The specific drainage requirements for any given skatepark will be a function of the design and the topography of the site.  Drainage will fall into one of two categories, above or below grade.  In only the most extreme circumstance (solid rock) will the substrate composition prohibit the use of below grade drainage. 

Above Grade Drainage

Above grade drainage relies upon gravity and the slope of the park to drain water across the surface of the park and away without drainpipes, etc.  This drainage technique is the least expensive approach.  However, this technique will tend to control the skatepark design, because the outside edges of the park must remain clear to allow the water to exit the slab and all obstacles must sit above ground.  This means that you cannot have bowls, snake runs or other popular obstacles. 

If you choose this drainage option, the minimum slope amount in order to effectively drain water away is your best choice.  The standard for good drainage is ¼- inch per foot, which is a bit much for a skatepark.  The slab can be pitched (sloped) in any direction, or crowned (made higher) in the center allowing the water to run off both sides.

Below Grade Drainage

Below grade drainage relies upon gravity and the slope of the skatepark to carry water into a series of underground drainpipes where it flows into the municipal drain system.  Because of maintenance issues it is not advisable to design a park with a drainage system that relies upon sump pumps or other mechanical forms of drainage.  Leaves and other debris will surely cause mechanical failure of these systems in a short amount of time.

Drain pipe.

Drain pipes are used when you choose below grade drainage.  A minimum of 4-inch PVC pipe should be used for drain pipes.  Use rigid PVC couplers for all joints, as flexible couplers are prone to crushing, sagging or other failures.  The slope of the drain pipes should be the standard ¼-inch of downward pitch for every foot of pipe.  As an example, a 10-feet length of pipe would have 2½-inches (10 times .25) of downward pitch from one end to the other.  Stick to that formula for the skatepark drain pipes.  If you do not, water and debris will not drain effectively.  A greater slope will allow water to drain away so rapidly that it does not carry the debris with it, which will lead to clogging.

Drain boxes.

Drain boxes are used when you choose below grade drainage.  In most instances it is preferable to cast your own drain box instead of trying to fit a commercially manufactured box to your application.  The grates for most commercially manufactured boxes are dangerous to skate on and can be difficult to fit perfectly flush with the concrete, and a smooth fit is what we are aiming for.

Assuming that the drain lines are already in place, cut out a 1 foot long section of pipe at the location where you want to place the drain box.  Then dig back another 6 to 8 inches past the ends of the pipe.  Fashion a box out of ¾ inch plywood that will fit within the hole and touch the ends of the drain pipe or pipes.  The box should extend 8 to 10 inches below the lower edge of the drain pipes to act as a debris trap.  This is a place that leaves and other debris can accumulate before entering the drainpipe and clogging the line.  With a debris trap, the drain box will only have to be cleaned out about once a year.

Around the top edge of the drain box form build a frame out of 1 x 2 lumber that extends out at least one inch past the form for the drain box.  This frame creates a space where the grate can sit securely without falling into the box.  Check with a laser transit to insure the drain box follows the slope of the bottom of the bowl or slab. Do not level the box with the surrounding ground.  If you do, one side of the box (downhill side) will remain higher than the finished concrete surface.  Take your time as this is very important.

When the concrete is poured in around the drain box form, it encases the drainpipes in concrete so that when the form for the box is removed, only the edge of the pipe is visible.  After the concrete has cured, carefully remove the form, making any needed repairs.  If the bottom of the box was not completely covered with concrete, pour a few more inches into the bottom of the box to finish it.

Drain box grates.

Fabricate a drain box grate from plate steel equal in thickness to the frame that surrounds the drain box (3/4- to 1-inch).  Plate steel will sit flush with the floor of the park and is heavy enough to discourage removal or vandalism.  Drill a series of holes in the plate steel in a circular or other desired pattern.  Begin with a ¼-inch drill bit followed by a ½-inch bit.  Afterward, remove all burrs from around the holes with a chamfer bit.  In order to facilitate the removal of the grate, you will want to tap the center hole to accept a large bolt.  On the top of this bolt, weld a piece of pipe.  Anytime the grate needs to be removed (to clean the trap, etc) the handle is screwed into the center hole and the grate lifted.

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