Abstract or Summary
NJDEP has undertaken this project in order to trial the beneficial use of dredged material to enhance salt marshes that benefit coastal communities in advance of the widespread use of this practice in the state. This practice combines salt marsh enhancement with routine and post-storm dredging required to keep waterways navigable. The coupling of dredging and enhancement may decrease the cost of dredging and can yield significant ecological and socio-economic benefits. Enhancement is accomplished by placing dredged material on a salt marsh site at varying depths to increase marsh elevation according to the specific site characteristics and enhancement objectives. Dredged material is transported to the site through a pipe as it is being dredged. Placement of dredged material is accomplished through direct pumping or broadcasting, depending on the desired result. This project will trial various placement techniques. The first technique is the placement of a layer of dredged material over an existing marsh platform to increase marsh elevation. The objective was to use raise the elevation of the marsh interior such that it would create positive drainage and alleviate the stress associated with increased depths and durations of flooding within the marsh interior. A secondary objective was to create some high marsh habitat within the area to contribute to wildlife habitat diversity. The second technique is the placement of dredged material in large interior pools to fill them to an elevation that it is similar to the surrounding marsh platform. The third technique is the concentrated placement of dredged material over a small area of marsh platform to create elevated nesting habitat for black skimmer, a state-listed endangered water bird.
The project includes a series of four trial enhancement projects incorporating these various placement techniques to enhance salt marshes. The enhancement objective of each trial project is to increase the elevation of the marsh platform such that the elevation increase improves local coastal community resiliency, provides ecological uplift and does not have any harmful impacts on the marsh. Salt marshes in NJ that are suffering from a loss in elevation could benefit from the increases in elevation provided by the placement of clean dredged material. This loss in elevation is caused by decreased local sediment budgets, regional subsidence and hydrologic alteration, and is exacerbated by sea level rise. Increases in elevation will increase the resiliency of marsh ecosystems in the face of these stressors.
These trial enhancement projects will provide the opportunity for analysis of the effects of this practice on the ecosystem. NJDEP and its project partners intend to determine whether or not this practice increases marsh elevation and enhances a marsh’s ability to provide valuable ecosystem services such as habitat provision, wave attenuation and flood reduction. Project partners also intend to document the technical capabilities and cost-effectiveness of this type of work which is relatively new to New Jersey. These summary reports will help inform future projects of this kind and help to determine the feasibility of scaling up this work within the state. As such, all project work is being carefully documented and project sites are being monitored.