Northern Water manages the Colorado Big-Thompson project, the state’s largest transbasin diversion project which collects, stores, and delivers more than 200,00 acre-feet of supplemental water to the eastern slope of Colorado each year. Constructed by the U.S. Bureau of Reclamation between 1938 and 1957, the project includes a network of dams, reservoirs, tunnels, and canals, the centerpiece of which is the 13.1-mile Alva B. Adams Tunnel which carries water beneath the Continental Divide. The C-BT project provides water for irrigation, municipal, industrial, and hydroelectric power uses, benefiting over 30 cities and towns and supporting hundreds of thousands of acres of farmland. It is a critical resource for managing Colorado's water supply amid varying climate conditions.

On November 1 each year the Northern Water Board of Directors sets an initial quota for the project which represents the yield of each C-BT Project unit for that year. Quotas are expressed as a percentage of 310,000 acre-feet, the amount of water the C-BT Project was designed to deliver on an annual basis. A 100 percent quota makes 310,000 acre-feet of water available for delivery, meaning each C-BT allottee receives 1 acre-foot of water for each unit owned. Under a 70 percent quota each allottee receives 7/10 of an acre-foot per unit, and so on. The Northern Water Board has the ability to supplement the initial quota the following April based on a number of factors, most notably water availability within the project’s collection system and water demands throughout the project’s service area.

Since the project is intended to provide supplemental water to project allottees, lower water availability and higher demands on the eastern slope typically contribute to a higher project quota. Accurate seasonal streamflow forecasts for the projects contributing watersheds, namely the Granby and Willow Creek basins, are also critical to the Board’s decision making process.