Written by Kathleen Gueymard (Entrada Resident) & Ed Andrechak (Conserve Southwest Utah’s Vice President and Water Program Manager).
Every summer the monsoon rains fall and swell the Virgin River, often causing disastrous flooding in Zion National Park, St George, and surrounding communities. Several CSU members have asked us recently: Why can’t the flood water from the Virgin River be recaptured in our large, local reservoirs to offset water shortfalls from the drought?
In short, the answer is: During monsoons, the modest flow of the Virgin River rises abruptly from ~100 cubic feet per second (cfs) to nearly 2,000 (cfs) in a matter of minutes—a 20-fold increase. At normal river flows, most of the water is diverted to a channel and associated piping to the Quail Creek Reservoir. Unfortunately, as this large, fast-moving volume of water plows down the river channel it gathers a huge mass of rocks, timber, mud and debris at its leading edge. Because this material would clog the piping inlet (and related inlet reservoir infrastructure), the main sluice gate is lowered and most of the monsoon river flow is diverted back to the main river. The net effect is this excess water goes downstream and not into the reservoir.
The photos show the debris from a 2018 monsoon flood event that must be diverted back to the main river instead of piped to a reservoir. While the current diversion infrastructure does not allow for collection of this water, stormwater management infrastructure solutions could be implemented—at a price—to help capture more flood flows in the future. As our region continues to grow, and available water for growth becomes limited, creative solutions will be critical to Washington County’s water security.
