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. PART IV --HYDROLOGY WATER RESOURCES . The water resource analyses included examination of records of available surface and ground water supplies for the period of study 1947 through 1961, Flows available for diversion under water rights held by the cities in the basin were also determined in order to estimate ultimate yields from these rights, The period 1947 through 1961 was chosen as the period on which to base the analyses because this period includes the drouth of the 1950's as well as several years of high flow and because the average annual basin supply for the period closely resembles the long-term average. Surface Supplies The total historic surface water supply available to the basin accrues from several sources, Table 1 lists these sources and the average annual supply for the study period, 1947-1961, The flow at the mouth of the canyon constitutes the gross surface water supply available for irrigation and M&I uses in the basin, while the flow at the mouth of the river near Greeley is essentially unused return flow. However, during some spring snow- melt periods, the flow is so great that the entire volume cannot be controlled by the existing diversion facilities, This uncontrolled water flows from the basin unused, and constitutes the supply which could be regulated in the potential Idylwilde Reservoir for use during periods of shortage, The time of occurrence and the quantity of these unused flows, which will henceforth be designated as' "storable surplus flows" were determined by making a point flow analysis, which is a detailed accounting of monthly flows and diversions, A sunnnary of the results obtained by the point flow analysis and also the estimates of surplus flows made by the Colorado Water Commissioner are shown in table 2, Although the first water deliveries to the Cache la Poudre Basin were made from the Colorado-Big Thompson Project in 1952, it was not until 1957 that full operation of this project was achieved, Thus, the water supply records for the study period, 1947-1961, are incomplete with respect to the total water supply that is now and will in the future be available to the Cache la Poudre Basin, There- fore, in order to make estimates of future water needs, it was necessary to determine the supply that would have been available had the the Colorado-Big Thompso~ Project been in full operation throughout the study period, This analysis was based on a study made by the South Platte River Projects office, Region 7, Bureau of Reclamation, and reflects the adjusted monthly deliveries to each ditch system in the Cache la Poudre Basin for the study period, Table 3 is a sunnnary of this analysis, . 13