12. Continuous Backwater
This scattergraph displays data obtained during dry weather from a flow monitor installed in a 27-in sewer just upstream from a 12-in Parshall flume. By design, the flume causes the upstream sewer to operate under continuous backwater conditions. This flume is no longer used for flow measurement. What would happen if the flume were removed?
Based on as-built records, the Design Method is used to estimate the flow conditions without the flume. Following an iso-Q from the maximum flow depth to the pipe curve, the maximum depth is estimated to decrease 9 inches. As a result, the sewer capacity is expected to increase nearly two-fold.