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January 2017 Issue

Collaborative Monitoring of
US Coastal Water Levels

Suzette M. Kimball,
Acting Director, U.S. Geological Survey

Four years ago, Hurricane Sandy devastated the most densely populated coastal areas of our nation. With a storm surge peaking at more than 19 ft., the powerful landscape-altering destruction wrought by Hurricane Sandy is a stark reminder of why the nation must become more resilient to coastal hazards. Hurricane Matthew’s long trek up the Atlantic Coast is a more recent reminder that there is a compelling need for a national water level network strategy. The U.S. Geological Survey (USGS) and NOAA’s National Ocean Service (NOS) are developing a diverse partnership effort to address this need. Growing coastal populations and rising sea levels are increasing the nation’s vulnerability to storm surge, coastal inundation, nuisance flooding and tsunami hazards. Effectively addressing these hazards requires data—a lot of data.

Part of the solution toward building more resilient coastal communities lies in expanding and improving the nation’s coastal observation systems. Of particular importance are the aspects of the system that report water levels and flows in real time, as well as the data and post-flood information needed for storm surge and flood forecasting models. The USGS and NOS established networks and capabilities are crucial and complementary components of a national water level network strategy.

USGS and NOAA Network
The USGS water level network consists of some 8,100 streamgages located in watersheds throughout the nation (http://waterwatch.usgs.gov). The streamgages primarily measure and record streamflow, the volume of water passing downriver per unit of time. But determination of streamflow records also requires collection of water level data, generally referred to as “river stage”. Now, with the advent of near-real-time data transmissions and the Internet, it amplifies the importance of having a host of applications for USGS water data to inform flood warning systems and flood inundation maps (http://on.doi.gov/2gL6PWB). USGS water level information goes hand-in-hand with NOAA’s monitoring systems.

After Hurricane Sandy made landfall in 2012, the USGS carried out scientific investigations to assist with protecting coastal communities and resources from future flooding. The work included development of the USGS Surge, Wave and Tide Hydrodynamics (SWaTH) network that extends along the Atlantic seaboard from North Carolina to Maine. SWaTH comprises a suite of 40 previously existing and 28 new water level gages, all flood-hardened, to provide real-time, continuous water level data. And to ensure coverage of overland surge flooding where and when it is most needed, SWaTH included fabrication of 62 mobile monitoring and telemetry units for temporary, real-time reporting of water level data, and establishment of approximately 500 sites prepared for rapid installation of new “storm-tide sensors” (self-contained, data-logging water level pressure transducers).

The NOS Center for Operational Oceanographic Products and Services is responsible for managing the coastal National Water Level Observation Network (NWLON). With 210 continuously operating water level stations on U.S. shorelines and the Great Lakes, the NWLON provides the water level-derived datum reference framework for the nation. With many stations in operation continuously for more than a century, it is also the source of authoritative base data for studying long-term sea level trends. And, its real-time data support safety of life and property decisions. NOS operates the NWLON to rigorous standards to ensure data accuracy and reliability. NWLON stations are established for long-term operation with redundant sensors, power supplies and communications systems. Many are storm “hardened” to ensure data are available when most needed as storms occur. However, recent NOAA assessments identified approximately 111 gaps in NWLON coverage.

One Collaborative Strategy
SWaTH represents a blended approach to observing and monitoring coastal storms that builds on the USGS streamgage network and complements NOAA’s NWLON. NOS leadership recognized the opportunity to fill a portion of the NWLON gaps by working with the USGS to ensure that the new and upgraded USGS tide gages met NOS data accuracy and reliability requirements. The effort involved extensive review and comparison of the data standards of the two agencies, their instruments, telemetry standards, and surveying and maintenance protocols. Overall, the effort identified several areas for improvement. A pilot effort was launched to test the new protocols and procedures, resulting in the filling of eight of the 43 NWLON gaps identified on the East Coast. The data will be distributed via both USGS’s National Water Information System (NWIS, http://waterdata.usgs.gov/nwis/rt) and NOAA’s NOS Tides and Currents website (http://tidesandcurrents.noaa.gov).

Maintaining an observation network, let alone expanding it, requires dedicated, long-term resources. A key element of the SWaTH strategy included extensive consultation and collaboration with state and local agencies to identify data needs and select priority sites. An outgrowth of those discussions included agreements between the USGS and the state and local agencies to secure state and local contributions to fund the long-term operation and maintenance of the sites, particularly the real-time tide gages.

NOAA’s NWLON and the USGS water level networks are two of the 15 U.S. Earth observing systems that were identified as “Tier 1” systems, having high impact on a majority of societal benefit areas, in the National Plan for Civil Earth Observations by the White House Office of Science and Technology Policy. The two agencies are committed to continuing to work together, not only to fill in NWLON network gaps, but also to share technical developments and innovations that will strengthen both networks. Emergency management officials and the public will be able to use the data, along with information provided by storm surge forecasts driven by the newly available data, to make real-time decisions on evacuation plans and protection of property. As the data are collected and accumulated, they will provide invaluable coastal intelligence for both USGS and NOAA to feed and inform new FEMA floodplain maps, land-use decisions and building codes; support safe and efficient maritime commerce and sound coastal management; and ultimately to lead to more disaster-resilient coastal communities.

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