Groundwater modeling to consider effects of drought on river base-flow

A river and groundwater system interacts in two forms as a river may feed the groundwater or groundwater may feed the river. In later case which river drains the plain, droughts may decrease groundwater level and consequently decreases river base-flow. In this condition, groundwater modeling can be used as a useful tool to evaluate effects of droughts on river base-flow in various drought conditions. In this research, Roodan plain was selected as a case study. All input files were prepared according to hydrological and hydro-geological data and were converted to GIS layers in order to develop an accurate conceptual model. A total of 27 piezometers were used for model calibration process and mean absolute error were calculated to evaluate accuracy of the model. Model calibration was conducted for both steady and transient conditions and the results were compared to the results of water resources balance in plain. Four periods including three months in each period were selected for transient calibration. At the end of each period results of model calibration for each piezometer were compared to historical data. Results of model verification show that a reliable model was developed in calibration process and can be used for forecasting purposes. Successive drought during previous years decreased groundwater level and result of model forecasting indicates that in such condition, river discharge base-flow may be decreased, significantly. In this case, river discharge may be decreased to 37% for a normal year with long term rain fall; however this value increases in droughts.

Keywords:

Conceptual model , GIS , forecasting , drought , base-flow