A drainage trench is a trench which is designed to provide drainage. Drainage trenches are used in a number of settings, and they can be designed in an assortment of ways. In order to function effectively, a drainage trench must undergo regular and routine maintenance to keep the trench clean and clear. Failure to maintain the trench can result in problems such as flooding.
Drainage trenches can be used to collect water as it streams from areas of high ground to areas of lower ground, to pull water away from areas of concern, to prevent pooling and puddling, and to drain areas of marshy or wet ground so that they will be usable. People have been using drenches to manage the movement and flow of water for centuries, and some very ancient examples can be seen in cultures all over the world.
One of the classic examples of a drainage trench is the ditch or gutter seen along the roadside in many areas of the world. These drainage ditches allow water to flow freely from the road into the ditch, keeping the roadway dry and preventing the buildup of water. The water which collects from the ditch has an outlet such as a storm drain which allows the water to be harmlessly discharged. More sophisticated roadside trenches may be covered to prevent debris from entering and clogging the trench, and may include other features as well.
Trenches dug to drain a yard, keep the area around a house clear, or provide irrigation drainage are often filled with rock or gravel. Filling accomplishes several goals in a drainage trench. The first is that the filling prevents the walls of the trench from collapsing. Filling also acts as a filter, trapping large particulate matter above the trench so that it will not clog the trench. Finally, filling allows people to walk on ground which has been trenched; French drains, another example of a drainage trench, can be installed under pathways, for example, without impairing freedom of movement in the area being drained.
In order for a drainage trench to work, it needs to have an outlet which will discharge the water in a location where it will not cause problems. The outlet needs to be large and kept clear so that water will not back up in the trench, and it may have a grating to prevent animals from entering the trench. The trench itself also needs to be kept clear so that water diversion will occur along the length of the trench without impedance. This can be accomplished with filters and gratings which are regularly cleaned out, or by periodically recutting the trench to remove dirt and buildups of material.