MRGWCON_ALLXYZRES.SHP: Point shapefile of continuous resistivity profiling data below the sediment water interface processed with a varying water conductivity value from Indian River Bay, Delaware, on U.S. Geological Survey Field Activity 2010-006-FA in April 2010 (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，为圈定美国特拉华州印第安河湾（Indian River Bay）下方的淡水-咸水地下水界面及其相关的海底下部沉积构造，研究团队开展了一项地球物理勘探工作。本次勘探在霍尔特登陆点（Holts Landing）的研究站点周边采用了更高空间分辨率的测线，该站点后续完成了密集的陆上与海上研究。连续电阻率剖面法（continuous resistivity profiling, CRP）测线总长度达145千米，同时在海湾周边布设了36千米的chirp地震测线进行勘探。全海湾网格的中分辨率CRP勘探采用50米长的拖缆（streamer）开展作业。勘探与数据反演结果显示，印第安河湾下方埋藏有大量古河道，在现代支流、潮汐水道及沼泽分布区域，这些古河道总体上与岸线垂直延伸。在海湾东南部靠近怀特溪（White Creek）的区域，成像到了一处规模尤其宽大深邃的古河道系统。多数古河道伴随有高电阻率异常，对应着与其相关的低盐地下水羽流，这一现象大概率源于河道充填物中赋存的细粒河口泥质沉积物与泥炭，此类物质可作为海底隔水层发挥作用。在这类隔水层分布的区域，陆上补给的低盐地下水羽流能够穿越岸线向外运移，在地下形成复杂的淡水-咸水地下水界面。该界面的相关特征是构建精准海岸地下水流模型的重要考量因素。此类模型可用于预测此类农业流域内补给的富营养地下水如何进入海湾，进而对地表水水质与河口生态系统造成影响。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。