Understanding Upstream-Downstream Interactions of Rainwater Water Harvesting: Approach

1. Understanding Upstream-Downstream Interactions of Rainwater Water Harvesting: Approach Bongani Ncube, Manuel Magombeyi, Walter Mupangwa , Paiva Manguambe, David Love

2. PRESENTATION • Introduction • Rainwater harvesting studies under PN17 • Proposed approach of assessing up-stream/down stream interactions

3. INTRODUCTION • Water scarcity in the Limpopo basin • FFBAR studies on rainwater harvesting (RWH) • Phase 2 – rainwater management • Propose approaches of assessing up-stream/down stream interactions

4. Rain Water Harvesting • RWH 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 harvesting • Tillage and other in situ soil water management / conservation agriculture strategies • Basins (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 capture • Runoff catchments (check dams, rock outcrops), roof catchment, dams, weirs and natural streams

5. RWH Technologies: PN17 • Zimbabwe • Mzingwane Catchment (Conservation Farming, basins) • Mozambique • Chokwe (Zai Pits) • Use of plastic material • South Africa • Olifants Basin - Chololo Pits • Supplemental irrigation – water collected from a weir

6. Conservation Farming-Zimbabwe

7. Benefits of basins • promote infiltration of rainwater • minimize soil, water and nutrient losses from the field • reduce siltation and pollution (by agrochemicals) downstream of the fields • groundwater recharge as soil water is lost through deep drainage especially on sandy soils • BUT • Water logging occurs in high rainfall seasons

8. Zai Pits - Mozambique • Results • 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?

9. Use of plastic material-Mozambique • Increase area for in-field rainwater harvesting • Possibility of increasing yield by increasing water availability during the growing season • System costly, is there a possibility to use local material?

10. Chololo Pits – South Africa

11. Chololo Pits–South Africa

12. Chololo Pits – South Africa • Higher yield obtained under Chololo pits compared to ridges • Ridges performed better than the conventional practice

13. Proposed Methodology

14. Concluding Remarks • RWH techniques have been tried at field scale • Out-scaling and up-scaling approaches of successful RWH technologies is in the future • Socio-economic analysis of the RWH technologies needed

15. THANK YOU