| Utilizing RiverWare accounting to calculate depletions from ESA actions on the Pecos River |
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Lucas Barrett —Bureau of Reclamation, Albuquerque Area Office, Water Management Division |
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ABSTRACT |
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Reclamation is responsible for managing the storage and release of Pecos River irrigation water for the Carlsbad Irrigation District (CID), under the Carlsbad Project. In 1987, the Pecos bluntnose shiner (shiner) was listed as a threatened species under the Endangered Species Act (ESA) and critical habitat was designated on the Pecos River. Reclamation has developed measures intended to minimize or otherwise offset the adverse effects of the Project operation on the shiner and other listed species. Reclamation has also agreed to offset increased depletions to Carlsbad Project supply as a result of ESA operations. To do so, Reclamation initiated a Water Offset Program that secured additional water sources to supplement the Carlsbad Project. To determine whether supplemental water is sufficient to offset depletions as a result of ESA operations, multiple methods have been developed since the early 90s, ranging from a simple equation, to spreadsheets, to computer models. The model prior to this work was implemented in 2016 and called the Pecos 2-Stream Depletions RiverWare Model. After in-house and contract analysis of the model, in 2023 it was determined that the model had multiple issues and did not correctly calculate the depletions from Reclamation’s ESA actions, and a new method was needed. Instead of completely starting over, Reclamation utilized their current Pecos River Operations Model (PROM) and implemented the needed accounting within the model to calculate depletions from ESA operations. The model works by tracking individual water accounts of project water and ESA water, and then utilizing two “no action” reservoirs to calculate the difference between the amount of water that would have made it to the downstream reservoir if no actions were taken as compared to actual operations that include the ESA “actions”. Along with working out how to simulate a model that includes an action and a no action scenario within one accounting model, it also required a way to route accounts downstream that was different from the physical part of the model, which used Muskingum Cunge routing that could not be directly applied to the accounts. After working cooperatively with the State of New Mexico and Carlsbad Irrigation district, this model was agreed upon in early 2024 and is now used for official depletions accounting. |
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