Performance of Model Storm Sewer Junctions

The design of an effective storm water junction structure requires calculation of the energy losses, and associated backwater effects, in the vicinity of the junction under anticipated maximum flows in the incoming sewers. In the case of hydraulically inefficient junctions, energy losses due to stream mixing and from drag can lead to surcharged conditions in the conduits. Under these conditions Sangster suggests appropriate energy loss coefficients based on extensive tests on small-scale junction structures in which the inflow and outflow pipes were surcharged. However, efficient storm sewer systems normally operate under free surface conditions. Consequently the experimental program, described in this note, had the following main objectives: 1. To provide data on the relative efficiency of different-shaped junction structures operating under free surface conditions; 2. to investigate junctions having large inlet pipe diameters and small incoming pipe slopes; and 3. determination of suitable modifications to junction geometry in light of recent attempts to improve the performance of some inefficient junctions in an existing sewer system.