The probable maximum water level at which shad enter is at a tailwater 

 elevation of lU.5 ft. (above mean sea level). At this water level the 

 velocity of the water through the entrance is reduced to about 0.3 ft. 

 /sec. and water flows through the opening in the wall of the second 

 pool at about 1 ft/sec. Above this tailwater level the water in the 

 vicinity of the fishway entrance becomes excessively turbulent 

 (Figure 6) „ 



Estimates of the number of shad annually ascending the ladder at 

 Lawrence range from 1, 500 to more than 3,000. The size of the total 

 shad run in the Merrimack River is difficult to estimate. In 19U6 a 

 catch of 75,000 pounds of shad in Newburyport harbor was reported. 

 However, commercial shad fishing at the mouth of the river is sporadic 

 and in some years the Merrimack is not fished commercially at all. 



MODEL STUDY 



In order to examine in detail the characteristics of flow in the 

 Lawrence fishway under varied water conditions, a plastic model of 

 the lower six pools (Figure 13) was constructed and installed at the 

 Alden Hydraulic Laboratory, Worcester Polytechnic Institute. The model 

 was built according to the original plans (Figures 1 and 2) with re- 

 movable inserts for the later modifications.' Patterns of flow were 

 studied by the addition of dye to the water. 



A comparison was made of the flow patterns in the fishway pools 

 with the two different types of weirs, the original wide weir and the 

 notched weir with its sloping floor. The direction of the main flow 

 (Figure 12) was approximately the same with both types of weirs, al- 

 though the flow from the notched weir was much more concentrated. The 

 greater depths created by the addition of notched weirs resulted gener- 

 ally in lower velocities and reduced turbulence, particularly in the 

 lower areas of the pools. However, the maximum velocities in the jet 

 produced by the notched weir were about 0.8 ft/sec. higher than the 

 maximum velocities produced by the wide weir. Thus, with the notched 

 weir, there was a much sharper contrast between the velocity of the 

 water in the jet and the velocity of the rest of the water in the 

 pool. With the broad weir and the shallower depth, velocities through- 

 out the pool were more uniform. The condition at the approximately 

 180* change in the direction of flow in certain pools (Figure 12) is 

 probably accentuated by the concentrated flow from the notched weirs. 



