Swale Construction in Rocky Terrain — Feasible or Not?

Assessing Rocky Terrain for Swale Construction

Before embarking on a swale construction project in rocky terrain, it’s essential to assess the site’s topography. Walk the land, taking note of the existing contour lines, and identify areas where water naturally collects or flows. Rocky terrain can be challenging, but with proper planning, you can create a functional and effective swale.

Designing Swales for Rocky Terrain

To design a swale for rocky terrain, follow these key steps: (1) Identify the lowest point on the land and design the swale to converge at this location. (2) Use the 1% rule: for every 100 feet of length, the swale should drop 1 foot to ensure adequate water flow. (3) Create a berm on the down-slope side of the swale to help filter and slow down water flow. This berm should be at least 3-4 times the height of the swale. For example, if your swale is 6 inches deep, create a berm that is 2-3 feet high.

Construction Techniques for Rocky Terrain

When constructing a swale in rocky terrain, use the following techniques to mitigate the challenges: (1) Use a ‘V’ shaped trench instead of a straight one, which will help to break up the rock and make excavation easier. (2) Employ a ‘swale within a swale’ design, where you create a smaller swale within the larger one, using the larger swale as a filter to prevent rocks from entering the smaller one. This design helps to reduce the amount of rock excavation needed. (3) Line the swale with a geotextile material or a natural soil like coconut coir to prevent erosion and provide a stable surface for plant growth.