The purpose of this page is to define alteration of a watercourse, a commonly used term in floodplain management.
Alterations are often made to the channels of rivers, stream, or drainageways, usually to improve drainage, relocate the channel, or to increase its flood carrying capacity. There are two requirements for maintaining the flood carrying capacity of an altered watercourse. The altered or relocated watercourse must have the same or greater capacity as the original watercourse. Additionally, once the alteration is made, the capacity of the altered or relocated watercourse must be maintained over time.
If a development permit application proposes a stream alteration, the local official must notify adjacent communities, the State Coordinating Agency for the National Flood Insurance Program (NFIP), and provide a copy to the FEMA Regional Office. If an adverse impact is suspected, the neighboring community will be able to voice its concerns prior to any modification. Federal and state permits will usually be required for any alteration or relocation. It is recommended that the community require the submittal and approval of a Conditional Letter of Map Revision (CLOMR) for large-scale proposals. This assures that FEMA will recognize the project for a map change when construction is completed.
National Flood Insurance Program (NFIP) Requirement
- 60.3 - Flood plain management criteria for flood-prone areas
- (b) (6) - Notification Requirement
- (b) (7) - Maintenance of flood carrying capacity
Other Applicable NFIP Regulations
- 60.2 - Minimum compliance with flood plain management criteria
- (h) - FEMA Approval of Modified Data
- 65.3 - Requirement to Submit New Technical Data
- IS-9 Managing Floodplain Development Through The National Flood Insurance Program (NFIP) (page. 5-54)