understanding upstream-downstream interactions of rainwater water harvesting: approach
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PRESENTATIONIntroductionRainwater harvesting studies under PN17Proposed approach of assessing up-stream/down
stream interactions
INTRODUCTIONWater scarcity in the Limpopo basinFFBAR studies on rainwater harvesting (RWH)Phase 2 – rainwater managementPropose approaches of assessing up-stream/down
stream interactions
Rain Water HarvestingRWH is the process of concentrating rainfall as
runoff from a larger/small area for use in smaller target area (Botha et al, 2003).
In-field rainwater harvestingTillage and other in situ soil water management /
conservation agriculture strategiesBasins (Zambia, Zimbabwe), Zai (Mozambique, Mali and
Burkina Faso), Chololo (Tanzania) , Trus system in Sudan, and the Tassa system in Niger – differ in size and spacing
Ex-field water management practices and runoff captureRunoff catchments (check dams, rock outcrops), roof
catchment, dams, weirs and natural streams
RWH Technologies: PN17 Zimbabwe
Mzingwane Catchment (Conservation Farming, basins)
Mozambique Chokwe (Zai Pits)Use of plastic material
South AfricaOlifants Basin - Chololo PitsSupplemental irrigation – water collected from a weir
Conservation Farming-Zimbabwe
0
5
10
15
20
25
30
Mpofu N Ncube J Ncube Sibanda
Farm
Sea
sona
l run
off
(mm
) .
CP DP Ripper Basins
Benefits of basinspromote infiltration of rainwater minimize soil, water and nutrient losses from
the fieldreduce siltation and pollution (by
agrochemicals) downstream of the fields groundwater recharge as soil water is lost
through deep drainage especially on sandy soils
BUTWater logging occurs in high rainfall seasons
Zai Pits - MozambiqueResults
Maize and cowpea yields increased under Zai Pits compared to conventional methods
21% of farmers in the study area adopted the pits
Which crops do we use under RWH?Need to think of a model to assess the potential
payoffs of RWH?
Use of plastic material-MozambiqueIncrease area for in-field rainwater
harvestingPossibility of increasing yield by increasing
water availability during the growing seasonSystem costly, is there a possibility to use
local material?
Chololo Pits–South AfricaWorcester Enable
Chololo pits Conventional Ridges Conventional
Rainfall (mm) 268 268 361 361
Maize grain yield (kg/ha) 585 0 335 0
Grain yield/crop evapotranspiration (kg/mm)
1.74 0 1.05 0
Person days 43 10 15 10
Cost (ZAR/ha) 1512 316 521 316
Chololo Pits – South AfricaHigher yield obtained under Chololo pits
compared to ridgesRidges performed better than the
conventional practice
Assess catchment bio-physical characteristics (landsat, GIS)
Assess suitability of RWH types and crop type
Assess socio-economic conditions of farmers that affect adoption of RWH
Find % (agriculture) area suitable for each type of RWH in the catchment
Determine flow reduction at different scales and catchment outlets
Determine crop yields and crop economics
Determine naturalized or current (with effects of developments) river flows from hydrological model
Apply different levels of adoption (25%, 50%, 75% & 100%) for each RWH type
Concluding RemarksRWH techniques have been tried at field
scale Out-scaling and up-scaling approaches of
successful RWH technologies is in the futureSocio-economic analysis of the RWH
technologies needed
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