Developing Cost-Effective Design Guidelines for Fish-Friendly Box Culverts, with a Focus on Small Fish.

Area of Science:

• Environmental Engineering
• Aquatic Ecology
• Hydraulic Engineering

Background:

• River crossings like culverts can impede upstream fish passage, disrupting freshwater ecosystems.
• Restoring waterway connectivity is crucial for the survival of various small-bodied fish species.

Purpose of the Study:

• To develop cost-effective, physically-based design methods for culverts that ensure upstream fish passage.
• To propose new guidelines for fish-friendly multi-cell box culvert designs.

Main Methods:

• Designing culverts optimized for fish passage at low to medium discharges and flood capacity at high discharges.
• Defining low-velocity zones (LVZs) based on a percentage of wetted flow area where velocity is less than characteristic fish swimming speeds.
• Analyzing the influence of discharge thresholds, fish swimming speeds, and flow area percentage on culvert size and cost.

Main Results:

• Culvert size and cost can increase significantly when specific conditions are met (Ufish < 0.3 m/s, Q1/Qdes > 0.3) for smooth barrels providing 15% flow area with low velocities.
• Similar cost-increasing trends were observed for culvert barrels with recessed cells.

Conclusions:

• The proposed physically-based design approach provides a novel method for enhancing fish passage in culverts.
• These guidelines contribute to maintaining or restoring aquatic ecosystem connectivity through improved culvert infrastructure.