Laboratory Evaluations of Fish Return Systems – What Designs Work

Guidelines for fish conveyances and other fish handling systems have been developed by federal, state and professional organizations. These guidelines were developed through an understanding of the hydraulic conditions likely to produce injury and mortality to adult fish.  However, little information exists on the effects of fish return systems on larval or early juvenile survival. The Electric Power Research Institute (EPRI) funded laboratory studies on factors affecting larval fish survival through a fish return system.  Initially, the effects velocity and height of discharge were evaluated.  Two 21.6 m (71 ft) pipes were pitched such that a velocity of 0.6 m/sec (2 ft/sec) and 1.8 m/sec (6 ft/sec) could be achieved.  Discharge heights evaluated were sub-surface, 0.6 m (2ft), and 1.2 m (4 ft).  The system was modified to a length of 131 m (430 ft) and several 90 degree drops, a sweeping curve, and a serpentine section were added. The test velocity was 1.8 m/sec (6 ft/sec) with a sub-surface discharge.  Testing also included three replicates (50 fish) with each combination of species (6), lifestage, and release locations plus controls.  A summary of the results is as follows:

• Survival (48-hr) for all species was poor (20-60%) during the transition from yolk-sac to post-yolk-sac larvae.  Survival ranged from 70-100% after the fish were approximately 12 mm in length. 
• Velocity had no effect on survival within length groups.
• Except for common carp, discharge height [subsurface to ≤1.2 m (4 ft)] had no effect on survival within length groups among species.
• Increasing the length and adding drops and bends did not affect survival within length groups.

Based on these results, transit of fish ~12 mm through a well-maintained fish return system should not result in increased mortality.  The influence of debris and roughness were not assessed.