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Brice Lee <br /> December 20, 2002 <br /> Page 2 <br /> the analysis tends to be drier than average over the 83-year period of record. The annual flow at <br /> Hesperus during six out of the 10 years recorded is less than the 84-year average annual flow <br /> (see Table 1). <br /> ANNUAL DIVERSION RECORDS <br /> The subject work includes the use of historical diversion data at each major diversion structure <br /> (greater than one cubic foot per second) in the La Plata River Basin. The historical diversion <br /> data used in the model are shown in Appendix A. The actual demands from the administrative <br /> record for the New Mexico Compact also were used. The New Mexico demands from the <br /> administrative record often are less than half of the Hesperus flow, as required in the New <br /> Mexico Compact. This is a result of the administrative record reflecting the actual request of <br /> water from New Mexico, especially in February and March. <br /> MASS BALANCE ANALYSIS <br /> Using monthly diversion and stream flow data in the river basin, unmeasured demands and <br /> inflows were estimated through a mass balance of the measured inflows and outflows (see <br /> Appendices A & B). The measured flows include the Hesperus, Cherry Creek, Hay Gulch and <br /> Long Hollow stream flows, ditch diversions and the recorded river flows passing the Stateline <br /> Gauge. The unmeasured inflows account for creeks, gullies, seeps and springs, including return <br /> flows from irrigated agriculture that are not gauged or routinely measured. The unmeasured <br /> outflows include smaller diversions that were not included in the analysis and losses from <br /> phreatophytes, infiltration and evaporation. The annually measured and unmeasured inflows and <br /> outflows are shown in Table 2. <br /> The unmeasured inflows and outflows are included in the model. The unmeasured outflows are <br /> included as demands and are given the highest priority. Thus, small historical diversions that <br /> were not accounted for explicitly in the model are accounted for in the unmeasured outflows and <br /> are satisfied before the reservoir is allowed to fill. <br /> LIMITATIONS OF THE MODEL <br /> The locations of the unmeasured inflows and outflows discussed in the mass balance section are <br /> unknown, (i.e. return flows may occur further upstream than the location estimated in the model, <br /> resulting in more water available for upstream demands). There were no gauges on the main <br /> stem of the La Plata River between the Hesperus Gauge and the Stateline Gauge during the <br /> modeled period (1989-1998). In addition, any errors in diversion records and water gauging <br /> stations would be reflected in the model. <br /> The 10-year period of record is relatively short. However, historical Cherry Creek and Long <br /> Hollow flow records are not available and would have to be estimated. The estimation of Long <br /> • <br />