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time often constitutes a more common cause of crop failure than absolute water
scarcity due to low cumulative annual rainfall. This is why it is important to distin-
guish between droughts and dry spells. An agricultural drought occurs when the
cumulative plant available soil water is significantly lower than the cumulative crop
water requirement, i.e.; there is absolute water scarcity. A dry spell is a short period
of water stress, often only for a couple of weeks during crop growth. A short period
of water stress can have a serious effect on crop yield if it occurs during water-
sensitive development stages such as flowering (Rockström and de Rouw 1997 ).
5.2 Land Use or Vegetation Cover
Working to reduce erosion and redirect runoff into appropriate catchments can lead
to high labor inputs due to the need to keep the catchment area free of vegetation so
that it is as efficient as possible. The vegetation of the selected area will heavily
influence runoff, infiltration and retention levels, and must be taken into account
prior to implementation to reduce high labor costs in the future. Maintenance of the
catchment system must also be understood when selecting the size of the catchment.
The system may be damaged during heavy rainstorms or require regular mainte-
nance which could prove problematic in the future (Qadir et al. 2007 ).
5.3 Topography and Terrain Profile
Topography is an important aspect of WH as the slope of the terrain and gradient
will greatly impact the size and type of catchment area of the WH system (Prinz and
Singh 2000 ).
5.4 Soil Type and Soil Depth
The soils of a WH site must function as a water storage facility, a medium for plant
growth and a water collection surface. These soil conditions must be met in a single
area. As such, soil depth and texture are important physical elements for under-
standing how to design a successful WH system. Soil type and depth help judge
percolation and infiltration rates, potential for runoff and the storage potential of
water within the soil itself (Prinz and Singh 2000 ).
A. Yazar and A. Ali