Estimating Joint Probabilities of Design Coincident Flows at Stream Confluences.

摘要

Highway drainage structures are often located near the confluence of two streams where they might be subject to inundation by relatively rare hydrologic events from either stream. These structures must be designed to meet specified performance objectives for floods. Because the flooding of structures on one stream can be affected by high flows on the other stream, it is important to know the relation between the exceedance probabilities for flows emanating from the main and tributary streams in a confluent stream pair, that is, the joint probability of the coincident flows. The joint probability question arises where a structure is located at a site where flows emanating from the main (larger) watershed and tributary (smaller) watershed might result in critical hydraulic design conditions. A portion of the tributary stream is influenced by both the discharge of the tributary stream and the backwater caused by flows in the main stream. This portion of the tributary stream is referred to as the influence reach. The location of the structure within the influence reach, as well as the joint hydrologic behavior of the confluent streams, will determine the importance of the joint behavior of the confluent streams on the appropriate design conditions for the structure. The objective of this research was to develop practical procedures for estimating joint probabilities of design coincident flows at stream confluences and to provide guidelines for applying the procedures. The scope was limited to riverine areas and did not include consideration of coastal areas.