Groundwater balance and safe yield of middle Khorat aquifer in the Khwae Hanuman sub-basin, Changwat Prachinburi

The lower Khwae Hanuman sub-basin covers about 900 km2 in the Nadi and Kabinburi Districts, Prachinburi province. Recently, people have developed groundwater used for various activities, particularly in agricultural areas and industrial estates. In this area, the demand for groundwater usage tends to be gradually increased and may result in declining of groundwater levels in the future. The objectives of the study were to evaluate the groundwater recharge amount into the middle Khorat aquifer and to assess safe yield in the aquifer. The groundwater recharges potential was estimated by the overlay method for several thematic layers, consisting of lithology, soil, land use, slope, lineaments density and drainage density, and finally multiplied by the annual 30-year rainfall by the ArcGIS software. According to hydrogeological characteristics and field survey, the groundwater aquifers can be divided into two aquifers: the Quaternary sediment (Q) and the Middle Khorat aquifer (Jmk). The groundwater level ranged from -37 to 35 m amsl. and groundwater flow generally orients in the north-south direction. The high recharge potentiality was about 33.9 km2 (2.3% of the area), located in the center of the area. Only 12.8% of the total precipitation infiltrates into the groundwater aquifer. As per the model results, the groundwater balance in Jmk aquifer of dry and rainy seasons in 2015, as well as the consecutive dry season in 2016 are 0.33, 0.32, and 0.38 Mm3/day, respectively. The study area can pump groundwater up to 27,286 m3/d or about 2 times the current pumping rate. Interestingly, when increasing pumping rate from 10 to 200%, drawdowns in the central of the study area around the industrial areas, appeared to be intensively increased in the range of 2.5-4.0 m. The first-hand recharge potential and safe yield information can be used to develop an effective groundwater exploration for agricultural purposes and to estimate suitable pumping rates in order to obtain long-term sustainable groundwater utilization without adversely affecting the environment.