Colorado’s Stringent Floodplain Rules

By Rick Behning, PE

In an effort to increase public safety and reduce flood losses across the state, the Colorado Water Conservation Board issued new floodplain rules and regulations that became effective on January 14, 2011.  These rules build off the FEMA rules.  The hope is to provide uniform standards for regulatory floodplains in Colorado and activities in those floodplains.

One of the more stringent criteria found in the CWCB rules concerns floodway designation.  The floodway is defined as the channel of a river or other watercourse, and the adjacent land areas that must be kept free of obstructions in order to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height.  In the past this designated height was one foot. However, with the new Colorado rules this has been reduced to ½ foot.  The following is an exerpt from the CWCB rules concerning floodway designation:

The CWCB recognizes that Designated Floodways are administrative limits and tools used by communities to regulate existing and future Floodplain developments within their jurisdictions. This Rule 8(A) does not require communities to automatically map ½ foot floodways within their jurisdictions. However, at such time when floodways are to be delineated through Physical Map Revisions involving local government participation, communities shall delineate floodways for the revised reaches based on ½-foot rise criteria. Letters of Map Revision to existing floodway delineations may continue to use the floodway criteria in place at the time of the existing floodway delineation. Until such time that floodways are revised and designated, communities may continue to regulate their mapped one-foot floodways. For reaches where a transition must be shown to connect new studies to existing studies with different floodway criteria, the transition length shall not exceed 2,000 feet.

Special interests within the state have expressed their opposition to the floodway change.  Sand and gravel pits are often located adjacent to rivers.  By reducing the floodway height to a ½ foot the limits of the floodway will expand thereby pushing the sand and gravel operations further from the river.

If you have a question for Baseline’s experts, please email rick@baselinecorp.com.  For more information, visit the Colorado Water Conservation Board and floodsafety.com