GROUNDWATER BALANCE OF PHRAE BASIN USING MODFLOW AND GIS IN CHANGWAT PHRAE

Abstract

Changwat Phrae has faced water shortage problem for a long time. Hence, the aims of this study were to estimate the groundwater recharge of aquifers and assess groundwater movement and groundwater balance. From secondary data incorporated with primary data derived from field investigation during years 2012-2013, the results of hydrogeological conceptual model revealed three aquifer types as follows: floodplain deposited, terraces deposited aquifers, and the consolidated aquifers. The main groundwater direction of the unconsolidated and consolidated aquifers flow from the northern to the southern area with a mean hydraulic gradient approximately 0.0013, which is corresponding to the groundwater flow simulated by MODFLOW, the central part of the region and the Yom river were found as discharge areas. The groundwater recharge rates were spatially determined by WetSpass module for estimating seasonal variability patterns of groundwater recharge which were vary between 0-320 mm/ year. In addition, the results showed that the potentiality of recharge area corresponds to the topography and hydrologic characteristics. Groundwater recharge derived from WetSpass was then imported into MODFLOW for calibration and verification of groundwater modelling. The results revealed that the variations of groundwater balance are seasonal dependent, which found relatively high recharge rates and groundwater inflow during the rainy season. According to groundwater modelling, the groundwater inflow is relatively higher than the groundwater outflow approx. 111,320 cubic meters/year. Finally, in order to determine groundwater safe yield and propose the sustainable groundwater management, the groundwater model was simulated by increasing the pumping rates under three situations: 25, 50 and 100%. The results showed that the availability of the pumping rate is not higher than 50% relatively compared to the base condition. These contributions will be further applied as the fundamental data for appropriately sustainable groundwater management.