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Rainwater Harvesting Potential for Semi Arid Smallholder Farming

Rainwater Harvesting Potential for Semi Arid Smallholder Farming. PhD Research Presentation to WaterNet Challenge Programme Final Scientific Workshop 15-18 June 2009 By Alexander Mhizha Witwatersrand University Supervision Dr. J. Ndiritu (Wits University)

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Rainwater Harvesting Potential for Semi Arid Smallholder Farming

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  1. Rainwater Harvesting Potential for Semi Arid Smallholder Farming PhD Research Presentation to WaterNet Challenge Programme Final Scientific Workshop15-18 June 2009 By Alexander Mhizha Witwatersrand University Supervision Dr. J. Ndiritu (Wits University) Dr. I. Nyagumbo (University of Zimbabwe) Acknowledgements for funding to: Murray & Roberts South Africa

  2. Introduction • Most smallholder farmers in Southern Africa rely on rain fed cropping; • (e.g., Malawi, 90 %; Botswana, 76 %; Kenya, 85 %; and Zimbabwe, 70 –80 %, of the population) (Rockström, 2000). • Average yields are low (0.5-1 t/ha) compared to on station yields (5-6 t/ha.) • Rainwater harvesting can be used to improve water availability to crops Murray & Roberts South Africa

  3. Definition • Rainwater harvesting is defined as a method for inducing, collecting, storing, and conserving local surface runoff (Boers and Ben-Asher 1982 quoted in Boers 1994) Murray & Roberts South Africa

  4. Introduction • Various types of rainwater harvesting (RWH) strategies exist • In-situ RWH, e.g. terracing, contour ridges (bunds) • Off field e.g. runoff catchments (check dams, rock outcrops etc), roof catchments, dams or reservoirs on natural streams /rivers. • Growing interest in the use of contour ridges for water harvesting. • Appropriate rainwater harvesting strategies suited to local environments are critical for effectiveness. Murray & Roberts South Africa

  5. The Problem • Knowledge on hydrological functioning of contour ridges is limited to soil erosion control & not on runoff harvesting. • Current designs geared to safely dispose off excess runoff and prevent rill & gulley erosion Murray & Roberts South Africa

  6. Justification • Limited knowledge on the effectiveness of contour ridges in improving water availability to crops limits the design options available for them and their adaptability by farmers. • Potential to channel runoff harvested from adjacent catchments into cropped areas. Murray & Roberts South Africa

  7. Objective of the study • To quantify the rainwater harvesting potential of contour ridges in a semi arid catchment and develop a model for guiding improved contour ridge design incorporating water conservation. Murray & Roberts South Africa

  8. Specific Objectives • To establish the hydrological processes controlling water conservation from contour ridges. • To compare water conservation in fields with different contour ridge designs and that with no contour ridges. • To evaluate the water conservation benefit of contour ridges. • To develop a model for guiding the design of contour ridges for water conservation. Murray & Roberts South Africa

  9. Location of Study Area Zhulube Catchment Bulawayo Filabusi Beitbridge Mzingwane Catchment Murray & Roberts South Africa

  10. Study methods • On farm field trials • Modeling water movement in a field with contour ridges Murray & Roberts South Africa

  11. Continuity equation for storage in ridge

  12. On farm field trials plot arrangement Murray & Roberts South Africa

  13. Instrumentation on one of trial fields Murray & Roberts South Africa

  14. Soil moisture measurement

  15. Preliminary Results Objective 1 Hydrological Processes controlling water availability 22 Jan 2009 15 Jan 2009 • Groundwater seepage from the water that infiltrates into the ridge • Increased infiltration in the field Murray & Roberts South Africa

  16. Comparison DLC versus NC Soil moisture variation within a DLC plot Soil moisture variation within a non C plot

  17. Experimental challenges

  18. Comparison DLC versus GC Soil moisture variation within a DLC plot Soil moisture variation within a GC plot

  19. Preliminary Observations Crops close to contour ridges tend to be healthier Generally farmers neglect weeds in areas around contour ridges Murray & Roberts South Africa

  20. Outstanding Work Work in all objectives is continuing but major works still to start on: Evaluation of water conservation benefits from contour ridges Developing a model for designing contour ridges for water conservation Murray & Roberts South Africa

  21. I Thank You Acknowledgements for funding to: Murray & Roberts South Africa

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