towards a better design of micro catchment water harvesting schemes l.
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Towards a Better Design of Micro-Catchment Water Harvesting Schemes. By Dave Best. Direct rainwater harvesting from micro-catchment schemes (within field catchment systems). Overland flow harvested from a short catchment. 1-30 metres.

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direct rainwater harvesting from micro catchment schemes within field catchment systems
Direct rainwater harvesting from micro-catchment schemes (within field catchment systems)
  • Overland flow harvested from a short catchment. 1-30 metres.
  • Concentration of surface runoff from a catchment into lower lying cropped area.
  • Ratio of catchment to cultivated area- from 1:1 to 20:1.
  • Offers a passive, low cost means of increasing the amount of water available to crops
advantages over alternative irrigation schemes
Advantages over alternative irrigation schemes.
  • Systems relatively easy to maintain and operate.
  • Simple and easy to construct
  • Once constructed little maintenance is required.
  • Runoff water low salt content
examples of micro catchment water harvesting systems
Examples of micro-catchment water harvesting systems

1) Negarim micro-catchments

2)Contour bunds

slide5

3) Semi circular bunds

4). Contour ridges

design considerations
Design Considerations
  • To improve catchment efficiency runoff can be increased, and infiltration and interception reduced.
  • Balance between the efficiency of a catchment in producing runoff and its susceptibility to erosion
    • Increasing runoff by clearing slopes of vegetation and compaction of surfaces may lead to greater erosion with longer slope lengths and steeper gradients.
determination of catchment yield
Determination of Catchment yield.
  • Rainfall Characteristics.
    • average annual rainfall, peak rainfall intensity, and minimum expected annual precipitation.
  • Physiographic factors.
  • Infiltration Capacity.
catchment cultivated area
Catchment : Cultivated area
  • Rainfall
  • Runoff
  • Crop water requirements.
catchment cultivated area calculations
Catchment : Cultivated area-calculations…….
  • Water Harvested = Catchment area x Design rainfall x Runoff coefficient x Efficiency factor.
example
Example.
  • Crop Water Requirement = 525 mm
  • Design Rainfall = 310 mm
  • Runoff Coefficient == 0.5
  • Efficiency Factor == 0.75

C = 525 – 310 = 1.85

Ca 310 x 0.75 x 0.5

surface treatments
Surface treatments
  • Mechanical treatments (smoothing and compacting).
  • Colloidal dispersion methods (slaking, sodium).
  • Hydrophobic applications (water repellents).
  • Surface binding materials (cementing and sealing)
  • Surface covering (asphalt, rubber and plastic)
slide13
Experiment testing different techniques for catchment lining on a plantation of Jujube (Zizyphus mauritaina)
  • Shallow conical micro-catchments of 1.0m radius were constructed around the plant