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<br />From:Rqn Brle!lner To: ShIrley Mondy <br /> <br />~ <br />(~"'I <br />t... <br />:-, , <br />~, <br /> <br />10 <br /> <br />Date: 01/11102 TIme. 2:56:42 PM <br /> <br />Pege5of: <br /> <br />Where daily flows are not available, a key station or gage would be used to estimate the <br />period of missing record Table 1 shows the gage, the missing period of record and the <br />likely key station that may be used to fill in the missing period of record. La Plata at <br />Hesperus has very good record since 1929 and has been used in disaggregating the' <br />monthly flows in the current model. It has the limitation of being less influenced by <br />upstream depletions and manipulation than the locations for which disaggregation are <br />necessary, but no better gage has been found. It may be possible to correlate the <br />Hesperus gage to the three analysis gages during periods of overlapping records to <br />provide an adjusted daily flow percentage that would better reflect flow distribution. It is <br />proposed that this analysis be completed and checked against using the key gage <br />percentages without adjustment. If there is not statistically significant improvement in <br />the disaggregation, the key gage would be used without adjustment. Since the flows of <br />these tributaries are typically small relative to main stem flows and the monthly flow is <br />being maintained, the error from using the key gage will likely be small. <br /> <br />Table 1. <br /> <br />GaQ& <br />LoP'oto C!l Formlngton <br />Mancos near TOYI'Boc <br />McElmo C!l Co-UT Slot.One <br /> <br />Kay <br />La Plata G Hesperus <br />La Plata G Hesperus <br />Le Plata 0 Hesperus <br /> <br />llIlsslnD <br />10/28 to 3138 <br />10/43 to 3151 <br />10/28 to 2151 <br /> <br />Calculation of Dally Irrigation Demands <br /> <br />All irrigation demands modeled in the main stem daily model must be expressed as a <br />daily demand. The approach we recommend is to develop the daily consumptive <br />irrigation requirement (CIR) time series for the crop mix at all irrigation nodes as <br />follows : <br /> <br />1. Develop the daily CIR for the same crops included in the monthly calculation. <br />The same climatic stations would be used for this computation as is used for the <br />monthly computation. It is proposed that we use the Hargreaves-Samani <br />temperature difference method as it is the least data intensive of the daily ET <br />methods and provides reasonable accuracy. Multiple CIR time series for the same <br />crop may be required if climate is significantly different from node to node. <br />2. The resuh of step one typically produces a saw-tooth type curve reflecting daily <br />differences in temperature and precipitation. Since irrigation deliveries do not <br />vary on a daily basis, the time-series data set will be smoothed using a running <br />average (7-days is the most probable, but this will be evaluated during <br />development). <br />3. A single curve for the crop mix in the node will be developed by combining the <br />CIR curves using an area weighted average for each demand node in the model <br />that has a different crop-miis: or climatic zone. <br />4. Daily percent distributions will be computed by dividing the daily CIR by the sum <br />of daily values for the month. The actual daily CIR will be the product of the <br /> <br />Keller-Bliesner Engineering <br />Draft San Juan Model Input Data Generation <br /> <br />January 11, 2002 <br />Page 4 <br />