Determination of Snow Melt Flood Peaks for Highway Drainage Design

摘要

Highway designers are often faced with the need to estimate small watershedrunoff during the spring breakup season. During this time, culverts and small bridges are often clogged with ice and snow. In order to provide adequate drainage capacity, designers need an accurate estimate of spring runoff flow. An initial study focused on several alternative ways to estimate spring runoff flows for small basins. The estimation methods were tested on ten drainage basins in Interior Alaska. Two flow characterizations appear to be useful and worthy of further consideration. The first method tabulates the peak of the first significant rise in the stream hydrograph during the spring season. The second method selects the peak flow that occurs anytime during the spring quarter months of April, May or June. The selection process was carried out with the Lotus 1-2-3 spreadsheet program and used the streamflow data base from a CD-ROM. Once the peak flow record was tabulated, the rank order was created and the return period estimated for each flow series values. The results are presented as plots of the four combinations of flow and log-flow vs. return period and log-return period. The results were compared to the standard annual flood series. For most of the test basins the spring quarter peak flows values are very close to the annual flood series. The first seasonal peak series is usually 1/2 to 1/3 of the other two series. However, several watersheds indicated first seasonal peak values very close to those of the annual and spring quarter best explained by the log-normal frequency distribution.