Wyoming's Powder River Basin — Geology and geography of the nation's largest coal field

Abstract

Springs are the natural discharge points of groundwater. They are of considerable value for drinking water supply and some springs are of historical and tourism value. However, increasing industrial and urban expansion has led to serious problems of overdraft of groundwater resources, which in turn had caused the disappearance of springs globally. Thus, the protection of springs while at the same time allowing for the use of local groundwater resources is an important task of water resources management. In this study, we propose a new multi-objective simulation and optimization (S/O) model to find an optimal extraction strategy which balances the competitive relationship between spring outflow and groundwater extraction. In the newly developed model, the extraction rates of different groundwater wells are taken as the decision variables, and maximization of groundwater extraction and maximization of spring outflow are taken as the two objective functions. Baotu Spring which is located in northern China has been famous since the Shang Dynasty (1600 BCE). However, Baotu Spring has been drying up since the 1990s due to over extraction of the local groundwater. Thus, we take Baotu Spring as a case study to demonstrate the applicability of the newly developed model. Simultaneously, a multi-objective evolutionary algorithm (MOEA), the multi-objective fast harmony search algorithm (MOFHS) which is coupled with the commonly used groundwater flow code MODFLOW, is adopted to search the Pareto optimal solutions (the optimal extraction strategies). The optimization results of Baotu Spring field during the management period from July 2013 to June 2014 show that more groundwater resources could be extracted without threatening the sustainable outflow of Baotu Spring and Black Tiger Spring. The optimization results for different hydrological years show that climate variability (mainly in precipitation) is an important factor when choosing the optimal extraction strategy. The optimization results of Baotu Spring in northern China show that the newly developed model is a promising tool to find the optimal groundwater extraction strategies which can protect springs while maximizing the extraction of groundwater resources in a spring field.