Surface drainage systems are canals that are created for runoff water. They contain shallow ditches that are dug in a parallel pattern. Knowing the different types of surface drainage systems, their purpose, and how to choose will allow you to decide on the best route for a given property.
The Purpose
The purpose of surface drainage systems is to keep water from flooding or pooling on property. The longer water sits stagnant, the more susceptible it is to becoming contaminated by outside influences. Some water will undoubtedly be absorbed into the ground and surrounding foliage; however, an improperly sloped yard, lack of surface drainage systems, or excessive precipitation falling could cause issues.
Whether the diversion or removal of this excess water in an orderly fashion comes from constructed drains, land shaping, or grading to guide the water to drains, it must happen. Improved channels maintain the water that eventually is collected by natural bodies of water in the area, or by sewer systems to be cleaned, filtered, and resupplied.
Advantages
As touched on briefly, the advantages of implementing surface drainage systems are that it minimizes the length of time water is ponded. Prolonged saturation of soil restricts gas exchange within the soil and root system of plants. It also prevents cultural operations and can inundate crops and essentially kill them.
Have you ever noticed a patch of land that floods regularly, and the water never seems to drain and is muddy and patchy regarding plant growth? This is because prolonged saturation which can choke crops or cause nutrient loss in soil.
Design Goal
The whole reasoning behind the various designs of surface drainage systems is to execute a surface drainage plan that’s effective. There are many factors you should take into consideration when mapping these systems out. The goal is to shape the land into a watershed. Every single body of water has a watershed, which is where the water is drained or “shed” into larger bodies of water. Rainfall water drains into streams and rivers, and those into larger bodies of water such as the sea or the ocean.
The watershed conveys the water runoff into a drainage system, whether it’s a type of basin, a trench drain, or a storm sewer. There will be a detrimental impact on a surface with an improper surface drainage system, which will then affect the subsurface drainage. ABT offers polycast trench drains that fit seamlessly in concrete. These high-quality drains require less onsite labor, are incredibly versatile, fire-resistant, and well-suited for a variety of applications. The polymer concrete is not degraded, as different substances such as salt, oil, alkalis, and most acids pass through it. Finally, it contains pre-sloped and non-sloped drain channels, amongst other important features that make it an excellent drain solution.
Types
When looking at different types of surface drainage systems, here are four main possibilities and some of their subgroups.
Open Drains
Shallow
Shallow, open drains can be created with the use of a hand shovel. They are never deeper than one foot. Their purpose is to help remove water in shallow depressions. Though they direct water to larger drains or streams, a shallow drain is only suited for draining small areas and is considered more of a temporary arrangement.
Medium Depth
Medium depth open drains range between a foot to a meter deep. Typically, an excavator is used to dig these into a V-shaped trench with a flat bottom. It has a gradient that must be steep enough to allow water to flow through swiftly without causing damage to the walls or bottom of the drain. These are most suited for areas that are flat.
Large
Large open drains can be wide and several meters in depth. A dragline excavator, bulldozer, or scraper may be used in the creation of a large open drain. These types of drainage systems are used to evacuate large volumes of water.
Humps and Hollows
This is exactly what it sounds like. Parallel humps are shaped into the surface with hollows in between them. The humps help shed excess moisture, which then is collected in the hollows that serve as shallow surface drains. The two features work together to create a series of lateral surface drains. From there, water is discharged into headland drains. The spacing between humps depends on the speed at which the water needs to be removed. The range can be between ten and twenty meters. The greater the space, the slower the water will discharge.
Levees
Levees are usually formed on land with a gradient where soil is removed to create these forms of levees on the channels’ downslopes. It keeps surface runoff from building velocity while flowing to keep the land from eroding. Levees have to follow the lay of a slope, and their water flow has to move gently to avoid landslips. It is ideal that levees are spaced between thirty and fifty meters apart. The channel could erode quickly if the construction does not carefully account for the establishment of a grass cover immediately after creating a levee.
Grassed Waterways
Grassed waterways are typically shallow and often narrow. They are used to regulate the outflows from drains going down slopes to help prevent erosion. These can only be used where there is a dense stretch of grass. The size and shape of the waterway determine the amount of water that can be evacuated and the steepness of the slope in grassed waterway surface drainage systems.
There are many different types of surface drainage systems, and utilizing both natural and manufactured elements can provide the necessary relief to an area where flooding often occurs. Other terminology to become familiar with includes subsurface drainage, slope, and downspouts. Surface drainage systems are not only the first defense against pooling water, but they are also a necessary mode of transportation to the next phase of water collection. The more useful and effective these systems can be, the higher the purity of the runoff collected and the area around it.
The main takeaways regarding which surface drainage system is best for a particular area will depend on many things. You’ll need to consider where the area is—if it’s in a field-type area, you’ll need a natural option; if it’s in a populated area, you’ll want to seek a commercial product that can withstand traffic, conditions, toxins, and time. Your decisions will also be heavily based on the sloping of the land and how much water passed through the area. While some systems are meant to remove large quantities of water from an area in a certain amount of time, others are either designated to divert a smaller volume of runoff or work more slowly.
