There was a city council work meeting on March 21st to discuss potential problems a proposed Dry Wash reservoir could create. It wasn’t a public hearing, but more than 80 residents attended. Thank you! Your attendance made a difference.
Even though it wasn’t a public hearing, the Mayor invited a number of residents to speak about their concerns. Ivins resident Wayne Pennington spoke and recommended changes to the size and shape of the reservoir that would help mitigate some of the negative impacts. Wayne is a PhD geophysicist and a retired Dean of Engineering at Michigan Technological University. he has done a lot of research on the proposed reservoir on behalf of the community.
He also provided a detailed explanation of the history of the reservoir planning. That was an eye opener. That history shows the current plan is for a larger reservoir than was ever recommended, studied, or discussed.
Listening to Wayne’s history made me think of the story, Goldilocks and the Three Bears. One proposal, namely no reservoir, might be too small. One proposal, like the current 1,500-acre-foot proposal, seems too big. Is there one proposal that’s just right? Wayne thinks so. And his report does a good job explaining why.
Click here for a PDF of Wayne’s report that includes the history as well as his recommendations. Here is a summary of the history from his report along with his recommendation.
A reservoir proposed for Dry Wash has undergone studies by geotechnical engineers and environmental specialists, proposed as the third phase (after Graveyard Wash) of the St George Water Reuse Project. In 2004, they specified that a reservoir at Dry Wash should not exceed 3,040 ft for safety concerns; any larger reservoir would need to be created by a dam further upstream, which was not included in the Environmental Assessment.
In 2021, the Washington County Water Conservation District (WCWCD) agreed to a reservoir of 1000-1200 acre-ft (smaller than the 1335 acre-ft specified by the EA), but the Ivins City Council approved consideration of a larger reservoir. The WCWCD then proposed a 1500 acre-ft reservoir with 3,044 ft high-water level, violating safety concerns expressed by earlier studies due to incompetent rock (soil) at that elevation at the dam site. [I believe that the proposal by the WCWCD likewise violates the conditions of the geotechnical and environmental studies.]
The maximum capacity for a reservoir with a dam at the proposed location and a high-water level of 3,040 ft is 1335 acre-ft (excavation could increase the capacity). But a reservoir with these characteristics would still create problems due to a broad, shallow area on the western flank, creating a mudflat when the reservoir is low, and allowing wind to pick up dust and other materials, carrying it to populated areas.
Mitigation of this problem will require adjustments of dike location, high-water level, and excavation and relocation of the excavated material in strategic locations.
There may be many ways to resolve these issues; one approach, which will allow a trail with open space, is presented in Wayne’s report. His model would have a capacity of about 1000 acre-ft (after excavation), which is a size that had in 2021 been stated as acceptable by the WCWCD and would permit the needed access/egress of westernmost Ivins through the future Anasazi roundabout.
Download Wayne’s 11-page report. This is an important and complex issue, but Wayne makes it easy to understand the problems and possible solutions to at least some of the problems.