January 15, 2004 — The NOAA Ocean Service operates and maintains the National Water Level Program whose backbone is a network of 175 long-term, continuously operating water level stations. Tidal datums derived from these stations have traditionally been used for navigation (e.g., establishing chart datum and all nautical chart products and reference datum for the Physical Oceanographic Real-Time System — PORTS® operations) and shoreline boundary purposes, however, there are other beneficial applications and services that water level and datum information can provide.

In fact, the NOAA Center for Operational Oceanographic Products and Services — part of the NOAA Ocean Service — created its Coastal Oceanographic Applications and Services of Tides and Lakes (COASTAL) Program in 2003 to focus on non-navigational applications. Through this program, water level information is used for a number of diverse non-navigational applications, including marsh restoration projects, beneficial use of dredged material, coastal planning projects, long-term sea level assessments, storm surge monitoring, evacuation route decision-making and emergency preparedness. Most of the projects require that additional water level stations be installed, tidal datums computed and water level analyses conducted. To accomplish this, the COASTAL program often partners with other NOAA offices, federal agencies, state and local governments and non-profit organizations. The applications of tide and water level information to these projects are critical to their success in protecting life, saving property, restoring the environment and maintaining the economic vitality of the nation. This paper focuses on one application of water level and datum information — marsh restoration projects — and describes several NOAA marsh restoration projects that have benefited from this application.

The Value of Marshlands
Coastal areas have intrinsic economic, cultural and aesthetic value. Specifically, wetlands play a crucial role in the productivity of coastal waters, biogeochemical cycling and geomorphological stability. They act as nurseries for fish and crustaceans and feeding grounds for birds, they store pollutants and nutrients and serve as buffer zones to flood events and wave action. However, these fragile ecosystems have been degraded and/or destroyed at an alarming rate over the last few centuries. The United States has lost more than half of its wetlands since the late 18th century and an average of 60,000 acres of wetlands have been lost nationally each year between 1986 and 1997.

Coastal wetland loss can be attributed to both anthropogenic (e.g., human population growth and coastal development), as well as natural phenomena (e.g., sea level change and erosion from coastal storms). With ever increasing awareness of wetland habitat loss, coastal habitat restoration has become a national priority. To ensure success, restoration projects should take into account critical factors such as the necessary requirements for successful vegetation growth, an environment which allows the target species to flourish, long-term stability of the habitat and even the preservation of surrounding properties. Information on the frequency and duration of inundation and drying is also required since the physiographic range of vegetative marsh species is generally related to the elevation of mean high water — information which can be used to guide planting activities. Other considerations include how often marsh surfaces are irregularly flooded due to storm tides and maximum astronomical tides. Lastly, erosion, subsidence and sea level change information should be monitored to ensure that created or modified marsh habitats are stable over the long-term.

Water Level Analyses
There are three categories of water level analyses that are conducted for each marsh restoration project under the COASTAL Program: 1) local tidal datums; 2) long-term sea level change and 3) frequency and duration of inundation analyses.

• Local Tidal Datum: First, tidal datum elevations are determined relative to present and future marsh surfaces by establishing a water level station (typically, for one year to capture seasonal effects) with local bench marks. The figure to the right shows a generic marsh restoration study site (Click on the image to the right for a larger view of a typical marsh site). Then tidal datums are linked to a geodetic benchmark network using global positioning system and/or leveling techniques, thus referencing them to standard geodetic datums. Kinematic GPS surveys of the marsh topography can also be made. Collectively, these data allow researchers to generate digital elevation models that display all of the different datum elevation relationships. DEMs of tidal and geodetic datum relationships are particularly beneficial in the planning and construction phases of marsh restoration efforts because they provide excellent baseline information.
• Long-term Sea Level Change: Secondly, long-term sea level change, trends and variations are assessed and analyzed to ensure that possible sea level rise is taken into account in the extended restoration planning phases of the project. The average rate of global sea level rise is estimated at 1.6 to 2.1 mm/year, yet local rates of sea level change is variable and is affected by the local rate of vertical land movement. Likewise, long-term viability of functioning marshes is dependent upon proper accretion rates and sediment accumulation in response to local sea level rise. By conducting simultaneous comparisons of the high waters between the short-term station at the marsh and a nearby, long-term NWLP control station, similar long-term sea level trends can be expected at the marsh. Seasonal effects are determined and extrapolated in a similar manner.
• Frequency and Duration of Inundation: Finally, frequency (occurrence of high waters for different elevations above marsh surface) and duration (amount of time marsh surface is inundated by water) of inundation analyses of the high waters are performed because marsh vegetation is sensitive to how long and how often it is inundated. This information is used to determine where best to plant the different vegetative species. Such analyses are important because overall marsh stability relates to the tolerance of specific plant species and the complexity of the tidal hydrodynamics in relationship to the marsh surface and channels. The frequency and duration of inundation during a major seasonal flood can also affect the stability of a marsh.

Together, these three types of water level analyses assist with the proper engineering and design marsh restoration projects, as well as contribute to assessments regarding the health of marsh plants and animals.

Marsh Restoration Case Studies
To follow are three examples of NOAA marsh restoration projects that have benefited from the use of the tide and water level analyses described above. The first site, the Qwuloolt marsh in Marysville, Wash., is an example of farmland which is being converted back to marshland in a populated area surrounded by levees. The second site, the Barren Island marsh in the Chesapeake Bay, is an example of a "disappearing" marsh that has been subjected to primarily natural destructive forces. The third site is an example of a marsh that was actually constructed as part of a mitigation effort near the Fort McHenry National Historic Monument and Shrine in Maryland.

• Qwuloolt Marsh Restoration (Marysville, Wash.): NOAA’s Qwuloolt Marsh restoration project along the Ebey Slough in Marysville, Wash., entailed the restoration of approximately 350 acres of farmland back to wetlands. Ebey Slough is a part of the Snohomish River delta and is tidally influenced by Puget Sound. The site is protected by levees and has been since the early 1900s, most recently for grazing cattle (for a dairy farm) and before that for farming hay. NOAA purchased the property — with restoration in mind — using funding from litigation due to pollution of the slough from a landfill two miles west 20 years ago. The original intent of the project was to breach the levees and flood the property, thus recreating wetland and marsh habitat, without flooding surrounding houses and developments. NOAA CO-OPS started the project by installing a water level station at the site for more than a year, while the U.S. Army Corps of Engineers performed most of the detailed hydrologic and hydraulic studies to support the project. NOAA and the USACE then used tidal and geodetic datum relationships for conducting technical hydrologic and hydraulic analyses and design work that were ultimately used to generate models of the marsh system. The image to the right shows the existing elevations of the site. A development exists in the northwest corner of the site just inside of the levees, and there is a new development being built east of the site just beyond the levees. Tidal datums showed that breaching the levees would cause the marsh surface to become a pond and would flood the development to the northeast. Likewise, the highest estimated tide suggests that the new developments on the eastern border of the site would also be flooded. In the end, this tidal information was critical for the USACE feasibility study, which recommended that levees needed to be built up higher in certain areas to prevent the neighboring developments from being flooded.

NOAA is engaged in several tidal marsh restoration projects in the Chesapeake Bay. The following two examples are highlighted below: Barren Island and the Fort McHenry Wetland Construction Project. Other similar restoration projects in this area include marshlands within (or along) the Eastern Neck National Wildlife Refuge, Blackwater National Wildlife Refuge, Poplar Point, Anacostia River, Swan Creek and Middle Branch.

• Barren Island, Blackwater National Wildlife Refuge (Chesapeake Bay, Md.): The Barren Island marsh is located on a subsiding island in the Chesapeake Bay’s Blackwater National Wildlife Refuge. Unlike the Qwuloolt Marsh described earlier, this area contains no levees or surrounding properties. It is a mid-Chesapeake Bay island that is subjecting to subsidence and is eroding at an alarming rate. In an effort to preserve the area, NOAA CO-OPS partnered with NOAA Restoration Center, NOAA Office of Response and Restoration, NOAA National Geodetic Survey, National Aquarium in Baltimore, U.S. Fish and Wildlife Service and U.S. Army Corps of Engineers during the spring of 2001 to join an ongoing effort to restore Barren Island. For this project, the NOAA Ocean Service performed a detailed tide and geodetic study of the marsh system. NOAA CO-OPS also established a tide station on the northwest corner of the island for one year, computed tidal datums and performed frequency and duration of inundation analyses. The NOAA NGS connected the tidal datums to geodetic datums through GPS and leveling techniques. The inundation analyses were overlaid on DEMs of the marsh elevations, as well as the tidal and geodetic datums. This information assisted with restoration planning efforts to determine the best restoration activities for the system. As part of the marsh restoration effort, dredged material from the channel has been placed on the island helping to stabilize it, active planting is occurring and geotubes are in place in front of the island to help reduce coastal erosion. Due to the hydrodynamics of the location, wave and current data have been collected and analyzed along with tide data to assist with proper restoration of the island.
• Fort McHenry (Chesapeake Bay, Md.): In the past two decades, creation and restoration of tidal wetlands has become a required form of mitigation, including many areas in the Chesapeake Bay, such as the wetlands adjacent to the Fort McHenry National Historic Monument and Shrine. These wetlands were originally constructed in 1982 as mitigation for the construction of the Fort McHenry Interstate 95 tunnels. They are now being reconstructed from mitigation credits for filling in a nearby port slip that will allow more containers to be offloaded. The construction plans were generated by using NOAA's tidal and geodetic information. The intent of this restoration project is to improve the ecological function of the Fort McHenry tidal wetlands mitigation site through hydrologic modifications and continued maintenance and monitoring of the site. Modifications are being planned to promote regular, natural tidal flooding at the site; control debris accumulation and enhance its habitat value to plant and animal species. These modifications will benefit those marsh areas that are either being converted to new aquatic habitat or re-vegetated with native marsh vegetation. The engineering designs for the new marsh have incorporated tidal and geodetic datum elevation relationships, along with a DEM developed from a KGPS survey of the existing marsh surface.

The use of water level and datum information has greatly enhanced the success of NOAA's marsh restoration projects. In the future, NOAA will continue to improve this application and apply it to marsh restoration projects across the nation.

Relevant Web Sites
NOAA Ocean Service

NOAA National Water Level Program

NOAA Water Level Observation Network

NOAA Marine Navigation Services

NOAA Physical Oceanographic Real-Time System

Aerial Photography and Shoreline Mapping

NOAA Center for Operational Oceanographic Products and Services

NOAA Sea Levels Online

National Tidal Datum Epochs

NOAA El Niño Page

Blackwater National Wildlife Refuge

NOAA National Geodetic Survey

NOAA Community-Based Restoration Program Photo Album

NOAA Office of Response and Restoration

The NOAA Restoration Center

Media Contact:
Glenda Powell , NOAA Ocean Service, (301) 713-3066 ext. 191 or Ben Sherman, NOAA Ocean Service, (301) 713-3066 ext. 178