Ensemble Streamflow Prediction Traces

Seattle District Water Managers use Ensemble Streamflow Prediction (ESP) "traces" developed by the National Weather Service, Northwest River Forecast Center to inform operational decisions one to six months in advance in the Kootenai and Pend Oreille Basins.

The ESP program uses current hydrologic basin conditions (e.g. soil moisture, snowpack, etc.) in a physically-based basin model.  Historical precipitation and temperature sequences are applied to this model, and the model generates a group of possible future streamflow sequences (“traces”). 

The ESP sets do not predict the exact reservoir elevation or flow that will occur at a given date in the future, but rather give a range of elevations or flows that may occur.  Operational projections incorporate estimated biological and flood risk management operations that are required at Libby and Albeni Falls Dams.

Water Supply & Flow Forecasts

• Dworshak Water Supply Forecast (NWS)
• Dworshak Volume Inflow Forecasts 1999 to 2022 (USACE)
• Libby Volume Inflow Forecasts 1998 to Present (USACE)

Columbia River Flood Risk Management Requirements

• Flood Risk Management Requirements (USACE)
• Summary of Flood Risk Managment Requirements (USACE)
• Columbia River Treaty Flood Risk Operating Plan - Arrow Dam 3.6 Million Acre-Feet

Variable Flow Forecasts

Variable Discharge (VarQ) was developed to improve multi-purpose operations of Libby and Hungry Horse dams while maintaining the system flood control protection levels in the Columbia River. VarQ reduces the reservoir space contribution at Libby and Hungry Horse dams for system flood control of spring runoff in the Columbia River in years with low to moderate potential for flooding.

The procedure was designed to provide higher outflows from the projects during spring runoff than under the current flood control operation as outlined in the Columbia River Treaty Flood Control Operating Plan. These outflows are more consistent with releases made to meet flow objectives for the listed Endangered Species Act Kootenai River white sturgeon and Columbia and Snake River salmon and steelhead.

• Libby Dam - (USACE Dam) Operations require steady discharges to protect resident fish. Flows in the Kootenai River are typically maintained to benefit bull trout spawning, wetted perimeter productivity, and water temperature moderation.
• 2023 VarQ and Temperature Operations at Libby Dam
• Hungry Horse Dam - (BoR Dam) A critical storage dam in the Columbia River system, operations incorporate stable seasonal flow targets to augment salmon and bull trout habitats downstream, while balancing regional power generation and system inertia.  

A January 1999 report documents the progress of Variable Discharge (VarQ) studies in response to the Supplemental Biological Opinion on the Operation of the Federal Columbia River Power System dated, May 14, 1998.

• Executive Summary
• Section 1. The Effects of VARQ at Libby and Hungry Horse on Columbia River System Flood Control, with appendices, Appendix A. VARQ Operating Procedures
• Section 2. Kootenai River Flood Control Study, Analysis of Local Impacts of the Proposed VARQ Flood Control Plan
• Section 3. Local Effects of the Proposed VARQ Flood Control Plan at Hungry Horse Dam, Montana
• Section 4. The Effects of VARQ at Libby and Hungry Horse on Columbia River System Hydropower

Storage Reservation Diagrams

Storage Reservation Diagrams define the flood control space required in each reservoir to provide flood protection for the Columbia River. Required storage space depends on the time of year and seasonal runoff volume and diagrams are designed to provide orderly storage evacuation at each reservoir prior to the refill period with consideration to operating limits and Columbia River reservoir system regulation. The May 2003 Columbia River Treaty Flood Control Operating Plan contains a complete description of Columbia River flood control operations.

Columbia River Treaty Flood Control Operating Plans (FCOPs)

The principles of Columbia River flood risk management regulation as documented in Treaty FCOPs are listed below and available on request.

• Treaty Flood Control Operating Plan, May 2003
• Treaty Flood Control Operating Plan, October 1999
• Treaty Flood Control Operating Plan, October 1972

Annual hydropower operating plans are developed for the U.S. Army Corps of Engineers, Canadian Treaty projects, and other Columbia River projects under the Columbia River Treaty and Pacific Northwest Coordination Agreement. Short and long-range operational studies are performed using the Hydro System Seasonal Regulation (HYSSR) model to simulate various runoff and operating conditions. Constantly refined procedures address the complex, inter-related issues involving system operations for endangered and listed species, power generation, flood control, navigation, recreation, irrigation, water supply, and water quality. Regional plans and routine model studies evaluate the hydropower impacts of specific operational measures toward recovery of anadromous Snake River salmon, Kootenai River white sturgeon, resident fish and other listed species as identified in the Biological Opinion.

Hydrologic Engineering addresses flood risk for the Columbia Basin including operational guidance, long and short term studies, operating manual review and approval, and any requested operational deviations in basin hydro projects.  

Water Management Power deals with hydropower operational planning for USACE reservoirs in the North Pacific Region primarily performing the following tasks:

1. Develop hydro operating plans for Columbia River Basin USACE and Treaty reservoirs,
2. Coordinate regional power planning studies,
3. Support USACE-BPA Joint Operating Committee activities,

Power Summary Reports