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Surface Drainage for Recreational Areas



The greatest single factor in the deterioration of recreational surfaces is the presence of standing water on or free water beneath the surface.

Surface drainage (above ground) and subsurface drainage (below ground) are both essential components of properly constructed recreational surfaces. There are three basic tasks of water drainage:

1.         Collect;
2.         Conduct; and
3.         Dispose of excess water.



The intention of this guideline is to equip the reader with a basic understanding of systems in order to plan properly for new construction or to recognize and correct existing problems.


General Requirements-一般的要求


Subsurface Drainage-表層下的排水
A peripheral subsurface drainage system is installed where needed to intercept and redirect the flow of subsurface water that might otherwise accumulate beneath recreational areas.

Where it is necessary to lower the water table at a given site, a subsurface lateral or parallel drainage system may be required to direct free water from the subsurface to other areas.


Surface Drainage-表面排水
Surface drainage usually consists of a series of swales or a fabricated system designed to redirect surface water that might otherwise flow over the recreational surface, and to prevent seepage of water beneath the surface.


Procedures -過程



Subsurface Drainage -表層下的排水
There are three types of subsurface drainage systems used to redirect subsurface water:

Conventional Vertical Stone Drains常規的垂直的石塊


This type of drain is classified as an interceptor drain. It intercepts subsurface water in a stone "wall" and causes it to drain downward into a perforated pipe which carries the water to an outlet.


A trench is dug 1’-2' wide on the full or partial perimeter of the facility as directed by local conditions. The depth of the trench will depend on the predetermined water level, but should have a minimum depth of 18". Since the trench must be sloped a minimum of 0.28% (1:360), the depth of the trench will also be determined by the length of the trench before the water outlet. Multiple water outlets or catch basins may be necessary to minimize trench depths. Place 2" to 4" of permeable aggregate in the base of the trench.

Note: Non-woven geotextiles are usually used as a filter fabric to protect either the entire stone trench or the pipe only. Corrugated, perforated pipe is available with a "sock" over it. In either case, filter fabrics tend to clog when used in clay or silty soils.


A porous or perforated pipe with a minimum diameter of 4" should be placed on the aggregate in such a way as to have not less than 0.28% (1:360) of pitch and not more than 0.83% (1:120) of pitch. A larger pipe may be required as dictated by the amount of free water to be conveyed, the surface area to be drained, or available pitch on the pipe.


Back fill of the trenches should be of permeable aggregate of no larger than 1 1/2" placed in 6" lifts, each of which should be compacted to minimize the risk of subsequent settlement.

Note: It is generally recommended when using a filter fabric around the stone to use 1 1/2" stone size and when not using a filter fabric, to use smaller aggregate to act as a natural filter.


The trench is then filled to the surface with smaller washed stone where an open drain is desirable.


Where a closed drain is desired, the trench is filled to 8" below the surface, after which a porous type membrane is placed over the stone, and a sod or an impervious type swale formed over this.



Subsurface Horizontal Stone Drain Layer-細長的孔道排水
This drainage layer is a "capillary breaker" used in areas with ground water problems or heavy clay soils. When installed properly, it prevents vertical movement of ground water under a surfaced area. It is highly recommended that this system be used in conjunction with a perimeter interceptor drain system.


Installation includes excavation of all vegetation and topsoils under the surfaced area and to a minimum of 5' beyond. The soil subgrade must be sloped. The slope of the stone drainage layer is then graded to match the proposed finish slope requirements of the surfaced area. Installation includes a 6" to 12" stone layer of two inch (2") minimum washed aggregate installed and compacted in 6" lifts. Compaction should be 95% of the maximum density determined by ASTM Method D1557.


On the low end of the drainage layer, a perforated pipe should be installed with a proper slope to collect and dispose of water at the outlet area.


The horizontal drain layer does not necessarily take the place of subgrade gravel materials.


Design of this system should be done by a geotechnical engineer.

"Prefabricated Rockless" or "Geocomposite Drain"無石預制件"及"滲透式排水"
This system is also classified as an interceptor or curtain drain.


The system consists of a plastic dimpled or waffle sheet that forms a channel to permit the vertical and horizontal flow of water on each side covered by a non-woven geotextile fabric. Curtain drains usually have a corrugated pipe inserted along the bottom to carry the accumulated ground water to the outlet area.


Geocomposites are available in various heights ranging, depending on the manufacturer, from 2" to 60'. The installation requirements may differ from manufacturer to manufacturer but, in general, the installation requires excavation of a trench wide enough to install the geocomposite (usually 4" to 8"). The trench is backfilled with the excavated material. Some clay type soils may require backfilling with a coarse sand. Consult with your local contractor, geotechnical engineer or architect for design and installation specifications.


Surface Drainage - Tennis Courts-表面排水

There are several types of systems.

Open Drain System-開放式排水
Open drains are shallow swales using gravity to move water around the recreational area. Swales used to collect and conduct surface water should be a minimum of 5' wide and 6" to 8" deep in the center. Slope requirement should be a minimum of 2% (1:50) on grass and 0.56% (1:180) on pavement. Swales can be located on the ends or sides of a facility and carry water to the outlet area.

Closed Drain System-隱藏式排水
A closed drain system utilizes the swale design to collect and conduct water to inlets located (at a minimum of every 200') in the center of the swales. The water inlets are connected below ground to pipe (size is determined by volume of water being collected) which carries water to catch basins or other outlet areas.

Combination Systems-結合系統
Combination systems utilize swales and/or conventional open or closed vertical stone drains or "prefabricated rockless" geocomposite drains as discussed in the above section on subsurface drainage.

Prefabricated Channel Drain Systems-預制水渠通道系統
Another functional system being used for surface drainage is the prefabricated channel drain. These vertical lineal drains have been used for years in the track industry to drain both the field and the track surface. Their application with tennis courts and other related surfaces are also being used successfully. They require shallow excavation and some manufacturers offer sections with "built in slopes". Channel drains are available in radius, angles and straight lengths. They also have removable grates to allow for easy cleaning.

To obtain the correct system for your facility, you should consult with an experienced contractor, qualified architect and/or engineer.