Groundwater Recharge Assessment for the Kalahari Catchment of North-eastern Namibia and North-western Botswana with a Regional-scale Water Balance Model

Abstract

Groundwater is the only source of drinking water for the inhabitants of the Kalahari. Thus understanding spatial and temporal variations in groundwater recharge is very important and a regional-scale water balance model has therefore been set up for a 209,149 km 2 catchment in north-eastern Namibia and north-western Botswana. The model has a spatial resolution of 1.5×1.5 km, daily model time-steps, and climatic input parameters for 19 years are used. The distributed, GIS-based, process-oriented, physical water balance model (MODBIL) used in this study considers the major water balance components: precipitation, evapotranspiration, groundwater recharge, and surface runoff/interflow. Mean precipitation for the study area is 409 mm a −1 , while mean actual evapotranspiration is 402 mm a −1 and mean groundwater recharge is 8 mm a −1 (2% of mean annual precipitation). The recharge pattern is mainly influenced by the distribution of soil and vegetation units. Groundwater recharge shows a high inter-and intra-annual variability, but not only the sum of annual precipitation is important for the development of groundwater recharge; a large amount of precipitation in a relatively short period is more important. Published independent data from the Kalahari in Namibia, Botswana and the Southern African region under similar climatic conditions are used to verify the modelling results.

Sensitivity of simulated hillslope subsurface flow to rainfall patterns, soil texture and land use

“…In addition, in our scenario analysis, short-term heavy rainfall with high intensity substantially increased the hillslope subsurface flow. This was consistent with the study by Wanke et al (2008), who found that high rainfall intensity is important for the development of soil water leakage.…”

“…This was consistent with the study by Wanke et al . (), who found that high rainfall intensity is important for the development of soil water leakage.…”

Hand dug wells in Namibia: An underestimated water source or a threat to human health?

“…If direct recharge is the most important process, then the chloride mass balance method which is a reliable method can be used and the parameters for this methodology and its determination must be obtained. These parameters are relatively easy to obtain (e.g., Brunner et al, 2004;Wanke et al, 2008).…”

The combined use of MODFLOW and precipitation-runoff modeling to simulate groundwater flow in a diffuse-pollution prone watershed

“…On the other hand, numerical models are useful and robust tools to quantify recharge. Precipitation-runoff modeling or sometime referred to as watershed modeling is a surface-water focused approach, which generally yields groundwater recharge estimates as a residual term in the water budget Equation (Wanke et al 2008). These models are usually lumped and provide a single recharge estimate for the entire watershed.…”