CONSTRUCTION NOTES 351 



an air vent, otherwise the overflow becomes a siphon and will remove the 

 entire contents of the pool. This type of overflow is desirable where the 

 U-shaped portion of the pipes can be installed in a specially constructed 

 pit and revolved on the joints at points "C" in order thus to control the 

 depth of the water in the pool at certain times when the pool may be used 

 for wading purposes by small children. 



All outlets should be provided with a proper strainer in order to pre- 

 vent large particles of foreign material entering and clogging the pipes. 

 The outlet for completely draining the pool should be located at the lowest 

 point at the bottom of the pool and connected with main drainage lines as 

 shown in figures 2 and 4 on Plate 147. If in connection with the overflow 

 from any pool where the supply of water is extremely limited it is desired 

 to get considerable action and a small cascade effect, the type of overflow 

 shown on Plate 147, figure 6, is very desirable. 



Dams and spillways. Dams for informal pool and pond areas may be 

 constructed in one of three ways as shown on Plate 148. (i) Complete 

 reinforced concrete dam (Plate 148, figure i). (2) Dam constructed of clay 

 properly puddled and provided with a concrete spillway (Plate 148, figures 

 2, 5 and 6). (3) Earth dam provided with a concrete core wall and also 

 provided with a concrete spillway (Plate 148, figures 3 to 6). 



The type of concrete dam in figure i is constructed on the principles 

 of the common practice in general engineering work. The type of clay 

 puddled dam shown in figure 2, Plate 148, should be made permanent by 

 a line of piles or by one or two cut-off trenches extending parallel with the 

 long axis of the dam. Such a dam is constructed by using natural heavy 

 clay in layers not exceeding eight to nine inches in depth. Each layer is 

 distributed beginning at the point nearest to the borrow pit. The surface 

 of the layer is first carefully gone over with a disk harrow and then thor- 

 oughly soaked with water. On the succeeding day the next layer is put 

 in place, using a similar process, and this is continued until the full height 

 of the dam is complete. Both the upstream face of the dam and the down- 

 stream face are then carefully graded on a proper slope. (See Plate 148, 

 figure 2.) 



Winter protection of pools. Winter protection is important in connec- 

 tion with the maintenance of any pool. The author believes that one of 

 three ways as shown on Plate 149 is desirable. The following are the three 

 ways: (i) (See Plate 149, figure i.) To construct a complete roof over the 

 entire surface of the pool. This roof to be made in sections easily removed 

 and adapted for storage in any available place. The edge of the roof should 

 extend beyond the outer edge of the coping. (2) (See Plate 149, figure 2.) 

 To erect within the pool a series of two by fours between which may be 



