Bridges

A bridge is a structure that spans a waterway, supported on abutments at the ends, and by piers at intermediate points. Usually bridges and associated approach works encroach upon a floodway, reducing the waterway area and making water back up. Upstream water levels are raised and downstream levels are lowered. The net rise upstream of the bridge is called the afflux.

DRAINS employs procedures developed by the U.S. Federal Highway Administration and presented in the AUSTROADS Waterway Design Manual to estimate the effects of bridges on upstream water levels.

Following a run, peak water levels upstream and downstream of a bridge are presented in the Main Window. If multiple storms are used, the results for a particular storm can be selected using the pull-down menu that appears in the top-left corner of the Window.

The flowrates upstream and downstream of a bridge can be found in the information for the links entering and leaving the bridge.

Water levels upstream and downstream of bridges can be examined using the Pop-Up (right mouse button) menu, which provides options for plotting levels calculated during a run, or for displaying the numerical values.

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