Abstract
The ACRU agrohydrological model, in the form of ACRU2000 and its salinity module, ACRUSalinity, was employed in catchment-scale assessment of widespread irrigation with low quality mine-water in undisturbed (un-mined) and rehabilitated soils in the Upper Olifants basin of South Africa. The study area comprised a small catchment of 4.7 km2 located in a coal-mine environment, known as the Tweefontein Pan catchment. The catchment drained to a surface reservoir (Tweefontein Reservoir) of maximum capacity and surface area 4 000 Mℓ and 1.5 km2, respectively. The catchment was instrumented to measure hydrodynamic responses and simulated as a hydrological system. Consideration was given to runoff, groundwater storage, evapotranspiration, baseflow, interception, irrigation water supply and rainfall, thereby accounting for all the dominant hydrological components of the system. Three scenarios were simulated using the available records for 5 years (1999 to 2004). The first was a baseline scenario representing the prevailing condition in the study area and the other 2 scenarios represented widespread irrigation with the mine-water on undisturbed and rehabilitated soils. In simulating the widespread irrigation on rehabilitated soils, a distinction was made between a rehabilitated irrigated area before and after the re-establishment of the equilibrium water table. Comparison of the results from the simulated scenarios indicated that a greater undisturbed area (max of 160 ha) than rehabilitated area (max of 120 ha) could be irrigated with mine-water from the Tweefontein Reservoir. Irrigation on rehabilitated soils depleted the water in the reservoir more rapidly than irrigation on undisturbed soils, due to lower runoff and higher ingress to groundwater in rehabilitated areas.Keywords: mine-water, widespread irrigation, mined land irrigation, Upper Olifants, catchment scale, hydrological assessment, ACRU2000
Highlights
A large amount of low quality mine-water is generated by the coal mines in South Africa
The general problem of the disposal of the generated low quality mine-water has been well recognised in South Africa (DWAF, 1993; Pulles et al, 1995; Bell et al, 2001; Younger, 2002; Coleman et al, 2003; Heath et al, 2004)
In setting up ACRU2000 and ACRUSalinity for the catchment, the interception loss, consumptive water use coefficient and the fraction of the plant roots active in extracting moisture from the soil were dependent on the identified land use type for the non-irrigated area and on maize in the irrigated areas
Summary
A large amount of low quality mine-water is generated by the coal mines in South Africa. The objective of this study, was to use a catchment as the basis for comparing the impact of widespread irrigation of undisturbed and rehabilitated soils, using mine-water, on the water resources of parts of the Upper Olifants basin. It aimed at the integrated assessment of the volume of water and the mass of salt in the different components of the hydrological system in the catchment. Coal mining in the Upper Olifants, by as many as 29 collieries, generates large quantities of low quality minewater and has been recognized as the dominant activity in the Witbank Dam catchment with respect to the pollution and degradation of surface water resources (DWAF, 1993). An estimated seepage of 2 400 m3/day occurs from the Tweefontein Reservoir into the underground reservoir
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