Geophysical investigation of the hydrogeologic setting of Delaware's Inland Bays

The fundamental goal of this dissertation research project was to use geophysical imaging to provide additional constraints on the hydrostratigraphic framework for ground-water discharge to the Inland Bays of Delaware. This dissertation was part of an EPA-funded Coastal Intensive Sites Network project entitled "CISNet: Nutrient Input as a Stressor and Net Nutrient Flux as an Indicator of Stress Response in Delaware's Inland Bay Ecosystem". The dissertation research was part of the ground-water component of the CISNet project. This component concentrated on the identification of sites of ground-water discharge within the bays and the relationship of this discharge to the underlying geology of the region.; Extensive coring by previous investigators in the Inland Bays of Delaware has been conducted in order to understand the Quaternary history of this region. However, prior to this dissertation no attempt had been made to use shallow marine seismics to map the Inland Bays in order to better understand the influence of the subsurface geology on the hydrostratigraphic framework. In this project, an Edgetech chirp sub-bottom profiler was used in Rehoboth and Indian River Bays, the larger two of the three Inland Bays of Delaware, to obtain greater horizontal resolution than that afforded by isolated cores. Processing of the chirp data using Promax(TM) seismic software resulted in sub-decimeter scale resolution of shallow layers below the bay bottom including a high-amplitude, relatively continuous reflection that was interpreted as the Pre-Holocene/Holocene surface.; At two sites, the Thorneby-Purnell property along Herring Creek, a tributary of Rehoboth Bay, and the Pete Okie property along Indian River, on-land ground penetrating radar (GPR) data were collected using a Sensors and Software GPR PulseEKKO 100 system with both 50 and 100 MHz antennas. The water table, occurring at depths on the order of 6 m beneath the surface, was imaged along GPR profiles collected at the two properties. The GPR data were correlated with gamma logs and descriptions of sediments from augers collected at both of the properties. These data indicate the heterogeneous nature of the near surface sediments. The dominant lithologies were coarser-grained sands to silty sands to finer-grained muds.; At the TP property, chirp data collected in the bordering Herring Creek and on-land GPR data were integrated with gamma logs and thermal signature information from Landsat 7 and aerial surveys to further constrain the location of ground-water discharge into Herring Creek. A paleochannel beneath the creek was imaged by the chirp data. Core data confirmed the presence of the paleochannel and indicated that its in-fill was finer-grained muds. The results at the TP property illustrate the important role that subsurface paleochannels may play in the hydrostratigraphy of the Inland Bays region. The finer-grained in-fill of paleochannels may act as a plug to ground-water flow creating situations where ground-water discharge would preferentially occur along the edges of paleochannels. (Abstract shortened by UMI.)...