The two most frequently used type of drain pipe systems for residential and commercial drainage applications are Corrugated and Sewer & Drain (smooth wall) pipe (Figure 3-1). In general terms, whether using corrugated or sewer and drain pipe, perforated pipe is used for subsurface drainage and solid pipe is used to convey water from surface and/or subsurface drainage systems.
Corrugated pipe is manufactured from high density polyethylene (HDPE) and is available by the foot or in rolls of 100 or 250 foot coils. The longer the coil the fewer couplings necessary and the less labor required. Since corrugated pipe is flexible, it can follow the contours of the ground, change directions in the trench, and adapt to underground obstacles more easily than rigid pipe. Labor savings and flexibility are two important advantages of corrugated pipe. Several disadvantages of corrugated pipe are prevalent. Plumber's snakes cannot be used to clean out the pipe as they get caught in the pipe's corrugations. Corrugated pipe and fittings snap together and, henceforth, are not watertight. If slope is critical, the flexibility of corrugated pipe makes it difficult to obtain constant slope unless the trench bed is sloped properly, Figure 3-2. Corrugated pipe has more friction loss than smooth wall sewer and drain pipe reducing flow and increasing sediment deposits in the drain pipe.
Corrugated pipe is available in solid or perforated. The perforated version is sometimes known as slotted drain tubing. Perforated pipes are used for subsurface drainage applications.
Smooth Wall Sewer & Drain Pipe
Sewer and Drain pipe is much more rigid than corrugated pipe and manufactured from PVC, ABS and Polyethylene. It is easier to maintain a continuous slope in critical areas with sewer and drain pipe. They will compensate for peaks and valleys in the trench bed (Figure 3-2). PVC and ABS connections can be solvent welded or glued together ensuring watertight connections. Drain snakes can be used on Sewer and Drain pipe if the pipe line becomes clogged. However, Sewer and Drain Pipe is more labor intensive and less flexible than corrugated pipe.
Smooth wall plastic pipe or Dual Wall Smooth Interior Corrugated Pipe - Manning "n" - 0.010-0.013
Manning "n" values are used for estimating internal volume flow rates. Typically, the lower the "n" value the greater the flow volumes. Drain pipe with a smooth interior wall has greater flow characteristics than single wall corrugated drain pipe.
Figure 3-1: Type of Drain Pipe
DWV (Drain Waste & Vent) and PVC schedule 40 pipe may also be used in drainage applications. They are, however, more expensive and an unnecessary expense for the task of draining surface or ground water. DW pipe is typically used in indoor sewer applications, while schedule 40 pipe is commonly used in pressure applications such as lawn sprinkler systems.
Figure 3-2: Influence of trenches
Perforations in single wall corrugated pipe are slits surrounding all sides of the pipe. Perforations in smooth wall drain pipe and coextruded dual wall corrugated pipe are small diameter holes located in rows on one side of the pipe which should always face downward to prevent soil from infiltrating the pipe.
French drains are the most common method for evacuating excess ground water that has infiltrated into the soil. However, french drains require labor, large trenches, rock or stone, filter fabric and therefore are more expensive than surface drainage systems. Also migrating soil fines will accumulate on the filter fabric or in the drain pipe, potentially inhibiting water flow and eventually clogging, limiting the life of the drain system.
Filters and Envelopes for French Drains
Envelopes for French drains are gravel, stone, rock or sock surrounding pipe. These are permeable materials placed around pipe or drainage products to improve flow conditions in the area immediately around the drain and for improving bedding and structural backfill conditions.
Most geotextiles used during drainage applications are used to prevent contamination of soils into aggregate backfill materials or perforated drain pipe. Using geotextiles as a screen helps maintain the natural integrity of the products used in your project. The need for geotextiles as a screen should be evaluated for each particular site, especially French drain applications. The solution is as easy as wrapping the perforated pipe or aggregate backfill material with non-woven geotextiles. Very light weight geotextiles should be used to cover the top gravel layer. Light weight geotextiles should be used to line the sides and bottom of a French drain. It will be important to know the K factor of the soil, relating the K factor to the fabric '-permeability factor." To select the proper screen AOS opening size of the fabric, consider the following: Pick the soils' gradation sieve size (inches/min) for which 85% of the soil (by weight) will pass. Multiply the sieve size (inches/min) by two. This value should be greater than the AOS of the fabric. AASHTMO M288 sets standards for selection of the proper geotextiles.
Non-woven fabrics are used in subsurface drainage applications because of their high flow capacity and small pore size. Non-woven fabrics are produced by a variety of processes. Geotextiles are frequently produced by a combination of two different type processes. The first process is fiber formation and results in either a continuous filament or a staple fiber (a short fiber). Fibers are then bonded by needling, heated calendar or other processes or combinations.
Prefabricated Drain Systems
Prefabricated drain systems are typically rectangular with a narrow profile and available in 4" through 60' depths. Common lengths are 10 ft. to over 100 ft. They are used in both natural and synthetic turf applications to collect and convey water away from the problem areas. Compared to French drains, their narrow cross-section allows them to be installed in more narrow trenches without significantly disrupting natural turf areas. In many cases, the area can be returned to play the same day.
Prefabricated drain systems can be installed in lieu of a French Drain and offer the same or slightly better results. As compared to French drains, they convey a relatively high volume of water at low hydraulic gradients due to the large degree of open surface area.
Catch Basins and Inlets
Catch basins or inlets, surface drains, used in conjunction with a drain pipe system will remove large amounts of surface water from an affected area. These are typically used in low areas of turf landscapes, hardscapes, driveways, parking lots, etc. Catch basins and inlets are traditionally available in sizes from 3" round to 48" square and different materials including concrete, brick, and plastic basins, cast iron, steel, brass and plastic grates.
For instruction purposes, a catch basin differs from an inlet in that an inlet is located on top of a pipe riser and does not have a sump area. However, inlet is also a term that may be used to describe all surface drains. The sump area of a catch basin collects debris from runoff water that might clog drain lines. The debris is cleaned out periodically. A catch basin should be used in areas where debris like mulch, leaves, sand, silt or grass clippings are prevalent.
Channel drains are linear surface drains connected together to a length appropriate for the specific installation, (Figure 3-8). Runoff water collected in the drain is discharged to bottom or end outlets, or catch basins, all of which are connected to drain pipe. They are available in widths from V to 16" wide and different materials including concrete, steel, plastic or formed in place. Grates are available in cast iron, steel, brass and plastic.
Channel Systems operate on the same principle as a roof gutter. Instead of grading a deck surface to a low area, the deck is gradually sloped in one direction or plane, and the channel drain acts as a perimeter drain at the edge of the slope.
Hardscapes generate more runoff than landscapes due to the lack of water absorption. Channel drain systems provide more overall open surface area than conventional area grates (basins and inlets) to handle the larger volume of runoff. Ideal applications for channel drains are hardscapes or large flat work areas of concrete, asphalt, brick, pavers, etc.
Driveways Tennis courts Parking Lots Sidewalks Warehouses Patios Swimming pools and spas Sports facilities Wash down areas Nurseries and greenhouses
Natural surface drain swales are the least expensive method of removing undesired surface water run off. A typical swale can be approximately 2' - 60' wide and can have a depth from 2" to 60".
The primary purpose of terracing is to move surface runoff water from sloping areas. Bench terraces and tile outlet terraces are the two types of terraces that have been used in turf drainage.
Generally speaking fill dirt is not a positive solution to addressing drainage problems, as it generally routes the water problems to another area. However; there are times where fill dirt, preferable a mixture of humus and sand, will be used to fill in minor low areas and direct water to safe areas.
Culverts can be installed under flat work, gravel or dirt to allow water to pass under an obstruction.
Preferred for moving water and adding a boost. This system is totally dependent on rainfall and gravity. Boost is gained via connecting all of the gutter downspouts into the drain.
Use of a submersible pump is a last resort if
there are no other options available. Runoff water may need to be pumped uphill
to a higher elevation safe area if adequate fall is not available for a sloped,
gravity flow, drain pipe.