Because the basin in Botswana has several major towns, including Gaborone, intersector competition for water is predicted and therefore the FAO considered the irrigation potential of 5 000 ha more realistic than the calculated amount of 15 200 ha from the country report from SADC Conference in 1992 (SADCC-AIDAB 1992). Of the current 1 381 ha currently used for irrigation, 56 % is extracted from the Limpopo River and its tributaries or from storage reservoirs while 44 % is extracted from groundwater. Most of the irrigation is for horticulture.
Irrigation techniques used predominantly include sprinkler irrigation which accounts for 64 % of the total (FAO 2004). Localized irrigation (i.e. drip and micro-sprinkler) accounts for 20 % of the total while surface irrigation (i.e. furrow and basin, hoses, and hand-watering) is 16 %.
Irrigation in Mashatu, Botswana.
Source: Vogel 2010
( click to enlarge )
Irrigation with Gypsiferous Coal Mine Water
A simulation study in Botswana with gypsiferous coal mine water with an electrical conductivity (EC) of about 310 mS/m³ (Jovanovic et al., 2001) led to the conclusion that, under the particular climate and soil conditions of Selibe-Pikwe, large amounts of effluent mine water can be disposed successfully of through irrigation.
Between 18 and 32 percent of the total amount of salts added through irrigation was predicted to leach after 11 years, the remainder being precipitated in the soil profile in the form of gypsum. A slow process of gypsum dissolution and leaching by rainfall was predicted after the cessation of irrigation with mine water. This means that large quantities of salt can be immobilized in the soil profile, removed temporarily from the water system, and released in small amounts into the groundwater over an extremely long time period.
Source: FAO 2004
