Modeling Investigation on the future Permissible Yield in upper Chiang Rai Aquifers System

The Chiang Rai area situated in northern Thailand is becoming to serve as a regional trade hub for China, Myanmar, Laos P.D.R and Thailand, as laid out in the quadrangle economic cooperation policy. The ensuing economic growth in the region will, despite its positive social impacts, put an increased stress on its natural resources, namely, surface and groundwater. Groundwater which at present time is still abundant in the upper Chaing Rai aquifers system is supposed to support most of the water needed to sustain the envisioned future economic growth. Yet, no thorough investigation with regard to the quantity (yield) and the future availability of the groundwater resources in the basin exists up-to-date. Here we investigate this issue by means of a 3D groundwater flow model for the upper Chiang Rai aquifers, whereby the study focuses on the estimation of the future permissible groundwater yield. Based on first observational results of a hydrogeology investigation of the Department of Groundwater Resources (DGR), the groundwater flow model is calibrated in steady-state and transient mode using observed piezometric heads for the year 2009. The permissible yield of the aquifers system is then computed based on management criteria of the DGR, whereby permissible yield is “the maximum total pumping rate that ensures the average piezometric head in each layer does not fall below a vertical distance of 20 meters from the land surface in the next 20 years”. Employing these constraints for the future head variation into the model, the transient MODFLOW computations result in a total permissible yield of 1.3 m3/Rai (1600 m2)/day for the aquifer system. Using a zone budget module within the groundwater model, the permissible yields have then been calculated also sub-district-wise. The present modeling study gives policy makers a first tool at hand for future sustainable groundwater resources management in basin.