An open drainage system is a canal created to channel runoff water and prevent flooding or pooling on a property.
If you’re interested in creating an open drainage system on your land, keep reading.
We’ll discuss the different types of surface drainage systems, the purpose of these systems, and how to choose the best one for your property.
Let’s get started.
1. What are open drainage systems?
Open drainage systems, also called natural drainage systems, consist of uncovered channels or ditches that pick up wastewater flows and stormwater.
These systems can remain unlined, but they often perform better if they are lined with concrete, brick, or mortar.
Open drainage systems are designed to accommodate heavy flows of runoff.
While they can handle both stormwater and wastewater, they are not suitable for transporting sewage.
You’re more likely to see open drainage systems used on farmlands than in urban areas.
2. What factors impact stormwater flows?
Did you know that not all water falling as rain needs to be removed by the drainage system?
Some of this water will infiltrate the ground while other water might stand in puddles and eventually evaporate.
The proportion of water that runs over the ground surface and must be carried in the drainage system is known as the runoff coefficient.
Practically speaking, there’s little chance for evaporation during a rainstorm.
Thus, the runoff coefficient that will be used when calculating the size of the drains required is based on the infiltration capacity of the ground.
This will depend on the following factors.
Soil conditions: Water seeps more readily into certain types of soil.
Runoff coefficients are higher in areas of clay soil or rock.
Terrain: Water flows more rapidly down a steep slope, which leaves it less time to infiltrate than when it stands or moves slowly over a flat area.
Runoff coefficients are higher on steep slopes and in densely built-up areas with little vegetation.
Land use: Vegetation traps a lot of the water and loosens the soil, which makes infiltration easier.
Roots and paved surfaces can prevent infiltration.
3. What are the different types of open drains?
There are four main possibilities when looking at different types of surface drainage systems.
There are a few different types of surface drainage systems that utilize both natural and manufactured elements and provide relief to an area during flooding.
Surface drainage systems are not the first or only defense you can use against pooling water.
However, they are a necessary mode of transportation to the next phase of water collection.
Determining the best type of surface drainage system comes down to where the area is, how populated the area is, how sloped the area is, how much water passes through the area, etc.
Open drains
Open drains can be created at different depths: shallow, medium, and large.
Shallow, open drains can be dug with 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 suitable for draining small areas.
It is considered more of a temporary arrangement than a long-term solution.
Medium-depth drains are between one foot to one meter deep.
Normally, 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 quickly without damaging the walls or bottom of the drain.
We recommend medium-depth open drains for flat areas.
Large open drains are wide and several meters deep.
A dragline excavator, bulldozer, and scarper may be used in the creation of a large open drain.
These types of drains are used to evacuate large amounts of water.
Humps and hollows
In this type of open drainage system, parallel humps are shaped into the surface with hollows in between them.
The humps help to shed excess moisture, which is collected in the hallows that serve as shallow surface drains.
The two features work together to create a series of lateral surface drains.
From these surface drains, water is discharged into headland drains.
The spacing between humps helps control the speed at which the water is removed.
It normally ranges between 10 to 20 meters.
When there is more space between humps, the water is discharged more slowly.
Levees
Levees are typically formed on land with a gradient or the banks of a river.
When used on a slope, the purpose is to prevent runoff from building too great a velocity or volume in order to prevent erosion.
Levees will follow the lay of a slope with a gradual decline so that the water flow will move gently and avoid buildup.
It’s best if levees are spaced between 30 and 50 meters apart.
If the construction doesn’t consider the establishment of grass cover immediately after creating the levee, then the channel could erode quickly.
Grassed waterways
Grassed waterways are often shallow and narrow.
They help to regulate the outflows from the drains going down slopes, which prevents erosion.
You can only use grassed waterways when there’s a dense stretch of grass available and the slope is not too great (no greater than 1:4).
The size and shape of the waterway determines the amount of water that can be evacuated as well as the steepness of the slope and the type of soil.
4. What are the advantages of open drainage systems?
Here are some of the reasons that open drainage systems are popular.
Cost
Unlined open drainage systems are easier to construct than covered piping.
They are also less expensive and less labor-intensive.
Farmers can create channels and ditches for open drainage systems on their own as long as they have the correct equipment.
Compared to maintenance on underground pipes, maintenance on open drainage systems is inexpensive and less labor-intensive as well.
Pipes typically need to be dug up for any repairs, which takes longer and costs more.
Surface drainage
Open drains serve as surface drainage because they receive overland flow.
They also collect more silt and rubbish than pipes and permit increased residency of water to break down pollutants.
Installing open drainage systems parallel to roads is a great way to guide water off the roadway and ensure roads remain safe even in wet conditions.
Maintenance
Because they are open in design, these drainage systems are much more accessible and easier to maintain.
Inspections and cleaning operations are easily performed, and any repairs can be made without significant expense.
If you have an open drainage system, we recommend conducting inspections regularly to prevent major issues from occurring.
You can also prevent erosion near open drains by seeding grass or planting vegetation.
5. What are the disadvantages of open drainage systems?
Here are some of the reasons that installing an open drainage system may give you pause.
Expensive investment
While open drainage systems can be affordable, they still come with an upfront cost, especially if you don’t want to install it yourself.
Hiring a professional to install an open drainage system is pricey.
You may also require a permit to install open drainage systems depending on your municipality.
A permit is more likely necessary if the project has multiple channels and deep excavations.
Maintenance
Again, though open drainage systems are more manageable than closed, you still need to maintain your drainage system to ensure it functions properly.
A lot of different maintenance can come with this system, including:
- Clearing blockages from sediment buildup
- Checking that debris doesn’t seal inlet covers
- Replacing any tile that breaks
- Removing water-loving trees (willow, elm, soft maple, and cottonwood) within 100 feet of the drain to prevent blockages caused by overgrown roots, fallen leaves, and branches
- Looking out for ochre, an iron oxide that can build up and block your drainpipe
Contamination
Open drainage systems can contribute to numerous contamination problems when they’re not properly maintained.
Open drains can carry nitrate through the drainpipes, channeling it directly into bodies of water, such as streams, rivers, and lakes.
6. What does open drainage mean in the context of a basement?
When it comes to basements, open drainage refers a series of open channels along the basement walls that allow water to collect and drain from the basement.
A closed system, on the other hand, is one in which vapor barriers are installed over the basement walls to prevent moisture from entering the house.
For years, open drainage systems were the preferred type of system across the country.
However, more recently, contractors have started to install closed systems or convert open systems to closed systems.
The Basement Health Association recommends a closed waterproofing system due to the following reasons:
Radon and soil gases can easily come through an open system.
Bugs and other pests can come up an open system.
Stack effect sucks up ground moisture into the living space through an open system.
Problems like iron bacteria and mildew seem to flourish in an open drainage system.
More ground humidity is drawn up through an open drainage system if the basement also has a dehumidifier.
Homes with open drainage systems typically have higher heating and cooling costs.
However, with all this said, some closed drains have their own disadvantages, including:
They cost more to build because they require deeper excavation, must withstand heavy loads on the street overhead, and require expensive additional works such as manholes and inlets.
Construction defects, deterioration, and accumulation of debris or sediment are more difficult to monitor than in an open drain.
The design, construction, and maintenance of closed drains require more sophisticated engineering techniques.
Mosquito breeding in closed drains is more difficult to control.
Slowly-moving sewage produces gases that can accumulate in a closed drain if it’s not well ventilated.
The primary advantage of closed drains, and the reason they are preferred by engineers and administrators, is that they don’t take up surface space.
They also reduce the risk of children playing in or falling into polluted water.
7. How do you construct DIY drainage?
If you’re interested in installing an open drainage system on your land without assistance, here are some tips that can help you get started.
Obtain a map of the area.
You can normally get a map from your city planning department, land registry, or national survey department.
If you’re not able to get a map, you can use aerial photographs, or a tracing created from the original photograph.
A map with a scale of 1:1000 is best.
Walk around the area.
If you do not currently live on the land, ask neighbors about the probable causes of recent flooding or landslides.
Residents may not have a technical background, but they can typically identify the source of water that has caused issues in the past.
Establish the water levels reached during a specific flood.
Ask residents to describe the depth in terms of their anatomy (ankles, knees, waist).
Use a tape measure to express this as a depth in inches and centimeters and write down the measurement on your map of the area at the appropriate point.
Keep in mind that the greatest depths will be in the lowest-lying areas.
Note the natural direction of flow of wastewater from houses as well as surface water from rainstorms.
Mark existing lines of drainage on the map plus natural streams and manmade channels.
Note the discharge point and the water level in the receiving stream, river, or sea.
Ask the residents about the water level fluctuations in the receiving body of water.
Has the maximum water level been reached in the last few years?
If so, when?
If the receiving body is a river, the water resources or hydrology department may be able to help.
Prepare a sketch of the drainage improvements most necessary and show where the expansion of existing channels is required, where new drains will need to be dug, and where you’ll protect against erosion.
Design the initial improvements starting with unlined channels for flood control and boulder check walls to control erosion.
Excavate the channels working first from the downstream and then upstream.
If you’re working to drain flat areas, fix the downstream end of the stream at the lowest level possible without its becoming submerged by a typical flood of the receiving water body.
Final Thoughts
Drainage systems help to remove the excess water on your land.
When you have a proper drainage system, you’ll prevent flooding in low-lying areas.
This eliminates property damage and health risks.
An open drainage system is just one of the options when it comes to installing drains.
Before you make a decision, weigh the pros and cons and enlist an expert to determine the best type of drainage for your land.
Generally, speaking, open drains are primarily used to collect wastewater that isn’t sewage.
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Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.
Prior to starting Gokce Capital, Erika received a Bachelor of Architecture from the University of Southern California and a graduate degree in Urban Policy from Columbia University. She worked as both an architectural designer and engineer in New York before joining the New York City Department of Housing Preservation and Development.
Erika currently lives in the New York Metropolitan area with her spouse, daughter and cat. She is originally from Chicago and still considers herself a midwesterner at heart.
Erika also loves to read, write and travel (fun fact, she has visited all 50 states and more than 30 countries!). Her new book, Land Investing Mistakes: 11 True Stories You Need To Know Before Buying Land, is now available on Amazon.