Bridge-Site Study Data for Selected Highway Crossings in Mississippi, 2023

The U.S. Geological Survey (USGS) works closely with the Mississippi Department of Transportation (MDOT) to provide information to be used by the MDOT for design of highway-drainage structures. MDOT spends millions of dollars annually for highway construction. Streamflow records, hydrologic analyses of basins, and hydraulic analyses of flooding potential at proposed highway crossings help the MDOT to make more informed decisions on the use of highway construction funding. Flood-frequency and hydraulic characteristics at highway crossings are determined from historical flood-elevation data recovered by the USGS, cross-section data, and correlations with data from nearby gaging stations. Additional streamflow data are collected for ungaged sites when substantial flooding occurs in an area of interest to MDOT. This information not only provides the basis for the design of highways and drainage structures, but is also used by local agencies and the public as a guide in flood-plain management. Data for twenty-eight sites in Mississippi that were studied during the State fiscal year 2023 (July 1, 2022, to June 30, 2023) are provided in this data release. The geospatial dataset includes one point feature class shapefile with associated FGDC-compliant metadata representing selected basin characteristics and estimates of eight flood-frequency peak streamflows with corresponding stages, or water-surface elevations for twenty-eight sites in Mississippi. Flood-frequency streamflows were determined using methods described by Anderson (2018). Water-surface elevations were determined using methods described by Rantz (1982a, 1982b). Also included are input files of the step-backwater model described by Shearman (1990).

美国地质调查局（U.S. Geological Survey, USGS）与密西西比州交通运输部（Mississippi Department of Transportation, MDOT）紧密协作，为后者的公路排水结构设计提供支撑信息。密西西比州交通运输部每年在公路建设上的投入高达数百万美元。河道流量记录、流域水文分析以及拟建公路交叉点的洪水潜力水力分析，可帮助该部门更科学地决策公路建设资金的使用方案。公路交叉点的洪水频率与水力特征，通过美国地质调查局获取的历史洪水高程数据、河道断面数据，以及与邻近水文站数据的相关性分析得以确定。当MDOT关注的区域发生大规模洪水时，项目团队还会为无实测流量的站点补充采集河道流量数据。此类信息不仅可为公路及排水结构的设计提供核心依据，同时也可供地方机构与公众作为洪泛区管理的参考指南。
本次数据发布涵盖了2023财年（2022年7月1日至2023年6月30日）期间针对密西西比州28个研究站点的相关数据。该地理空间数据集包含一个点要素类形状文件，以及符合联邦地理数据委员会（Federal Geographic Data Committee, FGDC）规范的元数据，用于表征选定的流域特征，同时包含28个密西西比州站点的8种洪水频率峰值流量估算值与对应水位（即水面高程）。
洪水频率峰值流量采用Anderson（2018）所述方法计算得到；水面高程则采用Rantz（1982a、1982b）所述方法确定。本次发布内容还包含由Shearman（1990）提出的回水演进模型（step-backwater model）的输入文件。