Long Lake Hydroelectric Development Total Dissolved Gas Abatement Phase III Feasibility Study

CLIENT: Avista Utilities

In 2006, Avista Utilities managed the Phase I total dissolved gas (TDG) feasibility evaluation for Long Lake Dam. The Phase II evaluation, which included the development of conceptual level designs including additional hydraulic analysis, civil design, cost estimates, constructability reviews, and drawings for five TDG alternatives from the Phase I study, was completed by NHC in 2010. The Phase III studies included developing construction cost estimates for three of the most promising alternatives, and the construction and testing of a 1:30 scale physical hydraulic model to further evaluate these three alternatives.

NHC assembled, managed, and provided an accomplished team of experts and advanced tools such as 3-D CFD analyses and physical hydraulic modeling to provide a comprehensive evaluation of the design alternatives. The physical model demonstrated that a proposed stepped spillway alternative was not effective and could lead to dam safety concerns. The physical model was instrumental in verifying the performance and refining the designs of the selected flow deflector concept.