Quantitative Changes in Groundwater Resources of Miandoab Plain Under the Influence of Contractionary Water Allocation Policies

Background and Objective: Due to limitations in renewable freshwater resources, proper management of resources and demands is one of the key factors for achieving sustainable management. This is a critical factor in achieving sustainable water management. This study aims to investigate the impact of government contractionary policies on the reduction of surface and groundwater rights in the Miandoab plain and quantitatively examining their impacts on groundwater resources.
Materials and Methods: The quantitative modeling of groundwater in the Miandoab plain utilized data from 120 observation wells. Geological, soil layer, and recharge layers pertinent to the region were collected. Groundwater level changes from October 2010 to September 2016 were modeled and analyzed in both stable and unstable)transient) states using the MODFLOW code. The model calibration stages were performed based on adjusting the hydrodynamic parameters of the aquifer, such as hydraulic conductivity and recharge, for 50time steps from November 2010 (70% of the modeling period). The best fit between computational and observational values was achieved both manually and automatically. 30% of the data was used for model validation. The model’s sensitivity to the aquifer’s hydrodynamic coefficients was examined. Finally, various scenarios related to water allocation reduction policies of the region and their effects on groundwater behavior, such as reducing extraction and recharge by decreasing surface water entering the plain, were quantified.
Results: The results demonstrated that the Root Mean Square Error (RMSE) was approximately 1 and 1.68 meters for the stable and unstable(transient) states, respectively. The hydraulic conductivity values within the aquifer ranged between 3.5 and 28 meters per day, and the specific yield values varied between 3 to 24 percent. The model exhibited the highest sensitivity to surface recharge and the least sensitivity to specific yield. The Pearson coefficient for the calibration and validation period of the unstable state exceeded 0.98, indicating a high degree of model accuracy. All effects of the government’s contractionary policies on reducing 40% of surface water and balancing the aquifer with the levels of natural aquifer recharge were implemented. Given that the average drop in groundwater level is approximately 0.1 meters per year, a scenario of reducing extraction from all operating wells has been applied to balance the aquifer. With a 5% reduction in extraction, the aquifer is projected to experience a half-meter increase in the static level. The Miandoab aquifer, due to the low slope of the plain, is sensitive and shows a part of the plain as a water ponding in reducing extraction at a high rate, hence any policy-making should be based on modeling.
Conclusion: To improve the conditions of the Miandoab aquifer, one of the country’s most unique aquifers, suggestions have been made for changes in the cultivation pattern of agricultural products, monitoring of water extraction from operating wells, and examination of the impact of climate change and drought on groundwater resources in terms of quantity and quality. Various scenarios, including optimization and change of cultivation pattern, as well as the construction of drainage in areas where evaporation from the aquifer is high, should be evaluated to improve the aquifer situation.