To control water coming down a hillside, the simplest solution is to construct a French drain or rock drainage ditch. To stop water from running downhill and prevent erosion, terrace the hillside or construct a berm to divert water. When applying any of these methods, plant grass or deep-rooting plants that help to hold the soil in place.
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5 Ways to Control Water Running Downhill
If stormwater is coming downhill, flooding your yard, and causing erosion, you need to put measures in place to protect your property and keep your lawn and garden dry. Uncontrolled water running downhill can cause mudslides, flood your home, and kill plants. Even at lower rates, excessive water on a hillside strips nutrients and minerals from the soil, leading to a barren slope. To control stormwater and protect your property, implement one of the following methods.
Install a French Drain
You can control stormwater by digging a drainage ditch that contains gravel and a perforated pipe—a French drain. The key is to plan a drainage ditch so that water flowing downhill enters the side of the ditch. However, the ditch must still be sloped downhill so that the water flows safely down to a dry well or water garden.
- Plan a drainage trench that captures water on the hillside and channels it safely downhill. At a minimum, it must slope downward 1 inch (2.5 cm) for every 10 feet (3 meters) of distance.
- A single trench that slants or curves across the hillside can be effective. So can a system where smaller slanted trenches feed into the main trench that runs straight down the hill.
- Using the proper tools, dig and construct a drainage trench using gravel, landscape fabric, and perforated pipe.
- Terminate the trench at a water garden, dry well, or pond.
Any water that flows into the side of the trench will filter up through the gravel and enter the perforated pipe, which will then safely conduct the water downhill to a place of your choosing. We recommend a dry well, which will distribute the water safely underground.
Swale or Rock Drainage Ditch
A swale or pipeless drainage ditch is another great option for controlling water downhill runoff. Similar to a French drain, it can be dug down into the hillside. Alternatively, if hillside runoff floods flat portions of your yard, you can construct a swale near the foot of the hill to conduct water away.
- Plan your ditch or swale to capture water and conduct it downhill.
- To channel water along a pipeless trench, make sure it has a slope of at least 6 inches (15 cm) every 10 feet (3 meters). This will prevent stagnant water from collecting.
- You can construct a functional rock drainage ditch using gravel, landscape fabric, and decorative stones.
A rock drainage ditch can work as a manmade creek bed, channeling water downhill. You can even build smaller trenches that feed into it. With a few tweaks, you can give your rock drainage ditch a dry creek bed look.
Terrace the Hillside
Terracing a hill is an age-old strategy that stops water from flowing downhill. Not only that, but terracing collects rainwater to feed trees and grass planted on the hill at the same time it prevents soil erosion. This can be a bit more work than digging a drainage trench, but the benefit is you’ll turn your hillside into a thriving garden or orchard. To terrace your hill:
- Plan your terrace: you will essentially need to cut steps into your hillside and hold them in place with retaining walls.
- You can use wood, stone, or concrete blocks to construct terrace retaining walls.
- Terrace “steps” should be 4–8 feet (1.25–2.5 meters) wide. Retaining wall height should be no more than half the terrace width.
Start at the bottom of the slope and terrace up the hillside. By creating flat terrace sections, water will soak into the soil instead of flowing downhill.
Construct a Berm
A berm is a mound or raised ridge that diverts water away from problem areas. By constructing a mound garden bed, you can channel stormwater to other areas and prevent it from washing uncontrollably downhill. A great way to use a berm is to channel water toward drainage trenches.
- Construct a raised mound flowerbed or ridge to divert water to a drainage trench or swale.
- Build a berm by bringing in soil and compost, or by digging and mounding areas of the hillside.
- Make sure your berm does not channel water onto neighboring property.
It’s essential to relieve hillside flooding and erosion responsibly. Any berms, swales, or drainage ditches should lead to a safe termination point on your property. Do not divert water into your neighbor’s yard.
Plant the Slope
Trees, plants, and grass on a slope can help manage runoff. Plant roots perform two functions: soaking up excess water and preventing erosion. Whether you’ve installed a drainage ditch or terraced your hillside, it’s essential to follow up by planting the bare soil to help manage stormwater.
- Plant bare areas of your slope with grass, trees, or other plants.
- Plant roots absorb water and prevent erosion.
- A terraced hillside is perfect for fruit trees and herbs. A sloped hill with drainage ditches is ideal for grass.
If you wish to plant trees, shrubs, and other substantial plants, a terraced hillside is your best bet. The stable, flat surface allows for proper soil watering. If your hillside is steeply sloped, plant it with grass or ground cover plants.
How Do You Keep Water From Running Down a Hill?
The best options for stopping water from flowing downhill, where it can damage property and flood your basement are:
- Construct a French drain.
- Build a rock drainage ditch or swale.
- Terrace the hillside to stop soil erosion.
- Build a berm or mound that redirects water.
- Plant the slope with trees or grass to soak up floodwater and hold soil in place.
These strategies yield real results and will protect your home and yard from mudslides and swampy conditions. Even better, they can be constructed on a DIY budget and easily maintained.