Reservoirs play a critical role in managing our water resources, serving as vital infrastructure for flood control, water supply, and environmental conservation. We learned this the hard way… However, balancing these often competing priorities requires a nuanced and proactive approach to reservoir operations. As an experienced flood control specialist, I’ll explore strategies for optimising reservoir management to mitigate flood risks while also safeguarding water supplies – a delicate dance that has significant real-world implications.
Now, this might seem counterintuitive…
Integrating Weather Forecasts for Adaptive Reservoir Management
Traditionally, reservoir operations have relied on historical precipitation patterns and static “guide curves” to determine release schedules. But this rigid approach often falls short, as demonstrated by the case of California’s Lake Mendocino nearly a decade ago. In 2012-2013, the reservoir experienced record precipitation, only to be followed by an extended drought – a stark illustration of the need for more flexible, forecast-informed reservoir operations.
Recognising this, the U.S. Army Corps of Engineers has been working to implement Forecast-Informed Reservoir Operations (FIRO), a process that leverages advancements in weather and hydrologic forecasting to optimise reservoir management. By incorporating real-time data on atmospheric rivers and other meteorological phenomena, FIRO enables water managers to make more informed, adaptive decisions about storage levels and release timing.
As the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography explains, atmospheric rivers are “rivers in the sky” – concentrated bands of water vapour that can deliver massive amounts of precipitation upon landfall. These events are a primary driver of floods and droughts in the Western U.S., making them a crucial consideration for reservoir operators.
Rather than relying solely on observed precipitation and snowpack, FIRO allows reservoir managers to proactively adjust operations based on forecasts of atmospheric rivers and other storm systems. This enables them to strike a better balance between flood risk management and water supply preservation. For example, by releasing water in advance of an anticipated atmospheric river, operators can create storage capacity to capture the incoming deluge, reducing downstream flood impacts while also retaining water for future use.
Enhancing Flood Control through Coordinated Reservoir Operations
Effective flood control often requires a coordinated, systems-level approach to reservoir management, especially in watersheds with multiple impoundments. The case study of Lake Mendocino illustrates this well – as the reservoir is owned by the Corps but its water supply releases are managed by the local Sonoma Water agency, requiring close collaboration between the two entities.
Similarly, the Corps is currently assessing the viability of FIRO at two reservoirs in Northern California – the New Bullards Bar Reservoir on the Yuba River and Lake Oroville on the Feather River. Because the operations of these facilities are closely linked to mitigate downstream flooding, the FIRO evaluation is being conducted jointly, exploring how forecast-informed management at one reservoir can benefit the entire system.
Coordinated reservoir operations can also extend beyond a single watershed, as seen in Southern California’s Prado Dam project. Here, the Corps, the Center for Western Weather and Water Extremes, and the Orange County Water District are studying how FIRO can improve the management of stormwater captured by the dam, ultimately enhancing flood protection and water supply reliability for the region.
By taking a holistic, systems-based approach to reservoir management and leveraging the power of weather forecasting, water managers can unlock significant benefits in terms of both flood control and water supply resilience.
Balancing Flood Risk and Water Supply Needs
Reservoirs are often designed and operated with the primary goals of flood control and water supply in mind. However, these objectives can sometimes come into conflict, requiring careful trade-offs and optimization.
Traditionally, reservoir guide curves have been designed to double-check that adequate storage capacity ahead of the flood season, while also maximizing carryover storage for the dry season. But as the Lake Mendocino example demonstrates, this rigid approach can lead to suboptimal outcomes, with precious water being released during wet periods only to be sorely missed during subsequent droughts.
Forecast-Informed Reservoir Operations (FIRO) offers a way to break free from this zero-sum mentality. By leveraging atmospheric river forecasts and other advanced weather data, reservoir managers can make more nuanced, adaptive decisions that serve both flood control and water supply needs.
As Cary Talbot, chief of the Flood and Storm Protection Division at the U.S. Army Engineer Research and Development Center, notes: “You can actually improve not just water supply, but you can also improve the flood-risk management aspect of the reservoir as well by using the forecast to inform operators about what they might need to know going forward.”
The FIRO assessment at Lake Mendocino provides a prime example of this dual benefit. During the exceptionally wet 2019 water year, reservoir operators were able to use FIRO to effectively manage flood risks. But the true value of the approach became even more apparent the following year, when FIRO enabled them to retain 19% more water in the reservoir than would have been possible under the standard operating protocols.
“That’s a huge win right there,” says Jay Jasperse, chief engineer and director of groundwater management for Sonoma Water. “I think it pretty much demonstrates the water supply benefits for FIRO.”
Screening Reservoirs for FIRO Suitability
As the U.S. Army Corps of Engineers works to expand the use of Forecast-Informed Reservoir Operations nationwide, it has devised a multi-stage screening process to identify the most suitable candidate sites.
The initial “Stage A” screening involves a high-level assessment of 74 dams within the Corps’ South Pacific Division, which encompasses the Sacramento, San Francisco, Los Angeles, and Albuquerque districts. This stage aims to quickly eliminate reservoirs that lack key prerequisites for FIRO, such as a controlled outlet or an existing water control plan.
Reservoirs that pass the Stage A screening will then undergo a more detailed “Stage B” evaluation, which will consider factors like atmospheric forecast skill, hydraulic and hydrologic parameters, and the level of stakeholder collaboration. Sites deemed to have a “high” or “medium” FIRO suitability ranking will then move on to Stage C, where experts and local stakeholders will discuss the assessment findings and chart the next steps.
Beyond the South Pacific Division, the Corps plans to eventually apply this screening process nationwide, assessing its entire portfolio of dams to determine the feasibility of implementing Forecast-Informed Reservoir Operations. However, Marty Ralph, director of the Center for Western Weather and Water Extremes, cautions that continued research is essential to double-check that the greatest potential for FIRO adoption.
“To double-check that the greatest potential for FIRO to be found viable at the most reservoirs, it is vital that focused research continue to improve forecasts of the extreme precipitation, the storms that produce them, the runoff they create, and the water resources management tools needed and that these advances make their ways into operations,” Ralph emphasizes.
Conclusion: Unlocking the Full Potential of Reservoirs
Reservoirs are critical pieces of infrastructure that might want to balance the competing demands of flood control, water supply, and environmental stewardship. By embracing innovative, forecast-informed approaches to reservoir operations, water managers can unlock significant benefits for their communities.
The implementation of Forecast-Informed Reservoir Operations (FIRO) holds great promise, as demonstrated by the success stories at Lake Mendocino and other sites. By leveraging advancements in weather forecasting and hydrology, reservoir managers can make more adaptive, proactive decisions that simultaneously enhance flood protection and preserve precious water resources.
As the U.S. Army Corps of Engineers expands its FIRO screening and assessment process nationwide, we can expect to see a growing number of reservoirs optimised for the 21st century’s complex water management challenges. This shift towards a more dynamic, data-driven approach to reservoir operations will be essential for building resilient, sustainable water systems in the face of increasing climate variability and extreme weather events.
Ultimately, the future of effective flood control and reliable water supply lies in our ability to harness the full potential of our reservoirs through innovative, collaborative, and forecast-informed management strategies. By embracing this opportunity, we can safeguard our communities, environments, and economies for generations to come.
Tip: Implement real-time monitoring to swiftly respond to flood risks
