right).
0
50
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Len
gth
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aso
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Length of the dry season
- 14 - Draft report
Figure 13 shows spatial variation of evapotranspiration in Garissa county. Differences of
evapotranspiration are very high within the county, with a clear gradient going from
northwest to southeast. Lowest values are observed in the interior (<200 mm/y) and
highest values at the coast (>1000 mm/y).
Figure 12: Annual evapotranspiration of Garissa County (left) and mean monthly precipitation with its
20th and 80th percentile (right) based on MODIS data
Figure 13: Average annual evapotranspiration in Garissa County (source: MODIS)
Support for water sector plan development - 15 -
Net precipitation
Net precipitation is the amount of precipitation after subtraction of evapotranspiration.
It represents a surplus or shortage of water, expressed as a positive or negative balance,
and through this gives an indication of available water. The actual net precipitation
varies between months and between years. The accumulated annual net precipitation
gives information on how large the water surplus or shortage is. Since the northern
counties of Kenya have an arid climate, only in wet years there will be a surplus of
water, in all other years net precipitation will be zero or negative. The monthly net
precipitation gives information about in which months there is an opportunity for water
harvesting: when in certain wet months, there is a net surplus, this water can be
harvested, in order to make water available for the dry months.
Net precipitation values are low throughout the county (Figure 14). Values are just
positive in the northwest, but the rest of the catchment shows a negative balance. The
abnormal negative values however at the coast are due to a possible error in the
precipitation data.
Figure 14: Net precipitation of Garissa County, calculated using ARC2 and MODIS satellite data
- 16 - Draft report
Figure 15 (right) shows that, even though for most months throughout the year a
negative balance occurs, around April and November a positive balance occurs of about
30 mm on average in both months. These are the periods where the most potential is for
rainwater harvesting and the retention part of 3R measures. The rest of the year
however, net precipitation values are mostly negative.
Figure 15: Annual net precipitation of Garissa County (left) and mean monthly precipitation with its
20th and 80th percentile (right) based on ARC2 and MODIS data
The interannual variation of the net precipitation however is quite high, as can be seen
in Figure 16. In very dry years (min net prec, blue line), the March - April rainy season
does not happen at all, which results in a very negative annual net precipitation. Good
rain in these months however, can result in an annual positive water balance (max net
prec, green line).
Figure 16: Running net precipitation per hydrological year between 2000 and 2013 (source NOAA
ARC2 and MODIS)
River in & outflow
Tana River
The most important water source for the western part of the county is the Tana River.
While Garissa County is only for a very small part located into the Tana River catchment,
Tana River flows along the full western border zone of the county. Because Tana river
has water, nearly the whole year around, this makes the river an important source of
water for the county.
Support for water sector plan development - 17 -
Figure 17: Discharge variation per year of the Tana River at Garissa, based on discharge data
between 1942 and 2015 from gauging station 4G01 at Garissa (WRMA 2016)
For the Tana river quite good discharge data is with WRMA, the Garissa river gauging
station (RGS 4G01) has data between 1942 and 2015, with data gaps.
Figure 17 shows the discharge variation per year (in m3/s), with the bandwidth based on
over 70 years of discharge data. The figure shows that the discharge varies a lot over the
years. The average flow of the Tana river at Garissa is around 170 m3/s, which is around
14.7 mln m3/day. It can vary between nearly 0 (observed in October and November 2000)
and 2000 m3/s (observed in December 1968).
Figure 18 shows the variation of the average monthly river discharge (in m3/s).
As the figure shows, varies the average monthly discharge with the rainy seasons:
discharge peaks in April, May and November. The average monthly discharge varies
between 80 m3/s in September (or nearly 7 mln m3/day), just before the rains start and
300 to 350 m3/s in May (or 26 to 30 mln m3/day).
Figure 18: Monthly discharge variation of the Tana River at Garissa, based on discharge data from
gauging station 4G01 at Garissa (WRMA 2016)
- 18 - Draft report
According to WRMA (WRMA, 2016) the baseflow in around 40 m3/s. This baseflow
should always flow through the river for downstream environmental purposes. Based on
this 130 m3/s, or 11.2 Mm3/day is available for water allocation through water rights.
Other rivers
The Ewaso Ngiro rives flows into the northern parts of Garissa county in very abnormal
wet years, also reaching parts of Wajir county. In regular years, this river will flow into
the Lorian Swamp and recharge the Merti aquifer.
Furthermore other ephimeal streams flow through Garissa County:
- Lagga Gorealle,
- Lagga Afwein,
- Lagga Mura,
- Lagha Kundi,
- Lagha Dodoi,
- Lagga Garabey,
- Lagga Dodori,
- Lagga Handaro
- Lagga Ijara.
These streams only carry water when there is rainfall. After the rainfall events water
flows through them only for a few hours to a few days.
Groundwater resources
Shallow groundwater
In order to identify locations with the highest likelihood for shallow groundwater, a false
colour composite is made from three data sources: the digital elevation model (DEM),
mean NDVI and the Topographic Wetness Index (TWI).
Shallow groundwater is related to elevation since surface run-off as a result of
precipitation will generally flow and infiltrate at the lowest parts in a terrain. Higher
elevations and/or steeper slopes are often higher in the catchment and typically less
favourable for shallow groundwater. Obviously the local soils as well as geology play a
role as well in order to inhibit good conditions for local infiltration and shallow
groundwater. Impermeable soils will create water logging and high evaporation rates,
rather and groundwater infiltration for example, while if the soil overburden is very
thick and ‘fresh’ basement rock is at deep depths (>30m), the conditions are neither
favourable for shallow groundwater. This is, however, not taken into account in the false
colour composite map presented in Figure 19.
NDVI is directly dependent on soil moisture, and thus a good indicator for presence of
shallow groundwater.
TWI is defined as follows:
ln(𝐶𝑎𝑡𝑐ℎ𝑚𝑒𝑛𝑡𝑠𝑖𝑧𝑒𝑢𝑝𝑠𝑡𝑟𝑒𝑎𝑚
tan(𝑠𝑙𝑜𝑝𝑒))
This means that a steep slope translates into a low value and a large upstream
catchment area translates into a high value. High values then represent a high potential
for trapping of water, and thus a high potential for shallow groundwater storage.
The combined false colour composite is shown in Figure 19. To read the picture, the
following should be realised:
Support for water sector plan development - 19 -
- The redder, the higher the altitude;
- The bluer, the larger the catchment and/or the gentler the slope;
- The greener, the more NDVI;
- Together, the green-blue / turquois colour means a greater likelihood for
presence of shallow groundwater.
The locations with a potential for shallow groundwater are those locations, where a lot
of water can be stored (large catchment and low slope) and where vegetation does well.
As can be seen in Figure 19, there are a few flat areas in the middle of the county where
water can remain standing, due to low slopes. Most high vegetation occurs at the coast,
but the combined zone (very green and large catchment combined with low slope) seems
not to occur a lot.
- 20 - Draft report
Figure 19: False colour composite of elevation (red), NDVI (Green) and TWI (Blue)
Support for water sector plan development - 21 -
Deep Groundwater
Garissa County is largely located in a sedimentary formation. The main aquifer in the
county is the Merti aquifer. In a small part of the north, a small part of the Gachuru-
Kula-Mawe-Bovi aquifer is just located in Garissa County. An overview of the aquifers
locations is given in Figure 20.
Merti Aquifer
The area underlain by the Merti Aquifer comprises a thick and complex sequence of
Mesozoic to Tertiary sediments and volcanics, which overlie metamorphic rocks of the
Precambrian Basement System. Tertiary sediments consist of sandstones grits and
conglomerates. The exposure is relatively poor, since they erode easily. Tertiary
volcanics outcrop on the Merti Plateau where they are observed to overlie the Tertiary
sediments. The most recent deposed sediments are composed of Lacustrine sediment
with limestones, calcretes and superficial deposits belonging to Pleistocene and
Holocene periods (WRMA, 2013). Alluvial sand, silt and clay probably occur along the
drainage channels, influencing permeability and recharge.
Recharge from the Marsabit volcanics with lateral flow through intermediate zones and
recharge from the Yamicha plateau, is considered as the most important aquifer
recharges sources (GIBB, 2004; Vreugdenhill, 2013). Mount Marsabit and surrounding
plateaus, especially the Kaisut area south of Mt. Marsabit, has quaternary sediment and
hosts local aquifers within its volcanic rocks. Together with the underlying sediments
they form the headwaters of the Merti aquifer. From Mount Marsabit the aquifer
continues south through the Yamicha basin beneath the Yamicha plateau towards the
central Merti-aquifer (Oord, 2012).
Gachuru-Kula-Mawe-Bovi aquifer
The geology of the area consists of basement rock covered with a thin layer of eroded
material (Matheson, 1971). The basement rocks consist of metamorphic gneisses and
intrusive granitic rocks. These rocks are impervious and not suitable for the condition of
storage of groundwater. Groundwater occurrence within the basement area is confined
and depends on fractured zones and weathered parts.
- 22 - Draft report
Figure 20: Overview of the known aquifers in Garissa County
Water quality
Having enough water is not the only thing, the water that is to be consumed, and
specially for domestic supply needs to have good quality as well.
Figure 21 shows the available water quality data of the different boreholes. As can be
seen, from quite a few boreholes no water quality data is available (grey dots). However,
data coverage is much concentrated in the northern parts of the county due to the high
density of boreholes in the Merti aquifer.
Based on the geology probability of fluoride is estimated: in various volcanic
depositions, fluoride is present with a higher or lower probability (IGRAC, 2004). The
result of this study is a map with probability range of how likely it is that there can be
fluoride in the groundwater. Based on geology also salinity of groundwater is estimated.
But because this is a map showing probabilities, it needs to be verified with actual
groundwater data that needs to be collected from boreholes. Therefore, additional water
quality testing from various boreholes is vital for further assessment of the water
quality data.
Support for water sector plan development - 23 -
Figure 21: Quality and quantity of different interventions and the linkage of these interventions to
water usage.
Garissa County itself has generally low probability of fluoride in groundwater. However
there are boreholes, more in the northern part of the county, where high fluoride levels
are measured. Furthermore, saline groundwater is something that is expected to occur
as well. This has also been confirmed for a few of the boreholes in Garissa County.
Finally, water quality is not a static thing and can be affected by anthropogenic sources.
Even during the operations of a borehole, the water quality can deteriorate by careless
placing of the installations:
- If the sealing of the borehole is not done properly, contaminations can leak via
the borehole into the aquifer and contaminate the groundwater. If the borehole
is drilled via a shallow aquifer, a shortcut can be created, resulting in change of
water quality in the deeper aquifer.
- Toilets and other sources of defecation (humans and livestock) can slowly by
slowly leak into the ground, eventually reaching the aquifer, causing pollution of
the groundwater. Especially in sedimentary and fractured rock depositions this
can occur.
- 24 - Draft report
Water budget
Based on the data mentioned before, a total water balance of the county can be made.
This is shown in Table 1. As this table shows, the net balance in Garissa County based
on the available data is negative due to semi-arid climate:, most water is lost to
evaporation / evapotranspiration.
River water is contributing a significant amount of water in Garissa County (nearly 33%
of the annual precipitation). However this is only providing limited extra water, since
this water is also for base flow of the Tana river, and downstream use, while the readily
available volume of water changes significantly throughout the year depending on rainy
and dry seasons.
The amount of net-precipitation however is so negative that these numbers should be
used with care. A long lasting negative water balance is not possible, since water cannot
evaporate when it is not available. Also, since groundwater storage assessment was not
taken into the water budget figures, in the end some water will potentially be available.
This is why on the ground measurements are so extremely important. Initiatives like the
Trans-African Hydro-Meteorological Observatory (TAHMO) initiative can provide
possibilities to make more information available.
Table 1: Overview of the water budget in Garissa County based on the available data
Mean
[mm/year]
Mean
[Mm3/year]
Percentage
[%]
Precipitation 366 16,153 100%
Evapotranspiration 558 24,627 152%
Net precipitation -192 -8,474 -52%
River throughflow of Tana
River
121 5,361 33%
Groundwater storage n.a. n.a. -
Total water availability -71 -3,113 -19%
Support for water sector plan development - 25 -
4 Demand for multiple uses
Introduction
The only way how it is possible to know how much water needs to be provided is when
you know what the demand and different users are: by humans, livestock, agriculture,
industry, but also the demand by wildlife and rangeland. When you know the users
demands and associate it to police developments, you can plan accordingly and
intervene to meet the demand. In this process it is also very relevant to inventory the
existing water gap to improve availability and plan interventions to ensure meeting the
future demand.
The Water Need Tool developed by Acacia Water has been used to access the figures for
the water demand in 2025 for domestic, agricultural and livestock purposes, for an
average scenario. The assessment of the current water use has been done based upon
census data from the year 2009 and the growth prognoses have been abstracted from
literature. Because there is a huge uncertainty in the current water use anno 2017, the
analyses of the current water use has been determined for the year 2009 (the year of the
census). Total water use and demand has been summarized in Table 6 and Table 7.
Domestic water demand
With change from pastoralism to agro-pastoralism, settling of pastoralists is occurring
more and more with increased domestic water demand focused on villages and towns.
Capital investments under Kenya Vision 2030 and the LAPSSET Corridor are expected to
boost (urban) population growth and, thus, water demand further.
Assuming a water use of around 5 L/c/d in 2009, if water supply is brought up to
national standards (20 L/c/d with the water source within 1km distance) and population
will grow with 3,7 % (KNBs 2009) per year this means that water supply will increase
with more than 500% in 2025. This all calls for comprehensive domestic water planning
in the coming years (CIDP).
Domestic water demand in 2009 was relatively low due to the low population density in
the different parts of Garissa County. Assuming a water demand of 5 L/c/d, and a
population of approximately 623,000 inhabitants, water use lied around 3,100 m3/ d and
1.14 Mm3/y. With an expected population growth of 3.0 %/y and a demand of 20 L/c/d
this will grow in 2025 to around 999,800 inhabitants and a water demand of 7.32
Mm3/d.
Such demand increase represents around 500% supply in 2025 compared to the 2009
calculated water use. This all calls for comprehensive domestic water planning in the
coming years.
The domestic water demand figures are summarized below in Table 2.
- 26 - Draft report
Table 2: Domestic water use in 2009 and expected demand in Garissa County in 2025
Current water use
(2009)
Future water demand
(2025)
5 l/c/d 20 l/c/d
623,060 999,828
3,100 m3/d 20,050 m3/d
1.14 Mm3/y 7.32 Mm3/y
0.07 m3/km2/d 0.45 m3/km2/d,
0.03 mm/y 0.17 mm/y
Livestock drinking water demand
In order to determine the total water demand by livestock, Livestock Units (LU) are used.
Since each LU uses 50 l/day, the total water consumption of all livestock can be
determined. Table 3 presents the respective amount of Livestock Units by one animal of
the each livestock species (first row); number of livestock based on the 2009 census
(second row) and the total amount of livestock Units of each type of livestock (third
row); and the total water consumption in m3/day (fourth row).
Table 3: FAO Livestock Units and water consumption.
Cattle Goats Sheep Camels Donkeys Pigs
Livestock Unit 0.5 0.1 0.1 1.1 0.6 0.2
Number of livestock 903,678 2,090,613 1,224,448 236,423 75,178 59
Number of LU 451,839 209,061 122,445 260,065 45,107 12
Water consumption [m3/d]
22,592 10,453 6,122 13,003 2,255 1
Garissa County has large amounts of livestock, with an equivalent of around 1.1 million
LU (census 2009). Exact figures of livestock population growth are not known, but it is
expected since county policies are aiming at it and estimated at 1% per year.
As a result, water demand for livestock is expected to increase as well. This amounts
from around 54,500 m3/d in 2009 to around 64,000 m3/d in 2025 and is over three
times higher than domestic demand (see Table 4).
Table 4: Livestock water use in 2009 and estimated future water use in Garissa County for 2025.
Water use
(2009)
Future water demand
(2025)
50 l /LU/d 50 l /LU/d
232,450 LU 294,976 LU
54,500 m3/day 64,000 m3/day
19.9 Mm3/year 23.3 Mm3/year
1.23 m3/km2/d 1.45 m3/km2/d
0.45 mm/year 0.53 mm/year
What is not yet taken into account in the livestock water demand is the migration of
livestock within Garissa County nor the influx of livestock herds into the county.
Current calculations is purely based on available livestock census data for Garissa
County only and in-situ water demand. Actual water demand might locally differ and
Support for water sector plan development - 27 -
possibly be higher due to internal migration within the county as well as influx of
livestock from neighbouring counties and countries, especially during the dry season. A
more in-depth study about regional migrating patterns by pastoralists should be carried
out.
Knowing that climate change will result in higher temperatures, hence increase in
evapo(transpi)ration, vegetation growth – thus carrying capacity - might suffer under
these higher temperatures. Consequently, growth of livestock population might be
evaluated carefully and be included in policy integration.
Rangeland water demand
Besides water, livestock needs food as well: rangelands for grazing. The water
requirements of the grazing lands highly depends on how healthy the grazing lands are.
Healthy grazing lands use water, while poor lands are often barren and have a very high
surface runoff. The amount of water that a rangeland uses is fully dependent on the
amount of rain that falls and the type of vegetation that grows there. The actual amount
of water that is used is made visible in the evaporation data as shown in section 3.3.
Agricultural water demand
Irrigated and rain-fed agriculture uses a lot of water. Thus, impact of agriculture on the
water balance is large.
Due to the fact that Garissa County is located in arid lands, rainfall is lower than the
evaporation. In an average year, Garissa County has a rainwater surplus of 18% of the
total rainfall. This surplus happens in April, May and November and is partly flowing
into rivers, but mainly stored in the ground to support plants in the months after the
rains.
In a dry year, still a surplus can happen in April. Low rainfall in dry years, will also have
an significant impact on the river throughflow into the county.
Figure 22: Comparison between the water usage per crop, the area planted and the % of the
annual rainwater surplus (source: WaterTool - Acacia Water).
- 28 - Draft report
In order to be able to compare the water availability with the water usage by the crops, a
comparison has been made between the water usage per crop, the area planted and the
% of the annual rainwater surplus. This comparison, shown in Figure 22, illustrates
which crops will use more water than others. Following the red arrows, one can notice
that for cultivating a 10,000 ha, maize will consume about 2,2% of the rainwater surplus
while beans will use about 1,4%.
According to the CIDP around 2,000 ha was under irrigated agriculture in 2009 which
means that these areas use 0.27 and 0.44% of the annual rainwater surplus, which is
around 93,000 m3/d.
The ambition of Garissa County is to increase this significantly. The CIDP mentions an
increase from 2,000 around 10,000 ha (680 ha in rainfed lands, 150 ha along the river,
250 ha in sub counties, 3,400 ha of new irrigation schemes, 3,100 ha along the river).
This means that if 10,000 ha will be under irrigation, water demand will increase to 1.35
to 2.2 % of the annual rainwater surplus, which is around 467,000 m3/d.
This represents an increase from the total amount of water use from 11,1 Mm3/y to 54,7
Mm3/y (see Table 5). Both water uses are quite limited, compared to the river discharges
(see section 3.5), however Tana River rights are limited. Compared to the amount of
rainfall in Garissa County water demand is significant.
Table 5: Irrigated agriculture in 2009 and estimated future water use in Garissa County for 2025.
Water use (2009) Future water use (2025)
2,000 ha 10,000 ha
93,000 m3/day 467,000 m3/day
11.4 Mm3/year 54.7 Mm3/year
0.25 mm/y 1.24 mm/y
Wildlife drinking water
Data on wildlife water demand is not available, and deserves further investigation by the
Government of Garissa County.
Industrial water demand
Data on industrial water demand is not available, and deserves further investigation by
the Government of Garissa County.
Support for water sector plan development - 29 -
Conclusions on demand
Based on the different estimations the total water use for domestic, livestock, and
agriculture based upon the census year 2009 and the future demand for year 2025 is
calculated.
The total water use in 2009 and 2025 is also estimated during the growing season (when
the irrigation water use is at its highest). Total water use in this period is estimated on
around 150,700 m3/d in 2009, which will grow to around 551,000 m3/d in the growing
season in 2025. Table 6 gives an overview of the water use during the growing season in
m3/d per user and its respectively percentages.
Table 6: Estimated water use and demand per users group in m3/d during the growing season for
years 2009 and 2025.
Demand Water use in 2009
[m3/d]
Percentage Water demand in
2025 [m3/d]
Percentage
Domestic 3,124 2.1% 20,051 4%
Livestock 54,531 36.2% 63,942 12%
Agriculture 93,000 61.7% 467,000 85%
Wildlife n.a. n.a. n.a. n.a.
Industrial n.a. n.a. n.a. n.a.
Total 150,655 100% 550,993 100 %
Table 7 given an overview of the future demand in Mm3/y per users group for an entire
year. The total demand will increase from around 23 Mm3/y to over 85 Mm3/y. This
increasing in demand will ask for comprehensive water management plans. For more
detailed information on the calculations using the Water Need Tool, see Annex 1 (Acacia
Water, 2017).
Table 7: Estimated total water use and demand in Mm3/y per users group for years 2009 and 2025.
Demand Water use in 2009
[Mm3/y]
Percentage Water demand in
2025 [Mm3/y]
Percentage
Domestic 1.14 4% 7.32 9%
Livestock 19.90 62% 23.34 27%
Irrigation 11.10 35% 54.74 64%
Wildlife n.a. n.a. n.a. n.a.
Industrial n.a. n.a. n.a. n.a.
Total 32.15 100% 85.40 100%
The future water demand is also presented below in Figure 23 (2009) and Figure 24
(2025). This is a graph extract from the Water Need Tool.
- 30 - Draft report
Figure 23: Graphic representation of the estimated water use in 2009
Figure 24: Graphic representation of the expected water demand 2025
Support for water sector plan development - 31 -
5 Integrating water availability and
demand
Introduction
In the previous chapters the biophysical context is depicted (chapter 2), water resources
are estimated (chapter 3) and water demand is estimated (chapter 4). In this chapter this
all comes together.
If we look at the water demand, we want to know how much water is needed. When we
look at the water resources, how much water is available in a sustainable way, and what
kind of things can we do to make this water available during the drier periods.
County scale balances
Annual water balance
The water balance on an annual scale (-52%) is negative: there is more evaporation than
rainfall, as is shown in Fout! Verwijzingsbron niet gevonden.. An annual surplus of
water does not happen often, only in wet years.
The total water demand however is very small compared to the average yearly amount
of precipitation. The total annual rainfall is approximately 16,150 Mm3 on an average
year. The total estimated use in 2009 and demand in 2025 is respectively 32.15 Mm3 and
85.40 Mm3. These water uses/demands are a very small portion of the total rainfall on
an annual basis. Compared to the rain fall, it is expected that the total demand will
increase to 0.56% in 2025.
While this is a small portion, the challenge however is twofold:
- What area will be used for harvesting the surface runoff
- how can the rain water been stored so that it is available when needed
Monthly water balance
While on an annual basis, there seems to be a negative water balance, the monthly water
balance shows that there are monthly surpluses during the year, that offer
opportunities, so that more water can be made available. Figure 25 shows that in an
average year (the red line) there is a surplus of water in November, March and April. This
surplus is around 36 mm in March and April and 30 mm in November (see Figure 25 the
red line).
Figure 26 shows the average monthly surplus and deficit of water. As can be seen is the
surplus in November and April both around 12E+8 m3 = 1,200 Mm3/year.
In 2025 the water demand is expected to have grown to around 85 Mm3/year
So the question is how this surplus of water during the wet season can be made
available for water users during the dry season.
- 32 - Draft report
Figure 25: Average monthly net precipitation in a dry, average and wet year.
Figure 26: Annual net water availability in Garissa County (left) and average annual water needed
(right), based on estimated water usage for Garissa County.
Requirements, opportunities and challenges for meeting the water
needs
Different water resources have different characteristics
When water is needed, different resources can be used: rain water, flowing surface
water, standing surface water or groundwater.
The spatial availability of these resources varies: rain falls everywhere, but more often
on hills; rivers only flow in riverbeds; groundwater is widely available but uncertainties
for borehole location are high; etc.
The seasonal availability of these four resources is also different: standing surface water
can be very reduced during the dry months; groundwater on the one hand is always
available (unless the aquifer is depleted), while rain water on the other hand is only
available during few months. Finally, also the quality of all resources varies, but can also
change over time.
Support for water sector plan development - 33 -
All these different aspects that should be taken into account are presented in Table 8.
Table 8: Simplified aspects of water resources to be taken into account if water infrastructure is
developed
Resource Availability Rechargeability Provided quality Allocation
Rain water Only in
rainy
season
Every year Pretty good Everywhere, but
more on slopes
with upward
moving air
Flowing
surface
water
During and
after rainy
season
Every year Depending on
upstream
In rivers
Standing
surface
water
During and
after rainy
season
Every year Becoming poorer in
the dry season
Instream and off
stream, if there
is a catchment
Shallow
groundwater
During and
after rainy
season
Every year Can be quite good,
vulnerable to
anthropogenic
pollution
In sandy soils
with catchment
Fossil deep
groundwater
Whole year,
but finite
Very poorly, can
be enhanced
Bacteriologically
good, but can
contain fluoride,
arsenic or salts
In porous
geological
formations or
fractures
The different demand types all have different requirements in time and in space:
domestic water requires water of good quality; the amount of water provided needs to
be the same every day. Water for livestock differs during the year, because of migration,
so multiple water points have to be created at several locations, which will provide water
at different moments during the year, depending where the herds are. The different
aspects that should be taken into account for water demand can be found in Table 9.
Table 9: Simplified aspects of water demand to be taken into account if water infrastructure is
developed
Demand Variability in time Needed quality Variability in space
Domestic Constant High Varies
Irrigation Varies Low - medium Varies
Livestock Varies Medium – high Varies
Wildlife Varies Medium – high Varies
Industrial Constant High Varies
Multiple uses- different requirements
In order to harvest water, different solutions can be used. Because the solutions applied
focus on their local biophysical context, the type of water they use differs as well.
If you harvest water from a stream in a reservoir, the water can already be polluted
upstream, while if you harvest rainwater directly from the roof, water is likely to be of a
better quality. However, rainwater harvested from the roof has a limited volume, since
the roof is relatively small, while a stream has a larger catchment upstream, so that it
can provide more water. So the roof provides limited volume with relatively good quality,
while the reservoir can harvest more water, but with lower quality.
- 34 - Draft report
Type of water harvesting Intervention 3R intervention
classification
Quantity Quality Domestic Livestock Agriculture
Groundwater recharge/storage in
river beds
Subsurface dam C - - √ √ √
Sand dam B - - √ √ √
Permeable dams F - - O √ √
Groundwater recharge/storage in
aquifers
MAR / Tube recharge D - - O √ O
Riverbank infiltration D - - √ √ √
Surface water storage in rivers Dams - large reservoirs A - - O √ √
Valley dams A - - - X O √
Charco dams or small hillside storages F - - - X O √
Surface water storage off stream Valley tanks A - - - X O √
Water pans or small ponds A - - - X √ √
Hard surface water harvesting/
storage
Rooftop harvesting G - - √ X O
Road harvesting G - - - - X √ √
Rock catchments G - - - X √ √
Underground cisterns G - - O √ √
Overland water storage Flood water spreading or Spate irrigation E - - - X √ √
Groundwater abstraction Drilled borehole or tube well with hand pump H - - √ √ O
Deep borehole/well with motorized, solar
power or generator
H - - √ √ √
Shallow well with hand pump D - - √ √ O
Figure 27: Quality and quantity of different interventions and the linkage of these interventions to water usage.
Domestic Livestock Agriculture
√ Good option, check water quality Good option Good option
O Treatment is needed Treatment might be needed Limited amounts or
very expensive
X Not advised, if no other options
treatment is necessary
Limited amounts, very
expensive
-
Annexes - 53 -
Fout! Verwijzingsbron niet gevonden. is showing an overview of different solutions in
relation to the source, amount and user: The first column shows the type of water that is
harvested, the second column shows the solution implemented. The third column makes
an association with the classification used in the 3R Potential map (see A
: Pan
s an
d v
alle
y d
ams
B: S
and
dam
s
C: S
ub
-su
rfac
e d
ams
D: S
hal
low
gro
un
dw
ater
: wel
ls
and
riv
erb
ank
infi
ltra
tio
n
E: F
loo
d w
ater
sp
read
ing
and
spat
e ir
riga
tio
n
F: G
ully
plu
ggin
g, c
hec
k d
ams
and
oth
er r
un
off
red
uct
ion
/in
filt
rati
on
me
asu
res
G: H
ard
su
rfac
e an
d c
lose
d t
anks
H: D
eep
gro
un
dw
ater
ab
stra
ctio
n:
wel
ls/
bo
reh
ole
s
Zone 1A x1 xxx x x
x x (x)2
Zone 1B x1 xx xxx x x ∆ x (x) 2
Zone 2
x1 xx1
Zone 3A x1 xx xx x
x x (x) 2
Zone 3B x1 x xx x x
x (x) 2
Zone 3C x1 ∆ ∆ ∆
x x x2
Zone 3D x1 ∆ ∆ ∆ ∆
x x2
Zone 3E x
x
x x x2
Zone 3F x
x1
x x x2
Zone 4A x
xx xx
x x2
Zone 4B x1 (x) (x) ∆ X ∆ x x2
Zone 4C x
∆ (x) x ∆ x x2
Zone 4D x
xxx
∆ x x2
Zone 5A x
x
Zone 5B x
∆
∆
Zone 6
(x)
xxx
). The fourth and fifth columns show the quality and quantity of the water that can be
expected when choosing for ones or another solution (less drops mean less quality and
quantity). The last three columns show which type of demand could better use the water
provided for each respective solution.
Linking water resources to demand
The spatial availability, quality and allocation of the resources does often not match
with the locations of the demand and the needed quality. Because of that, infrastructure
needs to be developed so that the right amount of water of the right quality is brought
at the right moment to the right user.
The type of infrastructure that is needed, depends of all the characteristics of the
resource and the requirements of the demand (see Figure 28) , as well as the socio-
economic and geological aspects.
Annexes - 53 -
Using the biophysical landscape
It is the most sustainable way to depend on rainwater harvesting (since this is recharged
every year), and use other water sources as buffer for times of high needs (droughts). In
order to be able to focus on rainwater harvesting, a wide range of solutions can be
implemented. Different solutions are developed for different locations within the
biophysical context, for instance:
- Sand dams can only be made in rivers with basement rocks and sandy river beds
- Surface water reservoirs are best made in places with clay soils, to prevent
infiltration of the stored water
- Etc.
Figure 29 shows an example of a landscape with a wide range of solutions that can be
applied. All these different solutions help to harvest and retain water, in order to make
more water available in the dry period.
Figure 29: Different locations ask for different solutions
In chapter 2 the biophysical context of Isiolo has been explained. Within the context of
the Isiolo climate rainwater harvesting in the wet season offers a lot of opportunities to
make more water available for the dry season.
Different solutions can make more water available (as explained in section Fout!
Verwijzingsbron niet gevonden.), but they need to be applied within the right
biophysical context. In order to take into account the “where can be done what”, the
biophysical context is translated into potential maps. Three types of maps have been
developed by Acacia Water within the scope of Kenya-RAPID program:
- 3R potential (landscape approach for water harvesting)
- Deep groundwater potential
- Grazing land potential
- 54 - Draft report
Another very relevant aspect when allocating infrastructure is the socio-economic aspect
which determines where demand is higher and increase the cost-benefit of planning
infrastructure. This aspect is certainly investigated by the implementation partners of
Kenya RAPID and need to be taken into consideration when choosing for allocating 3R
interventions.
In the section bellow we present the potential investigated by Acacia Water.
3R potential (landscape approach)
Based on all the biophysical data that is described in chapter 3, a potential map has been
compiled that gives an overview of the different opportunities that Garissa County
offers for rainwater harvesting in order to Retain, Recharge and Reuse (3R) rain water.
This map is shown in Figure 30. A larger version of the map is added in Annex 1:
Calculation Water Need Tool
Annexes - 53 -
County Garissa
Location Garissa County
Scenario: (Type of year) Average
Area size [km2] 44175
Month Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total
Days per month 31 30 31 31 28 31 30 31 30 31 31 30 365
Precipitation [mm] 37,6 91,1 49,2 13,5 4,6 40,4 86,1 31,0 4,7 4,3 1,4 1,9 365,7
Actual evaporation [mm] 40,4 61,1 61,7 42,0 31,7 34,0 55,7 64,8 50,9 39,9 37,4 37,9 557,5
Net precipitation [mm] -2,7 29,9 -12,5 -28,5 -27,1 6,4 30,4 -33,9 -46,2 -35,7 -36,0 -36,0 -191,8
River inflow [m3/month] 0,0
River outflow [m3/month] 0,0
net river usage [m3/month] 0 0 0 0 0 0 0 0 0 0 0 0 0,0
net river usage [mm/month] 0 0 0 0 0 0 0 0 0 0 0 0 0,0
net water availability [mm/month] -2,7 29,9 -12,5 -28,5 -27,1 6,4 30,4 -33,9 -46,2 -35,7 -36,0 -36,0 -191,8
Year of census 2009
Current year of calculation 2009
Population in 2009 623.060
Annual population growth 3,0%
Future target year 2025
Population in 2025 999.828
Current domestic water demand
[l/pers/d]5
Future domestic water demand
[l/pers/day]20
Annual livestock population growth 1,00%
Animal l/day/animal l/day l/day/animal l/day
Cattle 903678 25 22591950 1059634 25 26490838
Sheep 1224448 5 6122240 1435762 5 7178808
Goat 2090613 5 10453065 2451408 5 12257041
Camel 236423 55 13003265 277225 55 15247351
Donkey 75178 30 2255340 88152 30 2644564
Pig 59 10 590 69 10 692
Chicken 104295 1 104295 122294 1 122294
Total water use [l/day] 54.530.745 63.941.587
Total water use [m3/year] 19.903.722 23.338.679
Annual wildlife population growth 0,00%
Animal l/day/animal l/day l/day/animal l/day
African Elephant 0 205 0 0 205 0
Giraffe 0 25 0 0 25 0
Grevy Zebra 0 20 0 0 20 0
Hunter's Hartebeest 0 2 0 0 2 0
Thomson's Gazelle 0 1 0 0 1 0
Total water use [l/day] - -
Total water use [m3/year] - -
Wildlife 2017 Wildlife 2030
Water resources
WIL
DLI
FELI
VES
TOC
KW
ATE
R IN
& O
UTF
LOW
PO
PU
LATI
ON
WA
TER
USA
GE
Livestock 2009 Livestock 2025
Water demand
- 54 - Draft report
Crop - growing period Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Area [ha]
Beans x x x 333,3333333
Maize x x x x 333,3333333
Wheat x x x x 333,3333333
Millet X X X X 333,3333333
Tomato x x X X 333,3333333
Wheat X X X X 333,3333333
0
0
Crop - estimated water usage
[m3/month] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total
Beans 421053 435088 421053 1277193
Maize 520000 537333 520000 537333 2114667
Wheat 478261 494203 478261 494203 1944928
Millet 440000 454667 440000 454667 1789333
Tomato 500000 516667 500000 516667 2033333
Wheat 478261 494203 478261 494203 1944928
0
0
Total water usage [m3/month] 0 0 0 0 0 0 2837574 2932160 2837574 2497072 0 0 11104381
Crop - growing period Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Area [ha]
Beans x x x 1666,666667
Maize x x x x 1666,666667
Sorghum x x x x 1666,666667
Millet X X X X 1666,666667
Tomato x x X X 1666,666667
Wheat X X X X 1666,666667
0
0
Crop - estimated water usage
[m3/month] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total
Beans 2105263 2175439 2105263 6385965
Maize 2600000 2686667 2600000 2686667 10573333
Sorghum 2200000 2273333 2200000 2273333 8946667
Millet 2200000 2273333 2200000 2273333 8946667
Tomato 2500000 2583333 2500000 2583333 10166667
Wheat 2391304 2471014 2391304 2471014 9724638
0
0
Total water usage [m3/month] 0 0 0 0 0 0 13996568 14463120 13996568 12287681 0 0 54743936
122
0
Length of growing period
Growing period too short
Growing period too long
CU
RR
ENT
IRR
IGA
TED
CR
OP
S
91
122
122
122
122
0
Explanation growing period
Growing period correct
122
122
122
122
0
122
0
FUTU
RE
IRR
IGA
TED
CR
OP
S
Length of growing period
91
Annexes - 53 -
Agricultural water demandTotal water usage per growing period per crop for different area of irrigated land as percentage of annual rainwater surplus
Actual water availability (net precipitation) Current water demand (2009)
Water situation for an Average year in Garissa County, Garissa County
Water resources
Water Balance
Cumulative net precipitation for dry, average and wet years
Precipitation Actual Evaporation
Monthly net precipitation for dry, average and wet years
Total water usage per day for different crops for different areas of irrigated land
Future water demand (2025)
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Am
ou
nt
of
aver
age
pre
cip
ita
tio
n
Month
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Am
ou
nt
of
aver
age
pre
cip
ita
tio
n
Month
-400,0
-300,0
-200,0
-100,0
0,0
100,0
200,0
300,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Cu
mm
ula
tive
net
pre
cip
itat
ion
[mm
]
min net prec average net prec max net prec
-75,0
-50,0
-25,0
0,0
25,0
50,0
75,0
100,0
125,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Mo
nth
ly n
et p
reci
pit
ati
on
[mm
]
min net prec average net prec max net prec
-2,5E+09
-2,0E+09
-1,5E+09
-1,0E+09
-5,0E+08
0,0E+00
5,0E+08
1,0E+09
1,5E+09
2,0E+09
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Wat
er
avai
lab
ility
[m
3]
Month
0,0E+00
5,0E+05
1,0E+06
1,5E+06
2,0E+06
2,5E+06
3,0E+06
3,5E+06
4,0E+06
4,5E+06
5,0E+06
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Wat
er
dem
and
[m3]
Month
Human consumption Livestock + Wildlife consumption Agriculture
0,00%
0,50%
1,00%
1,50%
2,00%
2,50%
3,00%
3,50%
4,00%
4,50%
5,00%
0 2500 5000 7500 10000 12500 15000 17500 20000 22500
% o
f an
nu
al ra
inw
ate
r su
rplu
s
Area [ha]
Maize
Beans
Sorghum
Millet
Tomato
Wheat
0
200000
400000
600000
800000
1000000
1200000
0 2500 5000 7500 10000 12500 15000 17500 20000 22500
Tota
l wat
er
usa
ge p
er d
ay [
m3/
d]
Area [ha]
Maize
Beans
Sorghum
Millet
Tomato
Wheat
0,0E+00
2,0E+06
4,0E+06
6,0E+06
8,0E+06
1,0E+07
1,2E+07
1,4E+07
1,6E+07
1,8E+07
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Wat
er
dem
and
[m3]
Month
Human consumption Livestock + Wildlife consumption Agriculture
- 54 - Draft report
Water availability [m3] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total [mm]
Precipitation 1.662.584.067 4.022.541.629 2.173.303.747 597.352.663 201.587.238 1.784.559.446 3.802.793.236 1.367.532.122 207.380.975 188.805.697 61.877.549 83.148.795 16.153.467.163 100% 365,67
Actual evaporation 1.783.794.126 2.700.041.398 2.723.866.886 1.856.339.862 1.400.872.629 1.500.777.560 2.458.968.438 2.863.551.927 2.247.539.658 1.764.534.857 1.652.897.633 1.674.677.619 24.627.862.594 152% 557,51
Available water -121.210.060 1.322.500.231 -550.563.139 -1.258.987.199 -1.199.285.391 283.781.886 1.343.824.798 -1.496.019.805 -2.040.158.683 -1.575.729.161 -1.591.020.084 -1.591.528.824 -8.474.395.431 -52,5% -191,84 18%
Human consumption 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 1.140.200 0,007% 0,03 0,04%
Livestock + Wildlife
consumption 1.690.453 1.635.922 1.690.453 1.690.453 1.526.861 1.690.453 1.635.922 1.690.453 1.635.922 1.690.453 1.690.453 1.635.922 19.903.722 0,12% 0,45 0,67%
Agriculture 0,0 0,0 0,0 0,0 0,0 0,0 2.837.574,4 2.932.160,2 2.837.574,4 2.497.072,5 0,0 0,0 11.104.381 0,07% 0,25 0,38%
Total water demand 1.785.470 1.730.939 1.785.470 1.785.470 1.621.878 1.785.470 4.568.513 4.717.630 4.568.513 4.282.542 1.785.470 1.730.939 32.148.303 0,20% 0,73 1,09%
Water availability -122.995.529 1.320.769.292 -552.348.609 -1.260.772.669 -1.200.907.269 281.996.417 1.339.256.285 -1.500.737.435 -2.044.727.196 -1.580.011.703 -1.592.805.554 -1.593.259.763 -8.506.543.734 -52,7% -192,56
Water availability [m3] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total [mm]
Precipitation 1.662.584.067 4.022.541.629 2.173.303.747 597.352.663 201.587.238 1.784.559.446 3.802.793.236 1.367.532.122 207.380.975 188.805.697 61.877.549 83.148.795 16.153.467.163 100% 365,67
Actual evaporation 1.783.794.126 2.700.041.398 2.723.866.886 1.856.339.862 1.400.872.629 1.500.777.560 2.458.968.438 2.863.551.927 2.247.539.658 1.764.534.857 1.652.897.633 1.674.677.619 24.627.862.594 152% 557,51
Available water -121.210.060 1.322.500.231 -550.563.139 -1.258.987.199 -1.199.285.391 283.781.886 1.343.824.798 -1.496.019.805 -2.040.158.683 -1.575.729.161 -1.591.020.084 -1.591.528.824 -8.474.395.431 -52,5% -191,84 18%
Human consumption 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 7.318.744 0,045% 0,17 0,25%
Livestock + Wildlife
consumption 1.982.189 1.918.248 1.982.189 1.982.189 1.790.364 1.982.189 1.918.248 1.982.189 1.918.248 1.982.189 1.982.189 1.918.248 23.338.679 0,14% 0,53 0,79%
Agriculture 0,0 0,0 0,0 0,0 0,0 0,0 13.996.567,5 14.463.119,8 13.996.567,5 12.287.681,2 0,0 0,0 54.743.936 0,34% 1,24 1,86%
Total water demand 2.592.085 2.528.143 2.592.085 2.592.085 2.400.260 2.592.085 16.524.710 17.055.204 16.524.710 14.879.766 2.592.085 2.528.143 85.401.359 0,53% 1,93 2,89%
Water availability -123.802.144 1.319.972.088 -553.155.223 -1.261.579.284 -1.201.685.651 281.189.802 1.327.300.088 -1.513.075.009 -2.056.683.393 -1.590.608.926 -1.593.612.169 -1.594.056.967 -8.559.796.790 -53,0% -193,77
m3/d Mm3/y mm/y m3/km2/d % m3/d Mm3/y mm/y m3/km2/d %
Human consumption 3124 1,14 0,03 0,07 4% 20051 7,32 0,17 0,45 9%
Livestock + Wildlife
consumption54531 19,90 0,45 1,23
62%63942 23,34 0,53 1,45
27%
Agriculture 30423 11,10 0,25 0,69 35% 149983 54,74 1,24 3,40 64%
Total 88078 32,15 100% 233976 85,40 100%
Current water demand (2009) Future water demand (2025)
Current water balance in 2009
Total [m3]
Total [m3]
Water demand
compared to annual
rainwater surplus
[m3]
Water demand
compared to annual
rainwater surplus
[m3]
2.950.106.915
1.140.200
19.903.722
85.401.359
2.950.106.915
7.318.744
23.338.679
11.104.381
32.148.303
Water balance in 2025
54.743.936
Support for water sector plan development - 43 -
Annex 2: 3R potential map.
Figure 30: 3R potential map of Garissa County
The 3R potential is translated into ‘zones’ that gathers certain geological and
hydrogeological conditions and makes the landscape more or less suitable for one or
another kind of intervention. The aim of the potential map is to give users a first
understanding of the water harvesting potential in the area, and to guide them towards
choosing the kind of solutions that are more feasible in a certain area.
The map is part of a wider package of tools and guidelines developed by Acacia Water
that can be used for infrastructure planning. Local surveys and field investigation are
always necessary in the planning of infrastructure to ensure the potential matches the
field reality.
Figure 31 presents the 3R zone intervention table for Kenya RAPID. Note that there can
be multiple 3R intervention groups possible within one 3R zone, while each intervention
group is also already classified with its potential effectiveness when implemented in a
- 44 - Draft report
certain 3R zone. The potential of an intervention group is classified ranging from
uncertain (∆)/limited ((x)) to very high potential (xxx).
A: P
ans
and
val
ley
dam
s
B: S
and
dam
s
C: S
ub
-su
rfac
e d
ams
D: S
hal
low
gro
un
dw
ater
: wel
ls
and
riv
erb
ank
infi
ltra
tio
n
E: F
loo
d w
ater
sp
read
ing
and
spat
e ir
riga
tio
n
F: G
ully
plu
ggin
g, c
hec
k d
ams
and
oth
er r
un
off
red
uct
ion
/in
filt
rati
on
me
asu
res
G: H
ard
su
rfac
e an
d c
lose
d t
anks
H: D
eep
gro
un
dw
ater
ab
stra
ctio
n:
wel
ls/
bo
reh
ole
s
Zone 1A x1 xxx x x
x x (x)2
Zone 1B x1 xx xxx x x ∆ x (x) 2
Zone 2
x1 xx1
Zone 3A x1 xx xx x
x x (x) 2
Zone 3B x1 x xx x x
x (x) 2
Zone 3C x1 ∆ ∆ ∆
x x x2
Zone 3D x1 ∆ ∆ ∆ ∆
x x2
Zone 3E x
x
x x x2
Zone 3F x
x1
x x x2
Zone 4A x
xx xx
x x2
Zone 4B x1 (x) (x) ∆ X ∆ x x2
Zone 4C x
∆ (x) x ∆ x x2
Zone 4D x
xxx
∆ x x2
Zone 5A x
x
Zone 5B x
∆
∆
Zone 6
(x)
xxx
Figure 31: Zone classification for the 3R potential for Kenya RAPID.
xxx: very high potential; xx: high potential; x: possible; (x): limited potential; ∆: uncertain
Zone 1: combined with 3B, 3D, 3F, 4C, 4D, if impermeable layer is present
Zone 2: combined with 0A or 0B; with 0C additional measures (A-G) are recommended
The main sustainable way in Garissa County in making more water available is by
storing rain water on the ground or in the ground. Where which solution applies
depends mainly on the type and thickness of the soil, but also for example on the slope
and the land use.
Most part of Garissa County are sedimentary formations (see the geological map in Fout!
Verwijzingsbron niet gevonden.). The impact of these soils determines the landscape
water harvesting potential strongly.
Due to the fact that Garissa County is an arid county, salinization of soils was, is and
will always be a risk. Soils in a part of the county have already become saline. The saline
soils in Garissa County are the solonetz soils (saline soils, zone 5b, red dotted areas, in
Figure 30). This zone 5b should be kept under vegetation and should be used for
extensive grazing. Water harvesting in surface water structures in these areas is
Support for water sector plan development - 45 -
possible, but soils can leach the salts, which will affect the water quality of the stored
water.
A major other parts of the Garissa County are planosols and lixisols, which can have
slow surface water drainage so that waterlogging can occur (zone 5a, blue dotted areas,
in Figure 30). These areas should also be kept under vegetation and should be used for
extensive grazing because of the potential of holding water and sustain vegetation.
These slow drainage characteristics of the soils can also create opportunities for surface
water reservoirs and water pans. Road water harvesting also has a relevant potential in
Garissa county.
The remaining parts of Garissa County are classified as zone 4, which are areas that
have a potential for shallow groundwater. Especially in these arid lands, groundwater
storage is useful, because water does not evaporate, water quality remains pretty much
the same, and water can be even purified, because of the filtration capacity of the
sediments. Here floodwater spreading and spate irrigation is also an option.
Deep groundwater potential
To access the potential for exploitation of deep groundwater, Acacia Water used the
‘Groundwater Potential Maps’, developed by the British Geological Survey (BGS).
In Annex 3 the background information of this analysis is given, explaining the
methodology and limitations of this data set.
Figure 32 presents the Deep Groundwater Potential Map that Acacia Water has compiled
based on the BGS publication. The classification of the different zones for deep
groundwater potential has been done based both on the storage and productivity.
Potential of groundwater ranges from low storage and low productivity on one hand and
medium high storage and high productivity on the other hand.
The low potential occurs in a small area in the northwest of Garissa County. However it
does not means that there is no groundwater available. In these formations (basement
rock), groundwater is only present in the fractures. So here water can be found, but the
fractures needs to be identified. In these fractures, water can be present, but yields are
due to groundwater recharge, interconnection of fractures, seasonal variation, among
other factors.
- 46 - Draft report
Figure 32: Groundwater potential map for Garissa County based upon analyses BGS data with the
areas with most boreholes (red hatch)
On the opposite of the spectrum, high productivity and medium to high storage, are
mainly unconsolidated sediments. Sedimentary formations are often characterized by
intercalations of clayey layers (low production) and sandy layers (higher production).
One of the aspects in being successful in groundwater abstraction is to identify the
coarse layers, where the productivity is the highest. Exploration drillings can help to
identify these layers and drilling companies have often knowledge of the most
productive boreholes depths. Having good borelogs of earlier drilled borehole is
therefore very useful, in order to build up an understanding about the different layers in
the sedimentary depositions and allocating boreholes. Hydrogeologists are often able to
access these data sets and help making an informed decision.
Drilling a successful borehole is not always a guarantee of continuous use of the
groundwater. Pumping tests often gives indications of the productivity of the boreholes
and can estimate the amount of groundwater available. A good monitoring network of
productive boreholes will also provide information to help hydrogeologists to indicate
Support for water sector plan development - 47 -
the sustainable yield and prevent over exploitation as well as provide information of the
hydrogeological environment as a hole.
Since long term groundwater exploitation can only be possible when recharge of the
aquifer is ensured, we advise very strongly the planning of infiltration interventions to
enhance aquifer recharge and improve sustainability. These kind of interventions are
often planned in the case of shallow groundwater abstraction, but will certainly help the
recharge of deep aquifers in the long term.
Another zone, named ‘high borehole density’ has been defined in the assessment of the
deep groundwater potential. This zone indicated where a high density of boreholes is
present aiming to ‘warn’ authorities and project partners for the risks of overexploiting
the aquifer. This is specially the case of the Merti aquifer in western part of Wajir
County.
An assessment of the groundwater quality also needs to take place to express the
suitability for the different users. A high potential for groundwater exploration does not
implies that the water is not saline, free of fluoride or has other water quality
constraints. Investigation and assessment of the chemical parameters need to be carried
out in order to determine if it meets standards requirement for human consumption.
Grazing area potential map
Grassland in arid lands are becoming more and more fragile. This is why rangeland
management is becoming increasingly important. Understanding how to keep the
grazing lands healthy is essential. This is explained in Box 2.
The main reason why grasslands have to be managed is because:
- In order to keep grasses alive, you have to graze them.
- But in order to keep them alive, you should not over graze them.
Because at different places, grasses are dying earlier or later, rangeland management is
much less straightforward than water management. Rangelands produces grasses which
the livestock feed on. These grasses need water to grow, but are also very much
dependent on grazing management practices. It is still important to take water
availability into account, but bad grazing management practices are believed to be a
large cause of rangeland degradation seen in many parts of the world the last decades.
Research is still being done about this, but it seems that growth characteristics of grass
are a key factor. The main approach that takes the characteristics of grasses into
account is applying short periods of very intensive grazing after a wet period, and then
letting the area rest to regenerate till the next wet period. Areas that are dying the first
should be grazed first, before the areas that remain green longer. In the end all grasses
should be grazed, in order to prepare the soil for the new growing season. This utilizes
the rangeland as effectively as possible without degrading the lands.
- 48 - Draft report
Figure 33 shows a reclassified map using the average NDVI and variance of the NDVI
(see section 2.4). The basis of the reclassification is explained in Table 10. Green areas
(high average NDVI) with a low variance are always green (very green in Table 10), while
green areas with a high variance are sometimes very green and sometimes less green
(light green in Table 10). On the other hand, areas with a low average NVDI but a high
variance are sometimes green (orange in Table 10), while areas with a low variance and a
low average NDVI are always poorly vegetated (red in Table 10). So by combining the
average and the variance, a division is made to determine barren areas, green areas, and
areas in any degree variation between these extremes.
In order to achieve the best grazing practices, grazing management systems needs to be
set with the local communities. Figure 33 gives the grazing area potential classification.
Areas that have a generally low mean NDVI and a high variance, only have vegetation for
short times (orange and red in) should be grazed first after rainy seasons. The areas
with a medium NDVI and a low to high variance remain green longer (yellow and light
greenFigure 33) should be grazed later in the season.
Changing the grazing patterns can also be pushed with water infrastructure and 3R
measures. If water sources in the red and orange areas will only be available directly
after the rains, and they will close or be finished/empty after a few months, herdsmen
and their livestock are discourage to go through these areas.
For the areas that should be kept untouched until the rest is grazed, the opposite
approach can be used: there is no water available (water sources are closed) in the
beginning of the dry season.
Box 2: The importance of grazing management
Considering growth, grasses are different from most other types of vegetation.
Grass has the special characteristic that the growing cells, called meristems, are
located in the top of the grass stem and close at the surface level, at the base. This
means that grasses only grow at the top, or at the bottom.
Grasses die off above the ground in the dry season, so the top meristem dies off as
well. When the grasses are not eaten by livestock or mowed, the old grass stems
remain standing and prevent new grasses to grow: there is no space and light for the
new stems to grow, the new grasses are smothered by the old grasses. Due to the
fact that standing grasses decompose very slowly, the new grass is suffocated by its
own old grass stems, if they are not removed.
This is why grazing all the land is vital: to keep the land healthy, it needs to be
grazed before the start of the new rainy season.
At the same time, when grasses are grazed, the grass-plant need to reduce their root
activity: less sugar is produced by the remaining leaves, so also less roots can be
supported. If the plant is eaten over and over again, roots are becoming shorter and
shorter, and the plant is weakened and weakened until it dies.
Support for water sector plan development - 49 -
Table 10: NDVI classification. Legend of Figure 34.
Low mean NDVI
(<0.25)
Medium mean NDVI
(0.25 - 0.5)
High mean NDVI
(>0.5)
Low
variance
(<0.1)
Poorly
vegetated,
barren
Mostly a bit
green
Always green
Medium
variance
(0.1 - 0.2)
Sometimes a
bit green,
mostly barren
Sometimes very
green,
sometimes
poorly
vegetated
Sometimes very
green,
sometimes
poorly
vegetated
High
variance
(>0.2)
Sometimes
green,
sometimes
barren
Sometimes very
green,
sometimes
nearly barren
Often very
green,
sometimes
nearly barren
Figure 33: Vegetation abundance in Garissa County, based on NDVI data. Legend in Table 10
- 50 - Draft report
These principles should be applied in the Garissa County context. However, other
factors local circumstances, culture, climate and others can play an equally important
role, and the system of managed grazing must be tailored to these factors as well. But by
implementing good rangeland management plans that keep the characteristics of
grasses into account (all grassland should be grazed every year, but not too much),
grazing lands can be made more healthy and can even be revitalised. In general there are
five themes that should come back in a good rangeland management plan:
1) Land use planning;
2) Water infrastructure planning;
3) Rotational grazing;
4) Bunched grazing;
5) Land rehabilitation; and
6) Institutional building.
To conclude, livestock and rangeland management should be in line with county
policies. If it is the county’s ambition to let pastoralist communities change to semi- or
agro-pastoralism, livestock and rangeland management policies will have to be adjusted
accordingly, and resources for this process being made available. The ambition and
preconditions for that purpose should then also be reflected in the CIDP.
Support for water sector plan development - 51 -
6 Conclusions and recommendations
Water demand and availability
Even though there is a negative annual net precipitation in Garissa County, rainfall
analysis shows that the three months with rainfall surplus in an average year (typically
the months April, May and November) provide sufficient rainwater to accommodate the
estimated annual water demand.
Section Fout! Verwijzingsbron niet gevonden. shows that the total water demand in
2009 was very small compared to the total amount of precipitation. It is expected that
the total estimated demand in 2025 is around 0.56% of the total annual rainfall.
In order to make more water available for improving the current situation and for the
development of new economic activities, two main measures should be taken into
consideration in Isiolo:
- Choosing for alternative techniques to prevent evaporation of water, such as
drip irrigation and focussing on drought tolerant crop production and.
- Retention and recharge of water during the wet period (when there is a surplus
of water) in covered reservoirs and in aquifers.
Development of water use
Domestic water development
With the expected population growth domestic water demand will grow (3% per year). If
water use are brought to national standards as well (20 l/c/d), domestic water demand
in 2025 will increase to 7.3 Mm3/year. This is very small compared to the annual rainfall
16,153 Mm3/y. The challenge however is how to make the needed infrastructure, so that
this can be covered by shallow groundwater, or treated river water, so that borehole
water abstractions can be reduced. For rural populations implementation of 3R
measures for domestic water development can be a very good alternative. The demand
is relatively low and if infrastructure is planned accordingly, water van be stored and
made available during the dry periods. To meet the water quality demands for this user
group, depending on the type of intervention, the water harvested might need however
treatment.
Livestock water development
Development of water points for livestock is a very important factor, but it is uncertain
how this will develop; while there should be enough water for livestock (23,3 Mm3/y is
needed for drinking water for livestock in 2025), grazing grounds in the arid lands of
Northern Kenya are fragile. Interviews with local leaders and livestock specialists
generally indicate that current livestock herds and the available rangelands overall are
already at their maximum carrying capacity. More livestock can result in more
overgrazing, resulting in desertification. Strict livestock and rangeland management,
- 52 - Draft report
directed by the (County) government is therefore recommended. Thematic areas that
should be included in rangeland management are: land use planning, rotational grazing,
bunched grazing, land rehabilitation and institutional building.
Creating more economical value from the livestock, however could be more promising.
This includes milk production and dairy products combined with selling the cows for
meat. This however, this means that livestock needs to be kept at farms, so that milk
can be shipped to a factory. This means that these farms then will depend on the import
of externally produced fodder.
Because of the widespread saline soils, but also because of the fact that Garissa County
is located in arid land, special attention needs to be given to grass and rangeland
management in order to keep them in good conditions and prevent them from
degradation. Good planning of the grazing throughout the year needs to be aligned with
the needed infrastructure, so that grazing will only happen at the times that the grasses
should be grazed (the grasses that dry out should be grazed first).
Agricultural water development
Agricultural water use has a much larger impact on the water balance. With about 2,000
ha under production in 2009, water use in the growing season is nearly 2 times higher
than domestic and livestock water use combined. Water usage will increase with the
development of new irrigation schemes from 93,000 m3/d to around 467,000 m3/d in
the growing period.
The water use during the growing season in 2009 is estimated to have been around 0.15
Mm3/d, of which approximately 62% of the water is used for agriculture. Due to a further
planned increase in irrigation schemes, total water use will increase to 0.55 Mm³/d
towards 2025, whereby the portion of (irrigated) agriculture will increase to 85%.
Because irrigated agriculture in arid lands will always eventually result in salinization of
the fields, dryland farming with water harvesting measures (e.g. agroforestry) is
preferred over irrigated agriculture.
Due to the fact that Garissa County is located in arid lands, annual rainfall is lower than
the annual potential evapo(transpi)ration. In an average year, Garissa has two months
(November and April) with a higher rainfall than actual evaporation, resulting in a
rainwater surplus. In a dry year however, there is no surplus: none of the months have a
higher rainfall than the actual evaporation. Taking this into account means that in dry
years no rainwater is available for agriculture.
Considering the agricultural development ambitions of Garissa County, and the water
demand which comes with this, available water sources and how these can be used
should be critically reviewed. Efficient methods of water abstractions as irrigation, such
as drip irrigation or covered rainwater harvesting tanks, should be investigated. The
preferred and most sustainable option is, however, still rain-fed dryland farming in
combination with water harvesting measures. Worldwide experience in dryland farming
is increasing quickly, exchange of experiences in different countries around the world is
becoming more and more easy thanks to internet access and social media.
Some information is given in Annex 4 regarding sustainable agriculture in arid land
Support for water sector plan development - 53 -
Water potential
To meet the water demand necessities, decision makers need to face the challenge of
planning and developing infrastructure based on the principles of IWRM. The different
demands need to be met not only in terms of quantity and quality, but also in terms of
time and space. Rainwater harvesting is therefore the most sustainable way, since it is
the largest water input and recharged every year. Other opportunities can be found in
the use of river discharge and the groundwater resources. Both need to be evaluated
carefully to be developed in a sustainable way to avoid overexploitation and generate
conflict among the different users group.
Rainwater harvesting potential
The biophysical landscape of Garissa County also provides very effective, low-cost
alternatives for the harvesting and buffering of (rain) water through 3R measures,
especially for times of high needs (droughts). In Garissa County storage of rainwater
mainly on the ground, and in some parts also in the ground shows a lot of potential for
interventions such as road water harvesting, water pans and sand dams.
Parts of the county have soils with poor drainage, these soils can be used for surface
water storage, while other more sandy soils have good potential for rainwater storage as
shallow groundwater. Large parts of the county have smaller potential because soils
have become saline. This should be a warning for the county to implement these
projects where salinization of this soils is not worsened. Smart implementation of small
scale water harvesting solutions together with the right vegetation measures, where soil
fertility is improved will prevent salinization and help to keep soils healthy, so that
grazing grounds remain vital.
The starting point for choosing for interventions should be the 3R potential map for
Kenya RAPID, given in figure 30. By crossing the zones classification (1 to 6) of the 3R
potential with the possible intervention and its potential given in figures 27 and 31, one
will be able to make a pre-selection of possible interventions. When moving towards
planning interventions, it is advisable to have a field recognition of the area for
assessment of the suitability of the pre-selected interventions. In ‘Guidelines & tools for
3R Water Plan Support’ (Acacia Water, 2017), more detailed information is given on the
technical aspects of each kind of intervention and limitations, expected costs and
productivity.
Deep groundwater potential
Some areas in Garissa County show a relatively high potential for deep groundwater
exploration. However, around Garissa town and in the south of Garissa County, hitting
very saline groundwater is likely. More in general, a high potential for groundwater
exploration does not guarantee that water is there, whilst it neither implies that the
water is not saline, free of fluoride or has other water quality constraints.
Rural communities in Garissa rely on the groundwater resources through borehole
exploitation for their livelihood activities. Groundwater is a reliable resource, especially
when it is stored in porous media and needs to be developed carefully, respecting the
concepts of sustainability. An aquifer has always a limited amount of water. Many cases
have been registered of boreholes that are not functioning anymore and many of the
have simply ‘dried out’. Stressing the importance of recharging the groundwater
resources is very important to ensure that it will remain available throughout the
seasons and will support user in the periods of the year when rain is absent.
- 54 - Draft report
Using the groundwater resources also mean thinking about enhancing recharge to
ensure that groundwater will remain available in the future.
Stakeholder engagement and policy integration
IWRM is, however, not only a process of water resource development and
implementation, but also includes stakeholder engagement and policy integration. It will
be up to the County Government, water resources planners and IPs to consult
stakeholders, such as local communities, to identify what their water needs and issues
are and where priorities lay, presently as in the future. Only based on this engagement –
which should run parallel with creating a clear, on-the-ground picture of the biophysical
landscape, water resources, availability and demand – identification, selection and
planning of water infrastructure development can commence. Hence, identification and
selection of different water development opportunities (e.g. 3R interventions) should
already be a participatory and bottom-up process.
Based on the IWRM principles, including stakeholder engagement and integration of the
biophysical landscape, water availability and demand which are described in this report,
there will be a better knowledge base for identification of water development and
infrastructure opportunities. This should then also be reflected in the CIDP and adjusted
accordingly. It is recommended that county governments refrain more and more from
in-situ, location specific water infrastructure, but rather provide a clear, structured but
flexible framework and working environment to make well-informed strategic decisions
for water development. This report, but also the ‘Guidelines & tools for 3R Water Plan
Support’ report developed by the technical advisor in Kenya RAPID, will provide valuable
guidelines and practical tools for water resource planning. It will assist them to
overcome the barriers of choosing for one or another water source infrastructure,
including 3R interventions. This should then also be integrated and reflected in the CIDP
in such a way that planning of (3R) interventions can be used for future up-scaling to
other parts and regions in the county, and even to other counties.
Support for water sector plan development - 55 -
7 Literature
British Geological Survey (BGS), 2011. MacDonald AM, Bonsor HC, Calow RC, Taylor RG,
Lapworth DJ, Maurice L, Tucker J and Ó Dochartaigh BÉ. - Groundwater resilience
to climate change in Africa.
Garissa county – County Integrated Development Plan 2013 - 2017
IGRAC, 2004. Fluoride in groundwater: Probability of occurrence of excessive
concentration on global scale
KNBS (2009). Census data 2009 for Kenya on national, provincial, county and district
level, Kenya National Bureau of Statistics (KNBS)
Tuinhof, A., Van Steenbergen, F., Vos, P. and L. Tolk, 2012. Profit from Storage. The costs
and benefits of water buffering. Wageningen, The Netherlands: 3R Water Secretariat.
WRMA, 2016. Consultancy Services for Water Resources Assessment for Decision Making
in Garissa County, KinConsult Associates Ltd. Consulting Engineers, Final Report, June
2016.
Acacia Water, 2017 Guidelines & Tools for 3R Water Plan Support (yet to be published)
Acacia Water, 2017 Guidelines & Tools for 3R Water Plan Support (yet to be published)
Annexes - 59 -
County Garissa
Location Garissa County
Scenario: (Type of year) Average
Area size [km2] 44175
Month Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total
Days per month 31 30 31 31 28 31 30 31 30 31 31 30 365
Precipitation [mm] 37,6 91,1 49,2 13,5 4,6 40,4 86,1 31,0 4,7 4,3 1,4 1,9 365,7
Actual evaporation [mm] 40,4 61,1 61,7 42,0 31,7 34,0 55,7 64,8 50,9 39,9 37,4 37,9 557,5
Net precipitation [mm] -2,7 29,9 -12,5 -28,5 -27,1 6,4 30,4 -33,9 -46,2 -35,7 -36,0 -36,0 -191,8
River inflow [m3/month] 0,0
River outflow [m3/month] 0,0
net river usage [m3/month] 0 0 0 0 0 0 0 0 0 0 0 0 0,0
net river usage [mm/month] 0 0 0 0 0 0 0 0 0 0 0 0 0,0
net water availability [mm/month] -2,7 29,9 -12,5 -28,5 -27,1 6,4 30,4 -33,9 -46,2 -35,7 -36,0 -36,0 -191,8
Year of census 2009
Current year of calculation 2009
Population in 2009 623.060
Annual population growth 3,0%
Future target year 2025
Population in 2025 999.828
Current domestic water demand
[l/pers/d]5
Future domestic water demand
[l/pers/day]20
Annual livestock population growth 1,00%
Animal l/day/animal l/day l/day/animal l/day
Cattle 903678 25 22591950 1059634 25 26490838
Sheep 1224448 5 6122240 1435762 5 7178808
Goat 2090613 5 10453065 2451408 5 12257041
Camel 236423 55 13003265 277225 55 15247351
Donkey 75178 30 2255340 88152 30 2644564
Pig 59 10 590 69 10 692
Chicken 104295 1 104295 122294 1 122294
Total water use [l/day] 54.530.745 63.941.587
Total water use [m3/year] 19.903.722 23.338.679
Annual wildlife population growth 0,00%
Animal l/day/animal l/day l/day/animal l/day
African Elephant 0 205 0 0 205 0
Giraffe 0 25 0 0 25 0
Grevy Zebra 0 20 0 0 20 0
Hunter's Hartebeest 0 2 0 0 2 0
Thomson's Gazelle 0 1 0 0 1 0
Total water use [l/day] - -
Total water use [m3/year] - -
Wildlife 2017 Wildlife 2030
Water resources
WIL
DLI
FELI
VES
TOC
KW
ATE
R IN
& O
UTF
LOW
PO
PU
LATI
ON
WA
TER
USA
GE
Livestock 2009 Livestock 2025
Water demand
- 60 - Draft report
Crop - growing period Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Area [ha]
Beans x x x 333,3333333
Maize x x x x 333,3333333
Wheat x x x x 333,3333333
Millet X X X X 333,3333333
Tomato x x X X 333,3333333
Wheat X X X X 333,3333333
0
0
Crop - estimated water usage
[m3/month] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total
Beans 421053 435088 421053 1277193
Maize 520000 537333 520000 537333 2114667
Wheat 478261 494203 478261 494203 1944928
Millet 440000 454667 440000 454667 1789333
Tomato 500000 516667 500000 516667 2033333
Wheat 478261 494203 478261 494203 1944928
0
0
Total water usage [m3/month] 0 0 0 0 0 0 2837574 2932160 2837574 2497072 0 0 11104381
Crop - growing period Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Area [ha]
Beans x x x 1666,666667
Maize x x x x 1666,666667
Sorghum x x x x 1666,666667
Millet X X X X 1666,666667
Tomato x x X X 1666,666667
Wheat X X X X 1666,666667
0
0
Crop - estimated water usage
[m3/month] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total
Beans 2105263 2175439 2105263 6385965
Maize 2600000 2686667 2600000 2686667 10573333
Sorghum 2200000 2273333 2200000 2273333 8946667
Millet 2200000 2273333 2200000 2273333 8946667
Tomato 2500000 2583333 2500000 2583333 10166667
Wheat 2391304 2471014 2391304 2471014 9724638
0
0
Total water usage [m3/month] 0 0 0 0 0 0 13996568 14463120 13996568 12287681 0 0 54743936
122
0
Length of growing period
Growing period too short
Growing period too long
CU
RR
ENT
IRR
IGA
TED
CR
OP
S
91
122
122
122
122
0
Explanation growing period
Growing period correct
122
122
122
122
0
122
0
FUTU
RE
IRR
IGA
TED
CR
OP
S
Length of growing period
91
Annexes - 61 -
Agricultural water demandTotal water usage per growing period per crop for different area of irrigated land as percentage of annual rainwater surplus
Actual water availability (net precipitation) Current water demand (2009)
Water situation for an Average year in Garissa County, Garissa County
Water resources
Water Balance
Cumulative net precipitation for dry, average and wet years
Precipitation Actual Evaporation
Monthly net precipitation for dry, average and wet years
Total water usage per day for different crops for different areas of irrigated land
Future water demand (2025)
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Am
ou
nt
of
aver
age
pre
cip
ita
tio
n
Month
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Am
ou
nt
of
aver
age
pre
cip
ita
tio
n
Month
-400,0
-300,0
-200,0
-100,0
0,0
100,0
200,0
300,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Cu
mm
ula
tive
net
pre
cip
itat
ion
[mm
]
min net prec average net prec max net prec
-75,0
-50,0
-25,0
0,0
25,0
50,0
75,0
100,0
125,0
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Mo
nth
ly n
et p
reci
pit
ati
on
[mm
]
min net prec average net prec max net prec
-2,5E+09
-2,0E+09
-1,5E+09
-1,0E+09
-5,0E+08
0,0E+00
5,0E+08
1,0E+09
1,5E+09
2,0E+09
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Wat
er
avai
lab
ility
[m
3]
Month
0,0E+00
5,0E+05
1,0E+06
1,5E+06
2,0E+06
2,5E+06
3,0E+06
3,5E+06
4,0E+06
4,5E+06
5,0E+06
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Wat
er
dem
and
[m3]
Month
Human consumption Livestock + Wildlife consumption Agriculture
0,00%
0,50%
1,00%
1,50%
2,00%
2,50%
3,00%
3,50%
4,00%
4,50%
5,00%
0 2500 5000 7500 10000 12500 15000 17500 20000 22500
% o
f an
nu
al ra
inw
ate
r su
rplu
s
Area [ha]
Maize
Beans
Sorghum
Millet
Tomato
Wheat
0
200000
400000
600000
800000
1000000
1200000
0 2500 5000 7500 10000 12500 15000 17500 20000 22500
Tota
l wat
er
usa
ge p
er d
ay [
m3/
d]
Area [ha]
Maize
Beans
Sorghum
Millet
Tomato
Wheat
0,0E+00
2,0E+06
4,0E+06
6,0E+06
8,0E+06
1,0E+07
1,2E+07
1,4E+07
1,6E+07
1,8E+07
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Wat
er
dem
and
[m3]
Month
Human consumption Livestock + Wildlife consumption Agriculture
- 62 - Draft report
Water availability [m3] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total [mm]
Precipitation 1.662.584.067 4.022.541.629 2.173.303.747 597.352.663 201.587.238 1.784.559.446 3.802.793.236 1.367.532.122 207.380.975 188.805.697 61.877.549 83.148.795 16.153.467.163 100% 365,67
Actual evaporation 1.783.794.126 2.700.041.398 2.723.866.886 1.856.339.862 1.400.872.629 1.500.777.560 2.458.968.438 2.863.551.927 2.247.539.658 1.764.534.857 1.652.897.633 1.674.677.619 24.627.862.594 152% 557,51
Available water -121.210.060 1.322.500.231 -550.563.139 -1.258.987.199 -1.199.285.391 283.781.886 1.343.824.798 -1.496.019.805 -2.040.158.683 -1.575.729.161 -1.591.020.084 -1.591.528.824 -8.474.395.431 -52,5% -191,84 18%
Human consumption 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 95.017 1.140.200 0,007% 0,03 0,04%
Livestock + Wildlife
consumption 1.690.453 1.635.922 1.690.453 1.690.453 1.526.861 1.690.453 1.635.922 1.690.453 1.635.922 1.690.453 1.690.453 1.635.922 19.903.722 0,12% 0,45 0,67%
Agriculture 0,0 0,0 0,0 0,0 0,0 0,0 2.837.574,4 2.932.160,2 2.837.574,4 2.497.072,5 0,0 0,0 11.104.381 0,07% 0,25 0,38%
Total water demand 1.785.470 1.730.939 1.785.470 1.785.470 1.621.878 1.785.470 4.568.513 4.717.630 4.568.513 4.282.542 1.785.470 1.730.939 32.148.303 0,20% 0,73 1,09%
Water availability -122.995.529 1.320.769.292 -552.348.609 -1.260.772.669 -1.200.907.269 281.996.417 1.339.256.285 -1.500.737.435 -2.044.727.196 -1.580.011.703 -1.592.805.554 -1.593.259.763 -8.506.543.734 -52,7% -192,56
Water availability [m3] Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Total [mm]
Precipitation 1.662.584.067 4.022.541.629 2.173.303.747 597.352.663 201.587.238 1.784.559.446 3.802.793.236 1.367.532.122 207.380.975 188.805.697 61.877.549 83.148.795 16.153.467.163 100% 365,67
Actual evaporation 1.783.794.126 2.700.041.398 2.723.866.886 1.856.339.862 1.400.872.629 1.500.777.560 2.458.968.438 2.863.551.927 2.247.539.658 1.764.534.857 1.652.897.633 1.674.677.619 24.627.862.594 152% 557,51
Available water -121.210.060 1.322.500.231 -550.563.139 -1.258.987.199 -1.199.285.391 283.781.886 1.343.824.798 -1.496.019.805 -2.040.158.683 -1.575.729.161 -1.591.020.084 -1.591.528.824 -8.474.395.431 -52,5% -191,84 18%
Human consumption 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 609.895 7.318.744 0,045% 0,17 0,25%
Livestock + Wildlife
consumption 1.982.189 1.918.248 1.982.189 1.982.189 1.790.364 1.982.189 1.918.248 1.982.189 1.918.248 1.982.189 1.982.189 1.918.248 23.338.679 0,14% 0,53 0,79%
Agriculture 0,0 0,0 0,0 0,0 0,0 0,0 13.996.567,5 14.463.119,8 13.996.567,5 12.287.681,2 0,0 0,0 54.743.936 0,34% 1,24 1,86%
Total water demand 2.592.085 2.528.143 2.592.085 2.592.085 2.400.260 2.592.085 16.524.710 17.055.204 16.524.710 14.879.766 2.592.085 2.528.143 85.401.359 0,53% 1,93 2,89%
Water availability -123.802.144 1.319.972.088 -553.155.223 -1.261.579.284 -1.201.685.651 281.189.802 1.327.300.088 -1.513.075.009 -2.056.683.393 -1.590.608.926 -1.593.612.169 -1.594.056.967 -8.559.796.790 -53,0% -193,77
m3/d Mm3/y mm/y m3/km2/d % m3/d Mm3/y mm/y m3/km2/d %
Human consumption 3124 1,14 0,03 0,07 4% 20051 7,32 0,17 0,45 9%
Livestock + Wildlife
consumption54531 19,90 0,45 1,23
62%63942 23,34 0,53 1,45
27%
Agriculture 30423 11,10 0,25 0,69 35% 149983 54,74 1,24 3,40 64%
Total 88078 32,15 100% 233976 85,40 100%
Current water demand (2009) Future water demand (2025)
Current water balance in 2009
Total [m3]
Total [m3]
Water demand
compared to annual
rainwater surplus
[m3]
Water demand
compared to annual
rainwater surplus
[m3]
2.950.106.915
1.140.200
19.903.722
85.401.359
2.950.106.915
7.318.744
23.338.679
11.104.381
32.148.303
Water balance in 2025
54.743.936
Annexes - 65 -
Annex 3: Background information BGS
groundwater potential maps
In a study by MacDonald et al. (2012), the Groundwater potential maps were created for the
whole of Africa (Figure 34) by the British Geological Survey (BGS). These maps provide
information on aquifer productivity, groundwater recharge and depth to groundwater, in
which they appear quite reliable.
Figure 34: Quantitative groundwater maps for Africa (BGS, 2011).
Their approach can be summarized in four steps:
1. Use a geological basemap
2. Reclassify this map
3. Use hydrogeological data to attribute aquifer properties
4. Refine map attributes with local data
This method is used to make the groundwater potential maps for the 5 northern counties.
Use of the BGS potential maps
For the Garissa situation the geological map has been reclassified. The properties of each
group are shown in Fout! Verwijzingsbron niet gevonden.. In total there are 5 different
categories, ranging from low storage and low productivity to high productivity with medium
– high storage.
The groundwater potential map is shown in Figure 32. As can be seen in the figure Garissa
County has large parts with good potential for deep groundwater. Nevertheless, a high
potential for groundwater exploration does first of all not guarantee that water is there, and
secondly it neither implies that the water is not saline, free of fluoride or has other water
quality constraints.
- 66 - Annexes
Table 11: Aquifer properties per geological unit
Origin Aquifer flow/
storage type
Aquifer
productivity
GW storage
Basement rock Metamorphic Fracture Low
(0.1-1 l/s)
Low
(<1 m)
Volcanic rock Volcanic Fracture Moderate
(1-5 l/s)
Medium-low
(1-10m)
Limestones Sedimentary Fracture (karst) Moderate
(1-5 l/s)
Medium (10-
25 m)
Mixed
sedimentary rock
Sedimentary Intergranular
and fracture
Moderate
(1-5 l/s)
Medium (10-
25 m)
Isiolo-Nyambeli-
Mount Kenya
basalt formation
Volcanic Intergranular
and fracture
High Medium-low
(1-10m)
Unconsolidated
sediments
Sedimentary Intergranular High
(5-20 l/s)
Medium-high
(25-50 m)
When this map is used, the map still should not be used as the only source to decide what to
do where. This map is only providing water quantity potential and is mend to help guide the
project into a more plausible direction. On the ground fieldwork and other additional
information however is always necessary:
• Drilling failure: Numbers given for aquifer productivity are an indication – not every
borehole will necessarily produce these numbers. Generally 50% of boreholes are
expected to have yields that fall outside the expected range (British Geological Survey
– 2011);
• Water quality: Only water quantity is included, water quality (see Figure 21) is not
part of this map. A high potential for groundwater does not mean that the water is
not saline, free of fluoride, et cetera. Based on geology, soils and existing data from
wells and boreholes, an indication can be given of the water quality to be expected as
is shared in section 3.7;
• Local biophysical context: Local topography can influence aquifer properties. For
instance, some geological formations are so highly elevated compared to other
locations that no water remains long enough to infiltrate. Understanding the
landscape and flow patterns and knowing the static groundwater levels should guide
interpretation;
• Anthropogenic activity is not taken into account. If water levels have dropped due to
over abstraction, groundwater availability will be less;
• Fracture identification: In all hard rock formations water can be present in fractures.
Identification of these fractures is most important in siting of borehole locations in
such formations;
• Layered sediments: Sedimentary formations can be composed of a variety of textures.
Sandy layers have a high productivity and medium to high storage, while heavy clay
layers can have a high groundwater storage potential, but an extremely low
productivity. Knowing the different layers of the soil is important in sedimentary
formations.
Annexes - 67 -
Annex 4: Sustainable agriculture in
arid land
If irrigated agriculture is chosen, there are very effective low-cost (rain) water harvesting and
buffering options to bridge the long dry periods between the two rainy seasons, which can
extent up to 9 months in dry years. Construction of (covered) rainwater harvesting tanks is
one example of a water storage solution to provide agricultural water during the entire
irrigation season from April until July in sustainable and non-soil-harming way. Box 3
provides more information about this specific technology.
Box 3: Surface water harvesting tanks (source: Tuinhof et al., 2012)
Rainwater harvesting are large pits excavated at central points in the watershed to capture
overland flow during intensive rain events. Typically, the tanks have a trapezoidal shape with
the top of the tank measuring 10 by 9 metres and the bottom 6 by 6 metres. The depth of the
structures is 3 metres and the storage capacity is about 120 m³. A roof consisting of wooden
poles and plastic sheets covers the tank to reduce water losses due to evaporation. The walls
of tank are stone masonry and the floor is made of concrete, preventing percolation losses.
During the rains, overland flow is directed to the tank by a V-shape structure placed half
perpendicular to the direction of the slope. Before entering the tank the water is led through
a silt trap, preventing excess silt from entering the tank. Once the tank is full, it is closed and
the captured water is stored till the start of the dry irrigation season. At the start of the
season the water of the rainwater harvesting tank is lifted using a treadle (pedal) pump. Then
the water is being lifted to elevated barrels, enough head (pressure) is created to feed the
water into a drip irrigation system situated lower (see figures below). Over 10,000 of these
water tanks have been constructed in Amhara National Regional State, Ethiopia, in order to
prolong water availability.
- 68 - Annexes
Alterative to irrigated agriculture is dryland farming. This is becoming more and more
applied worldwide. It is however quite a type of agriculture that adopts quite a different
approach: maximising application of different plants and crops, mimicking nature, including
agroforestry etc. In this drought tolerant crops such as millet, sorghum, chickpeas etc. are
included. Box 4 provides more information on dryland farming.
Box 4: Dryland farming
Realising and understanding that all irrigated agriculture eventually leads to
salinization of agricultural lands (see Box 1), alternative farming methods have to
be adopted and implemented. One way of doing this, is via dryland farming.
Sustainable and regenerative dryland farming incorporates 3R measures and a
good understanding of the biophysical context, but includes also drought tolerant
cropping and perennial crops (agroforestry).
The main aspects for successful dryland farming are:
- Making water available: Harvesting all rainwater, and making sure it
infiltrated into the soil, so that soil moisture and shallow groundwater are
recharged. This is done by applying the earlier mentioned 3R measures
- Improving soil fertility: Covering the soil as much as possible with organic
matter (mulch) in order to prevent evaporation, prevent soil erosion and
increase soil fertility and infiltration of rainwater.
- Increasing plant cover: Planting a combination of as much different plants
as possible using different layers (tall and small trees, shrubs, climbers,
ground covering plants and annual crops) in order to maximise growth
during the whole year, keeping the soil covered and improving resilience
to droughts (different plants respond different to droughts)
van Hogendoornplein 4
2805 BM Gouda
Telefoon: 0182 – 686 424
Internet: www.acaciawater.com
Email: [email protected]