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

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

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

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

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

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

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

Specific Objectives 1.To establish the hydrological processes controlling water conservation from contour ridges. 2.To compare water conservation in fields with different contour ridge designs and that with no contour ridges. 3.To evaluate the water conservation benefit of contour ridges. 4.To develop a model for guiding the design of contour ridges for water conservation. Murray & Roberts South Africa

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

Study methods 1.On farm field trials 2.Modeling water movement in a field with contour ridges Murray & Roberts South Africa

Continuity equation for storage in ridge

On farm field trials plot arrangement Murray & Roberts South Africa

Instrumentation on one of trial fields Murray & Roberts South Africa

Soil moisture measurement

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

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

Experimental challenges

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

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

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

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