Abstract
Integrated Hydrological Modeling for Sustainable Water Resources Management in Arid Coastal Regions: Essaouira Basin (Morocco)
Groundwater, a critical resource for drinking and irrigation, faces significant challenges, especially in the coastal aquifers of arid and semi-arid regions, due to factors such as seawater intrusion, increasing anthropogenic pressure and decreasing groundwater recharge rates. In the Moroccan context, the challenge of water scarcity significantly impacts the country's economic development trajectory, making a comprehensive and strategic approach to water resource management not only critical but imperative for sustainable development and the resilience of Morocco's economy. This study focused on the Essaouira coastal aquifer in Morocco, exploring sustainable management strategies through an integrated approach. By combining hydrogeochemistry, stable isotopes, remote sensing data, and hydrological modeling, the research delved into groundwater quality characterization, recharge dynamics, and the impacts of development on groundwater depletion. The investigation highlighted the intricate interplay of various processes affecting groundwater quality and recharge patterns, emphasizing the necessity of tailored management strategies to ensure the sustainable utilization of water resources. Findings from the hydrogeochemical and stable isotopes analyses revealed that seawater intrusion was detected only after 2009 near the ocean, while hyper-salinity due to evaporite dissolution occurred primarily in the southern part of the aquifer throughout the study period (1990-2020). Moreover, stable isotopes analysis identified the roles of both diffuse recharge from direct precipitation infiltration during November and January, and focused recharge from the Ksob river in the northeastern region. A conceptual 3D hydrological model was constructed illustrating different hydrological and hydrogeochemical processes that affect groundwater quality and quantity in the Essaouira coastal aquifer. Integrated hydrological modeling, incorporating the Soil and Water Assessment Tool (SWAT) and MODFLOW groundwater models, enabled a detailed evaluation of the impacts of various pumping and recharge scenarios on groundwater levels. SWAT-estimated monthly diffuse recharge indicated that the majority of groundwater recharge within the study area occurs between November and March, contributing to over 99% of the total annual diffuse recharge to the aquifer, confirming findings derived from stable isotope analysis. The computed annual average focused recharge for the entire 1990-2010 timeframe estimated using SWAT was approximately 3,119 m³/day. A comparative analysis between the SWAT model estimates during 1990/1991 (approximately 3,110 m³/day) and the measured rate (3,629 m³/day) from the differential gauging measurements conducted in the Ksob River during the same period indicated a close agreement. Estimated values for both focused and diffuse recharge were subsequently used as boundary conditions for a MODFLOW groundwater model of the Essaouira coastal aquifer. Groundwater head simulations using the validated transient MODFLOW model highlighted the vulnerability of the aquifer to current pumping rates, emphasizing the need for immediate measures to mitigate excessive groundwater depletion. Notably, the study underscored the importance of sustainable management practices, such as managed aquifer recharge and use of non-conventional water resource strategies to increase groundwater recharge and alleviate the pressure on groundwater resources. The insights provided by this research contribute to the broader understanding of water resource management in arid and semi-arid coastal regions, shedding light on the intricate interactions between natural processes and anthropogenic influences in these areas. These findings offer valuable guidance for policymakers and water resource managers, emphasizing the significance of proactive and context-specific management strategies to ensure sustainable water resources management in vulnerable coastal aquifers.