Location and Design of Flow Control Structures Differentially Influence Salinity Patterns in Small Artificial Drainage Systems

Saltwater intrusion is a pervasive threat to coastal ecosystems. Common management strategies entail the installment of engineered flow control structures, though there is a dearth of work on their prevalence across the landscape and how different structures impact salinity under various hydrologic conditions. We manually classified more than 900 structures with most either being culvert pipes or riser structures. We then investigated how these structures impacted salinity in surface waters after the landfall of Hurricane Florence in 2018 and during the Summer of 2020. To accomplish this, we combined longitudinal and depth surveys, with long-term monitoring of salinity up and downstream of three flow control structures. Our results reveal that a flow control structure's ability to exclude or trap saltwater from/in upstream environments depends on its position inland and design. Engineered structures were effective at excluding saltwater, while unintentional structures sometimes trapped saltwater in upstream environments. This work sheds light on important factors land managers should consider when putting in place new structures for freshwater management purposes.

Automated summary

Saltwater intrusion poses a widespread threat to coastal ecosystems. The effectiveness of engineered flow control structures in managing salinity varies depending on their location and design. This study highlights the importance of considering these factors when implementing new structures for freshwater management.