As we all experience whiplash moving from one of the worst droughts on record to one of the wettest years, we are reminded that California’s rivers and dams must be thoughtfully managed during floods as well as droughts.
The near-disaster at Oroville Dam has served as a wake-up call that our flood management system is aging and relies on old infrastructure and even older science.
Don Pedro Dam has spilled – only the second time since it was built in 1971. As we continue to move through the spring, we hope these and other dams are able to avoid disasters, but we should also take this opportunity to consider what is needed to improve flood management along the Tuolumne.
Many of the largest dams in the state are “multipurpose” dams, providing water storage, hydropower generation, recreation and flood management for surrounding communities, irrigation districts and utilities.
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The most successful flood-management systems take a multipurpose approach downstream of the dams as well. Instead of managing river corridors simply as a way to move floodwaters through a system of levees, flood-management systems that work alongside Mother Nature have been shown to more effectively reduce flood risk while providing many other benefits.
A river with more room to roam will not only safely convey floodwaters; it will also improve water quality, fish and wildlife habitat, water supply and recreation.
Restored floodplains filter out pollutants as water flows through them. Riverside forests growing in floodplains provide homes for a tremendous variety of wildlife. Salmon and steelhead that can access floodplains grow much more quickly because they have more food. Floodwaters that spread out across floodplains recharge groundwater.
Wider floodplains also increase flexibility for dam operators by allowing them to release more water more quickly in advance of approaching storms. Reservoir operators can more safely store larger volumes of water if they know the floodplain downstream is wide and capable of safely conveying that water.
Along the Tuolumne River, we have been heading in the right direction.
Since the historic 1997 floods, over 2,500 acres along the river have been set aside for flood conveyance and habitat restoration. The old Tidewater Southern Railroad Trestle, whose footings were so closely spaced that debris and floodwater was impeded, burned in 2001 and was never replaced. The Ninth Street Bridge has been replaced with more widely spaced piers. And the Modesto wastewater treatment plant has received upgrades and might soon be moved altogether.
All such improvements support greater ability to move water safely down the river, and we must continue efforts to further widen the floodplain.
We also must consider other possible win-win solutions. First, the U.S. Army Corps of Engineers, who control flows during flood periods, should update the Don Pedro Flood Control Manual, which was written in 1972. The manual relies on science from a different era, not our latest and best understanding of Sierra storm systems, forecasting and runoff patterns.
Further, the manual doesn’t reflect the improvements that have been made on the ground along the river. Updating the manual will give operators the best information and greatest flexibility to release water as needed while storing as much as possible.
Second, we must explore opportunities for recharging groundwater during very high flows. Creative collaborations between Turlock and Modesto irrigation districts, the city and county of San Francisco and other partners could potentially divert water during very wet years (like this one) and store it in the ground. That water would then be available during drought like we experienced in the previous five years.
A successful groundwater banking program could be a significant contributor to regional groundwater supply/recharge and environmental sustainability.
It’s time to bring our flood- and water-management system out of the 1970s and into the 21st century. We can no longer rely on the same approaches to meet today’s flood and water management needs.
Patrick Koepele is executive director of the Tuolumne River Trust; he wrote this for The Modesto Bee. firstname.lastname@example.org