Modeling the inter-strata seepage effect near the Nanhua Reservoir, Taiwan

Abstract

A numerical groundwater flow modeling program, MODFLOW, was applied to simulate inter-strata seepage near the flooded region of the Nanhua Reservoir. It was concluded that groundwater seeping within the strata mainly flowed from northeast to southwest. The water loss rates caused by the seepage after the presumed operation of the reservoir were estimated. Relatively high hydraulic gradients, due to the seepage effect, were located near the villages of Yusun and Maopu. The greatest changes in water loss rate were found to correspond to the water level changes in the Hojuey River. The time required for the seepage effect to reach a steady state condition, based on different presumed settings for specific storage, was also estimated. The Chutouchi Formation may affect the seepage flow more within the studied region during the early phase of the simulation. However, during the later phase, the Maopu shale may have more effect. It was concluded that the numerical modeling technique is capable of predicting the effect of inter-strata seepage. It can also help us obtain a further understanding of the hydrogeological characteristics of the region.