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One of the more significant changes to StateMod related to simulating groundwater pumping was <br />the use of spatially and geologically based Unit Response Functions (URFs) rather than the <br />typical normalized delay functions for returns and depletions to the stream via the groundwater. <br />Because of the number and complexity of these URFs, a special preprocessing software utility <br />(makertn) was developed to support this effort. <br />Concerns <br />Hydrosphere's initial testing and review of the groundwater pumping enhancements led to a <br />change in the way the "owed to aquifer" accumulation total is used in the surface water modeling. <br />Initially, the "owed to aquifer" water was taken first from the available baseflow in the affected <br />rivers in the model as necessary up to the total baseflow. In subsequent versions of StateMod, the <br />stream depletions are limited to a maximum leakage rate to represent what occurs where there is a <br />hydrologic disconnect between the stream and aquifer. <br />As noted previously under the discussion for the Rio Grande Compact, the prior appropriation <br />doctrine is used to determine which structures (if any) can legally, physically and operationally <br />divert or store water. Water allocation occurs in the model during every time-step, and considers <br />the net immediate depletive effect of prior diversions and pumping. Depletions caused by wells, <br />however, can occur over a long period of time (20 years or more). For example, depletions <br />occurring in Month 20 from well pumping that occurred in Month 1 cannot be curtailed -the <br />depletions have already occurred as a result of earlier pumping when no curtailment was <br />necessary. <br />Futile Water Right Call <br />Overview <br />Several streams within Division 3 are hydrologically disconnected from the Rio Grande with <br />respect to surface flows (e.g. San Luis Creek). Therefore, water rights within these <br />hydrologically disconnected areas are administered separately from those on the mainstem (i.e. a <br />water rights call from the mainstem is "futile" to these areas because there is no surface flow). <br />Objective <br />Test StateMod's futile call capability which allows a point in the StateMod model network to be <br />specified above which downstream water right priorities will not effect water allocation. This <br />enhancement was necessary because in the Rio Grande Basin there are sub-basins that are <br />hydrologically disconnected from one another in terms of live surface flows. <br />Test Application <br />This enhancement to StateMod involved the creation of a new confluence node type used by the <br />DMI makenet to construct the model network file (rg.net). This new confluence node type, <br />"xconfl, " is used instead of the "confl" node to ensure a tributary network operates independently <br />of the rest of the network. StateMod networks use a tree structure and search algorithm where <br />nodes may have multiple upstream points, but only one downstream point. The "xconfl" node <br />allows makenet to tell StateMod to stop searching any further downstream when looking for a <br />constraint that may affect water allocation by priority. <br />The xconfl node in the rg. net file (makenet DMI input file) is translated by the makenet utility into <br />an entry in the rg. rin file (StateMod input file) which describes a network node without a <br />downstream neighbor. This is similar to the node at the "bottom" of the network. <br />C:Acdss\TaskS-5.doc StateMod Enhancements August 15, 2000 -Page 6 of 8 <br />