Depth grids of the flood-inundation maps for North Fork Salt Creek at Nashville, Indiana

Digital flood-inundation maps for a 3.2-mile reach of North Fork Salt Creek at Nashville, Indiana, were created by the U.S. Geological Survey (USGS) in cooperation with the Indiana Department of Transportation. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science Web site at http://water.usgs.gov/osw/flood_inundation/, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage 03371650, North Fork Salt Creek at Nashville, Ind. Real-time stages at this streamgage may be obtained on the Internet from the USGS National Water Information System at http://waterdata.usgs.gov/nwis or the National Weather Service (NWS) Advanced Hydrologic Prediction Service at http:/water.weather.gov/ahps/ (NWS site NFSI3). Flood profiles were computed for the stream reach by means of a one-dimensional, step-backwater hydraulic modeling software developed by the U.S. Army Corps of Engineers. The hydraulic model was calibrated using the current stage-discharge rating at the USGS streamgage 03371650, North Fork Salt Creek at Nashville, Ind. The hydraulic model was then used to compute 12 water-surface profiles for flood stages at 1-foot (ft) intervals, except for the highest profile of 22.9 ft, referenced to the streamgage datum ranging from 12.0 ft (the NWS “action stage”) to 22.9 ft, which is the highest stage of the current USGS stage-discharge rating curve and 1.9 ft higher than the NWS “major flood stage.” The simulated water-surface profiles were then combined with a Geographic Information System digital elevation model (derived from light detection and ranging [lidar] data having a 0.98-foot vertical accuracy and 4.9-foot horizontal resolution) to delineate the area flooded at each stage. The availability of these maps, along with information regarding current stage from the USGS streamgage, will provide emergency management personnel and residents with information that is critical for flood response activities such as evacuations and road closures, as well as for post-flood recovery efforts.

美国地质调查局（U.S. Geological Survey, USGS）联合印第安纳州交通部，针对印第安纳州纳什维尔市北岔盐溪3.2英里河段制作了数字洪水淹没地图。此类洪水淹没地图可通过美国地质调查局洪水淹没制图科学官网（http://water.usgs.gov/osw/flood_inundation/）获取，其展示了对应纳什维尔市北岔盐溪USGS水位站（streamgage）03371650处选定水位高程的洪水范围与水深估算值。该水位站的实时水位高程数据，可通过美国地质调查局国家水信息系统（http://waterdata.usgs.gov/nwis）或国家气象局（National Weather Service, NWS）高级水文预报服务平台（http://water.weather.gov/ahps/，对应NWS站点NFSI3）从互联网获取。
本次研究采用美国陆军工程兵团开发的一维回水演算水力学模型软件，对该河段完成了洪水演进剖面计算。该水力学模型采用纳什维尔市北岔盐溪USGS水位站03371650当前的水位流量关系曲线进行率定。随后，该模型被用于计算12个水位面剖面：其中除最高剖面为22.9英尺外，其余均以1英尺为间隔，基准参考为该水位站的基面，水位范围从12.0英尺（对应国家气象局的“警戒水位”）至22.9英尺——该值为当前USGS水位流量关系曲线的最高水位，较国家气象局的“特大洪水水位”高出1.9英尺。
随后，将模拟得到的水位面剖面与地理信息系统（Geographic Information System, GIS）数字高程模型（源自垂直精度0.98英尺、水平分辨率4.9英尺的激光雷达（light detection and ranging, lidar）数据）相结合，以勾绘各水位对应的淹没区域。
此类地图的可获取性，搭配美国地质调查局水位站提供的实时水位信息，将为应急管理人员与居民提供关键信息，可用于疏散、道路封闭等洪水应对工作，以及灾后恢复重建工作。