Sewer overflow in the urban model MURI

Sewer overflow is one of the main causes of urban floods. Using an urban model called MURI recently built by Irstea, a series of experiments are carried out in order to simulate overflowing cases. The first configuration that was studied is a single street of 5.4 m in length, 0.15 m in width with a slope of 0.1% and two street inlets (of which the orifice diameter is 14 mm) that ensure the connection with the sewer network. Inflows of 2 and 3 L/s are used for the street and an inflow of 0.5 L/s for the sewer network that is partially closed in order to obtain overflow at the street inlets. The rising of the weir downstream the street permitted to obtain same water depth and to measure the vertical profiles of velocities. This study allowed us to investigate how the overflow process influence the water depth and the velocity field around the street inlet. The exchange flow discharge can be calculated using either an orifice equation or the head loss in the two pipes connecting the street and the sewage network, both methods requesting calibration, which is made difficult by the complexity of the flow around the street inlets.