Case Study: Glendale Instream Flow Study

Glendale Hydroelectric Project / Housatonic River Instream Flow Study

Littleville Power Company (Housatonic River, Stockbridge, MA)


Gomez and Sullivan conducted an instream flow incremental methodology (IFIM) study in the 2,500-foot-long bypass reach below the Glendale Hydroelectric Project as part of the FERC relicensing effort. Six transects were collected in accordance with the requirements of the IFG-4 hydraulic model using a single velocity calibration data set. Stream hydraulic data (i.e., bed profile, depth, velocity, and water surface elevation) were collected at four calibration flows (70 cfs, 92 cfs, 174 cfs, and 299 cfs). In addition, substrate, percent embeddedness, and cover data were collected at each transect. In consultation with stakeholders, a list of species potentially inhabiting the bypass reach were grouped into species subsets (or habitat guilds) based on similar overall habitat preferences. An evaluation species was chosen from each guild to represent its habitat needs, as well as the other species within that guild. Evaluation species included brown trout, fallfish, white sucker, longnose dace, and macroinvertebrates. Habitat (in units of Weighted Usable Area [WUA]) versus discharge relationships were generated for each evaluation species and corresponding life stages. Habitat Suitability Indices (HSI) for the evaluation species were derived from previous IFIM studies and the scientific literature. A flow of 90 cfs, or inflow, whichever is less, was recommended to protect habitat conditions within the bypass reach. This flow provided optimal (i.e., >90% of maximum habitat) and near-optimal (i.e., >80% of maximum habitat) physical habitat conditions for juvenile and adult brown trout, respectively, the primary management species set by resource agencies for river reach.