Revised Guide Curve Modeling

As a part of the WaterSMART Basin Study Program, PWRE worked on the Truckee Basin Water Management Options Pilot (WMOP) Study to develop flexible reservoir flood control operational criteria without increasing downstream flood risk. The study evaluated Forecast Informed Reservoir Operations, flexible rule curves, and changes to downstream regulation goals. This study is in the process of being documented in a Viability Assessment document and will be provided to the United States Army Corps of Engineers (USACE) for a potential subsequent update to the Water Control Manual.

Guide curve diagrams, otherwise known as rule curve diagrams, prescribe flood space requirements in a reservoir for a given day. Guide curves are based on the amount that historical unregulated runoff exceeds a specified flood target flow at a location. This data is employed to determine flood space requirements as a function of forecasted remaining water year natural flow runoff. Specifically, they allow determination of the required flood space storage volume for a specified date of the water year given a forecasted runoff volume. These curves are both simple to read and easily interpretable. Current guide curves in the Truckee River Basin Water Control Manual (WCM) were implemented in July of 1985. These curves express some opportunities for improvement considering more recent guide curve guidelines set forth by the Natural Resources Conservation Service (NRCS) and USACE. Generally, these improvements include (1) flood targets informed by the latest available data, (2) improvements in forecast availability, and (3) increased water supply while ensuring conservative flood space requirements throughout a given water year. These improvements are realized by updating the WCM’s guide curves according to USACE and NRCS guidance with the latest data. Ultimately, the updated guide curves were utilized within the WMOP Study both as an alternative to the current WCM and as a component to the Forecast Informed Reservoir Operations in the Truckee Basin.