Morphology and Tidal Inundation of Tidal Wetlands in the Delaware Estuary

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An expanse of tidal wetlands fringes the Delaware Estuary and provides Delaware, Pennsylvania, and New Jersey with abundant ecosystem services including habitat for indigenous and migrating plants and wildlife, biogeochemical cycling of nutrients, preserving water quality, flood hazard mitigation, and recreational services. However, the tidal wetlands in Delaware, in particular the tidal saltmarshes, can only survive in a narrow band of elevation relative to the tidal water levels and are continuously degraded due to land use practices, coastal development, waves and inundation from coastal storms, and sea-level rise. The occurrence, timing, and duration of inundation on the marsh is a primary control in many physical, chemical, and biological processes, especially the transport of sediment onto the marsh platform resulting in vertical accretion and/or horizontal migration. Understanding this dynamic system of marsh hydrology is critical to assessing the current health of the marsh and modeling its behavior under future conditions.

The primary goal of this study is to improve our understanding of the hydrodynamic behavior of the tidal saltmarshes in the Delaware Estuary. The PIs have identified four tidal saltmarshes to focus our efforts, listed from north to south: Blackbird Creek, Leipsic River, St. Jones River, and Murderkill River tributaries. Water levels will be collected along these tributaries and tidal fluctuations modeled from the mouth to the head of tide. A quasi-bathtub model will be used to simulate inundation of the marsh on both sides of the tributary. Marsh platform elevations will be determined by correcting for the positive lidar-bias present in the bare-earth Digital Elevation Models (DEMs) of densely vegetated areas, such as saltmarshes. This will be accomplished through GIS and statistical methods based on GPS RTK collections across multiple vegetation communities throughout the four marshes. Using the modeled tidal water surfaces and “corrected” mini-DEMs, the inundation frequency and extent (i.e., hydroperiod) as well as spatial metrics related to the health and inundation vulnerability of the marsh will be computed.

The methodology for identifying and correcting for the lidar-bias will be applied to all tidal saltmarshes along the Delaware Bay from the City of New Castle to Broadkill Beach. The resulting set of mini-DEMs for each marsh will be available publicly from DGS website. Modeled water levels, marsh metrics and GPS RTK will also be shared with natural resources managers and coastal scientists, particularly at the Delaware National Estuarine Research Reserve (DNERR) and the US Fish and Wildlife agencies. Understanding gained from this work will help coastal communities prepare in real-time for upcoming storm events and long-term resiliency planning for sea-level rise. Additionally, the PIs will work  to help develop K-12 and High Education materials.

Project funded by Delaware Sea Grant.