Low-Water Crossings: Geomorphic, Biological, and Engineering Design Considerations

Abstract

From foreword: Low-water crossings are road-stream crossing structures designed to be overtopped by high flows or by debris- or ice-laden flows. They can be desirable alternatives to culverts and bridges on very low-volume roads and trails, and they can offer substantial environmental advantages in some stream environments. This publication reviews both the advantages and disadvantages of different low-water crossing structures in various stream environments and illustrates situations in which low-water crossings may be the optimal choice of crossing structure. The publication aims to provide multidisciplinary teams planning and designing road-stream crossing structures with answers to questions about where and how to best use overtoppable crossing structures. The publication's four objectives are as follows: (1) To address how low-water crossing structures affect stream functions and stability in various environments. (2) To provide guidance for selecting low-water crossing structures that minimize disruption of channel processes and habitats. (3) To summarize basic design parameters and requirements. (4) To examine a wide range of field examples that illustrate the performance, problems, and advantages of different types of low-water crossings.