Design Example: Analyzing Capacity Contours for Flood Risk Assessment

A bund is proposed across a small valley to store stormwater. The area of land that will be submerged upstream after construction is determined using capacity contours.

Capacity contours represent the contour lines that outline the extent of water spread at a specific water level in the bund.

Based on the proposed bund height and the valley's topography, the engineers estimate the high flood level.

First, the engineers determine the location of the bund and set a specific height for the high flood level.

The engineers place a leveling instrument and determine the staff reading for the high flood level. Then, the same staff reading is marked along the valley on the upstream side at fixed distances apart.

At the selected high flood level, the capacity contours extend into the nearby dwelling area, indicating that the locality would be flooded if the bund height remains as proposed.

To ensure safety, the engineers should lower the bund height and recheck the capacity contours. At this height, the water would remain at a safe distance from the nearby dwelling area.