Bowen et al. (2025) Water demand and management impacts on streamflow under the prior appropriation doctrine in the bighorn basin

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-11-20
• Authors: Justin A. Bowen, Ginger B. Paige, Fabian Nippgen, Jason Robison
• DOI: 10.1016/j.ejrh.2025.102947

Research Groups

• Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY, USA
• College of Law, University of Wyoming, Laramie, WY, USA

Short Summary

This study evaluates how the spatial and temporal distribution of water rights and associated management decisions, under the prior appropriation doctrine, affect streamflow in the over-appropriated Bighorn Basin. It demonstrates that water right network structure and seniority strongly shape streamflow, particularly at mid-elevations, and that improving irrigation efficiencies paradoxically reduces streamflow by increasing overall consumptive use.

Objective

• Evaluate how the spatial and temporal distribution of water rights and associated management decisions, under the prior appropriation doctrine, affect streamflow in the Bighorn Basin.
• Quantify the effects of allocation under the prior appropriation doctrine on streamflow volume.
• Assess how changes in irrigation efficiency affect the distribution of water resources under the prior appropriation doctrine.

Study Configuration

• Spatial Scale: Bighorn Basin, Wyoming and Montana, United States. The basin elevation ranges from 823 m to 4209 m. Simulations were conducted at the HUC12 sub-watershed scale (511 sub-watersheds), using a 30 m resolution Digital Elevation Model (DEM).
• Temporal Scale: Daily streamflow simulations for water years 2006–2022. Representative dry (2021), normal (2009), and wet (2011) years were selected for detailed analysis.

Methodology and Data

• Models used:
  • TUWmodel: A conceptually based, semi-distributed hydrologic model for daily streamflow generation.
  • Water Allocation Simulation Model (WASM): A coupled hydrologic-allocation model that determines streamflow availability, diversion demand, and water right curtailment based on state water laws and the Yellowstone River Compact.
• Data sources:
  • Water right records: Wyoming State Engineers Office (SEO) e-permit database and Montana Department of Natural Resources and Conservation for Points of Diversion (POD) and Places of Use (POU).
  • Hydrographic and surface features: National Hydrography Dataset (NHD) for HUC watershed boundaries and stream polylines, and U.S. Geological Survey (USGS) National Elevation Dataset (NED) for a 30 m resolution DEM.
  • Climate data: Temperature, precipitation, and potential evapotranspiration (PET) (quantified using the Priestley-Taylor equation) as inputs for the TUWmodel.
  • Observed streamflow data: For calibration (13 gauged reference watersheds) and validation (basin outlet gauge).
  • Water use data: Estimated annual consumed water (Wyoming Water Development Commission, 2010) for model validation.
  • Reservoir operations: Estimated from SEO hydrographer reports.
  • Crop data: Monthly crop coefficients (Kc) for irrigation demand calculations.

Main Results

• Streamflow Depletion: Allocation under the prior appropriation doctrine resulted in significant streamflow reductions at the HUC6 Bighorn outlet, with decreases of -70.4% (dry year), -65.0% (normal year), and -55.3% (wet year) compared to natural state conditions.
• Spatial Variability of Impacts: The greatest streamflow losses occurred between 900 m and 2100 m elevation, while the largest gains were observed at 2400 m and between 1200 m and 1500 m, influenced by trans-watershed diversions.
• Over-appropriation: The Bighorn Basin is highly over-appropriated, with total appropriations (excluding reservoirs and instream flow) representing 255% of the mean daily streamflow during the irrigation season. Consequently, only 40.3% (dry), 50.6% (normal), and 59.6% (wet) of the total diversion demand was met.
• Priority and Elevation: Senior water rights (prior to 1920) are strongly negatively correlated with mean elevation (-0.79), being concentrated at lower elevations (1500–2100 m). This spatial distribution drives upstream junior curtailment to satisfy downstream senior demands, particularly at mid-elevation zones (1200–1800 m).
• Return Flow Contribution: Return flow is a significant contributor to instream flow, especially at low- to mid-elevations, accounting for 54.1% during the non-irrigation season and 27.9% during the irrigation season basin-wide. Its contribution to streamflow increases from less than 1% at 2700 m to 12% at 2100 m, then slightly decreases to 3% at 900 m.
• Trans-watershed Diversions: Approximately 43% of potential return flow is transported trans-watershed at the HUC12 scale. Exports generally increase with elevation, while imports decrease with elevation. Lateral transfers (water diverted to non-directly downstream sub-watersheds) dominate at HUC12 and HUC10 scales (68% and 58%, respectively).
• Irrigation Efficiency Paradox: Increasing irrigation efficiencies from 30% to 70% paradoxically led to greater overall reductions in basin streamflow (e.g., from -51% to -78% in dry years). This occurred because the water "conserved" by higher efficiencies was re-allocated to upstream junior water right holders, resulting in increased overall consumptive use (evapotranspiration).
• Yellowstone River Compact: The Yellowstone River Compact was not triggered to regulate post-1950 water rights in the Bighorn Basin during any of the simulated scenarios.

Contributions

• Provides a novel, spatially explicit framework for evaluating the interactive effects of water demand and management decisions under the prior appropriation doctrine on streamflow dynamics across different hydrographic positions within a basin.
• Quantifies how the spatial structure of water rights, including priority dates and beneficial uses, and management factors like reservoir operations and trans-watershed diversions, collectively shape streamflow patterns.
• Demonstrates the "efficiency paradox" in an over-appropriated system, showing that improving irrigation efficiencies can lead to increased overall consumptive use and reduced streamflow rather than water conservation.
• Develops a detailed spatial dataset of water rights linked to hydrographic and topographic features for the Bighorn Basin, offering a transferable methodology for similar studies in other western U.S. basins.
• Offers insights for policymakers on the complex hydrological implications of water law and management strategies in water-scarce regions.

Funding

Not explicitly stated in the paper.

Citation

@article{Bowen2025Water,
  author = {Bowen, Justin A. and Paige, Ginger B. and Nippgen, Fabian and Robison, Jason},
  title = {Water demand and management impacts on streamflow under the prior appropriation doctrine in the bighorn basin},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.102947},
  url = {https://doi.org/10.1016/j.ejrh.2025.102947}
}