Concurrent Flooding Probabilities

Concurrent flooding the flooding at a location due to two or more causative factors, has not been adequately addressed in the literature. The estimation of stage probabilities is important to hydrologic engineers and becomes complex where a location can be inundated due to flooding of two or more rivers. A probability concept of concurrent flooding is developed to determine flooding probabilities on a tributary river where the stage-flow relationship on the tributary is affected by backwater due to a flooding event on a nearby main river. A systematic approach for determining concurrent flooding probabilities call the”critical combination” method was developed and applied to the Mearmec River near its confluence with the Mississippi River in Missorui. A “critical combination” is a tributary river flow and main river stage pair that could combine to cause a yearly peak stage at a point on the tributary. The stage resulting from each critical combination,computed using a backwater program, produces an annual stage series to which a probability distribution can be fitted. This procedure was used in the Meramec-Mississippi case and shown to be a valid approach.