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I I I 1- , Ii I I - ,I I I I I I I I I I I 3. WATER SUPPLY 3.1 Raw Water Supply and Water Rights The water supply and treatment facilities for the Town of Lyons are principally located in Sections I and 12, Township 3 North, Range 11 West, Boulder County, Colorado. A vicinity map is shown in Figure 1. At present, the water supply consists of diversions from North St. Vrain Creek, the northern branch of the St. Vrain River. The Town also owns shares in the Colorado-Big Thompson (C-BT) Project. These shares are administered by the Northern Colorado Water Conservancy District and delivered to the Town, via the St. Vrain Canal, during the growing season each year. This period is generally May 15 to September 15, but can vary from year to year. The Town utilizes its C-BT shares by exchange in the high demand months of summer, diverting additional water out of priority at its intake structure and releasing its C -BT shares to the St. Vrain River to protect senior water rights. The annexation policy of the Town requires new developers to tender C-BT shares for the water supply for properties to be served by the Town's water system. Additionally, subdivision agreements cover shared cost and scope of any system expansions or improvements on a cas e-by- case basis. Providing that the appropriate engineering analysis is performed to assure that the additional water shares can be delivered to the treatment facility, water supply assets should increase at the same pace as the additional demand. In brief, the Town has the following water supply assets: a 1.0 cfs direct diversion water right at the intake pipeline, 523 shares of C-BT, 300 acre-feet (af) of storage in Button Rock Reservoir, and minor irrigation ditch rights. Refer to Figure I for the location of the intake structure, about one-half mile upstream of the water treatment plant (WTP). These water supply assets are managed by the Town water utility personnel on a day-to-day and seasonal basis to meet the inflow requirements at the WTP intake strucWre. Natural stream flows (direct diversion) is available in the spring and early summer. C-BT shares are used in mid and late summer. Releases from the Button Rock Reservoir storage account are used in winter months, This pattern can be seen in Table 1. Taking the WYl993 data from Table I, use of these water rights is illustrated in Figure 2. Table 1 contains data compiled by the Water Commissioner, Division of Water Resources, State of Colorado. Flow data is recorded by the state in second-feet (sf) which is identical to cubic feet per second (cfs) , Volume data is recorded in second-feet-days, or the equivalent of 1.0 cfs for H