By Chris Rundall, PE, LEED AP
In an effort to increase public safety and reduce flood losses across the state, the Colorado Water Conservation Board (CWCB) issued new floodplain rules and regulations on January 14, 2011. These rules were built off the Federal Emergency Management Agency’s (FEMA) rules to provide uniform standards for regulating floodplains and activities within them.
One of the more stringent criteria found in the CWCB rules concerns floodway designation. Floodway is defined as the channel of a river or other watercourse. It also includes the adjacent land areas. These areas must be free of obstructions so the base flood can discharge without increasing the water elevation above a designated height. In the past, the designated height was one foot. The new Colorado rules reduce it to a half foot. Here’s an excerpt from the CWCB’s rules:
“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 opposition to the floodway change. One reason is that sand and gravel pits are often located adjacent to rivers. By reducing the height to a half foot, the floodway’s limits will expand–pushing sand and gravel operations further from the river.
Currently, municipalities are in the three-year transition period from the date the rules became effective. They should be undertaking compliance activities. With expertise in hydrologic and hydraulic modeling, Baseline can support governmental agencies and private interests through this process. For more information, please contact firstname.lastname@example.org or (303) 940-9966.