COLLECTING ELEVATION DATA FOR NATIONAL PARK SERVICE SALT MARSHES IN RESPONSE TO SEA LEVEL RISE AND POST- AND FUTURE STORM EVALUATION

In response to the effects of Superstorm Sandy, The University of Rhode Island and the National Parks Service’s (NPS) Inventory and Monitoring Program for the Northeast Coastal and Barrier Network have collaborated to integrate better planning and to develop comprehensive storm response strategies. One of these core strategies is the acquisition of more accurate elevation data that can be used to predict changes in the coastal environment. While Light Detection and Ranging (LiDAR) data exists for the majority of coastal parks its elevation accuracy can vary from 5-30 cm (RMS) and may vary within any one collection area. In salt marshes, the error range maybe even greater and is mainly due to the effects of salt marsh vegetation and the inability of the LiDAR laser pulse to reach the marsh surface or platform. In salt marsh environments, vegetation zones are typically based on elevation (i.e., tidal inundation) and sometimes differ by only a few centimeters. LiDAR data therefore, is not accurate enough for evaluation of critical ecosystem functions like salt marsh elevation capital (loss or gain of marsh elevation with respect to water level). To better measure the elevation of the salt marsh surface, we used survey grade (cm accuracy) GPS equipment. Dual-frequency, carrier phase GPS surveying not only provides more accurate measurements of elevation than LiDAR, but also the ability to consistently measure the marsh platform.

We present our field methods and initial results from 13 salt marsh sites at Assateague Island National Seashore collected in the fall of 2014. We collected comprehensive elevation data from the low marsh to the high marsh using a 20-m grid spacing. In addition, 8 water level loggers were deployed to better understand the tidal dynamics influencing these marshes.. Existing or temporary deep rod benchmarks established near each field site are utilized as survey control. These intensive on-the-ground kinematic GPS elevation data (along with water level data) will be used to tie all of these data to the North American Vertical Datum of 1988 and to calculate tidal datums specific to each salt marsh site. Thus, all of our data will be comparable which will help with the identification and prioritization of sites for management or conservation planning.