DESIGN OF ROAD SURFACE DRAINAGE FACILITIES BASED ON VARIED FLOW ANALYSIS

摘要

A computational model was developed for design of road surface drainage facilities.Design variables are a design storm causing the largest peak discharge for a given return period, and an appropriate outlet spacing (channel length) satisfying the condition that the maximum water depth in the channel will not exceed a given allowable depth. The design procedure is as followings: 1)Assume a duration of rainfall event and calculate rainfall intensity 2) Calculate inflow rate from road surface into a linear drainage channel 3) Assume an outlet spacing and compute flow profile in the channel based on the varied flow analysis 4) Repeat the procedure 3) until the maximum water depth in the channel is almost equal to a given allowable depth 5) Repeat the above procedure until the assumed duration is almost equal to the total travel time of road surface sheet flow and channel flow. The varied flow analysis for a linear drainage channel with two outlets at upstream and downstream ends of the channel includes the procedure for finding water dividend and calculating flow profile of upstream and downstream segments. The design based on the varied flow analysis is more reasonable and economical than that based on the uniform flow analysis for a drainage system including channels of mild slope.