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Thursday, October 10 • 11:30am - 12:00pm
Brianhead Fire Flood Mitigation within Parowan City, Utah

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On June 17, 2017 the Brian Head fire started within the mountains to the south and east of Parowan City and burned over 71,600 acres (112 square miles), with over 25,000 acres (39.4 square miles) of the burned area falling within the watershed above Parowan City. Burning of the ground cover significantly increases the runoff potential of the watershed and the potential for flooding debris flows. After the fire was extinguish, multiple summer rain events caused significant flooding and associated damage at the Parowan City’s Forebay Pond and within the City, particularly between 100 West and 600 West.
BC&A worked with Iron County, Parowan City, and the NRCS to design repairs and flood mitigation recommendations along Parowan Creek. The major project features included:
• Construction of a new Forebay Dam using a chimney drain embankment to satisfy NRCS Pond design requirements related to stability and seepage control. The existing dam was flown using drone technology to obtain aerial imagery and topography. This information was input into a three-dimensional Civil 3D model to develop the proposed design of the Forebay Dam. This model was then given to the Contractor to upload in their construction equipment to build the project.
• The outlet works of the Parowan Forebay Holding Pond were reconstructed.
• Erosion of Parowan Creek adjacent to the Forebay Dam was mitigated by providing erosion protection measures, including a grouted riprap channel that needed to withstand maximum velocities upward of 17 feet per second (fps).
• Two existing drop structures at 600 West and 200 West were repaired and reinforced with grouted riprap to prevent future headcutting during a large flood event.
• Sections of Parowan Creek were reinforced with riprap. Material excavated from the channel was placed on the channel banks to provide additional flood capacity and the channel banks were revegetated to help prevent minor erosion.
• Sediment was excavated from the channel to provide more flood conveyance capacity and help prevent flooding of downstream residential homes.
The project was designed, including environmental permitting, in about a three-month time period and bid in the spring of 2018. Construction took place from about May 2018 to September 2018 and the project was completed about a year after BC&A was contracted to complete the work.


Todd Olsen

Project Manager, Bowen Collins & Associates
Todd Olsen works for Bowen Collins & Associated working out of their St. George, Utah office and has over 15 year of experience in the planning, design and construction of large water, wastewater, stormwater, and flood control/irrigation projects and facilities. Todd has served as... Read More →

Thursday October 10, 2019 11:30am - 12:00pm MDT