140 



SEASON 1874-75. 



to be able at any time to run the dam dry without losing the fish. 

 I also required to feed a row of rearing-boxes outside the dam. I 

 trusted the inlet screen to moderate the water in spate, and as 

 it worked up to my expectations, I had no trouble in providing 

 against floods. The sluice at the hatching-house at Middlethird 



seemed a suitable model, and 

 I copied it to some extent 

 (Fig. 94). I fixed two uprights 

 in the stone-work of the sluice 

 of 3-inch plank, and cut a check 

 in each to receive the sluice- 

 boards. These were also of 

 3-inch plank, but only 4 inches 

 broad ; the tops and bottoms 

 were bevelled considerably, 

 except the lowest one of all, 

 which was only bevelled on 

 the top edge. A beech sole 

 was laid between the uprights, 



FIG. 94-scale T V &n( J J eve l ^fa t } ie bottom of 



the dam. A small cup-shaped depression was then scooped out 

 to hold a little water for the fish left in when the dam was run 

 down, and the lowest sluice-board dropped into the check. The 

 next sluice-board was then dropped with the sharp edge of the 

 bevel downwards. This fitted the bevel on the top side of the 

 lowest board, and the pressure of the water acting horizontally, 

 while the weight of the superimposed sluice-boards, acting verti- 

 cally, kept it absolutely water-tight. After the first month, when 

 the plank had swollen, the top board was bevelled on both edges 

 like the others, so the water had a sharp edge to fall over. The 

 height of the sluice to the top board was about 6 feet. There 

 was some difficulty in concreting round the beech sole-plate, and 

 a 2-inch lead pipe was laid below, passing from the bottom of the 

 dam under to the back of the sluice. After the concrete had set, 

 this pipe was closed by stunning together with a hammer. This 

 is a simple and effectual plan. Fig. 95 is a plan of the sluice. 



