Application of the rainfall infiltration breakthrough (RIB) model for groundwater recharge estimation in west coastal South Africa

摘要

Recharge estimation in arid and semi-arid areas is very challenging. The chloride mass balance method applied in westernSouth Africa fails to provide reliable recharge estimates near coastal areas. A relationship between rainfall events and waterlevel fluctuations (WLF) on a monthly basis was proposed in the rainfall infiltration breakthrough (RIB) model for thepurpose of groundwater recharge estimation. In this paper, the physical meaning of parameters in the CRD and previousRIB models is clarified, and the RIB model is reviewed with the algorithm improved to accommodate various time scales,namely, daily, monthly and annual scales. Recharge estimates on a daily and monthly basis using the revised RIB approachin 2 study areas, one in a sandy alluvial aquifer (Riverlands) and the other in the Table Mountain Group (TMG) shallowunconfined aquifer (Oudebosch), are presented, followed by sensitivity analysis. Correlation analysis between rainfalland observed WLF data at daily scale and monthly scale, together with recharge estimates obtained from other methods,demonstrates that the RIB results using monthly data are more realistic than those for daily data, when using long timeseries. Scenarios using the data from Oudebosch with different rainfall and groundwater abstraction inputs are simulated toexplore individual effects on water levels as well as recharge rate estimated on a daily basis. The sensitivity analysis showedthat the recharge rate by the RIB model is specifically sensitive to the parameter of specific yield; therefore, the accuraterepresentative specific yield of the aquifer needs to be selected with caution. The RIB model demonstrated in these two casescan be used to estimate groundwater recharge with sufficiently long time series of groundwater level and rainfall available insimilar regions. In summary, the RIB model is best suited for shallow unconfined aquifers with relatively lower transmissiv-ity; the utility of the RIB model for application in different climatic areas under different hydrogeological conditions needsto be further explored.