Minimum Flood Corridors are required as outlined below to conserve a vegetative buffer along stream channels. The Minimum Flood Corridor is defined as the channel bottom width plus 60 feet, plus 6 times the channel depth. The corridor is to be centered on the channel, as shown below, or aligned to follow the natural flow of flood waters.
In general, the major components of the revised Flood Standards as adopted on May 25, 2004 apply to "New Growth Areas." However, the Minimum Flood Corridor continues to be applicable within the "Existing Urban Area" outside of the floodplain. Thus in the Existing Urban Area outside the FEMA-mapped floodplain, Minimum Flood Corridors apply to streams which drain greater than 150 acres (this was an existing standard) as well as streams having a defined bed and bank, even if the drainage area is less than 150 acres (this reflects the revised standards). In New Growth Areas, the preservation of a Minimum Flood Corridor is required along all channels which drain greater than 150 acres or have a defined bed and bank, regardless of whether a floodplain has been mapped along the corridor.
Riparian vegetation and the existing grade within the identified flood corridors is required to be preserved or enhanced to the maximum extent practicable, or mitigated during the development planning and construction processes when impacted by allowable encroachments. Where land uses prior to development have an impact on the buffer, the area should be replanted with vegetation compatible with the minimum flood corridor and water quality benefits.
Individual areas of encroachments into the riparian vegetation and encroachments of fill into the existing grade are permitted for the following, provided a 'sequencing' process is followed:
- Operation, maintenance and repair
- Channel improvements
- Stormwater storage facilities
- Utility crossings
- Stream crossing structures
Individual areas of encroachments may also be permitted for the following uses, provided the encroachments are minimal and the uses are generally consistent with the purpose of the corridor (and a sequencing process is followed):
- Pedestrian/bike trails
- Recreational uses
- Public purposes
Prior to allowing encroachments for permitted purposes into the minimum flood corridor, a sequencing process is required which first seeks to avoid, then to minimize, then mitigate for impacts to the minimum flood corridor.
For detailed standards, including documentation and mitigation requirements, see the Lincoln Design Standards .