Bridges and Flooding

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Unrestricted development in and around floodways can heighten the severity and exacerbate the cost of flooding. Flooding can be significantly aggravated by runoff from land that has been stripped of vegetation or covered with buildings, pavements, and other impervious materials. Unchecked development has contributed significantly to increased magnitude and frequency of downstream flooding. Source: Sharing the Challenge – Floodplain Management into the 21st Century (the “Galloway Report”). Full text (272 pages)

When flood waters rise, any obstacle that impedes the flow of the water can dramatically amplify the depth and duration of the flood. Because of this, bridges are usually designed with special attention paid to their effect on floodwaters. New-terrain I-69 planners acknowledged this in their original studies.

“Since the proposed bridges would be designed to “pass” the 100-year flood volume with adequate clearance under the bridges, the I-69 project is not expected to increase flooding.” I-69 Sec. 3 FEIS, page 5-342

Unfortunately, this basic principle has been abandoned. INDOT has announced that it plans to shorten the span of many of the new-terrain bridges, raising flood levels up to a foot in some areas. The additional floodwaters will inundate nearly 6,000 acres, much of it economically valuable farmland.

SR 257 Closed by East Fork White River Flooding - May 2011

East Fork White River at SR 57 Bridge - May 2011

The biggest offender is the proposed bridge spanning the East Fork White River. At the point where the proposed I-69 would cross, the floodplain is over 2 miles wide but the bridge is only ¼ mile long. Nearly 2 miles of floodplain will be dammed by a causeway – a 20 foot tall embankment – which will obstruct the flow of flood water. The result will be major changes to the hydrology and ecology of the river and cause damage to farmland near the river.

It’s not too late to change direction.

Surcharge Map East Fork White River