HYDROLOGICAL RESPONSES TO STORM SURGES IN DITCHED AND UNDITCHED ATLANTIC COASTAL MARSHES

Coastal marshes have the potential to reduce the magnitude of storm surges through several mechanisms, including vegetative drag, water absorption and displacement/dampening, and the sheltering of low lying surface winds. About 90% of marshes from Maine to Virginia are ditched, therefore, in this study, we report data collected during Hurricane Sandy (2012) to evaluate storm surge attenuation and subsequence hydrological response in both ditched and unditched coastal marshes. In 2011, a year prior to Sandy, we instrumented two pairs of ditched and unditched marshes located on the Bay and Atlantic side of the Delmarva Peninsula with groundwater wells, tide gauges, and weather stations that recorded data at 15 minute intervals. Hurricane Sandy precipitation totaled 25 cm, which was the highest rainfall event during the project period from 2011-2015. Sandy’s wind speeds reached a maximum speed of 88.5 km/hr. Water level measurements in the marshes indicated that both ditched and unditched had similar hydrological responses to Hurricane Sandy, although they show significant differences in maximum and minimum water levels in the year prior to Sandy. Marsh water levels were sustained at high levels for three days after Hurricane Sandy. After the storm surge, marsh water levels declined to a new, higher, baseline water level. Marsh water levels slowly declined from this high base level until reset higher by another major storm. Time series data indicate that major changes in marsh hydrology occurred as consequences to major storms; these event-based changes in marsh hydrology were more significant than lunar cycles or seasonal hydrological responses.