The entrance to the fishway is h ft. in width and is located at 

 the edge of one of the main channels (Figure 3 ). In a normal year the 

 new wood used for flashboards on the crest of the dam is placed on the 

 north side of the dam. During the winter the weaker boards on the south 

 side of the dam frequently become damaged by ice and are washed out so 

 that in the spring the flow is concentrated in the channel next to the 

 fishway entrance. Large curved reinforcements on each side of the en- 

 trance (Figure 1), probably designed to strengthen the fishway struc- 

 ture at the opening, may actually be responsible for a large measure of 

 the fishway' s success with shad. 



In 1936, the fishway was severely damaged by flood waters. The 

 following year major repairs were undertaken and at the same time sev- 

 eral modifications were made. The most important of these changes was 

 an alteration of the weirs. In crossing the original weirs which were 

 k ft. wide (Figures 1 and 2), the deep-bodied shad sometimes had diffi- 

 culty because of the relative shallowness of the water (from 2 in. to 

 6 in. in depth). Fish examined in the upper part of the fishway were 

 frequently found to be badly scraped. To remedy this condition, in 

 1937 notched weirs were constructed on top of the original weirs. Each 

 of the notches (Figure 11) is 2 ft. wide at the top, 1 ft. wide at the 

 bottom and 1 ft. deep. The floor of each notch is sloped at an angle 

 of 30*. The top of the notched weir is 1.5 ft. above the original 

 weir. This modification not only resulted in a deeper flow across the 

 weir but it raised the average depth of the water in the pools when 

 the fishway was in operation from less than 3 ft. to more than h ft. 



Because the shad did not enter the fishway under high tailwater 

 conditions (tailwater elevations of 15 ft. above mean sea level or 

 greater) in 1937 an opening was cut in the side of one of the lower 

 pools (Figures h and 9) to allow the fish to enter the fishway without 

 passing through the turbulent area (Figure 7) near the entrance. £/ 



Another change that was made in 1937 was the replacement of the ad- 

 justable plank weirs in the lower 3 pools ("flashboards" of Figure 2) 

 with notched concrete weirs. 



THE SHAD RUN AT LAWRENCE 



At the present only the lower 27 miles of the Merrimack River, 

 heavily polluted with industrial wastes and sewage, are available as 

 spawning areas for shad. 



2/ There is no evidence that the shad have ever used this opening. 



