Spokane Creek hydraulics and floodplain permit

A hydraulics review was completed for a Joint Permit Application and bank stabilization project on Spokane Creek to evaluate the requirements of 44 CFR Section 60.3(d)(3) of the National Flood Insurance Program (NFIP). Based on the project review, the site in within the Zone A special flood hazard area (SFHA) and may result in a flood rise due to changes in channel conveyance (both roughness and hydraulic radius). However, the resultant flood rise was minor (less than 0.5 feet based on HEC-RAS hydraulic modeling) and it was therefore petitioned that the floodplain permit be issued per ARM 36.15.604 and the Lewis and Clark County Floodplain Regulations.

Based on KF2’s evaluation, the project will result in a minor flood rise that is well below the regulatory requirements above.