Tonina et al. (2025) When pools cool streams: A dimensionless framework for reach-scale thermal buffering

Identification

• Journal: The Science of The Total Environment
• Year: 2025
• Date: 2025-12-22
• Authors: D. Tonina, A. Bertagnoli, A. Hurst, A.W. Tranmer
• DOI: 10.1016/j.scitotenv.2025.181232

Research Groups

• Center for Ecohydraulics Research, University of Idaho, Boise, ID, USA
• Sedimentation and River Hydraulics Group, U.S. Bureau of Reclamation Technical Service Center, Denver, CO, USA

Short Summary

This study develops a physically-based dimensionless framework to explain and predict reach-scale thermal buffering of streamwater temperature by pools. It reveals that pools buffer diel temperature fluctuations by up to 80% when a new dimensionless river-pool coupling predictor (P*) drops below approximately 0.014.

Objective

• To develop a physically-based dimensionless framework linking pool volume and flow hydraulics to reach-scale thermal buffering of streamwater temperature, specifically due to pool stratification, using a transient-storage model.

Study Configuration

• Spatial Scale: Reach-scale (e.g., Bird Track Springs reach of the Grande Ronde River in Oregon, USA).
• Temporal Scale: Diel (daily) temperature fluctuations.

Methodology and Data

• Models used: Transient-storage model.
• Data sources: Field data from the Bird Track Springs reach of the Grande Ronde River, comparing pre-restoration conditions (single small pool) with post-restoration conditions (sixteen constructed pools).

Main Results

• The framework introduces two dimensionless quantities: A, the ratio of downstream to upstream daily water temperature amplitudes, which quantifies the magnitude of thermal buffering; and P, a new river-pool coupling predictor that combines the river-to-pool volume ratio and a hydraulic mixing number, quantifying the strength of thermal coupling.
• Field data demonstrate that when the dimensionless predictor P* decreases below approximately 0.014, pools initiate buffering of diel temperature fluctuations by up to 80%.
• The framework elucidates how measurable parameters such as morphologic storage (residual pool volume), stream discharge, and hydraulic mixing collectively govern reach-scale temperature variability.

Contributions

• Development of a novel physically-based dimensionless framework (comprising A* and P*) that explains and predicts reach-scale thermal buffering by river pools.
• Introduction of P* as a new dimensionless predictor that effectively links residual pool volume and hydraulic mixing efficiency to thermal buffering.
• Provides a simple, transferable tool for evaluating the thermal buffering capacity of natural river systems and for designing residual pool geometries in river restoration projects to enhance thermal buffering.

Funding

• Not specified in the provided text.

Citation

@article{Tonina2025When,
  author = {Tonina, D. and Bertagnoli, A. and Hurst, A. and Tranmer, A.W.},
  title = {When pools cool streams: A dimensionless framework for reach-scale thermal buffering},
  journal = {The Science of The Total Environment},
  year = {2025},
  doi = {10.1016/j.scitotenv.2025.181232},
  url = {https://doi.org/10.1016/j.scitotenv.2025.181232}
}