FLOOD MITIGATION MAPS

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In July of 2021, an intense localized storm event over Idlewild and South Middle Creek drainages moved a large amount of sediment, rock, and trees from the hillslopes and into the drainages. The main channel and all its tributaries channels' shapes changed dramatically, significantly widening and deepening in the process.

River Science completed pre-and post-flood drone flights of this storm event to collect aerial imagery for analysis. This remote sensing allowed River Science to map and quantify erosion and deposition of sediment in Idlewild creek.

ARWC contracted heavy equipment and used nearly 600 trees to create 132 features and structures, including bank protection, floodplain connectivity treatments, ramps, grade control structures, V-Structures, and crib walls to restore the channel shape and function. Treatments were completed along a one-mile-long reach of Idlewild Creek. SWIFT crews completed over 24 acres of hillslope treatments to reduce slope erosion in this area. 3.2 acres of seeding along 1 mile of the channel.

River Science will be flying the area with a drone after a flooding event to evaluate the function of treatments.

 

CWCB & CDPHE breakdown of funds used in Idlewild and South Middle Creek drainages

 

CWCB Funds:

·         Hillslope treatments by SWIFT crews (Task 3) Many of the trees felled at the bottom of the slope by SWIFT were used            in the channel structure treatments and bank reinforcements.

·         Culvert and sedimentation retention work at Tower Rd crossing of North Middle Creek (Task 3)

·         Photo Mapping and Monitoring (Task 5) – Stakeholder Dashboard with photos of pre and post-work, River Science                remote sensing data collection to evaluate the function of the treatments.

CDPHE:

·         One mile of channel treatment work using best management practices (BMPs) and seeding

·         River Science remotely sensed stream channel to complete a change detection and hydrology study work that was              used to guide the location of instream channel work

 

In our post-July flood survey of the drainages, we found evidence of past burn layers in the soil profile of one of the eroded tributaries drainage. Colorado Geologic Survey came out and took samples from four different layers in that spot to carbon 14 date them so we can get an idea of the fire history of the area. We are still waiting for the results.