National Weather Service – Streamflow Regulation Accounting

As part of an effort to provide Advanced Hydrologic Prediction Services (AHPS), the National Weather Service (NWS) is using the NWS River Forecast System (NWSRFS) to prepare long-range probabilistic forecasts of streamflow. The presence of extensive systems of streamflow regulation to capture and divert runoff in many parts of the country require additional effort and new procedures to characterize and accurately predict the effect of this regulation for developing long-range forecasts.

The goals of this project are to develop a general strategy and approach for NWS to address streamflow regulation in preparing 90-day probabilistic forecasts and to assist the Missouri Basin River Forecast Center (MBRFC) in developing, implementing, and evaluating a specific strategy and approach for the South Platte river basin. Riverside Technology, inc. (RTi) is completing this overall study in multiple phases.

Cache la Poudre River, Colorado

The objectives of the first phase were to identify regulation issues and develop strategies to better apply NWSRFS technologies and procedures in river basins where regulation has significant impacts. RTi compiled responses from River Forecast Centers around the country regarding regulation issues and approaches. RTi then outlined strategies for addressing various types of regulation, as well as an overall implementation plan that could be used as an outline for regulation modeling. Based on this general plan, a specific implementation plan was prepared for the South Platte basin.

Subsequent phases have focused on execution of the implementation plan for specific sub-basins of the South Platte, including the Cache la Poudre, Big Thompson, Saint Vrain, Boulder Creek, Clear Creek, and upper South Platte Rivers, with additional phases planned to complete the remaining sub-basins of the South Platte. The streamflow regulation along these rivers includes many small irrigators, large canal companies, off-channel storage, large trans-basin imports, and large systems of on-channel reservoirs supplying water for municipal and agricultural uses, all operating within the context of the water rights system in Colorado.

The implementation process has utilized information from the state of Colorado’s South Platte Decision Support System (SPDSS) to quantify regulation in the various basins. Unique modeling techniques have been identified to capture the effects of a wide range of regulation activities. RTi has worked with MBRFC staff to evaluate the degree to which the regulation modeling improves long term forecasts of streamflow variables by testing the implementation in an ensemble forecast mode using historical data.

The results of the South Platte implementation have been used to guide future implementation of streamflow regulation accounting models in the South Platte and elsewhere.

2290 East Prospect Road, Suite 1, Fort Collins, Colorado 80525
phone: (970) 484–7573  fax: (970) 484–7593 www.riverside.com