Improving groundwater sustainability through conservation strategies in a critical-prohibited coastal plain

Abstract

Over-abstractions of groundwater resources influence the ecology and sustainability of groundwater resources. In this study, we examined the effectiveness of various conservations strategies to improve the sustainability of groundwater resources in the critical-prohibited plain of Behshahr-Bandar-e-Gaz in the coastal area of northern Iran. The soil and water assessment tool (SWAT) was employed to examine this case. Calibration and validation of the model were done using flow data of the periods of 2007–2013 and 2014–2017, respectively, after analyzing the model's sensitivity. We simulated the groundwater table by determining the volume of recharge per hydrological response units (HRUs). The calibrated model was then applied to assess various management scenarios, including agroforestry (Agro-S1, Agro-S2, Agro-S3), no-tillage (NOT), conservation tillage (CST), rice straw mulch (RSM), and wheat Straw mulch (WSM). Sensitivity analysis revealed 14 parameters as the most sensitive parameters. The Nash-Sutcliffe Efficiency (NSE) and determination coefficient (R2) of 0.56–0.93 and 0.74 to 1.00 in the calibration stage and 0.56 to 0.84 and 0.66 to 0.92 in the validation stage, respectively, indicated the acceptable capability of the model in flow simulation. The model also showed acceptable performance in groundwater table simulation with NSE and R2 of 0.76 and 0.88, respectively. RSM scenario was considered the most effective conservation strategy as it reduced surface runoff by 27.22% and ultimately, increased soil water content (by 6.02%) and groundwater recharge (by 23.52%). Furthermore combined scenarios (RSM, NOT, and Agro_S3) were the best conservation methods among the scenarios that indicated a decrease of 18.64% in surface runoff and an increase of 4.92% in infiltration, 4.61% in total groundwater recharge, and 1.76% of soil water content (green water). The RSM scenario improved the sustainability of groundwater resources in the region by 17.5%. An additional improvement (5.4%) was achieved through a combined scenario. These changes were generally made in the form of increasing the most the essential components of the water balance. Furthermore, the combination of Agro-S3, RSM and, NOT scenarios was the most effective ones to increase groundwater recharge in the region. Based on the results, although complete restoration of prohibited-critical aquifers is almost impossible, relative stability can be achieved by adopting a combination of different effective management measures.