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<br />From: A~n BIl8sner To: Shlney Mondy <br /> <br />Date: 01111/02 Time: 2:56:42 PM <br /> <br />P;;ge 301 <br /> <br />o <br />(':) <br />~.... <br />l'.' <br /> <br />terminology, the depletion and diversion requests for any project would be computed as <br />follows: <br /> <br />00 <br /> <br />Depletion Request = (Irrigated Area. ET rate) · (1 +Incidental Loss Rate + Sprinkler <br />Evaporation Rate) <br /> <br />Diversion Request = Depletion Requested / Minimum Efficiency <br /> <br />Presently, the model includes the sprinkler evaporation rate as a portion of diversion <br />request, which is incorrect as it implies sprinkler evaporation is influenced by the <br />incidental and conveyance losses, which it is not. The above change would be <br />implemented in the model by including sprinkler evaporation rate in the overall incidental <br />loss rate so no Rivereware code change is required <br /> <br />Because incidental. losses and sprinkler evaporation are components of the total losses <br />due to inefficiency, the minimum efficiency used in computing the diversion request <br />needs to be thought of and adjusted (upward) accordingly. Since the minimum efficiency <br />is a calibration parameter, this should happen automatically; however, when determining <br />initial values and verifYing the model calibration this needs to be recognized <br /> <br />In the present natural flow calculations (at least since 1973) and in the model. Colorado <br />incidenta1loss rates come from the Type I study, for which no documentation can be <br />found It is not known what was used pre-1973. The New Mexico incidental loss rates <br />are typically 10% with a few exceptions. Colorado does not explicitly include incidental <br />loss rates, but includes the net effect in efficiency calibration and stream reach gainlloss. <br /> <br />Since incidental losses are important in the State's accounting of depletions in the system, <br />it is proposed that the incidental loss rates for historical projects be set by the two States, <br />subject to review and approval of the Hydrology Committee. By using the same rates for <br />natural flow computation as for model runs (see the above assumptions), the method of <br />computation or the amount of incidental loss will not affect model results as both the <br />natural flow rons and the model calibration runs close on gage flow.' In this way, the <br />model remains consistent with State depletion computations and model integrity is <br />preserved. For projects that have changed over time, the amount ofincidenta1loss will <br />have a small impact on the modeled case, as the baseline condition will be assumed. If <br />the incidental loss was over-stated during the natural flow analysis and the same rate is <br />applied to the modeled case, an increase in depletion will result in the simulation nms <br />during the years when the project was not in place. Since incidenta1losses are typically <br />low and most projects have been on-line for a long time, the potential error is not likely to <br />be great, even if the estimate of incidental loss is quite different from reality for a single <br />project. <br /> <br />For projects that are undergoing change or that are newly introduced, the case is different <br />Of most significance is the Navajo' puiian Irrigation Project (NIIP). Water balance data <br />exist for the duration ofNIIP with diversions accurately measured, acreages and crops <br />carefully recorded, phreatophyte area measured and return flow measured or estimated. <br /> <br />Keller-Bliesner Engineering <br />Draft San Juan Model Input Data Generation <br /> <br />January 11, 2002 <br />Page 2 <br />