Bongani Ncube, Manuel Magombeyi, Walter Mupangwa , Paiva Manguambe, David Love

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 Africa

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

THANK YOU