Hydraulic Performance of Small Scale Bridge Deck Drains

Efficient removal of stormwater runoff from bridge deck surfaces is an important safety issue. This study investigates hydraulic performance characteristics of a new type of rectangular bridge deck drain. A physical modeling study was conducted to evaluate the hydraulic performance of the innovative rectangular bridge deck drain as a function of the approach discharge, different drain configurations, and bridge characteristics. Experiments included different numbers of open drains in series for variable approach discharge cross slope and longitudinal slope. Measurements included gutter flow depth (Y) and ponding width (T) at different stations along the deck, and the capture discharge and bypass discharge. A model equation is presented for predicting the capture discharge as a function of drain size (L+W), the number of open drains (N), Manning’s coefficient (n), depth of approached gutter flow (Y), longitudinal slope (S0), and cross slope (Sx). For experiments considering one through five drains in series (1-5 drains), the rating curve for each individual drain is the same when the drain size is 4 by 8 inches; however, the rating curve decreases slightly with successive drains when the drain size is 6 by 8 inches.