||5 Rules for Design of Fishways in Rivers
General rules for design of fishways in rivers have been summarized for the benefit of engineers and consultants involved in fisheries enhancement work.
1. Fishways must be designed to maintain the hydraulic characteristics that exist naturally in the stream(s) prior to construction. Planning and design without regard for the local flow pattern observed prior to construction could render the structures ineffective. Without proper planning, unpredictable hydraulics might not be compatible with the layouts of fish entrance and exit points. Professionals in fisheries engineering must be employed to implement extensive investigation and planning of fishways to ensure adequate fish passage. This requires conducting detailed engineering and hydraulic surveys to document shoreline topography, water surface profiles and flow patterns in the river section considered for fishways; obtaining water surface profiles for the operational design range of the fishway(s) in level intervals of about 0.5m; and carrying out model testing to verify the maintenance of the original hydraulic river characteristics for the new structures in place.
2. The Fish Entrance and Exit ends of the fishways must be located and aligned to allow attraction by migrating fish to enter and swim through the structure and then move safely upstream from the exit. This requires extensive on-site observations of migrant fish at all concerned river stages, with documentation of resting & holding areas and difficult swimming sites. The resulting data are important factors in planning the most logical entrance and exit locations.
3. The fishways must accommodate all river water levels within the flow ranges fish are migrating, and are observed to be excessively delayed or obstructed.
This requires observation of fish passage at all periods when fish are present, and for more than one season where the natural river stage varies from year to year during the migration.
4. The size of the fishways (width, length, height) and the number of baffles must be determined based on the expected maximum rate of fish passage and the maximum water level differences in the river between the (upstream) fish exit and the (downstream) fish entrance points. This requires knowledge of the hydraulics in the river reach fronting the fishway, maximum hourly and daily rates of expected fish migration and the size, weight & swimming characteristics of the species that would use the passage structures. The above parameters are all-important factors that determine the dimensions of the pools between fishway baffles and the total number of baffles. Other factors are the theoretical space requirements (volume of water) for each fish within a fishway pool and the minimum water depth that will accommodate the maximum rate of fish passage (design capacity). The size of the baffle slots, and the head (drop) in water surface between fishway pools must be based on the average size of the fish and their swimming characteristics. Model testing of the fishways must be carried out to determine the acceptable hydraulics of the water jets through the vertical baffle slots, and the flow pattern within pools. Large-scale model testing of the fishways combined with observing the behavior of live fish moving through the passage must also be carried out before implementation of projects.
5. Structurally, all components of the fishway must be designed accounting for all possible external, internal and superimposed loads and pressures. External loads include soil and hydraulic pressure, hydraulic uplift, impact from flowing water or submerged & floating objects and surcharges such as equipment and vehicles. Internal loading is normally hydraulic pressure depending on differences in outside and inside water levels or full hydraulic head, e.g., plugged baffle slot(s). Various combinations of these forces can occur and each structure must be analyzed accordingly. This requires extensive knowledge of engineering and hydraulic principles as well as experience in the design and construction of fishway or fishpass structures. The safety of the general public and protection of the environment must be paramount in implementation of works. All structural design must be in accordance with current codes and standards and be carried out by professional engineers.