This multi-phase project aimed to help engineers and resource managers incorporate projections of future streamflow into designing structures that can accommodate fish passage and streamflow, with a particular focus on culverts. This long-term project has resulted in a culvert tool for the Washington Department of Fish & Wildlife that can help engineers and resource managers understand how the stream width at their project site may change in the future.

Culvert Tool WDFW Project Page Data Sets

Project Background

A culvert is a pipe or passageway that allows water to flow under a road or other obstruction. Well-designed culverts are crucial for connecting fish habitat that is fractured by roads and other development, yet many culverts in Washington State are currently inadequate for fish passage. For this reason, culverts are regulated on state and federal levels for the purposes of salmon recovery. The Washington Department of Fish and Wildlife designs fish passable structures, such as culverts, and permits and provides technical guidance to hundreds of other entities annually, specifying how to build and install fish passable structures.

In the Pacific Northwest, climate change is expected to exacerbate flood risks due to declining snowpack and more intense heavy rains. These changes will likely result in higher peak streamflows and more severe flooding than we have seen in the past. If the volume of water in the stream exceeds the capacity of a culvert, the well-being of both infrastructure and local fish populations are at risk. The expected service life of culverts is 50 to 100 years, so future as well as current streamflow must be considered in their design to ensure that they continue to function across their lifespan. While the Washington Department of Fish and Wildlife is aware of these projected climate-induced hydrological changes, current design standards are based on historical conditions and do not consider climate change.

We used new climate and hydrological projections to develop metrics that are directly applicable to culvert design — to date focusing on bankfull flow and its relationship to bankfull width. Thousands of culverts are expected to be replaced statewide over the coming decades, at great expense, and this project was well timed to ensure that those replacements are designed to accommodate future changes in flow.

Phase One Details + Report

Alongside researchers from the Washington Department of Fish and Wildlife, we evaluated existing projections of future streamflows under climate change. We analyzed the projections to directly apply to design standards developed by the state for culvert sizing. 

PHASE ONE REPORT PHASE ONE JOURNAL ARTICLE

Phase Two Details + Report

We developed a simple online culvert-design tool that engineers, managers, and regulators can use to explore the impacts of climate change on culvert sizing in Washington State streams. Users are prompted to select a location of interest, enter their measurement of bankfull width and culvert lifespan, then test out different culvert sizes and obtain the likelihood of failure for each. Information in the project report can aid interpretation of the tool’s results.

PHASE TWO REPORT

Phase Three Details + Report

We developed new streamflow projections using dynamically downscaled projections. Dynamically downscaled projections are expected to better capture changes in extreme precipitation than the statistically downscaled projections used in phases one and two. In addition, we tested a new approach to estimating the probability of designing the culverts to be too small (known as under-design). This new approach could support better decisions about how to balance the risks of over- and under-design. 

Unfortunately, our final evaluation of the model results revealed anomalous results that were not easily explained as related to the anticipated effects of climate change. As a result, we chose not to release the results, with the intention of instead further refining the modeling approach before new results are published.

PHASE THREE REPORT

Phase Four Details + Report

We analyzed and updated peak flow projections for Washington state using a new streamflow projection dataset: The River Management Joint Operating Committee’s version 2 hydrologic projections (RMJOC-II, https://www.hydro.washington.edu/CRCC, Chegwidden et al. 2019). This new dataset assesses future changes for multiple climate models, downscalings and hydrologic modeling approaches. Based on the findings we provided recommendations for estimating the central tendency and uncertainty of this dataset and discussed the benefits and drawbacks of different regionalization schemes.

PHASE FOUR REPORT

Acknowledgements

Phase 1 was funded by the North Pacific Landscape Conservation Cooperative (NPLCC).

Phase 2 was funded, in part, by the United States Environmental Protection Agency under assistance agreement 00J991-01 to the Swinomish Indian Tribal Community, through a contract agreement with the Skagit Climate Science Consortium. The contents of this website do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

Phase 3 was supported by The Department of the Interior Northwest Climate Adaptation Science Center, which is managed by the USGS National Climate Adaptation Science Center. Regional climate model simulations were provided by Ruby Leung at Pacific Northwest National Laboratory and Cliff Mass in the UW Department of Atmospheric Sciences.

Related Resources

An Overview of the Columbia Basin Climate Change Scenarios Project: The Columbia Basin Climate Change Scenarios Project (CBCCSP) was conceived as a comprehensive hydrologic database to support climate change planning, impacts assessment, and adaptation in the Pacific Northwest (PNW) by a diverse user community with varying technical capacity over a wide range of spatial scales.

Dynamically Downscaled Hydroclimate Projections: A database of dynamically downscaled climate projections for the Pacific Northwest, produced using the Weather Research and Forecasting (WRF) regional climate model, and implemented at an hourly temporal resolution and a spatial resolution of 12 km.

Heavy Precipitation Projections for Use in Stormwater Planning: A suite of products related to planning for extreme rain events.

Future Flooding in King County Rivers: This project developed hydrologic models for two basins of importance to King County and 12 new WRF projections for a high greenhouse gas scenario (RCP 8.5), providing a large enough ensemble to assess the mean and range among future peak flow projections.

Climate Change & Flooding in Snohomish County: New Dynamically-Downscaled Hydrologic Model Projections: Projections of future streamflow, with a particular emphasis on flooding, for the Snohomish and Stillaguamish Rivers.

NOAA Climate Guidance: This 150-page document provides guidance for building more climate-resilient fish passage. Developed and published by the West Coast Region NOAA Fisheries Department, with review by the Climate Impacts Group

An Overview of the Columbia Basin Climate Change Scenarios ProjectDynamically Downscaled Hydroclimate ProjectionsHeavy Precipitation ProjectionsFuture Flooding in King County RiversClimate Change & Flooding in SnohomishNOAA Climate Guidance

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Changing climate has far-reaching impacts, and is testing parts of society’s ability to continue doing business-as-usual. Among these are water utilities, the entities responsible for delivering clean, fresh water to our nation’s households and managing wastewater and stormwater.

2020 Climate Adaptation Leadership Award from the National Fish, Wildlife, and Plants Climate Adaptation Network: The Climate Adaptation Leadership Awards (CALA) recognize outstanding efforts to increase the resilience of America's valuable living natural resources and the many people, businesses and communities that depend on them.

Case Studies Illustrate how water utilities may adapt to climate changeClimate Adaptation Leadership Award