Highway drainage structures often are located near the confluence of two streams where they may be subject to inundation by high flows from either stream. These structures are designed to meet specified performance objectives for floods of a specified return period (e.g., the 100-year flood). Because the flooding of structures on one stream can be affected by high flows on the other stream, it is important to know the relationship between the coincident exceedence probabilities on the confluent stream pair (i.e., the joint probability of the coincident flows).
Accurate estimates of the joint probability of design flows at stream confluences are a crucial element in the design of efficient and effective highway drainage structures. No accurate generally accepted estimation procedure for determining coincident flows exists for use in the design of highway structures. A practical procedure for the determination of joint probabilities of design flows at stream confluences is needed.
The objective of this research is to develop practical procedures for estimating joint probabilities of design coincident flows at stream confluences and guidelines for applying the procedures. The scope of this research is limited to riverine areas and does not include coastal areas.
Status The final report is available as NCHRP Web-Only Document 199 here.