Volume 4 Issue 1
February 2009
BREAKING WAVES  

News from our Coastal Sciences, Engineering & Planning team spotlighting the coastal zone.

 

Coastal wetlands play a critical role in the overarching coastal/estuarine environment.  While the scientific community has long recognized the importance of coastal wetlands, their values, and their relationship to estuarine ecosystems, it is only recently that the general public has begun to understand their importance.

Due to the lack of understanding, many wetland systems have been severely impacted by anthropogenic activities, such as the construction of roads, railroads, and housing developments, and have ultimately become severely degraded.  As such, many wetland areas are in need of restoration to return to their integral role in the ecosystem. One of the challenges in restoring these impacted systems is assessment of the evolution of the system, and subsequently, projecting what changes in habitat may occur as a result of restoration activities. 


Restoration of the wetland, and specifically the alteration of the system hydraulics, often will result in a wide variety of potential impacts. These impacts include the potential for upland flooding and salt water intrusion, the change or loss of certain habitat areas (e.g., waterfront feeding, anadromous fish migration, among others) or vegetative systems, modification to the tidal exchange, alteration of surface and ground water quality and salinity levels, and potential impacts on the beach/inlet system. 

Addressing the concerns of stakeholders and regulatory agencies is often a balancing act that requires the project proponent to develop an accurate projection of the changes that will occur as a result of the restoration project.  Numerical modeling of these systems provides the ability to assess potential changes, evaluate a range of potential restoration alternatives, and is a cost-effective method to optimize designs, reduce construction costs, and ensure a successful project.

Numerical modeling of a wetland restoration project offers significant advantages, including:

  • More detailed quantitative information than can be obtained cost-effectively in a field data collection program alone

  • Long-term time series of important physical characteristics (e.g., water elevations, tidal velocities, hydroperiods, wetting and drying times)

  • Ability to simulate a wide range of natural occurring conditions (spring tides, storms, etc.)

  • Utility as a valuable engineering tool to evaluate a wide range of restoration alternatives and subsequent design requirements (e.g., changes to salinity levels, inlet scour, culvert and constrictions, fish passage, etc.).

However, numerical modeling of a tidally-forced wetland system is not straightforward.  There are a wide variety of hydraulic, hydrologic, and hydrodynamic models available, ranging from simple to complex, and from proprietary to community, but not all are applicable for tidally-forced, marsh restoration projects.


The correct model selection, which includes consideration of the dominant physical processes and driving factors within the wetland system, is a key component of the numerical modeling process.  For example, depending on the physical system, the model selection process should evaluate the need for the model to appropriately simulate wetting and drying of a marsh surface, salinity levels, potential stratification, control structures (e.g., culverts, dikes, weirs, etc.), flow resistance due to various vegetation types, upland flooding, and/or storm impacts.  Ultimately, the model developer must understand the abilities and utility of each model prior to selecting the appropriate model for the restoration project. You need the experience and flexibility to select the right tool for each job.


Woods Hole Group has 20 years of tidal wetland restoration and monitoring experience, and our approach has been founded on:

  • Establishing clear restoration objectives.

  • Ensuring that adequate baseline data area collected.

  • Determining the right analysis techniques and models to implement.

  • Working with the stakeholders to develop potential alternatives.

  • Accurate modeling of existing conditions and alternatives.

  • Engineering design of the preferred alternative.

  • Construction, monitoring, and adaptive management.

Using this approach Woods Hole Group supported the largest privately funded restoration project in the United States, consisting of restoration of over 10,000 acres of marsh in Delaware Bay (Estuary Enhancement Program by PSEG). Currently, Woods Hole Group is working on restoration and modeling projects for the Herring River Estuary System in Wellfleet, MA, the Stony Brook System in Brewster, MA, the Bride Brook System in East Lyme, CT, and the Town Creek System in Salisbury, MA. These projects all included a model selection and development task to help identify and simulate proposed alternatives for the restoration.


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