The effects of alien vegetation clearing on a coastal aquifer, Bushmans River Mouth, Eastern Cape

摘要

The Department of Water Affairs and Forestry's Working for Water Programme is currently involved in country-wide clearing of invasive alien plants. This has resulted in increases of 25percent to 120percent in streamflow after clearing. To date, however, limited work has been carried out in South Africa to quantify the effect of alien vegetation removal on the water balance of an aquifer. A hydrogeological investigation of the Bushmans River Mouth Aquifer determined that the 1997 clearing programme of this area resulted in a 31 cm rise in water levels from measured differences in the average level and a 41 cm rise determined using the cumulative rainfall departure method. This equates to a 6percent increase in aquifer storage and a 138percent increase in effective recharge. It was noted that groundwater salinity worsened immediately after clearing, considered to be a result of remobilisation of vadose zone salts with a water level rise. This study demonstrates the effectiveness of a clearing programme on improving the water balance of an aquifer, thereby increasing the groundwater volume available for abstraction.