HYDRAULIC CHARACTERISTICS OF KDOT FLUME INLETS. FINAL REPORT

Kansas Department of Transportation (KDOT) flume inlets are commonly used to intercept storm runoff on bridge decks and bridge approach sections. Safety related design constraints limit the discharge that a flume inlet can capture completely. Any flow that bypasses the flume inlet can cause erosion and maintenance problems. Hydraulic tests of model flume inlets were conducted in the hydraulics laboratory at the University of Kansas. The objectives of these tests were: (1) to determine the hydraulic characteristics of KDOT's standard flume inlet for a roadway with a shallow gutter; (2) to investigate possible design changes that would improve the hydraulic performance of this inlet; and (3) to develop a new flume inlet design for a roadway with a 102 mm (4 in.) edge curb and determine its hydraulic characteristics. The flume inlet and a 24 m (80 ft) length of roadway were modelled at one half scale. The flow intercepted by the inlet and the flow that bypassed the inlet were captured and measured. Tests were run with the roadway set at all possible combinations of six longitudinal slopes (0.5%, 1%, 2%, 3%, 4% and 5%) and three cross slopes (1.56%, 3% and 6%). The principal factor that determines the capacity of the standard flume inlet is the longitudinal slope of the roadway. A linear algebraic equation relates the recommended design capacity of the inlet to this slope. The capacity of the inlet can be increased substantially by the addition of a guide vane. The best alignment for the guide vane was determined by trial. An improperly located guard fence post can reduce the hydraulic capacity of the inlet. The region in which a guard post can be placed with no adverse hydraulic impact was determined. The recommended flume inlet for a roadway with an edge curb is twice as long as the standard flume inlet for a roadway with a shallow gutter. The longer inlet is necessitated by the greater spread of flow on a roadway with an edge curb. Guard fence posts can be placed anywhere within the inlet with no adverse impact provided that the standard minimum spacing is maintained. The capacity of the new flume inlet can be increased substantially by the addition of a guide vane on the same alignment recommended for the standard flume inlet.