CONSTRUCTION NOTES 345 



should even a small portion of any pool extend over soil which has been 

 recently filled or which is not thoroughly settled. The excavation for 

 informal pool and pond areas which are to be lined with concrete on the 

 bottom, should extend to the natural subsoil, thus removing all topsoil or 

 soil with any root growth or humus contained in it. 



Drainage for pools. Drainage for pools is installed for two principal 

 purposes: (i) To remove quickly all free surface water which might bring 

 foreign material in suspension into the pool or which might cause unde- 

 sirable soil conditions in the immediate area surrounding any pool (espe- 

 cially bird baths and small fountains). (2) To remove adequately all free 

 water in the subsoil the accumulation of which under freezing temperatures 

 might prove injurious to the bottom or to the walls of the pool. 



When the coping is raised above the surrounding finished grade (Plate 

 146, figure 2, right) this surface drainage is not so essential. When the 

 surface of the coping is flush with the surrounding finished grade (Plate 

 146, figure 2, left) it is very desirable that the surface water should be 

 promptly removed. In the case of swimming pools where it is very neces- 

 sary to keep all surface water away from the pool, a small gutter is often 

 installed immediately behind the coping. In the case of formal garden pools 

 where the surface of the coping is flush with the surface of the surrounding 

 walk, the walk should be sloped slightly away from the pool in order to 

 remove the surface water. 



The area around bird baths (Plate 146, figure i), due to the splashing 

 of the water by the birds, often becomes soggy and soft unless a proper 

 drain is installed to remove the surface water. The drainage necessary to 

 remove the free subsoil water from the area under the bottom of any pool, 

 and from the area immediately surrounding the walls, is provided as shown 

 on Plate 146, figure 2. A four-inch agricultural tile drain should be installed 

 at the base of, and immediately against the outside of the concrete wall 

 surrounding any pool. This drain should be connected with some main 

 drain which is easily accessible. This drain should have a fall of at least 

 one-eighth to one-fourth inch per linear foot. The drain to remove water 

 from the subsoil under the bottom of the pool should, in connection with 

 the average small pool (ranging from 10 to 20 feet in width or diameter), 

 be installed as shown on Plate 146, figure 2, and extend if possible parallel 

 with the longest dimension of the pool. The subgrade should be sloped 

 approximately one-eighth to one-fourth inch per foot toward the drain to 

 prevent accumulation of free water. 



Water supply. The problem of installing pipes for supply and control 

 of water for any pool is illustrated on Plate 146, figure i, and on Plate 147, * 



1 See also the article "Landscape Architecture Pool Control," by Robert Wheelwright, in Landscape Archi- 

 tecture, July 1920. 



