Effects of Culverts on Habitat Connectivity in Streams—A Science Synthesis to Inform National Environmental Policy Act Analyses

Scientific Investigations Report 2023-5132
Prepared in cooperation with the Bureau of Land Management
By: , and 



The U.S. Geological Survey is working with Federal land management agencies to develop a series of science syntheses to support environmental effects analyses that agencies conduct to comply with the National Environmental Policy Act (NEPA). This report synthesizes science information about the potential effects of culverts on stream connectivity and subsequent effects on fish. We conducted a structured search of published scientific literature to find information about (1) culvert design, installation, and degradation; (2) methods for analyzing culvert condition and quantifying stream connectivity; and (3) the effects of changes to stream connectivity on freshwater fish. We follow the organization first established in U.S. Geological Survey Scientific Investigations Report 2023-5114, in which the report sections align with standard elements of NEPA analyses. We found that, while the effects of dams on stream biota are well documented, smaller barriers at road crossings, like culverts, are prevalent and collectively have a substantial effect on habitat connectivity. Individual culverts differ in the degree to which they impede the movement of aquatic organisms, and we documented methods to assess and estimate the permeability of a culvert, or the ability of aquatic organisms to pass through it. Finally, we outlined methods for using culvert location and permeability information to quantify connectivity in a watershed based on the Dendritic Connectivity Index. Studies have shown that channel constriction, perched outlets, and extreme flow velocities are some of the characteristics of culverts that may hinder aquatic organism passage. Culverts can serve as daily and seasonal barriers to fish, disrupting access to habitat and essential resources like cold water or overwintering refuges. Reduced connectivity can have population-level effects, leading to lower fish species richness and abundance in affected watersheds. Public land managers can use this report by incorporating it by reference in NEPA documentation, as supplemental information, or as a general reference for literature about the effects of culverts on stream connectivity and freshwater fish.

Suggested Citation

Lehrter, R.J., Rutherford, T.K., Dunham, J.B., Johnston, A.N., Wood, D.J.A., Haby, T.S., and Carter, S.K., 2024, Effects of culverts on habitat connectivity in streams—A science synthesis to inform National Environmental Policy Act analyses: U.S. Geological Survey Scientific Investigations Report 2023–5132, 21 p., https://doi.org/10.3133/sir20235132.

ISSN: 2328-0328 (online)

Table of Contents

  • Acknowledgments
  • Executive Summary
  • Purpose of This Report
  • How to Use This Report
  • Science Synthesis—Effects of Culverts on Habitat Connectivity in Streams
  • Methods for Developing this Science Synthesis
  • References Cited
  • Glossary
  • Appendix 1. Option 1: “dci” R Package
  • Appendix 2. Option 2: Fish Passage Extension
  • Appendix 3. “dci” R Package Sample Script
Publication type Report
Publication Subtype USGS Numbered Series
Title Effects of culverts on habitat connectivity in streams—A science synthesis to inform National Environmental Policy Act analyses
Series title Scientific Investigations Report
Series number 2023-5132
DOI 10.3133/sir20235132
Year Published 2024
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Fort Collins Science Center, Northern Rocky Mountain Science Center
Description vii, 16 p.
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details