Incorporating Climate Change into the Design of Water Crossing Structures: Final Project Report

Category: Climate Change Science

Published: September 2016

Revised: November 2017

Pages: 51

Author(s): George Wilhere (WDFW), Jane Atha (WDFW), Timothy Quinn (WDFW), Lynn Helbrecht (WDFW) and Ingrid Tohver (Climate Impacts Group)


The following report describes a study conducted by the Washington Department of Fish and Wildlife (WDFW or the Department) from 2014 to 2016. The study represents the Department’s initial attempt to explore climate-related changes to stream channel morphology with the intent of determining how climate change could be incorporated into the design of water crossing structures. The Department received a grant from the North Pacific Landscape Conservation Cooperative (NPLCC) that provided essential support for this work. This report fulfills a required deliverable of that grant.

Using this Report

Please note that this report is presented as informational only. It is intended to provide information that managers or engineers might consider when designing new or replacement water crossing structures. Use of this report and the information it provides is voluntary.

Section 1 explains the importance of properly designed water crossing structures for fish movement, the basics of geomorphic culvert design, basics of channel hydraulic geometry, the projected impacts of future climate change on stream hydrology and channel morphology in Washington, and the motivations for this project. Section 2 describes our methods for translating climate projections to the key geomorphological parameter used in culvert design and permitting, and Section 3 presents the results and findings from our work. Section 4 explains how the information we have produced can be used for culvert design. Section 5 is a discussion of our results and the challenges of incorporating our projections into culvert design. Finally, Section 6 describes additional work needed to better address the information needs of policy makers, managers, and engineers.

The Importance of Water Crossing Structures

Washington State regulations require that water crossing structures (i.e., culverts and bridges) “allow fish to move freely through them at all flows when fish are expected to move” (WAC 220-660-190). Furthermore, Washington State law (RCW 77.57) grants WDFW authority to regulate the construction of water crossing structures along with other activities that use, obstruct, divert, or change the natural flow or bed of state waters. The Department issues approximately 400 permits per year related to water crossings throughout the state (WDFW 2006). In addition, the Department designs or co-designs water crossing structures throughout the state and provides technical guidance (Barnard et al. 2013) that explains how to design water crossing structures that will comply with current regulations.

Road crossings at rivers or streams are widely known to create barriers to fish movement when they are improperly designed or constructed (Price et al. 2010, Chelgren and Dunham 2015). Improperly designed or constructed culverts can become barriers for various reasons, including sediment aggradation at a culvert’s inlet, stream bed scour at a culvert’s outlet, and high flow velocity in the culvert . The consequences to fish populations associated with barriers at road crossings include the loss of habitat for various life history stages (Beechie et al. 2006, Sheer and Steel 2006), genetic isolation (Reiman and Dunham 2000, Wofford et al. 2005, Neville et al. 2009), inaccessibility to refuge habitats during disturbance events or warm water episodes (Lamberti et al. 1991, Reeves et al. 1995, Dunham et al. 1997), and local extirpation (Winston et al. 1991, Kruse et al. 2001).

The importance of restoring fish passage at water crossings in Washington has been highlighted with Washington’s Salmon Recovery Act of 1998, the Forests and Fish Report (DNR 1999), and United States v. Washington (2013), which is also known as the “Culvert Case.” All regional recovery plans for salmon (Oncorhynchus spp.) in Washington State emphasize the importance of restoring fish passage at stream crossings for recovering federally-listed threatened salmon populations. Likewise, under the Forests and Fish rules (WAC 222-24-051), large forest landowners are required to repair or replace all fish passage barriers before November 2016. Between 1999 and 2008, forest landowners replaced 3,500 fish passage barrier culverts with fish-passable structures, reportedly opening nearly 3,700 miles of fish habitat in Washington streams (Governor’s Salmon Recovery Office 2008). In the Culvert Case, Washington State government was ordered by a federal court to replace state-owned roadway culverts located on the Olympic Peninsula, in the Puget Sound Basin, or in the Chehalis River Basin that block salmon habitat (United States v. Washington 2013). About 1000 culverts are estimated to fit that description, and their replacement with culverts that pass fish is estimated to cost about $2.45 billion (Lovaas 2013).

Recent studies describe the magnitude of the challenge presented by culverts both in terms of the sheer number of structures across the landscape and in the proportion of those culverts that may be barriers to fish passage. The U.S. Forest Service and Bureau of Land Management reported that over half of the estimated 10,215 culverts that exist on fish-bearing streams in federal lands of Washington and Oregon may be fish passage barriers (GAO 2001). The Washington State Department of Transportation (WSDOT) is responsible for about 3,000 culverts on fish-bearing streams, of which approximately 60% are complete or partial barriers (WDFW 2009). In 2015, WDFW estimated that there may be as many as 35,000 culverts blocking or impeding fish passage statewide (D. Price, WDFW, personal communication). The goal of WDFW, WSDOT, other state agencies, and tribes is to restore access to existing freshwater habitat by replacing all impassable culverts. Hence, over the coming decades thousands of culverts must be replaced. The cost to replace 35,000 culverts could be as much as $60 to $86 billion.