Assessment of saltwater intrusion and mitigation strategies in a coastal agricultural region
Date
2023
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Saltwater intrusion (SWI) poses a threat to coastal water resources around the world. A significant portion of the global population and cropland could suffer due to salinization of freshwater. While the physics of SWI have been extensively studied for over one hundred years, studies often fail to capture the entire complexity of the natural hydrologic system and how it connects to human behavior. In the region east of Dover, DE, located in the center of the state, farmers compete with the city for use of the surficial Columbia aquifer. As the flattest and lowest-lying state, Delaware is vulnerable to SWI, and risk of salinization increases as sea-levels continue to rise and groundwater use is increased. The occurrence of widespread salinization in the region would not only contaminate drinking water supplies, but also lead to large economic losses from the reduction of crops. ☐ For this study, first a field-monitoring campaign was conducted in which water and conductivity levels were recorded in monitoring wells, irrigation ponds, marshes and tidal streams. Measurements were used to assess the current extent, pathways, and drivers of SWI in the Dover, DE, region. Secondly, the field data was used to construct a calibrated 3-D, variable-density, numerical, groundwater flow model using SEAWAT. The model was used to assess tidal streams as pathways for salinization of inland groundwater and to compare the impacts of sea-level rise and increased pumping on the impact of SWI. Additionally, the location of the irrigation and municipal wells allowed for the assessment of how the distribution of pumping (i.e., concentrated vs widely distributed) impacts SWI. Tidal streams were found to be the dominant pathway of SWI and that an increase in pumping at wells concentrated near tidal streams in the center of the model led to more intensive salinization than an increase of equal total magnitude at wells more widely distributed throughout the model. Lastly, the model helped to evaluate different strategies to mitigate SWI and compared the approaches of redistributing municipal pumping, collective reduction of irrigation, and targeted removal of irrigation wells. Results showed that shutting off more centrally located, larger wells often reduced salinization in vulnerable wells more than shutting off the vulnerable wells themselves. This work has implications for groundwater modelers and water managers who need to not only understand the complexity of the hydrologic system, but also how it is connected socioeconomics to develop effective SWI mitigation strategies.
Description
Keywords
Coastal aquifers, Groundwater management, Irrigation, Numerical modeling, Salinization, Saltwater intrusion