Synoptic Assessment of Repletion and Residual Water Dynamics in a Coastal Lagoon by Thermal Remote Sensing: Great Machipongo Lagoon (Hog Island Bay), Virginia, USA

Coastal lagoons are prominent features along many of the worlds sand coasts. Unlike estuaries, a large amount of lagoon volume is exchanged via tidal draining and repletion. We sought to quantify the repletion and residual water volumes in a coastal lagoon using satellite remote sensing. In the Great Machipongo Lagoon approximately 53% of the basin capacity drains out with each ebb tide, leaving a residual volume of about 47%. While the repletion footprint indicates the area of the lagoon that is completely flushed with each tide, residual water flushes at a much slower rate. The footprint of repletion water at full tide covers about 30% of the outer part of the lagoon. A fraction of the residual water is entrained into the repletion water mass along the plume frontal boundary. This allows a relatively small percent of the residual water to be exchanged with the coastal ocean. Thermal responses in ASTER imagery indicate zonation as well as areas of continuous mixing of repletion and residual waters. Comparison of remote sensing data with the tidal volume suggests that about 2-4% of the residual water mass is entrained along the frontal boundary during each tidal cycle and flushing of the residual water mass takes about 25-50 tidal cycles. The overall approach portends further application of thermal satellite remote sensing for monitoring estuarine and lagoon flushing and repletion.

I. Introduction

Coastal lagoons are prominent features along many of the world's sandy coasts situated behind baymouth barriers, barrier spits and barrier islands. Lagoons may comprise as much as 10–13% of the world's coastlines [1]. Some 47% of the United States' coast is bordered by barriers [2] and over 80% of the East and Gulf Coasts [3]. The extensive geographical distribution and numerous locations of coastal lagoons pose a challenge to their environmental characterization and monitoring.