1108 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [8] 



be retained in any desired position by screws or bolts, tip to the sur- 

 face of the water the four square posts are connected by horizontal 

 laths, which form a grating with intervals of 2 to 3 centimeters. This 

 is intended to keep out fish, leaves, &c. Above the surface of the 

 water the posts are connected by closely -joined boards and protected 

 on the top by a roof. This whole contrivance, which, in large ponds 

 having several tap-outflows, assumes considerable dimensions, is called 

 the tap-house (Plate III, Fig. 9). In order to show the tap-pole the 

 upper boards have been left out of the drawing. Whenever the tap is 

 raised the water flows into the pipe through the conical hole and through 

 the pipe finds its way outside the pond. Fish are kept back by the 

 grating. The tap-outflow is much cheaper than a sluice, but has the 

 same disadvantage that the water from the bottom of the pond flows 

 out at a high pressure and easily damages the outflow ditch. 



Of late years such outflows are in large ponds constructed of ma- 

 sonry, and, iu stead of the taps, valves are employed which are raised 

 by screws. But even these outflow arrangements have the above-de- 

 scribed disadvantages. 



The so-called "monk" or stand-pipe outflow (Plate TV, Fig. 10 and 

 Fig. 11) is without doubt the best outflow arrangement. As in the tap 

 outflow, a horizontal pipe is led through the base of the dike. This pipe 

 may be constructed of masonry, but generally it is made square in shd.pe, 

 of strong oak boards, which are carefully joined and thoroughly em- 

 bedded in tough clay. The height of the opening is generally 20 to 30 

 centimeters, the breadth the same in small ponds, whilst in large j)onds 

 it may be much larger; in this case, however, strong props should be 

 inserted at intervals to support the roof of the pipe, and protect it against 

 the pressure of the soil on the top. At the end of this horizontal pipe, 

 which x)rojects about 1 meter into the pond, a vertical pipe of the same 

 diameter is fastened, which projects about one meter above the highest 

 water-mark. This is, if necessary, supported by strong buttresses, and 

 its side towards the iDond is open from top to bottom (Plate lY, Fig. 11). 

 On the inside of the side planks two thin, but strong, strips are nailed 

 down, which form a deej) and broad groove, in which run a number of 

 closely-fitting boards, measuring 15 to 20 centimeters in height (Figs. 10 

 and 11). By the pressure of the water these boards are pressed against 

 the inner side of the groove, which should therefore be very broad, fast- 

 ened firmly, and — as well as the boards themselves — be planed down 

 very smoothly. The boards, however, should have room enough in the 

 groove to prevent their sticking fast and make it easy to remove and 

 insert them again. If broad " monks" are used, the side planks must 

 of course be firmly joined by horizontal beams on the side towards the 

 pond. In order to prevent the bending of the boards through the press- 

 ure of the water, the horizontal pipe should be divided into two halves 

 by a strong board, so that the center of the boards meet with a firm re- 

 sistance in this partition wall (Plate IV, Figs. 12, 13). In the center of 



