HIC MEETING July 12, 2005 Streamflow Regulation Accounting by Tom Gurss Missouri Basin River Forecast Center National Weather Service Pleasant Hill, MO

REGULATION ISSUES How do we provide long term probabilistic forecasts for locations heavily regulated for flood control, navigation, instream flows, irrigation, municipal water supply, power generation, etc.?

SRA GOALS Evaluate existing data sources and modeling approaches and develop a generalized strategy to account for regulation in long-range forecasts. Evaluate need for new tools, cost of development, and accuracy.

SRA TASKS Phase  Gather input and ideas from RFCs  Develop strategies to better apply current NWSRFS procedures  Develop National Strategy Plan  Develop South Platte Implementation Plan as prototype model  Collect regulation data for South Platte River

SRA TASKS Phase 2—  Implementation of South Platte Plan on Cache La Poudre River Basin  Evaluate the strategies and identify limitations in data, procedures and technologies  Test 3 different modeling approaches  Evaluate effectiveness by generating forecast verification statistics using hindcasting with ESPVS and ProbVS  Recommend Enhancements  Update Strategy Plans as needed

SRA TASKS Phase 2— (cont)  Poudre River chosen because of extensive available historical data  Trans-basin imports  Multiple upper elevation reservoirs  Dozens of lower elevation off channel storage areas  Multiple re-use of irrigation water  Base flows depend on return flows  Water Rights huge factor as water is traded between entities and storage facilities

SRA TASKS Phase 2— Verification.  Evaluated 90-day probabilistic forecasts for April 1 and July 1 for volume, maximum, and minimum  Looked at RPS, RPSS, reliability, and discrimination

SRA TASKS Phase 2— Results.  Complex operations required to describe psuedo reservoirs with very little data to adjust model to.  Verification showed some skill for maximum flows and volume, but little or no skill for minimum flows. Climatology better at some locations for low flows.  Verification statistics highly dependent on bin selection with limited sample size.

SRA TASKS Phase 3—  Expand implementation plan into other sub- basins with less data, but similar regulation— Big Thompson and St. Vrain Rivers  Simplify strategy based on results of Phase 2  Generate verification statistics using hindcasting  Revise list of enhancements and strategy plans

SRA TASKS Phase 3— Results.  Simplified operations provided similar verification statistics as the more complex operations for maximum flows, but little or no skill for minimum flows.

SRA TASKS Phase 4— (Proposed).  Expand implementation into other sub-basins with different types of regulation activities  Revise list of enhancements and strategy plans

Lessons Learned Poor verification statistics in low-flow forecasts because of inability to adequately simulate human behavior’s effects Data to support complex operations lacking Operational concerns using complex RES-J operations Limitations due to changing demands, uses, and variance from rules. Tools Enhancements would simplify operations

Future Concerns Need to decide whether low-flow forecasting of streams with heavy regulation is adding value to historical distributions Regulation in conjunction with Groundwater Pumping of Alluvial Aquifer Power Generation Large Multiple Reservoir System Simulation Additional Tools Enhancements