A trench drain is a drain which is made by sinking a trench into the ground to collect water and runoff so that it can be shunted to other locations. Trench drains are among the most basic and ancient of drains, and they can be used in a wide variety of applications. They are also very easy to install, which can make them good choices for dealing with drainage problems in the short term.
In its most basic form, a trench drain is made by digging a trench in an area where the ground slopes down. The downward slope of the ground will encourage the water to flow in the direction of the drain, while the trench will collect the water. Some trench drains are equipped with gratings which are designed to keep large debris out of the drain so that it will remain clear in heavy weather, although the gratings will need to be periodically cleaned.
Roadside ditches are a common example of trench drains. In this instance, the road is built with a slanting surface which encourages the road to shed water, with the ditches catching the water so that it cannot rise and flood the road. The ditches in turn move the water to a lake or another body of water, where it can be discharged. Ditches may also be combined with culverts, which run underneath intersecting roads.
In a version of the trench drain known as a French drain, a perforated pipe is mounted in the bottom of the drain, and the drain is packed with sand or gravel. The water filters through to the bottom of the trench, where it flows into the pipe for disposal, with the gravel acting as a filter. One major advantage of French drains is that once they are installed, they do not interrupt a surface like a lawn or pathway, in contrast with ditches, which will create distinctive divots.
Trench drains can also be utilized for irrigation, with sluice gates being closed or opened as needed to move water around a trench drain system. This crude method of irrigation has been in use for thousands of years, making it one of the oldest agricultural tools in the book. A trench drain system which connects with a stream or lake can greatly increase the amount of arable land in a given region, allowing people to expand their farms and cities.