GROUND WATER DISCHARGE AREAS IDENTIFIED USING REMOTE SENSING COMPARED TO WATER BUDGET ESTIMATES FOR DELAWARE'S INLAND BAYS

Locations of ground water discharge from a sandy, unconfined aquifer (Columbia aquifer) into Delaware's Inland Bays are delineated using multi-spectral satellite images (Landsat 7) along with aerial and ground-based thermal-infrared and visible imagery. Delineations are compared to those determined by water budget calculations. Remotely-sensed locations are identified in winter images by thermal anomalies (hot) in surface water images or the absence of ice in images of ice-covered surface water. Thermal anomalies are resolvable in areas of the bays not affected by strong currents and in smaller tributaries greater than one to two pixels wide (60 to 120 m in satellite imagery and 2 to 4 m in aerial imagery). The absence of ice is resolved to 15 m using the visible panchromatic band in satellite images to sub-meter scale with ground-based visible-band photography. Discharge was identified on the north shore of Rehoboth Bay (RB), lower Love Creek (LC), Herring Creek (HC), parts of Pepper Creek (PC), Indian River >2 km downstream of Millsboro Dam (IR), and the north shore of Indian River Bay west of Emily Gut (IRB). Using water budgets, areas identified as having high discharge (Q) and high watershed-area/shoreline-length ratio (Q*) were consistent with the remote-sensing delineations (e.g. IR, IRB, PC) except in some areas having strong tidal currents. Delineations were also consistent with areas having low Q but high Q* indicating more focusing of discharge (e.g. RB). Delineations are also consistent with areas having high Q and low Q* that are geometrically constrained to minimize tidal mixing (e.g. tributaries LC and HC). With the exception of weak signals in northeast Rehoboth Bay, any potential ground water discharge into open (deeper) water are either below the resolution of satellite imagery or masked by mixing with a larger volume of ambient surface water or tidal mixing.