rainwater harvesting and artificial groundwater recharge
TRANSCRIPT
Rainwater harvesting and artificial groundwater recharge to improve
Kwemakame Spring Yields
Harry Rolf SamSamwater
27/10/2014
Project Location
• Tanga region• Lushoto district• Kwemakame / Kwai villages
Kwemakame project history• Chamavita, Kees Kempenaar • <1989 construction of gravity water scheme• 2004 ‘depletion’ • 2007 practical research project
– Cause of depletion?– How to improve?
• 2007 – 2010 field investigations &monitoring• 2010/2012 pilot design & construction• 2013 ‘post-pilot’ monitoring and reporting• 2014 dissemination
Project PartnersLocal Partners:• Village Kemakame/Kai
• Chamavita (Chama cha maendaleo vijijini tanga)
• Pangani Basin Water Office
The Netherlands:• AquaforAll (funding)• Aquanet (funding)• PWN/SamSamWater (techn.
Assistance)• SPOT Tanzania
Kwemakame/Kwai Estimated 3000 people
• Kwai/Kwemamake Water Board• 9 sub-villages
Water demand 1 liter/sec
Scheme constructed 1989, but the yield dropped since the initiation
Present Water sources (dry season):• Dindira ‘spring’ catchment (0,35 l/sec)• Kidandi ‘spring’catchment (0,15 l/sec)
Total yield Dindira
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
01/0
1/11
01/0
3/11
01/0
5/11
01/0
7/11
01/0
9/11
01/1
1/11
01/0
1/12
01/0
3/12
01/0
5/12
01/0
7/12
01/0
9/12
01/1
1/12
01/0
1/13
01/0
3/13
disc
harg
e in
l/se
c
tot flow monthly avg
estimated demand (including animals)
domestic only
Study area
Water catchment is up in the mountains at Dindira
Dindira Valley 1950 – 2000 masl
Bedrock outcrop
Dindira shallow aquifer
Impervious base
2100 m
2000 m
1950 m
Gravity spring captation
Impervious base
Rainfall and evapotranspiration
Recharge
‘spring’ wall intake
Water intakes
Water scheme
From 11 intakes to 5 collection chambers
From collection chambers to main storage tank
From storage tank down to village distribution
Dindira main Storage tank 1850 m
Distribution area 1650 m
Water point Dindira hamlet
Research methodology
• Monitoring (Rainfall, evaporation, yields,…)• Field reconnaisance • Mapping• Analysis/ understanding
MonitoringRainfall & pan evaporation
Training
data collectors
Manual discharge reading in collection chambers
Groundwater levels
GPS mapping
Geo electrical sounding & profiling
Auger drilling
Water quality testing
AnalysisWenner profile Dindira (Kwemakame) intake nr.2 sub-catchment
1940
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
-10 -7.5 -5 -2.5 0 2.5 7.5 10 12.5 17.5 20 22.5 27.5 30 32.5 37.5 40 42.5 47.5 50 52.5 57.5 60 62.5 67.5
distance from centre (m)
altit
ude
(m)
100
1000
1000
groundsurface (waypoints)ground surface (interpret)apparent res (Ωm) 3x5mapparent res (Ωm) 3x10m
outcrop
Aquifer properties
Cumulative rainfall
0
200
400
600
800
000
200
Nov Dec Jan Feb March April May June July August Sept Oct
Dindira 2007/2008Dindira 2008/2009Normal Rainfall (New LocClim)Normal rainfall LushotoDindira 2009/2010
Rainfall analysis
Kwemakame total discharge
0
10
20
30
40
50
60
jan/
08m
rt/08
mei
/08
jul/0
8se
p/08
nov/
08ja
n/09
mrt/
09m
ei/0
9ju
l/09
sep/
09no
v/09
jan/
10m
rt/10
mei
/10
jul/1
0se
p/10
rain
fall
(mm
/day
)
00.511.522.533.5
disc
harg
e (l/
sec)
rainfall (mm
flow in ch 5
27/10/06 chamber 5
Rainfall discharge relationship
Reasons for depletion
• Over decades: deforestation.• Rapid population increase• Climate change? (no proof)• Since 1989: using up groundwater storage
Generally:Too little recharge,while still rainwater is flowing out overland
Reasons for depletion (2)Using up groundwater storage
Too little recharge
Rain water is running off , being lost out of the area
Intakes are just ‘scraping off’ recharge
Groundwater dropping in the years after initiation
Key to improvement
INCREASE THE AMOUNT OF RAINWATER INFILTRATION
(‘Recharge enhancement’)
Strategy options
• Plant trees (yes, good solution on the long run)
• (Let it rain more)• (Pump water)• (Deeper intake wall)• (Surface water storage and treatment)• Add water in the underground:
– ‘artificial recharge’
Strategy to improve
Artificial Recharge:– Harvest rainwater that is running of– Temporary storage– Infiltration in the underground– ‘boost’ groundwater > increase yield
3R RetentionRechargeRe-use
Dindira Pilot to prove strategy
)
Existing intake nr 2
Infiltration pit
storage (hillside) dam
Pilot 1
Hillside dam location
Runoff catchment & diversion channel
Hillside dam
Infiltration pit
Filter trench and infiltration pit
SHIDA KUBWARain disaster April
2012Dam repaired and
re-enforced summer 2012
Fillings of the dam Dec 2012 – May 2013
0.0
0.3
1 Dec 12 21 Dec 12 10 Jan 13 30 Jan 13 19 Feb 13 11 Mar 13 31 Mar 13 20 Apr 13 10 May 13 30 May 13
wat
erle
vel r
eser
voir
(m)
0
10
20
30
40
50
60
prec
ipita
tion
(mm
/day
)
Precipitation (mm/day) Level (m+diver) Manual measurements
as recorded by diver logger and handreadings
Run off
Run off from bedrock
Water diversion to the dam
Fillings of the reservoir
Infiltration through the reservoir bottom
Release to the infiltration pit(after 1 day settling)
Results
A total amount of 2,5 million liters has been infiltrated
This water is added to groundwater and slowly flows down to intake, flowing out in the dry season
Some intakes were closed,conserving groundwater for the dry season. This has been beneficial as well.
2013 dry season effect:The people from Kwemakame/Kwai noticed considerably more water.
“we don’t know exactly what you’ve been doing up there in Dindira, but it helped a lot. We didn’t experience having so much water for many years. Even in the last dry months we had water all day long”.
Dry season yield monitoring
year month yield (l/sec)2009 Oktober 0.152010 November 0.422011 September 0.312012 November 0.25
average before the project: 0.302013 November 0.702014 29/10/2014 0.90
Observed yield of the Dindira Water Catchment at the end of the dry season
•Yield increased from 0.30 to 0.80 l/sec•Kwemakame/Kwai requires is 1.0 l/sec•Kidandi source gives 0.15• The required water is now available
CONCLUSIONS• Rainwater harvesting and infiltration by
artificial recharge can significantly improve the water supply
• Water conservation by closing intakes during the rain season adds a positive effect as well.
• Proper maintenance and operation is a first requirement for sustainability
• The community, Chamavita and Pangani Basin Water were deeply involved in this project and gained a lot of new knowledge on how to improve the ‘spring’ water catchment system. They are eager to replicate and upscale the concept to similar water schemes.
CHALLENGES AND LESSONS LEARNED• Assessment of runoff (where, how much)• Proper operation and maintenance is crucial • Re-use Silts that are trapped in the dam• Construction of earth dams on steep slopes.• To replicate this in other areas, you first need to
understand the groundwater system• For this understanding hydrological monitoring
is required (yields, groundwater levels, rainfall,…)
Other (technical) lessons learned.• It is extremely difficult to manage extensive hydrological
monitoring without experts on the ground, who are continuously analysing and checking the quality of the data collection.
• Know your runoff in the early project stages. It is important to know how much runoff water is there to catch. In our case the runoff was less than expected. Runoff tracks must be identified (and quantified) beforehand during heavy rains.
• Rainfall variability is high. For quantification purposes it is essential to have multiple rain stations over the catchment, measuring not only daily totals but rainfall intensity as well.
• The results show that rationing is effective, saving additional water for the dry season. In particular think of closing the highest intakes during the rain season ( starting with nr.2)
• How much and how fast will the infiltration water flow out at the source/intake: a set of ‘design rules’ is required.
• Proper operation and maintenance of the facility and its surroundings is required to assure that it will continue supplying.
Water quality• Indication of raised Nitrate contents by
agriculture • Water source protection must be addressed• Artificial recharge preferably in the forest area,
lakini….
Asante
MASWALI ?
The other pilot, pilot nr.2
new intake
storage
(valley) dam
Pilot 2 DESIGN
Pilot 2 area
Valley dam location
construction
Auger drilling
Auger drilling
New intake
Auger drilling
outlet pipe trench
• Unfortunately the new intake has much less water than expected
• Permanent Groundwater seepage flow to the dam 5000 lita every day!
• This water is treated by a SSF (Slow Sand Filter)
4000 l/day5000 l/day
• Very unfortunately the new intake has much less water than expected due to bad siting (by us).
• The aquifer is largely blocked by clays• In stead the water is seeping to the
reservoir (4000 l/day)• Water is treated by a Slow Sand Filter
Slow sand filter
MASWALI ?
Rainwater runoff