Understanding Upstream-Downstream Interactions of Rainwater Water Harvesting: Approach

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Understanding Upstream-Downstream Interactions
of Rainwater Water Harvesting Approach

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

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PRESENTATION

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

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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

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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

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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

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Conservation Farming-Zimbabwe
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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

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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?

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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?

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Chololo Pits South Africa
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Chololo PitsSouth Africa
Worcester Worcester Enable 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
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Chololo Pits South Africa

• Higher yield obtained under Chololo pits compared
  to ridges
• Ridges performed better than the conventional
  practice

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Proposed Methodology
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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

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THANK YOU