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Incorporating River Network Structure for Improved Hydrologic Design of Transportation Infrastructure

项目名称：	Incorporating River Network Structure for Improved Hydrologic Design of Transportation Infrastructure
摘要：	Sustainable construction and maintenance of transportation infrastructure requires accurate hydrologic design. A critical element of the hydrologic design is the estimation of the flow rates that bridges and culverts must convey and their abutments must withstand. It is difficult to determine reliable design flows because most channels are ungauged. Furthermore, urbanization and climate change are altering basins and introducing additional uncertainty. For ungauged basins, storm flows are most commonly estimated using synthetic unit hydrograph (UH) methods. Synthetic UHs are closely related to the travel time distribution for runoff that is produced throughout the basin to the outlet, and they are commonly estimated from the physical characteristics of the basin. Using an assumption that the storm flows are linearly related to the excess rainfall amounts, the synthetic UH can be used to determine the flow rates that are produced by any selected storm. Several methods are available in software such as HEC-HMS to estimate synthetic UHs. For example, the Soil Conservation Service (SCS) method in HEC-HMS is based on a single dimensionless UH that is assumed to apply in all cases. To develop the synthetic UH for a given basin, the dimensionless UH is simply rescaled using values for the time to peak and the peak UH value. Those two values can be calculated from the basin area, length, slope, and curve number. Similarly, the Clark method in HEC-HMS is based on a single time-area curve that describes the distribution of travel times to the outlet. The time coordinates are multiplied by the time of concentration, which is estimated in a similar manner as the time to peak in the SCS method. The resulting UH is then routed through a linear reservoir to determine the final synthetic UH. The use of synthetic UHs has two recognized limitations. First, the approach assumes linearity between the excess rainfall amounts and storm flows at the basin outlet. However, it is well-known that higher volumes of flow tend to move faster. That behavior violates linearity and can increase the magnitude of the peak flow and potentially affect the suitability of a bridge or culvert design. Second, these synthetic UHs do not account for differences in the channel network structure. Channel networks are known to exhibit distinct structures (such as dendritic, parallel, pinnate, rectangular, or trellis) depending on the conditions under which they developed. Such diverse networks are abundant in the mountains-plains region, and they convey flow to their outlets using very different flow-path distributions. Some synthetic UH methods have been proposed to allow consideration of basin shape. For example, the modified Clark method (Kull and Feldman, 1998) replaces the standardized time-area curve with one that is derived for the basin of interest. The geomorphic instantaneous unit hydrograph (Rodr�guez-Iturbe and Vald�s, 1979) describes the channel network using locally-derived Horton�s ratios. Although these methods include the actual basin shape, they still rely on the linearity assumption. Other methods have been proposed to relax the linearity assumption, but they do not consider the channel network type.
状态：	Completed
资金：	59160
资助组织：	Research and Innovative Technology Administration
管理组织：	Mountain-Plains Consortium
项目负责人：	Kline, Robin
执行机构：	Dept. of Civil and Environmental Engineering
主要研究人员：	Niemann, Jeffrey D
开始时间：	20150625
预计完成日期：	20190930
实际结束时间：	20200413