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header image: San Juan Recovery Implementation Program Hydrology Committee Page

NOTE: Hydrology Pages are currently Under Construction

SJRIP Model Description

The San Juan Basin Hydrology Model is currently being revised. The technical aspects of the model revison (i.e., getting the model to run with the new changes) are expected to be completed December 2009. Model validation and verification as well as incorporation of a revised hydrologic baseline is projected to be completed December 2010.

The San Juan Basin Hydrology Model (SJBHM) is actually a collection of hydrologic models that are used together to model streamflow on the San Juan River. The hydrology model is in its third generation of evolution. Previous generations of the hydrology model were used in the development of flow recommendations and in Environmental Impact Statements (EIS) in the San Juan Riverbasin. Previous versions of the model are available upon request.

The San Juan Basin Hydrology Model (SJBHM) simulates flow in the San Juan River below Navajo Dam on a daily time-step.  The primary purpose of the model is to support San Juan River Recovery Implementation Program (SJRIP) goals to recover populations of the endangered razorback sucker and Colorado pikeminnow in the San Juan River while proceeding with water development in the Basin.  The model is used in Endangered Species Act section 7 consultations to determine the level of impact, if any, of a proposed action that deplete river flows on the Reclamation’s ability to meet the flow recommendations below Navajo Reservoir.  Note that model results are not the sole criteria used to determine the level of a proposed project’s impact and that model assumptions and model uncertainty are considered when interpreting results.  The SJBHM was used to evaluate and develop the current flow recommendations and will be used in developing future revisions to the flow recommendations.  In addition, the model will be used to develop and evaluate the revised hydrologic baseline.  The model currently uses natural flow data based on historic depletions (1929-2006); however, alternative inflow hydrologies may be evaluated in the future to evaluate current and/or future water availability under different climate change scenarios.

The SJBHM, like any hydrologic model, has error and uncertainty associated with it.  Sources of error include historical data, uncertainty about future inflows or depletions, and error in hydrologic methods selection. The SJBHM is not a water rights model and does not attempt to accurately model individual water rights.  Rather, the focus of the SJBHM is to accurately simulate the daily flow below Navajo Reservoir.  Model assumptions and error are evaluated to determine their net impact on the accuracy of daily flows below Navajo.

Reclamation is responsible for maintaining and improving the SJBHM and making model runs at the request of the Fish and Wildlife Service and the SJRIP Coordination Committee.  Reclamation is also responsible for maintaining and updating SJBHM documentation.  Model documentation and information are available on the SJRIP Hydrology Committee webpages.

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Last updated: April 15, 2010