Tile Drainage Outlets

Agdex#:	573
Publication Date:	12/90
Order#:	90-223
Last Reviewed:	12/90
History:	Revision of Factsheet "Tile Drainage Outlets", May 1985
Written by:	R. P. Stone - Engineer (Soil)/OMAF

Table of Contents

1. Introduction
2. Constructing a Good Tile Drainage Outlet
3. Maintenance
4. Assistance
5. Related Links

Introduction

The tile drainage outlet is the single most important component of a subsurface drainage system. It should receive adequate care and attention during installation and be inspected for necessary maintenance at least twice per year.

Where possible, the number of outlets should be kept to a minimum by using one large main (collector) line. Where it is deemed necessary to check flows or inspect submains or other drains, a junction box can be installed. A junction box can be constructed using concrete, steel or plastic or can be purchased from drainage material manufacturers.

The outlet should be protected from erosion, settlement, rodents, silting, shifting and damage by machinery and livestock.

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Constructing a Good Tile Drainage Outlet

Use non-perforated corrugated metal pipe or plastic pipe with a minimum length of 10 feet (3.0 m)
(Table 1). Plastic pipe must be chemically treated to resist degradation by ultraviolet light.

The drain outlet pipe should be angled downstream so as not to impede normal drain flow and discharge 1 foot (0.3 m) minimum above normal water level or ditch bottom (Figure 1).

Figure 1. Tile Drainage Outlet Flush with Ditch Bank

Flush mounted outlet pipes are recommended since they do not extend out beyond the channel bankslope to be damaged by ice and floating debris. Erosion control protection is to be provided around the flush outlet. A recessed apron of rock riprap with a filter cloth underneath should be installed below the outlet pipe on the ditch bank and extended across the ditch bottom to provide erosion protection. Rock riprap equivalents such as geoweb, interlocking concrete blocks or cable concrete block material will also provide adequate erosion control at the outlet.

Figure 2. A Tile Drainage Outlet Being Installed. Note Filter Cloth under Rock Riprap.

The minimum dimensions of the outlet pipes are shown in Table 1 below.

*These are minimum pipe dimensions for plastic subsurface drain sizes. Larger pipe outlet dimensions may be required for clay and/or concrete tile drains. Product availability may necessitate using larger diameter and/or length of pipe outlets.

The tile drain should extend into the outlet pipe 6 in. (0.15 m) minimum. The joint is to be tightly sealed so as to be leakproof. Concrete grout can be carefully placed in the space between the tile drain and the outlet pipe and filter cloth wrapped around the joint.

Install the outlet pipe immediately after digging the trench. Backfill material should be well compacted in 4 in. (100 mm) layers. The backfilled ditch/stream bank should be seeded immediately. A recommended seeding mixture is creeping red fescue at 18 lbs/acre (20 kg/ha) and bird's-foot trefoil at 11 lbs/acre (12 kg/ha). See OMAFRA Factsheet, "Seeding of Erosion Control Projects", Agdex 751.

In unstable soils, an anti-seepage collar may be required. The collar prevents water from tracking along the outside of the outlet pipe and causing a washout.

Figure 3. An Anti-Seepage Collar on an Outlet Pipe

Anti-seepage collars may be purchased from suppliers of drainage materials. They may also be constructed of light gauge metal, heavy polyethylene on a frame or concrete. An anti-seepage collar should have minimum dimensions of 30" x 30" (76 cm x 76 cm) for outlet pipes 10 ft. (3 m) in length. For longer outlet pipes, increase the collar dimensions by 6 in. (15 cm) total for each 2 ft. (0.6 m) increase of length over 10 ft. (3 m); e.g., 16 ft. (5 m) outlet pipe length requires a 48 in. x 48 in. (122 cm x 122 cm) anti-seepage collar.

A rodent grate on the outlet pipe is essential and should be in place when the pipe is installed. The grate should be hinged to allow cleaning and have openings with a maximum width of ¾ in. (20 mm).

Figure 4. Hinged Rodent Grate

The lower tips of the grate fingers should not overlap the pipe invert, but should swing freely inside the pipe.

When it is necessary to construct a title drainage outlet in a very high ditch bank, erosion can be prevented by the following methods:

1. A properly designed drop pipe structure to move the water down to the lower elevation. This structure could be sized large enough to serve as a junction box for several main lines. This drop pipe structure with an optional surface water inlet is illustrated in Figure 5. Also see OMAFRA Factsheet, "Drop Inlet Spillways", Agdex 751, for further information. The surface water inlet should be avoided if the tile drain may have winter flow, e.g., springs, since this could cause blockage by ice buildup. A trash guard or inlet grate should be secured on the drop pipe inlet to prevent small children or animals from entering.
2. Installing a non-perforated plastic main and outlet pipe as shown in Figure 6.

Figure 5. Drop Pipe Structure with Optional Surface Inlet

A. Surface Inlet with Trash Guard
B. Grassed Berm
C. Tile Drain Outlet Pipe with Rodent Gate
D. Geoxtextile Filter Cloth
E. Riprap or Equivalent Material
F. Rigid Outlet Pipe

Figure 6. Sloped Outlet Pipe

There should be no surface flow over the ditch bank at the tile drain outlet location. Where it is necessary to allow surface water to enter a ditch, a properly designed drop structure, e.g., Figure 5, or a rock chute spillway should be constructed. See OMAFRA Factsheet, "Use of Rock in Erosion Control Projects", Agdex 751.

The location of all drain outlets should be indicated by a marker which is highly visible above crops and tall grass (Figure 7).

Figure 7. A Good Outlet Marker. Black or Red Silhouette on Yellow Background. Mount on 10 Ft. "T" Bar or Pipe.

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Maintenance

A tile drain outlet must be kept clean and in good condition or the drainage system cannot function properly.

An inspection should be carried out in spring, fall and after severe storms to check for silting, debris, erosion, settlement and misalignment. All problems should be corrected immediately.

It is very important that the watercourse into which the tile outlet empties be maintained in an efficient working condition. Weeds, tall grass, brush, old fences, fallen trees, and any other debris should be removed. If not removed, the water flow is slowed down causing siltation and possible submergence of the tile outlet. Check culverts or bridges downstream for possible blockage and water backup.

Before doing any construction work along a stream or streambank, e.g., installing a tile outlet pipe, contact the Ministry of Natural Resources for prior approval.

Further information on drain maintenance may be obtained in OMAFRA Factsheet, "Maintenance of the Drainage System", Agdex 553.

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Assistance

Qualified drainage and erosion control contractors are available for the design and construction of tile drainage outlets. All projects must comply with existing legislation where applicable, e.g., Drainage Act, Lakes and Rivers Improvement Act, Fisheries Act, etc.

Related Links

• OMAFRA Factsheet, "Seeding of Erosion Control Projects", Agdex 751
• OMAFRA Factsheet, "Drop Inlet Spillways", Agdex 751
• OMAFRA Factsheet, "Use of Rock in Erosion Control Projects", Agdex 751
• OMAFRA Factsheet, "Maintenance of the Drainage System", Agdex 553

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