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<br />~ !<-' <br />, ' <br /> <br />Functional Specification for the Planning Model <br /> <br />'. . <br /> <br />INFLOW HYDROLOGY <br /> <br />General <br /> <br />. <br /> <br />With a few exceptions described below, the level of spatial detail of hydrologic inflow <br />representation will be the same as that of the existing basin model. Overall responsibility for <br />development of inflow data files resides with USBR hydrologists working on the parallel <br />climate change study. Hydrosphere is working closely with these hydrologists to insure that <br />the needs of the Planning Model will be met. . <br /> <br />Hydrologic inflows to the Planning Model will be of three types: 1) virgin flows, 2) <br />del?leted flows, and 3) return flows, Virgin flows will be used wherever modeled diversion <br />and storage operations may be different from historical operations-practically speaking this <br />encompasses most of the area covered by the Planning Model. Virgin flows will be developed <br />by deregulation of observed flows and by regional analysis methods which permit estimation of <br />flows at ungaged sites. <br /> <br />Depleted flows will be used in areas where historical diversion and storage operatioils <br />satisfactorily represent future conditions or where project resource limitations preclude <br />development of detailed representation, The largest of these areas by far is that comprised by <br />th~ Tongue and Surface Creek sub-basins on the southern slopes of the Grand Mesa. Other <br />such areas include Uncompahgre River tributaries from the Uncompahgre Plateau and certain <br />headwaters areas. Depleted inflows will be developed from observed flows using mass-balance <br />techniques . <br /> <br />Return flows will be computed internally by the model and will be subject to user <br />modification only via modification of consumptive use and lagging factors. <br /> <br />e <br /> <br />Review of Existing Inflow Data <br /> <br />Hydrologists from the USBR have reviewed the procedures used to derive the inflow <br />data contained in the existing model and have concluded that those procedures were sound. <br />Accordingly, most of the inflow files from the existing model will be used in the Planning <br />Model without modification except for extension to cover the 1984-90 period (the existing <br />model uses a 1952-83 period). However, there are a few sub-basins where the Sponsors <br />Committee has specifically requested detailed review of existing inflow data, <br /> <br />The existing model utilizes 9 virgin inflow files to represent the hydrology of the East <br />River sub-basin. The Sponsors Committee has expressed concern that these inflows may <br />incorrectly represent the distribution of water supplies in the sub-basin. A detailed assessment <br />of East River hydrology will be carried out prior to utilization of existing inflow data. This <br />will include a site visit, telephone interviews of knowledgeable local officials, and review of <br />secondary information sources such as geological reports. <br /> <br />Descriptions of this review of hydrologic data will be incorporated into the model <br />documentation. <br /> <br />Expansion of Hydrologic Data Coverage <br /> <br />The only major tributary areas of the basin to be covered by the Planning Model for <br />which inflow data do not already exist are the North and Smith Forks of the Gunnison. <br />Additional virgin and depleted inflow data files will be developed for these areas by USBR <br />hydrologists. Hydrologic data development will be described in the model documentation, <br /> <br />e <br /> <br />14 <br />