Digging Swales: A Comprehensive Guide to Water Harvesting

Swales are a powerful permaculture technique for capturing and managing rainwater runoff, allowing it to infiltrate the soil and nourish plants. They are essentially ditches on contour that slow down water flow, preventing erosion and replenishing groundwater reserves. This guide provides a detailed, step-by-step approach to digging swales effectively and safely.

What are Swales and Why Use Them?

Before diving into the ‘how,’ let’s clarify what swales are and their benefits:

* **Definition:** A swale is a shallow ditch dug along the contour of a slope, with the excavated soil mounded on the downhill side to create a berm. This berm often serves as a planting bed.
* **Purpose:** Swales primarily serve to:
* **Slow Down Runoff:** By intercepting surface water, swales reduce the speed of water flow.
* **Increase Infiltration:** Slower water allows more time to soak into the soil, recharging groundwater.
* **Reduce Erosion:** By slowing and capturing runoff, swales minimize soil erosion.
* **Improve Soil Moisture:** The berm created by the swale becomes a consistently moist environment, ideal for planting. This reduces the need for irrigation.
* **Create a Microclimate:** The swale and berm combination create a microclimate that can be more favorable for certain plants.
* **Enhance Biodiversity:** By providing diverse habitats, swales can increase biodiversity in the landscape.

Is a Swale Right for Your Property?

Consider these factors before committing to digging swales:

* **Slope:** Swales are most effective on gentle to moderate slopes. Very steep slopes may require terracing or other erosion control measures.
* **Soil Type:** While swales can benefit most soil types, sandy soils may require amendments to improve water retention. Clay soils may require careful drainage considerations.
* **Water Source:** Swales are designed to capture rainwater runoff. Ensure you have a sufficient source of water to justify the effort.
* **Existing Vegetation:** Consider the impact of swales on existing vegetation. You may need to clear some areas before digging.
* **Water Table:** Avoid digging swales if your water table is very high, as this could lead to waterlogging. Consult with a local expert if you are unsure.
* **Local Regulations:** Check with your local authorities to see if any permits are required for digging swales on your property.

Planning Your Swale System

Proper planning is crucial for successful swale implementation. Here’s how to approach it:

**1. Assess Your Site:**

* **Observe Water Flow:** Pay close attention to how water flows across your property during rain events. Identify areas where water concentrates and causes erosion. This observation is key to determining the best placement for your swales.
* **Identify Contours:** Understand the contours of your land. Swales must be dug along the contour line (a line of equal elevation) to effectively capture and distribute water evenly. Using a contour map (if available) or creating one yourself is highly recommended.
* **Soil Analysis:** Analyze your soil type. This will inform your plant selection for the berm and help you determine if any soil amendments are necessary. Consider a soil test kit.
* **Sun Exposure:** Evaluate sun exposure. South-facing slopes (in the northern hemisphere) will receive the most sunlight, while north-facing slopes will be shadier. This will influence your plant choices.

**2. Determine Swale Placement:**

* **Contour Lines are Key:** Swales *must* be dug along contour lines. Deviation from the contour will cause water to pool in some areas and overflow in others, defeating the purpose of the swale and potentially causing erosion.
* **Spacing:** The spacing between swales depends on the slope of your land and the amount of rainfall you receive. Steeper slopes require closer spacing. A general rule of thumb is to space swales so that the berm of the upper swale is roughly level with the ditch of the lower swale. This allows water to cascade down the slope in a controlled manner.
* **Length:** Swale length depends on the area you want to irrigate and the amount of runoff you expect. It’s often better to have several shorter swales than one long one, as this provides more even water distribution.
* **Outlets:** Consider providing outlets for excess water during heavy rainfall events. These can be natural depressions or strategically placed pipes leading to a drainage area.

**3. Design the Swale Dimensions:**

* **Width:** The width of the swale ditch will vary depending on the amount of water you expect to capture. A wider ditch can hold more water. Typically, swales are 2-4 feet wide.
* **Depth:** The depth of the swale ditch is also dependent on the amount of water you expect to capture and the type of soil. Deeper swales can hold more water but can also become breeding grounds for mosquitoes if not properly managed. A depth of 12-18 inches is a good starting point.
* **Berm Height:** The height of the berm should be sufficient to contain the water in the ditch during typical rainfall events. A height of 12-18 inches is usually adequate.
* **Slope of Berm:** The berm should be sloped gently to allow water to drain back into the ditch. A slope of 1:2 (one foot vertical for every two feet horizontal) is a good guideline.

**4. Select Your Plants:**

* **Water Tolerance:** Choose plants that are tolerant of both wet and dry conditions, as the berm will experience fluctuations in soil moisture. Native plants are often a good choice.
* **Root Systems:** Consider the root systems of your plants. Deep-rooted plants can help to stabilize the berm and prevent erosion.
* **Nitrogen Fixers:** Incorporating nitrogen-fixing plants (like legumes) can improve soil fertility.
* **Edible Plants:** Planting edible plants on the berm can provide a source of food.

Materials and Tools You’ll Need

* **Contour Leveling Tool:** This is *essential* for accurately determining contour lines. Options include:
* **A-Frame Level:** A simple and inexpensive DIY option. Two legs are connected at the top to form an “A” shape, with a level attached to the crossbar. Requires two people for accurate use.
* **Bunyip Level:** Another DIY option using two stakes, a clear tube filled with water, and measuring sticks. Uses the principle that water seeks its own level.
* **Laser Level:** The most accurate and efficient option, but also the most expensive. Projects a laser beam along a level plane.
* **Transit Level:** Used by surveyors and engineers; provides extremely accurate leveling but requires experience to operate.
* **Shovels:** For digging the ditch and building the berm.
* **Pickaxe or Mattock:** For breaking up hard soil.
* **Wheelbarrow:** For transporting soil.
* **Measuring Tape:** For measuring distances and depths.
* **Stakes:** To mark contour lines and swale boundaries.
* **String:** To connect stakes and provide a visual guide for digging.
* **Flagging Tape:** For marking important locations.
* **Gloves:** To protect your hands.
* **Boots:** For working in wet or muddy conditions.
* **Eye Protection:** To protect your eyes from flying debris.
* **First Aid Kit:** For treating minor injuries.
* **Optional Tools:**
* **Mini-Excavator or Tractor with a Backhoe:** Can significantly speed up the digging process, especially for larger projects. However, requires skill and experience to operate safely.
* **Soil Compactor:** For compacting the berm.

## Step-by-Step Guide to Digging Swales

**1. Mark the Contour Lines:**

* **Start with a Reference Point:** Choose a starting point on your slope. This can be a prominent feature or simply a convenient location.
* **Use Your Leveling Tool:** Following the instructions for your chosen leveling tool, identify points that are at the same elevation as your starting point. Place stakes at these points. With an A-Frame, one person holds one leg on the starting point, while the other moves the other leg up or down the slope until the bubble in the level is centered. Mark that spot with a stake. Repeat this process, moving along the contour line.
* **Connect the Stakes:** Once you have several stakes in place, connect them with string. This will give you a visual representation of the contour line.
* **Repeat:** Repeat the process to mark additional contour lines at the desired spacing.

**2. Dig the Ditch:**

* **Follow the Contour Line:** Begin digging the ditch along the marked contour line. Use your shovel to remove soil and create a trench.
* **Maintain Consistent Depth and Width:** Aim for a consistent depth and width throughout the length of the swale. Use your measuring tape to check your progress regularly.
* **Slight Slope towards Ends (Optional):** For long swales, consider a very slight slope (1-2 inches over the entire length) towards one or both ends. This will help to drain excess water away from the swale during heavy rainfall events.
* **Key the Bottom (Important):** “Keying” the bottom of the swale involves creating a slight inward slope on the bottom of the ditch towards the berm. This helps to prevent water from undermining the berm and causing it to collapse. Compact the soil on the key using a hand tamper.

**3. Build the Berm:**

* **Place Soil on the Downhill Side:** Place the soil you excavated from the ditch on the downhill side of the contour line to create the berm. This is what forms the raised planting bed.
* **Shape the Berm:** Shape the berm with a gentle slope away from the ditch. This will allow water to drain back into the ditch if the berm becomes saturated.
* **Compact the Berm:** Compact the berm to prevent erosion. You can use a soil compactor or simply tamp it down with your shovel.
* **Berm Height:** The top of the berm should be roughly level with the original ground level *before* you dug the ditch. This maximizes water capture.

**4. Stabilize the Swale:**

* **Plant Vegetation:** Plant vegetation on the berm to stabilize the soil and prevent erosion. Choose plants that are appropriate for your climate and soil type. Consider using a mix of grasses, shrubs, and trees.
* **Mulch:** Mulch the berm to help retain moisture and suppress weeds. Organic mulches like straw, wood chips, or leaves are ideal.
* **Rock Outlets:** If you have concerns about overflow, create rock outlets at strategic locations along the swale to safely channel excess water away from the berm. Line the outlet with rocks or gravel to prevent erosion.

**5. Test and Adjust:**

* **Observe During Rainfall:** Observe the swale during a rainfall event to see how it performs. Does the water flow evenly along the contour? Does the berm hold water adequately? Are there any areas where erosion is occurring?
* **Make Adjustments:** If you notice any problems, make adjustments as needed. You may need to deepen the ditch, raise the berm, or add more vegetation.
* **Monitor Regularly:** Continue to monitor the swale regularly and make adjustments as needed to ensure it is functioning properly.

## Important Considerations and Safety Tips

* **Call Before You Dig:** Before you start digging, contact your local utility companies to locate any underground lines. This is crucial for safety and to avoid damaging critical infrastructure.
* **Wear Protective Gear:** Always wear gloves, boots, and eye protection when digging. This will protect you from injuries.
* **Be Aware of Your Surroundings:** Be aware of your surroundings and watch out for hazards such as rocks, tree roots, and wildlife.
* **Work in Stages:** If you are digging a large number of swales, consider working in stages. This will allow you to assess the performance of each swale before moving on to the next.
* **Consider Soil Amendments:** Depending on your soil type, you may need to amend the soil to improve water retention or drainage. Incorporating compost or other organic matter can be beneficial.
* **Manage Mosquitoes:** If you live in an area with mosquitoes, take steps to prevent them from breeding in your swales. This can include adding mosquito dunks or planting mosquito-repellent plants.
* **Avoid Over-Watering:** While swales are designed to capture water, it’s important to avoid over-watering your plants. Monitor soil moisture levels and adjust your watering accordingly.
* **Consider Wildlife:** Be mindful of the impact of your swales on wildlife. Avoid creating barriers that would prevent animals from accessing water or food.

## Troubleshooting Common Swale Problems

* **Swale Fills Up Too Quickly:** This could indicate that your swale is not large enough to handle the amount of runoff you are receiving. Consider deepening or widening the ditch, or adding additional swales.
* **Swale Overflows:** This could be due to a lack of outlets or insufficient berm height. Add outlets or raise the berm.
* **Erosion Occurs on the Berm:** This could be due to a lack of vegetation or improper berm slope. Plant more vegetation, add mulch, and ensure the berm has a gentle slope.
* **Water Pools in Some Areas:** This indicates that the swale is not perfectly on contour. Adjust the ditch to maintain a consistent elevation.
* **Plants Die on the Berm:** This could be due to improper plant selection or poor soil conditions. Choose plants that are appropriate for your climate and soil type, and amend the soil as needed.

## Conclusion

Digging swales is a rewarding and sustainable way to manage water on your property. By following these steps and tips, you can create a functional and beautiful landscape that benefits both you and the environment. Remember to plan carefully, work safely, and be patient as you learn and adapt your swale system to your specific needs. Happy digging!