Plunging Flow 



In typical plunging flow, the directional flow 

 or jet strikes downward and becomes fully- 

 submerged as it sweeps the bottom of the pool 

 (fig. 4). Large air masses form around the 

 plunge of flow at the weir. The trapped air is 

 carried downward and then upward, where it 

 dissipates along the surface in the counter- 

 current. Relatively few air bubbles pass down- 

 stream over the next weir crest. 



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streaming Flow 



Streanning flow was produced by increasing 

 the flow to about 2.8 c.m.s., or a discharge 

 about 40 percent greater than that which gave 

 the plunging flow. Figure 4 illustrates the 

 streaming flow in the experimental fishway. 

 Note the strong directional flow at the surface 

 and lesser counterflows deflecting downward 

 and upstream along the bottom of the pool. 

 Air masses originating in the overfall jet are 

 only partially deflected toward the bottom of 

 the pool with the counterflow. Many air bubbles 

 pass downstream over the crest of the weir. 



Velocity profiles (average of three readings) 

 at each station showed a pronounced flow at 

 the surface that decreased from 1.1 m.p.s. 

 near the head of the pool to 0.8 m.p.s. at the 

 overfall. The weaker but still rather promi- 

 nent counterflow at the bottom of the pool 

 reached a peak velocity of 0.7 m.p.s. 



EXPERIMENTAL PROCEDURE 



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O METER I 



Figure 4. — Plunging (top) and streaming (bottom) flow 

 characteristics depicted In a sectional profile of atypi- 

 cal pool. Heavy arrows show the direction of greatest 

 flow; lighter arrows the lesser counter-currents. Ve- 

 locities In m.p.s. (meters per second) were taken on a 

 plane parallel to the floor of the pool. 



Velocities'* obtained at surface, middepth, 

 and bottom stations in the pool represented the 

 means of three readings of the current meter 

 at each station. Readings were taken on planes 

 parallel to the fishway floor and therefore may 

 not reflect the true maximum velocities in 

 the line of the flow. The highest recorded 

 velocity--0.8 m.p.s. (meters per second)--was 

 in the downward thrust of the overfall jet at 

 middepth. Undoubtedly velocities were higher 

 at the base of the overfall on a plane parallel 

 to the jet. If head between pools were 30.5 cm., 

 a maximum velocity of 2.4 m.p.s. would be 

 expected in the area imnnediately below and in 

 line with the overfall. Total discharge during 

 the plunging flow was about 2 c.m.s. (cubic 

 meters per second). 



*A cup-type current meter was used to determine ve- 

 locities of flow. 



Rates of ascent and behavior of the fish were 

 used to compare fish passage under conditions 

 of plunging and streaming flow. Comparisons 

 were based on the performance of individual 

 fish that completed six circuits of the l6-pool 

 fishway. Plunging and streaming flows were 

 tested alternately so that each fish connpleted 

 three circuits under plunging flow and three 

 under streaming flow. Behavior of fish was 

 observed from the chamber adjoining pool 13. 



Passage of Fish 



Fish-passage procedures were identical to 

 those developed and used by Collins et al. 

 (1963). Fish were diverted fronn the Washing- 

 ton shore fishway into an entrance channel lead- 

 ing to the laboratory collection pool (fig. 2). 

 From the collection pool, individual fish en- 

 tered a release compartment where they were 

 diverted into an introductory pool adjoining 

 pool 3 of the endless fishway. A gate connect- 

 ing pool 3 with the introductory pool was 

 raised, and the fish were permitted to swim 

 into the fishway. The gate was then closed, 

 and the test began with the fish now in the 

 closed circuit of the fishway. 



Two observers followed the fish during its 

 ascent to obtain a record of time spent in 

 each pool. These observations were made 

 from a walkway that encircled the entire fish- 

 way. As the fish moved from pool to pool, an 

 observer pressed a switch button on the hand 

 rail at each weir. This signal was transmitted 

 to a time-event recorder which noted the time 

 of passage on a moving tape. A third observer 

 operated the lock and transferred the chrono- 

 logical record of ascent from the recorder to 

 an operations sheet. Each circuit ended when 

 the fish entered the lock and the next one began 

 upon opening the gate between pool 1 and 2 



