This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
The value of a thorough knowledge of the possibilities of drainage in landscape work has been overlooked until recent years as a definite field entirely apart from general drainage for agricultural purposes.
Drainage under the headings of this article is installed with the following objects in view:
1. Maintaining well-drained areas for firm lawn surfaces.
2. Maintaining well-drained and firm surface conditions for recreation areas.
3. Draining of surface water and ground water from roads.
4. Draining foundations for walks.
5. Preserving the normal soil conditions for newly planted trees.
6. Draining swamp and marsh areas to prevent breeding of mosquitos.
1. Drainage for lawns.
The secret of a perfect lawn is attributed to drainage conditions which provide a well-drained subsoil and a firm surface that may be readily freed from any excess water during heavy rains. The installation of drainage for this purpose is required only in the more compact soils that do not drain naturally. Sandy soils seldom require artificial drainage unless immediately underlaid with a stratum of impervious clay. On any lawn the topography of which does not permit the ready surface run-off and the subsoil of which is compact clay, the necessity of installing sub-surface drainage is strongest.
A drainage system for providing ideal soil conditions for perfect lawns must be installed carefully. Four-inch tile, is often used in the lateral systems while either 6-inch vitrified pipe, or the No. 2 quality of 6-inch round tile, is used for the main lines. All drains should be laid on an even grade of not less than 1/8 of an inch fall to each linear foot of drain, and preferably not less than 1/4 of an inch fall for each foot of drain. If perfect drainage is desired, the distance apart of these drains should not exceed 20 feet. In accordance with the general laws of drainage, tile should be laid at a more shallow depth in the heavy soils than in the lighter soils, and should be spaced at closer intervals than 20 feet, this space varying largely with the desire to free the lawn immediately of any excess surface water.
In all tile drainage whether for lawns or other purposes, a space of approximately 1/8 inch should be allowed between the ends of the pipes. The covering of tar paper and cinders should be placed over each joint as shown in Fig. 1353. The tile should be placed on a firm bottom of clay or other natural soil, and surrounded on all sides, and covered to a depth of not less than 6 inches with cinders, crushed stone, or washed gravel (Fig. 1354). In very heavy clay, the trench excavated for the tile should be filled with cinders, crushed stone or gravel to a line separating the looser top soil from the clay subsoil (Fig. 1355). In heavy soil and for perfect lawn drainage, the lines of tile ought not to be laid deeper than 2 1/2 feet and the cinder fill should not be less than 15 inches in depth. In the lighter sandy loam soils, the tile may be laid to a depth of 3 to 3 1/2 feet.
It is often found necessary when lawns are constructed on sandy soil to prevent excessive drainage, rather than to encourage drainage conditions. In these extreme sandy soils, the surface water seeps away so readily that the lawns become exceedingly dry during the warm and dry months. To prevent this condition a layer of clay 4 inches deep should be distributed over the sandy sub-grade prepared for the lawn, at a depth varying between 10 and 18 inches below the proposed finished surface of the lawn. This clay is thoroughly compacted and serves as a partial barrier against abnormal seepage which would otherwise occur, and thereby retains the moisture necessary for the capillary attraction to feed the roots of the lawn grasses.
Areas naturally falling under this heading are' tennis-courts (clay and turf), bowling-greens, clock-golf areas, and croquet-lawns. All of these require a more careful study of drainage conditions than is given to the average lawn. It is essential that such areas be so completely drained that the surface condition is always firm, even after the average continuous heavy rains.
Fig. 1354. The filling of a drain.
Fig. 1355. Applying good top soil.
These areas require the most careful study of drainage conditions. The average tennis-court requires two types of drainage, - surface and sub-surface. Surface drainage is cared for in two ways, (1) either by giving the court a gradual slope to one end, or (2) as shown in Fig. 1356, where the surface of the court is sloped from either end toward the middle fine. This method, shown in Fig. 1357, gives probably the most satisfactory results, because, in this way, if surface conditions at the middle of the court are correct, the surface water is cared for most readily and with the shortest possible run-off. This drain across the middle of the court may be either an open concrete drain with a plank laid over the top and flush with the surface of the court, or a blind drain filled with a coarser crushed stone and fine crushed stone, over which is spread a thin layer of washed sand. The bottom of the drain ought to be approximately 6 inches lower, at the point where the outlet to the sub-drain is located, than the elevation at the extreme high points of the drain. The method of establishing these grades varies largely with the requirements of this particular problem.
The water, as it reaches the low point in the drain, is conducted at once into the main 6-inch drain, which also takes groundwater from the underground system of drains. When the court is so constructed that one end is lower than the other, in order to assist surface-drainage conditions the courts should be level from side to side. Fig. 1357 6hows the general distribution of the system of tile to care for the sub-surface water in tennis-court construction. This would apply equally well to the construction of other recreation areas, including clock-golf -greens, bowling-greens and croquet-lawns. In the construction of all tennis-courts, the trenches excavated for the tile should be filled with cinders or an equally porous material to a height not less than 6 inches below the proposed finished grade of the court.
Fig. 1356. Draining a tennis-court.