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The southern Chesapeake Bay region is experiencing land subsidence along with rising sea levels, both of which can contribute to coastal flooding. The rates at which these two processes are occurring are not exactly known. Mapping of land elevation change requires ground-truth survey data at multiple locations that are accurate and precise. With the exception of a few CORS sites that have continuous GNSS (Global Navigation Satellite System) antennae, existing benchmarks do not have the accuracy and precision required to quantify how elevation is changing over time. A baseline network of high-accuracy benchmarks is needed to assess relative land movement across the Hampton Roads region and to calibrate satellite data that will be used to map future land elevation changes.
The objectives of this study are to:
Establish a network of Class B, or greater, survey benchmarks designed for GNSS occupation.
Occupy the benchmarks with GNSS antennae and collect consistent long-term elevation data.
compute land surface motion velocities and relative differences in vertical land motion
across the Hampton Roads region.
The study consists of six main elements: (1) assessing existing benchmarks to determine which marks would be acceptable for long-term observations; (2) installing new benchmarks to fill gaps in existing network with focus on areas along the coast as well as areas of highest expected subsidence; (3) testing equipment and techniques to determine the best options for observation; (4) conducting initial surveys of all benchmarks in the network; (5) publishing descriptions of network design and initial results; and (6) annual operation and maintenance of the network, including data collection, analysis, publication, and equipment maintenance. Data collection is planned to start in early 2018.
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