Tanglewood Creek CLOMR/LOMR
Tanglewood Creek CLOMR and LOMR Westminster, CO
JR Engineering designed improvements on Tanglewood Creek in Westminster which involved stabilizing approximately 0.4 miles of existing natural drainageway following the UDFCD Big Dry Creek Outfall Systems Planning and extending a culvert under 128th Avenue. The channel stabilization measures involved sheet pile check structures and grouted stepped boulder drops for grade control, and fill and realignment of parts of the existing incised Tanglewood Creek channel. All improvements are in the final stages of review by UDFCD and will be eligible for the maintenance program.
The project was analyzed using HEC-RAS and used flow rates from the 2012 Big Dry Creek Flood Hazard Area Delineation report to determine the future conditions floodplain limits and evaluate the hydraulic stability of proposed improvements. The CLOMR and LOMR analysis relied on the FIS flow rates to remap the improved channel.
The CLOMR request involved revised effective, existing, and proposed conditions floodplain mapping with a regulatory floodway analysis. After construction was completed in 2018, a Letter of Map Revision (LOMR) was prepared to officially revise the current Flood Insurance Rate Map (FIRM) to reflect the Tanglewood Creek channel improvements. Also involved in the Tanglewood Creek improvements were coordination for an Individual Permit application to the Army Corps of Engineers for roughly 0.92 acres of impacted jurisdictional wetlands.
The goals of the channel improvement project were to protect existing wetlands and riparian corridors, repair and stabilize eroded reaches of the drainageway, and improve the conveyance of the drainageway to accommodate future basin development.