Articles | Volume 3, issue 3
Hydrol. Earth Syst. Sci., 3, 353–361, 1999
Hydrol. Earth Syst. Sci., 3, 353–361, 1999

  30 Sep 1999

30 Sep 1999

Hydrological processes and water resources management in a dryland environment IV: Long-term groundwater level fluctuations due to variation in rainfall

J. A. Butterworth*,1, R. E. Schulze2, L. P. Simmonds3, P. Moriarty1, and F. Mugabe4 J. A. Butterworth et al.
  • 1Institute of Hydrology, Wallingford, OX10 8BB, UK
  • 2Department of Agricultural Engineering, University of Natal, Pietermaritzburg, South Africa
  • 3Department of Soil Science, University of Reading, RG6 6DW, UK
  • 4Chiredzi Research Station, P.O. Box 97, Chiredzi, Zimbabwe
  • *Postal and e-mail address for corresponding author:
  • John Butterworth, National Resources Institute, Chatham Maritime, ME4 4TB

Abstract. To evaluate the effects of variations in rainfall on groundwater, long-term rainfall records were used to simulate groundwater levels over the period 1953-96 at an experimental catchment in south-east Zimbabwe. Two different modelling methods were adopted. Firstly, a soil water balance model (ACRU) simulated drainage from daily rainfall and evaporative demand; groundwater levels were predicted as a function of drainage, specific yield and water table height. Secondly, the cumulative rainfall departure method was used to model groundwater levels from monthly rainfall. Both methods simulated observed groundwater levels over the period 1992-96 successfully, and long-term simulated trends in historical levels were comparable.
Results suggest that large perturbations in groundwater levels area a normal feature of the response of a shallow aquifer to variations in rainfall. Long-term trends in groundwater levels are apparent and reflect the effect of cycles in rainfall. Average end of dry season water levels were simulated to be almost 3 m higher in the late 1970s compared to those of the early 1990s. The simulated effect of prolonged low rainfall on groundwater levels was particularly severe during the period 1981-92 with a series of low recharge years unprecedented in the earlier record. More recently, above average rainfall has resulted in generally higher groundwater levels. The modelling methods described may be applied in the development of guidelines for groundwater schemes to help ensure safe long-term yields and to predict future stress on groundwater resources in low rainfall periods; they are being developed to evaluate the effects of land use and management change on groundwater resources.