Hebgen Dam Part 12

Project Name: Missouri-Madison Hydro Project

Summary: Hebgen Dam probable maximum flood review

Client:   PPL Montana

Project Location: Hebgen, MT

Project Size: 905 square mile drainage area

Services Provided:
•  Hydrologic Analysis
•  FERC Part 12 Dam Safety Inspection

Project Timeframe:
2010 - 2012

Relationship with Client: Since 1994

Client Needs:
PPL Montana (PPL) was required by FERC to review the Probable Maximum Flood (PMF) that had been developed for the Hebgen Development of the Missouri-Madison Hydroelectric Project in 1994 and to evaluate the need for an operating rule curve for the dam.
Kleinschmidt Solution:
Kleinschmidt served as the FERC-approved Independent Consultant for the inspection and also conducted a review of the existing PMF model and resultsThe findings of the review led to the development of a new HEC-HMS watershed model for the 905 square mile drainage area above the dam. Sensitivity analyses consisted of determining runoff from the Probable Maximum Precipitation (PMP) occurring on the watershed when a seasonal extreme snowpack was present, and routing the runoff through the lake and dam. Kleinschmidt evaluated the sensitivity of the peak level of Hebgen Lake at Hebgen Dam to various assumed initial snow packs and various initial lake levels in order to determine whether an operating rule curved was necessary for the project. Kleinschmidt developed a Visual Basic-enhanced spreadsheet application to optimize the components of a proposed rule curve, based on the potential seasonal reservoir inflow, as estimated by the hydrologic model.
Client Benefits:
As a result of Kleinschmidt’s analysis, PPL has an enhanced decision support system for operating Hebgen Reservoir to mitigate risk, and is compliant with FERC requirements.