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Drainage Options11-01-00 | 16
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Drainage Options

Alternatives to the French Drain

 When the Sacramento Valley Amphitheater was constructed in Fall of 1999, the owners turned to Perma Corp. to supply 1,200 feet of Perma Panel (P-3000). The drainage system was installed in the grassy seating area that accomodates picnic and festival crowds

Controlling excessive groundwater has challenged land developers since before the days of the Romans. Early attempts at ground water drainage utilized open trenches, which have since been replaced by various forms of conduits, including concrete, steel, and plastic pipe. These conducts have typically been circular in shape, owing to the design's higher strength to weight ratio.

Traditionally, one of the more common methods of 20th century drainage incorporates a round pipe surrounded by crushed stone, and wrapped in a geotextile fabric. This method is often referred to as a "French Drain". A typical french drain may be 18" wide and 24" deep. The side walls of this trench induce the water in saturated soils to flow through the crushed rock and into the conduit. Although this system has proven very effective at collecting excess groundwater, it does have several draw backs.

The French drain requires a wide trench to install the fabric and crushed rock. This leads to considerable site disruption and significant labor costs. Typically, these trenches are made using large machinery such as a back-hoe, or very large trencher. Also french drains are highly susceptible to blinding and plugging from silts and fines, which leads to system failure.
It was this potential for failure that prompted several manufacturers to design alternatives to the French Drain.

Varicore

In the mid 1980's a new concept in drainage, the geocomposite drain, began to gain popularity. Geocomposite drains are typically 1" wide by 12" or 18" tall. They are constructed from a polyolefin core and wrapped in a geotextile fabric. Geocomposite drains are intended to be direct replacements for the French drain. Multi-Flow, manufactured by Varicore, based in Prinsburg, Minnesota, is a geocomposite drain.

The Multi-Flow Drainage System is available in three sizes, 6", 12", and 18" heights. It is comprised of a series of corrugated polyethylene pipes, stacked one upon the other, connected to each other, and wrapped in a polypropylene fabric. The pipes are 1.18" o.d., and are perforated with slots to allow for the passage of water. The true measure of a drainage system's efficiency is based on how much water the system will remove from the soil, not how much internal capacity it has. Multi-Flow is designed to collect water, not transport it. In contrast, traditional round pipes are much better at transporting than collecting.

 Panel-shaped composite drain systems, such as Multi-Flow drainage system are typically used in four different applications: 1) Highway edge drains - It drains water from under the pavement where it threatens to destroy the roadbed and the subgrade, 2) Sheet drains - typically installed behind retaining walls and along basements and foundations to relieve hydrostatic pressure, 3) Soil interceptor drains - remediates drainage problems in low-lying sections of parks, golf courses and athletic fields, and 4) Wick drains - installed horizontally to maximize flow rates under landfill sites, heap leach piles and hazardous waste sites.

Multi-Flow is a replacement for a more cumbersome, expensive method of drainage called the French drain. The French drain has been used extensively as a method of removing water from saturated soils around homes, athletic fields, roadways, parking lots and many other sites. Multi-flow is wrapped in a 4 oz. needle-punched, polypropylene fabric, which has been used in French drain applications in the past. Geotextiles in general are susceptible to blinding, or plugging, by silts or clay particles.

Installation

Multi-Flow is typically installed in a four inch wide trench that is dug to a depth of approximately 12 to 14 inches. Then the Multi-Flow system is placed vertically in the trench, which is backfilled with coarse sand to the surface of the trench. If you want to establish grass with seed, then rake enough topsoil into the sand for seeds to germinate. Turf also works well right over the top of the sand. Instead of digging another trench for irrigation lines, you can install the drainage system and irrigation pvc pipe in the same trench.

Conclusion

Drainage is an important consideration for every commercial and residential project. Without planning for it, foundations can be ruined and homes flooded out by runoff from nearby hillsides. Some of the applications for drainage systems include: golf courses, lawns and landscaped areas, athletic fields, retaining walls, parking lots, and highway embankments.

Perma Corporation

Perma Panels are rigid polyethylene panel devices that collect, and carry off, drainage water. Perma Panels were designed by Karl Adamson, a construction engineer, of Grass Valley, California. He wanted to address some of the problems he encountered with typical "pipe and rock" systems for French drain and curtain drain applications.

Adamson related that his idea for Perma Panels emerged when he was preparing a bid for a residence with drainage problems. "The french drain at the side of the house had failed and the runoff from an adjacent hill was flowing beneath the house," Adamson recalled. After investigating the site, he realized that the problem stemmed from gravel that clogged the pipe and formed a barrier.

Adamson explained that the project was extremely labor intensive because 11 truckloads of incoming gravel were needed in addition to 11 outgoing truckloads of dirt. Plus, the home was built in a gated community that only allowed two truckloads of dirt to be stored on the driveway. It was at this time that Adamson started to think about a drainage system that could be installed without a backhoe, which would cut a 12 foot swath for the 18 inch trench. The homeowners had spent thousands on landscaping and the backhoe would have destroyed their investment.

To address these concerns, Adamson designed a product that could separate the functions of intake and discharge of the collected drainage waters by using a process called twin sheet vacuum forming. This unique ability of separate intake/discharge allows all collected drainage water to be channeled to a desired collection/discharge area. Additionally, the slot size, and ability to flush a Perma Panel system, eliminates the need for any geotextile filter fabrics which often restrict flow after becoming clogged with soil fines or bio-matting. Soil fines collected by Perma Panels are typically washed out with the drainage water or may be flushed periodically by incorporating a clean-out at any point in the system.

Perma Panels are available in two sizes. The three-inch discharge panel (P-3000) is six inches high and is capable of discharging approximately 80 GPM or more depending on slope and surrounding water pressure. The four-inch discharge panel (P-4000) is seven inches high and is capable of discharging approximately 170 GPM or more.

Installation

One of the primary benefits of the Perma Panel drainage system is that a backhoe is not required for installation. A 4" to 6" (wide) trench made with a high-speed chain trencher is all it takes. Perma Panels require only "pea gravel" that can be distributed over the panels with a wheel barrow and shovel. To install a pipe and rock system correctly requires many more yards of larger drain rock, Adamson explained. This usually requires a two-man crew with a bucket loader to deposit the volume of rock.

The P-3000 and the P-4000 Perma Panel require a minimum 4" wide trench. The P-3000 panel is 6" in height while the P-4000 is 7". This accommodates the use of a standard walk behind type trencher. Generally, the panels are placed approximately 12 inches below grade. Trench depths should be determined based on the needed slope to allow for approximately 1" of pea gravel backfill above the shallowest panel and (if required for curtain drain) additional topsoil needed to establish turf growth.

Perma Panels are constructed with male and female ends. The panels are connected by pushing the male spout into the hole in the next panel. The male end of the panel should be facing down slope. If the panels are to be put together above the trench, they may then be secured by using a self tapping #8 x 1/2" Hex-head screw. This step is not necessary when installing the panels as-you-go in the trench.

 These three photos show the evolution of drainage systems. 1) First there was plastic drainage tile. It was able to move surplus water quickly. Typically, it consisted of a round, perforated pipe that rested at the bottom of a trench. 2) Then came panel drains. They consisted of tall plastic cores surrounded by a geo-textile. Due to their shape, they were more like to intercept water rather than carry it away effectively. 3) The Multi-flow drainage system combines the shape of a panel drain with the structure and water-carrying capacity of conventional corrugated tubing to produce an effective drainage system.

Perma Panels may be connected to fittings by cutting a 3" (P-3000 use 3" diameter) section of any common drain pipe-co-extruded, corrugated, or solid wall-to be used as the connector between the panel and the fitting. Pipe to panel connections may be secured by using a #8 x 1/2" pan-head screw. Connections may be made watertight by using a 2" wide PVC tape.

Backfill with native soil up to the top of the trough on the panel. The back fill should be as clean as possible and free of sharp or large rocks or other debris. continue to fill the trench with #4 pea gravel to 3" above the top of the panel. Backfilling may then be completed with native soil if you plan to establish turf.

In contrast, a typical Pipe and Rock system requires approximately six times the backfill media as a Perma Panel installation, Adamson claims. P-3000 installed in a 4" wide trench requires approximately 0.54 cu feet per lineal foot of gravel. A one hundred-foot run of Perma Panels requires only about a pickup load of backfill. The same run in a pipe and rock system would require about 3.78 cu feet of gravel. LCM

 When installing a Perma Panel drainage system, a backhoe is not required. A four to six inch wide trench made with a high-speed chain trencher is all it takes. Generally, the panels are installed approximately 12 inches below grade in an up-right position. Backfill with rock free soil to the top of the carry-off trough and then wet the soil to compact. Then continue to fill with 1/4" pea gravel to desired depth (minimum of 1" above top of panel). Finally, backfill with native soil and rake in seeds or install turf.
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