Water balance and safe yield in the quaternary aquifer of phrae basin

Abstract

Phrae province has experienced a drought problem, especially in dry season. The aims of this research were to evaluate the spatio-temporal distribution of groundwater recharge into the Quaternary unconsolidated sedimentary aquifers as well as to assess groundwater balance and suitable safe yield of the aquifers. The research was divided into two main parts as follows: in the first part, surface water modeling, namely, SWAT. The results showed that runoff after land use changes from 2003 to 2009 appeared to be significantly increased in all sub-watersheds in a range from 4.94% (station Y.38) to 77.64% (station Y.24). The groundwater recharge of each sub-watershed was in a range from 14.62 mm/yr to 433.86 mm/yr. Interestingly, not only the impact of land use causes the increase of runoff hydrograph, but it also results in gradually decreasing in the percentage of groundwater recharge (as compared to total annual rainfall) of each sub-watershed, ranging from 0.26% (station Y.6) to 5.12% (station Y.36).

In the second part, after evaluating the amounts of monthly groundwater recharge from the previous part by SWAT model, the groundwater model, so-called, visual MODFLOW. We found that groundwater balance in the aquifers was approx. +665.69 m3/yr and the suitable safe yield in the aquifers should not increase the pumping rate exceeding over 50%, as compared to the base case. The results of this research will benefit for implementing the sustainable water management plan, in terms of the integration of surface water and groundwater resources and can be further used as a database for government agency in the future.