Maintenance of the Drainage System
Table of Contents
A subsurface drainage system will repay any time and effort involved in maintenance. Even though the system is well constructed and expected to last a lifetime, it will not do so unless it is carefully maintained.
Vigilance is important. If a new subsurface drainage system is given careful maintenance for two or three years, it will require little effort thereafter, for within that time any weak spots in the drain line, and over sections in the backfill which have developed can be remedied.
Given four things, an under drainage system should serve a lifetime. They are: (1) good quality pipe; (2) the best possible design; (3) proper installation, and (4) continued maintenance.
It is important to preserve good maps of a drainage system if proper maintenance is to be provided. The maps should show the location of all ditches and underdrains, their size and depth, and their grade and distance apart. As repairs or extensions are made, the maps should be revised.
Deviations in construction from the original plan should be recorded on the map. The contractor should leave his plan of the drains with the owner.
The owner, for his own records, should make simple pencil sketches which provide the above mentioned information if a formal plan has not been made. These should be kept with the property deed so that even though there are changes in ownership, the information is kept on the farm.
Open ditches can be kept in efficient working condition only by careful maintenance. Trees, brush, and weed growth in the ditch slow down the water, causing excessive silting; this submerges the drain outfalls and reduces the ditch capacity. Trees, weeds, logs, brush, old fencing, and other debris should be cleared from the channel. These are a real hazard where culverts or bridges may be blocked by this refuse.
Burning and the application of chemicals are sometimes effective weed control, but the use of chemicals may create a hazard to livestock that use the drainage water for drinking purposes, or cause pollution downstream. A permit is required for burning and for the use of chemicals.
Figure 1. Ditch needing repair. Bottom is silted, banks are unstable and fence collects debris.
A good grass sod on the ditch banks will reduce maintenance problems.
Stock should not have access to the ditch either when the banks are saturated during freezing and thawing weather. Pigs should not be allowed in the ditch at any time.
The ditch will have to be mowed. Side slopes should be four feet horizontal for each foot vertical. After mowing, the vegetation should be used for hay. If left, it will wash downstream, collect at culverts and bridges, and cause local flooding. Check the ditch banks for erosion. The ditch may have to be widened to decrease velocity, increase capacity, or keep it on course. Rock gabions or other forms of bank protection may have to be used in critical areas to protect the banks.
When row crops are planted at right angles to the ditch, do not permit individual furrows to drain directly into the main ditch as the water will seriously erode the bank. Collect the water in a small head ditch for disposal into a sodded water-way. Controlling entry of the water to the main ditch in this manner also reduces silting.
Where abrupt changes in grade occur in a ditch, a sod chute, masonry drop structure, or pipe should be used to prevent erosion of the ditch bed.
Compared with open ditches, subsurface drains require little care if they are properly installed. The chief difficulty is keeping the outfalls in good condition. The outfall should be protected against washing or erosion of the ditch bank or backfilled trench. Examine outfall head walls for scour and undermining. Look for cracks, settlement and shifting that will misalign the drain. The outfall may be protected by using a 3 m length of pipe at the end of the drain line where it discharges into the ditch. Corrugated metal pipe, available from your drain pipe supplier, or other suitable pipe, may be used. The pipe should be sufficiently durable to resist ice or fire damage. It should extend into the ditch far enough that the flow will not erode the ditch bank. To prevent burrowing animals such as muskrats, rabbits and foxes from entering the drain pipe, a vertical grill or flap gate should be attached to the end of the outlet pipe.
Shallow drain tile
Shallow drain tiles are a hazard with modern farming methods, since deep cultivation and heavy machinery often crack or break clay tile or crush corrugated plastic drain tubing. The drain pipe should be protected as much as possible by steel pipe culverts across lanes and roads.
There are not many crops of commercial value which will have their roots that grow into drain lines and clog them. Some trees, however, such as willows, tamarack, elm, elder, poplar, and soft maples, will cause trouble if they are within 15 to 25 m of a drain. These trees should be removed or root-proof pipe or tubing used in their vicinity. If roots of trees enter the drain, it will usually have to be dug up, although a sewer-cleaning rod may clear them out. Roots from annual crops such as sugar beets will usually clear themselves when the crop is harvested. Difficulties with roots occur only in drains that carry water in dry parts of the year.
Figure 2. A good drain outlet with rodent guard and erosion protection.
Crop rotations and methods of cultivation that maintain a good soil structure help to keep drains working, especially in heavy clay soils. Drainage is also improved by growing deep-rooted legumes such as alfalfa or sweet clover.
Plugged tile drains
When there is a stoppage in a subsurface drain, water may rise to the surface at the point of the stoppage. The drain should be dug up at the wet spot and repaired. Broken drain tile or wide cracks cause cave-ins in surrounding soil; at a sign of the smallest surface hole, the damage should be repaired before too much silt enters the subsurface drainage system. Silt boxes and catch basins are often installed at crucial points in the system. These should be inspected and cleaned annually. Their covers should fit tightly and be locked.
Renovation of subsurface drains that have become filled or partly filled with sediment should be considered only when the cost of renovation does not exceed 70% of the cost of a new drain.
Clay or concrete drain tile can be dug up, cleaned and relaid. However, it is not generally economical to dig up and salvage drain tile 150 mm or less in diameter. It may pay to salvage larger sizes, if sound. Digging and relaying should only be considered where the drain tile has not been damaged, carelessly laid with wide spaces between the tiles, or not protected with a cover material to exclude sediment.
Lateral drains can often be cleaned through the use of sewer-cleaning rods if the deposit is only for a short stretch of pipe. Thick deposits over the length of the pipe are difficult to remove.
Cleaning subsurface drains uses the same procedures as those used with sanitary sewers. Holes are dug down to the drain at intervals of 10 to 25 m, depending upon the size of the drain and the amount of sediment to be removed. A short section of the drain is removed to allow a fabricated 6 m diameter steel rod with a hook or corkscrew end, or short- jointed sewer rods, to be inserted into the drain. It may be convenient to dig the hole below the level of the drain as a temporary sediment basin.
The steel rod with the corkscrew end is inserted from the lower end of the drain until resistance is encountered. The rod is screwed into the sediment and removed. This process is repeated. After the rod has been pulled through the drain several times, it is advisable to clean the drain further with a ball of barbed wire or a chain. Flushing, as described below would also be advisable.
Sewer rods are inserted into the drain in a similar manner to the corkscrew-end rod. The rods may be used plain or with various tools on the end such as scoops, hooks and augers.
Special drain flushing equipment is available. The nature of the deposit in the drain governs the success of the procedure.
To flush and clean a drain, a reasonable supply of water must be available. One method to consider is using an irrigation system. A large volume of flow rather than high pressure should be used. The effect of jetting with high pressure will not be felt any great distance down the drain. If the water supply is limited, a catch basin, or hole at the upper end of the plugged section will serve as a water reservoir. Block off the upper end of the drain and fill the catch basin or hole with water, then remove the block and allow the water to flush suddenly through the drain. This simple procedure of flushing may solve the problem.
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