Fort Collins, Colorado

Hydros developed a water-quality model of the Cache la Poudre River to evaluate potential changes in water quality due to the Northern Integrated Supply Project (NISP). The model was developed to evaluate NISP alternatives and their anticipated effects on water quality in the Poudre River as part of the NISP Final Environmental Impact Statement (FEIS).

Historical flow and water-quality data were reviewed to develop a conceptual understanding of the Poudre River. This conceptual understanding supported the design, constituent selection, development, and calibration of a custom, monthly mass-balance model of the river. A total of 19 constituents are simulated at 52 locations across more than 60 river miles, spanning approximately from the confluence with the North Fork of the Cache la Poudre River (NW of Fort Collins) to the confluence with the South Platte River (east of Greeley). The simulated constituents include ammonia, arsenic, chromium, copper, iron, manganese, mercury, nickel, nitrate, selenium, sulfate, total organic carbon, total nitrogen, total phosphorus, and zinc. The model accounts for in-river flow rates and concentrations from the upstream segment, outflows from diversions and losses, and inflows from tributaries, channelized returns, WWTF effluent, and un-gaged gains.  For a subset of constituents, the model also includes in-river loss mechanisms. The model was used for evaluating project alternatives for the NIPS FEIS, and was also used to support the water-quality analyses for the NISP 401 Certification.