There are several drainage components that are fairly common in most drainage systems. This section introduces some basic components that are part of the drainage systems described in the following section - Drainage Systems. Successful construction involves selecting the appropriate materials for the collection, conveyance, and discharge requirements of your system. Attention to proper capacity and durability of each drainage material is critical. The performance of your system will be improved by using good construction techniques and by performing routine periodic maintenance.
Drainage pipe is available in rigid wall and flexible wall lengths. On individual lots most applications require fairly small diameter pipe (4 inches to 12 inches). Generally, plastic pipe is used by contractors based on cost, ease of installation, and availability. The walls of pipe vary from thin and corrugated to thick and solid. Each pipe type has some degree of flexibility over the length which has many advantages in slope applications and some disadvantages. The biggest disadvantage is that the installer must check the grade of the pipe to confirm there are no reverse slopes or low points along the length of pipe which may reduce the performance of the drainage system.
|A variety of solid and perforated pipes shown with a strip drain.|
The least expensive pipe selection is usually the thin corrugated pipe which is available at most home centers and discount stores. The pipe is very flexible and is sold in coils of one hundred feet or greater. This pipe may be satisfactory for very shallow installations without significant backfill or backfill compaction, but it can fail easily by being crushed during installation with heavy equipment and by the weight and compaction of soil backfill. It may also be susceptible to degradation by ultraviolet light. Finding watertight connections (couplings) can be a problem with thin corrugated piping. Duct tape is not a long-term connection solution. Using corrugated pipe with thicker walls and watertight connections can help avoid the crushing and leaking problems common with thin-walled pipe installations.
Other plastic pipe is available including corrugated pipe with smooth interior walls, rigid pipe, light duty and heavy duty pipe, and perforated and non-perforated pipe. Aluminum culverts and concrete cylinder pipe are available for surface water routing under road surfaces and down slopes. Culvert pipes are usually purchased in diameters of 12 inches or greater.
Plastic drainage pipe are produced from different materials but are commonly made with polyvinyl chloride (PVC), polyethylene (PE), and high density polyethylene (HDPE) material.
Rigid pipe is sold in short lengths of approximately 10 to 20 feet and requires good connections at each end. Pipe sold in coils requires fewer connections which is a benefit but may have a low strength for wall crushing or buckling depending on the pipe manufacturer's specifications. Ask your pipe supplier about pipe details.
Perforated pipe allows water to enter or exit through small openings along a length of a pipe. The openings can be circular or slots. The more opening space per foot of pipe, the greater the capacity of the pipe to collect and move water. Slotted pipes have an advantage over pipes with small holes because they tend to reduce the amount of fine soil particles that get pulled into a drainage system and discharged downstream. Solid pipe has no openings in the walls and is commonly referred to as tightline pipe in drainage applications.
A geotextile is a permeable fabric material made from synthetic polymers. Geotextiles are used in many engineering applications. The primary functions of a geotextile in drainage applications are filtration and drainage. Simply, the geotextile retains the soil while water passes through the fabric and into the drainage collection system. Geotextiles used in drainage applications can be woven or nonwoven fabrics. The woven geotextiles have a weave pattern while the nonwovens are formed from a random pattern of fibers bonded together.
Typical drainage applications include interceptor drain construction, drainage blanket installation and geotextile wraps for pipes. For interceptor drains, the geotextile is used to line the trench prior to backfilling with gravel drain rock to limit the migration of the adjacent soil into the gravel backfill. For drainage blankets, the geotextile is used in a similar manner, except it is more commonly placed on a slope or a more horizontal location. Sometimes, the geotextile is wrapped directly around pipes for ease of construction at difficult locations.
It is important to differentiate between landscape fabric available at local hardware and garden centers and appropriate geotextiles for drainage applications. Typically, landscape fabric is not durable and will eventually clog which can lead to serious slope stability issues.
Drainage systems need a method to collect and concentrate water flow at a location. Catch basins and manholes allow pipes coming from different directions and elevations to converge at specific locations. They can convert surface flow to subsurface pipe flow. Catch basins and manholes can trap larger sediment and debris allowing only drainage with fine sediments to enter pipes. Also, they can provide a drop in elevation down a slope and dissipate the energy of pipe flows. Catch basin and manhole structures are commonly constructed of concrete or polyethylene and have a number of lid options ranging from open grates to watertight construction.
A pipe coupling connects one length of pipe to another without leaking. They are sold as rigid or flexible connections. Improper or poorly retrofitted connections on drainage pipes are very common failure locations. It is important to use a good connection system or couplings specifically manufactured for your pipe. The couplings should have a watertight gasket seal. When pipe is placed above ground on a slope and is not anchored correctly or has too much flow resistance, you will likely see a coupling failure in the future. By planning ahead, you can minimize the number of couplings by ordering longer lengths of pipe.
Pipe anchors should be used for pipes on steep slopes. Pipe bends should be adequately supported. Water flowing downhill can place tremendous forces on pipe connections and bends. Do not underestimate the need to resist these forces by anchoring and supporting the pipe. Pipe anchors are not purchased but are built in place. Pipes should be anchored above grade as well as below grade. Figure 10 (below) illustrates a number of anchoring systems.
Drainage gravel should be rounded rock ranging in size from 3/4 inches to 11/2 inches in diameter. The gravel provides a uniform bedding for drain pipes to create a consistent pipe slope and provide a free draining material adjacent to perforated pipes. Water moves through the spaces between the gravel before entering a pipe or other means of conveyance. This material is usually delivered to your property by a gravel supply company.
Drainage system installation should be done during dry weather periods except in emergency situations. Excavations can quickly be flooded with water making proper construction difficult and dangerous. If there is a lot of water present while excavating soil, you will have sediments accumulating in the gravel openings, on the geotextile, in pipes and catch basins, and in marine waters where the drainage will eventually discharge.
Avoid construction when the ground is wet. Your system will perform better with dry weather construction and not cause sedimentation in other areas.
Before you complete the installation of your system check to make sure pipes have not been crushed by heavy equipment. Make sure each connection is solid and not leaking. Check the slope of pipe runs. It is a common practice to water test your drainage system before covering it with soil (backfilling).
|Figure 10. Anchoring Systems.|
Water must move downhill so double check to see that water moves to your planned locations. If you do not do the installation yourself at least observe your construction so you can help troubleshoot any future problems. Make a photo record of the work if you have a camera handy. During construction you should take your plan drawing and sketch onto the plan what actually was installed. Important items such as locations, depths, sizes, and problems will help you improve or expand your system later. A system "as-built" will also help you or a future property owner avoid damaging the system during other site improvement work.Return to top
Every drainage system needs some periodic inspection to see that the system performs properly. Surface features like yard drains, roof drain catch basins, manholes, swales, above ground pipes and couplings, pipe anchors, and discharge areas can be quickly checked. Catch basins and manholes are usually designed to capture debris and heavier sediments and will require the removal of a few buckets of material from time to time to prevent pipe clogging and discharge of material into water bodies.
Below ground drainage features like pipes, strip drains, couplings, and overall system performance should be checked regularly for signs of failure during rainfall events. Overflows, leaks, wet areas, flow bypassing your system, and discharge interferences can be noted and immediately repaired if you detect the problems early.
For more information please contact us at (281) 340-9206 or go to our online request form.
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