Fish passage is now an integral part of compensatory mitigation under the new Nationwide Permit regulations. Engineered structures and stream restoration designs are common solutions to fish passage; however, in urban systems such solutions may not be feasible. Natural structures such as riffle grade controls and flow constrictor/step pools can provide low-maintenance stable solutions to fish passage in urban systems. Steps to designing such structures include an evaluation of the target fish species characteristics, site-specific baseflow hydrology, and hydraulics of the structure. Analyzing baseflow is essential because urban flood flows exhibit relatively high velocities and short durations precluding upstream migration. Fish characteristics, hydrology, and hydraulics are all used to generate fish passage design criteria.

Fish passage is now an integral part of compensatory mitigation under the new Nationwide Permit regulations. Engineered structures and stream restoration designs are common solutions to fish passage; however, in urban systems such solutions may not be feasible. Natural structures such as riffle grade controls and flow constrictor/step pools can provide low-maintenance stable solutions to fish passage in urban systems. Steps to designing such structures include an evaluation of the target fish species characteristics, site-specific baseflow hydrology, and hydraulics of the structure. Analyzing baseflow is essential because urban flood flows exhibit relatively high velocities and short durations precluding upstream migration. Fish characteristics, hydrology, and hydraulics are all used to generate fish passage design criteria.

This paper presents a standard list of procedures for designing natural fish passage structures in urban streams. Before any design can commence, designers need to thoroughly investigate the target fish species and the hydrology of the study reach. Designs of riffle grade controls (RGCs) and flow constrictor/step pools (FC/SPs) start with topographic surveys, geomorphic assessments, and tailwater measurements. Results of the geomorphic assessment will determine which structure should be constructed: RGCs for sand/gravel bedded streams and FC/SPs for cobble/boulder bedded streams. Each structure type has a unique hydraulic modeling approach; however, stone sizing and channel bank stabilization procedures are standard. Construction management is of great importance because installing these structures is not routine and it is incumbent on the designer to ensure that the contractor complies with the spirit and the intent of the design.

Fish passage is now an integral part of compensatory mitigation under the new Nationwide Permit regulations. Engineered structures and stream restoration designs are common solutions to fish passage; however, in urban systems such solutions may not be feasible. Natural structures such as riffle grade controls and flow constrictor/step pools can provide low-maintenance stable solutions to fish passage in urban systems. Steps to designing such structures include an evaluation of the target fish species characteristics, site-specific baseflow hydrology, and hydraulics of the structure. Analyzing baseflow is essential because urban flood flows exhibit relatively high velocities and short durations precluding upstream migration. Fish characteristics, hydrology, and hydraulics are all used to generate fish passage design criteria.

This paper presents a standard list of procedures for designing natural fish passage structures in urban streams. Before any design can commence, designers need to thoroughly investigate the target fish species and the hydrology of the study reach. Designs of riffle grade controls (RGCs) and flow constrictor/step pools (FC/SPs) start with topographic surveys, geomorphic assessments, and tailwater measurements. Results of the geomorphic assessment will determine which structure should be constructed: RGCs for sand/gravel bedded streams and FC/SPs for cobble/boulder bedded streams. Each structure type has a unique hydraulic modeling approach; however, stone sizing and channel bank stabilization procedures are standard. Construction management is of great importance because installing these structures is not routine and it is incumbent on the designer to ensure that the contractor complies with the spirit and the intent of the design.