JD103HYPACK.SHP: Parsed HYPACK navigation from April 13, 2010 of U.S. Geological Survey Field Activity 2010-006-FA in Indian River Bay, Delaware (Geographic, WGS 84)

A geophysical survey to delineate the fresh-saline groundwater interface and associated sub-bottom sedimentary structures beneath Indian River Bay, Delaware, was carried out in April 2010. This included surveying at higher spatial resolution in the vicinity of a study site at Holts Landing, where intensive onshore and offshore studies were subsequently completed. The total length of continuous resistivity profiling (CRP) survey lines was 145 kilometers (km), with 36 km of chirp seismic lines surveyed around the perimeter of the bay. Medium-resolution CRP surveying was performed using a 50-meter streamer in a bay-wide grid. Results of the surveying and data inversion showed the presence of many buried paleochannels beneath Indian River Bay that generally extended perpendicular from the shoreline in areas of modern tributaries, tidal creeks, and marshes. An especially wide and deep paleochannel system was imaged in the southeastern part of the bay near White Creek. Many paleochannels also had high-resistivity anomalies corresponding to low-salinity groundwater plumes associated with them, likely due to the presence of fine-grained estuarine mud and peats in the channel fills that act as submarine confining units. Where present, these units allow plumes of low-salinity groundwater that was recharged onshore to move beyond the shoreline, creating a complex fresh-saline groundwater interface in the subsurface. The properties of this interface are important considerations in construction of accurate coastal groundwater flow models. These models are required to help predict how nutrient-rich groundwater, recharged in agricultural watersheds such as this one, makes its way into coastal bays and impacts surface water quality and estuarine ecosystems. For more information on the survey conducted for this project, see http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2010-006-FA.2010年4月，美国特拉华州印第安河湾（Indian River Bay）下方开展了一项地球物理勘探工作，旨在划定淡水-咸水地下水界面及其相关的海底以下沉积构造。本次勘探在霍尔特兰丁（Holts Landing）研究站点周边采用了更高空间分辨率的测量方案，该站点后续完成了密集的陆上与近海研究。连续电阻率剖面（continuous resistivity profiling，简称CRP）测线总长度达145千米，同时在海湾周边布设了36千米的啁啾地震（chirp seismic）测线。本次勘探还采用50米拖缆（streamer）开展了全海湾范围的中分辨率CRP测量，布设了海湾级勘测网格。 勘探与数据反演结果显示，印第安河湾下方发育大量埋藏古河道，在现代支流、潮汐溪与沼泽区域，这些古河道大体垂直于岸线延伸。在海湾东南部靠近怀特溪（White Creek）的区域，还成像到一套规模尤为宽大深邃的古河道系统。多数古河道还伴随有高电阻率异常，对应着与其相关的低矿化度地下水羽流，这大概率是因为河道充填物中发育细粒河口泥与泥炭，充当了海底隔水层。当此类隔水层存在时，陆上补给的低矿化度地下水羽流便可越过岸线扩散，进而在地下形成复杂的淡水-咸水地下水界面。 该界面的相关属性，是构建精准海岸地下水流模型的重要考量因素。此类模型可用于辅助预测：在农业流域（如本次研究的流域）中补给的富营养地下水，将如何运移进入海湾并影响地表水水质与河口生态系统。如需了解本次项目勘探的更多信息，请访问http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2010-006-FA。