Water Level and Datum Applications
Coastal Oceanographic Applications and Services of Tides And Lakes (COASTAL)
Introduction
The National Oceanic and Atmospheric Administration (NOAA)/National Ocean Service's (NOS)/Center for Operational Oceanographic Products and Services (CO-OPS) operates 
and maintains the National Water Level Program and the National Water Level Observation Network. Tidal datums derived from these programs have traditionally been important primarily for navigation and shoreline boundary purposes.
There are, however, several other beneficial applications and services that water-level and datum information can provide. CO-OPS recently created the Coastal Oceanographic Applications and Services of Tides And Lakes (COASTAL) Program to focus on these non-navigational uses. They include beneficial uses of dredged material, coastal planning projects, marsh restoration projects, long-term sea-level assessments, storm-surge monitoring, emergency preparedness, and HAZMAT response. Through the COASTAL Program, CO-OPS partners with other NOAA offices and other Federal agencies, state and local governments, and nonprofit organizations. The application of tide and water-level information to these projects are critical to their success in saving lives and protecting property, restoring the environment, and maintaining the economic vitality of the nation. Some examples follow.
Marsh Restoration
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. Nevertheless, these fragile ecosystems have endured centuries of degradation and destruction. Thus, it is essential for restoration projects be properly designed and engineered, and subsequently to be monitored.
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 benchmarks. Tidal datums are computed and then referenced to geodetic datums, such as the North American Vertical Datum of 1988 (NAVD88). Kinematic GPS surveys of marsh topography are used to generate of digital elevation models (DEMs), which display visual representations of various datum elevation relationships and inundation scenarios. DEMs of tidal and geodetic datum relationships are beneficial in the planning and construction phases of marsh restoration efforts because they provide baseline information. They have been used successfully in the reconstruction of Maryland's Fort McHenry Wetlands and in the heightening of levees to protect the Qwuloolt Marsh in Washington state. Long-term sea-level changes, trends and variations are assessed and analyzed to ensure that any rise in sea level is considered during the extended planning phases.
Analyses are also performed on the frequency and duration of high waters because marsh vegetation is sensitive to how long and how often it is inundated. This information is then used to determine where to plant restorative vegetative species. For example, inundation trends at Barren Island in Blackwater National Wildlife Refuge are significantly different from those at Fort McHenry Wetlands because the upper Chesapeake Bay is heavily influenced by weather effects. Waves and currents are also measured and considered in the design of riprap in areas subject to severe coastal erosion, such as at Eastern Neck National Wildlife Refuge on Maryland's Eastern Shore.
Emergency Preparedness
During coastal storms, water levels can rise to excessive flood levels. It is useful to know and predict how high these water levels reach. This kind of storm-surge information is critical for emergency preparedness in most regions. Louisiana, for example, depends on this information becuase the state is highely susceptible to natural hazards including land subsidence and relative sea-level rise, hurricanes and other severe storms, and storm-surge flooding.
An example of a COASTAL Program project that focuses on emergency preparedness in Louisiana is the St. Charles Parish Water Level Monitoring System. The data from this real-time monitoring system are displayed on a local data acquisition system in the parish's Emergency Operations Center. Emergency managers monitor the data to assess storm-surge flooding and use them in decision-making regarding evacuation routes, the various opening and closing water-control structures, and public warnings.
New Frontiers
Technological advancements have allowed for various methods of shoreline compilation over the years. Each technique, however, must be tide-controlled. New high-resolution remote sensing data, such as airborne light detection and ranging (LIDAR)make it possible to display various layers of information and data on DEMs. This is useful not only for standard shoreline depiction, but also for coastal erosion, sea-level inundation, and habitat loss.
From traditional tide and water-level products to new analyses of high waters and other technological advancements, even more applications of water levels are likely to emerge. The COASTAL Program is young and has already expanded significantly with nearly a dozen projects and several partnerships. It is reasonable to expect that the program will continue to grow through additional partnerships, while enhancing existing partnerships and fostering the exchange of information. The ultimate goal is to provide improved products and services to all citizens and users of the coastal zone.