CRDSS_Task1_15-3_EvaluationOfBESTSM

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Applications The BESTSM model has been used by Boyle for a number of water rights planning assignments over the last 15 years, including applications for the City of San Diego; the Upper Big Blue Natural Resource District (Nebraska); the Rio Ruidoso Basin (New Mexico); the San Miguel River; the Colorado River, and the Arkansas River. In addition to the Green Mountain Reservoir model, Boyle is currently under contract to Denver Water to develop a model for the operation of Denver's water rights in the Colorado River basin from the Cameo gage upstream to the headwaters, and in the South Platte from the headwaters down to the Henderson gage. In this regard, Denver Water has elected to commit its time and resources to the current version of the BESTSM model and its allocation methodologies. Again, the current version of the model is not available for consideration in the CRDSS. However, during this evaluation process, the RTi team had the benefit of reviewing the documentation of the current version of BESTSM which enabled a better understanding of the model functions. Under contract to the State of Colorado, Boyle also developed a version of the model for application on the Arkansas River in connection with the Kansas versus Colorado litigation. It is our understanding that this version of the BESTSM code does not include a "virgin flow" module that automatically calculates the natural flows necessary for the model to allocate water to the rights. It is also our understanding that although the Arkansas version of BESTSM incorporates the same basic allocation methodologies, it must necessarily be used in conjunction with a ground water model (MODFLOW) and an external water budget model. This version is relatively project - specific to the applications in the Arkansas basin. It is generally accepted that the Arkansas version is not acceptable for the CRDSS. Basic Description of Model Operation and Function BESTSM is written in FORTRAN 77 in a PC environment. The Green Mountain version is not available in a UNIX -based workstation format. The model can be considered as a basic allocation and accounting model which starts by computing the "virgin flows," i.e., the natural flows available in a stream system absent any effects of man's diversions and use of the water resource. The model then allocates the available natural flows to the water rights (diversions and /or storage) in strict conformance with the Priority System. BESTSM represents the river basin using a network of nodes which are used to reflect the stream system's physical and legal operational parameters. The nodes are typically located at major stream features including stream gaging stations, reservoirs, diversion structures, and locations for imports /exports from the basin. Water rights (direct flow, storage, in- stream rights, exchanges, and certain types of operational rules) are connected to a node in the network and are also assigned a priority number. Each diversion structure can be further defined to reflect decreed water right amounts, structure capacity limitations, and ranking by priority. BESTSM computes the virgin flow data file by an inverse modeling approach in which the monthly stream flow data at the known gages are adjusted by adding back into the gage values the man-made depletions attributable to historic diversions and storage at the nodes. Once this natural flow file is created, the model begins to allocate water in the assigned priority sequence. For each priority, the amount of water available for diversion is calculated by observing the flow at that node and at all other downstream nodes to the lower end of the basin. The minimum flow available at any node is generally the amount available for diversion. After the diversion is ,4275 05.10.94 2 1.15 -3 Fosha, Hyre