15-year Tuacahn Wash Detention Basin project nears completion; tortoise habitat regarded

View of the Tuacahn Wash Detention Basin project from Tuacahn Drive, Ivins, Utah, Jan. 6, 2012 | Photo by Alexa Verdugo Morgan, St. George News

IVINS – When complete, the Tuacahn Wash Detention Basin will provide added protection for Ivins and Santa Clara in the event of a flood.

The Tuacahn Wash, Ivins, Utah, Jan. 6, 2013 | Photo by Alexa Verdugo Morgan, St. George News

The detention basin is located at the top of the Tuacahn Wash, a natural waterway running from the area of Tuacahn High School for the Performing Arts in Ivins City to the Laub Pond Dam in Santa Clara. The Laub Pond Dam breached on Sep. 11, 2012, causing devastating flooding, as a result of which attention to the Tuacahn Wash project was accelerated. Construction began in early December 2012 and is expected to be complete on Feb. 15, 2013.

Project origins

Though the main instigator for the advancement of the project was the Santa Clara flood, the Tuacahn Wash project has actually been underway with Ivins City for more than 15 years. All reference to “the city” in the remainder of this report is to Ivins City.

Larry Crist, field supervisor of the Utah Field Office for the U.S. Fish and Wildlife Service, said that installing flood control in the Tuacahn Wash was originally part of the Washington County Habitat Conservation Plan. But that plan was delayed by a series of financial and environmental roadblocks.

Tuacahn Wash drainage vicinity map | Photo courtesy of Chuck Gillette

Ivins City Engineer Chuck Gillette has been involved in the project since 2005. He has coordinated the environmental studies, design, permitting and funding for the project and will serve as project manager throughout the duration of construction.

“This project has been a long time coming,” Gillette said, “it feels good to finally get it accomplished.”

Project timeline

1995: The necessity of installing flood control in the wash was first realized after the Tuacahn Flood on Sep. 6, 1995.

1996: The city hired Sanderson Consulting to analyze potential future flood effects on surrounding areas, forming a plan for a flood control project.

1998: The city proposed the Tuacahn Wash Detention Dam to the Habitat Conservation Advisory Committee. However, the committee indicated that the project application could not be reviewed until the city purchased the property on which the dam would be installed.

Equipment at the Tuacahn Wash Detention Basin project, Ivins, Utah, Jan. 6, 2013 | Photo by Alexa Verdugo Morgan, St. George News

2001: Alpha Engineering completed the Tuacahn Wash Hydrology Study and provided conceptual criteria for the design of the project, which also identified the size and shape of the property needing to be purchased.

2002: The city bought a seven-acre parcel of land for the express purpose of installing the Tuacahn Wash Detention Dam. However, the surrounding land was owned by the state of Utah as one of its state parks, requiring the city to request an access easement. The easement prompted the need for an environmental assessment to be conducted.

2002: The Fish and Wildlife Service, lead agency behind the environmental assessment, was initially unsupportive of the project due to impacts on the habitat of the endangered desert tortoise. The City began meeting with FWS officials to discuss options for creating an acceptable alternative design.

2007: The project design was modified to eliminate the deepening of the detention basin behind the dam by building a taller structure, thus preserving natural tortoise habitat. The outlet culvert was also enlarged to eliminate basin inundation and destruction of tortoise habitat in the event of a major flood.

Tuacahn Wash study area diagram by the Alpha Engineering Company | Photo courtesy of Chuck Gillette

2007: The FWS prepared a Biological Opinion of the project, identifying a permanent loss of 1.53 acres and temporary disturbance of 1.33 acres of critical tortoise habitat, both of which must be replaced by the City.

2008: On Jan. 4, 2008, the FWS issued a finding of no significant impact for the project.

2008: Changes in the project design raised its cost beyond what the city could afford, indefinitely postponing construction.

2012: A massive flood caused the failure of the Laub Pond Dam in Santa Clara on Sep. 11, 2012, flooding numerous residences and businesses.

2012: With the assistance of the State Engineer, the city modified the project design to save costs. Officials approached both Gov. Gary R. Herbert and the Community Impact Board with requests for funding, but were denied. With no other options remaining, the city used an interfund loan from their own sewer fund to proceed.

2012: Ground was broken by JP Excavating the first week of December 2012.

Equipment and concrete pour at the Tuacahn Wash Detention Basin project, Ivins, Utah, Jan. 7, 2012 | Photo by Alexa Verdugo Morgan, St. George News

Design specifications

  • Dam height: 18 feet
  • Dam length: 650 feet
  • Dam crest width: 15 feet
  • Drainage area: 677 acres
  • Storage capacity: 26 acre-feet
  • Spillway: 63 feet wide at bottom, 80 feet wide at dam crest
  • Outlet: 60 inch diameter reinforced concrete pipe
  • Dam type: Earthfill with chimney and blanket filter drain

The design also includes several environmentally and aesthetically pleasing features, like its meandering centerline, which provides a more natural look. A specifically large outlet was installed to allow small floods to pass through with minimum inundation in the detention basin, protecting as much wildlife habitat as possible. Lastly, the dam will be revegetated with low growing native plants to mask its appearance.


The project is partially funded by a $3.5 million storm water bond obtained by the city in 2005. The city has already completed several storm water-related projects; only $275,000 of the bond remains, thus forcing the use of the interfund loan. Gillette said that the city hopes the state legislature will make an appropriation in the coming session to reimburse some or all costs.

Summary of Tuacahn Wash project costs | Photo courtesy of Chuck Gillette

“We knew we could not wait any longer to protect the citizens of Ivins and those downstream,” Councilman Ron Densley said. “This is a very important project.”

In the meantime, Dale Coulam, who recently became city manager in addition to city attorney, has taken it upon himself to help Ivins’ repayment of the loan by absorbing two positions into one salary. This will save the city budget approximately $130,000 annually. St. George News covered Coulam’s double-duty appointment in a Jan. 9 story.

The total cost of the project is estimated at $850,000.

Project benefits

The installation of the detention basin will provide added flood protection to an estimated 80 homes in Ivins, a number that could easily double in the future as the city continues to develop. Existing and future developments in Santa Clara will also benefit, especially while the Laub Pond Dam remains in shambles.

But the benefits of this project go far beyond flood control: The Tuacahn Wash crosses Center Street, a main artery used by nearly all Ivins residents, and Pioneer Parkway, another major route serving a much larger population. The detention basin will protect these two roads, directly contributing to an increase in values of property in the surrounding area.

“Some of these properties are considered prime commercial, which is needed in Ivins to improve economic development,” Gillette said. “But nothing is more important than protecting the people of Ivins.”

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Copyright St. George News, SaintGeorgeUtah.com LLC, 2013, all rights reserved.

View of the Tuacahn Wash Detention Basin project from Tuacahn Drive, Ivins, Utah, Jan. 6, 2012 | Photo by Alexa Verdugo Morgan, St. George News

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