Top 10 Reasons for a Rain Garden
 Make Your Soil Sponge-Like
 Reducing Hardscape

Water-Harvesting Earthworks and Landforms

Building water-harvesting earthworks into your landscape is the simplest way to capture the stormwater that would normally run off your property and instead, store it in the soil. They provide passive and low maintenance irrigation, filter pollutants and can add beauty, interest and resilience to any landscape. They can contribute to a reduction of flooding and erosion on your property as well as downstream. A variety of techniques and shapes can be used, depending on the specific needs and topography of a given landscape. 

For assistance with design or installation, see our resources section.

Note: Before incorporating any earthworks into your property, it is crucial to understand the various soil types, slopes and percolation rates of your site. Please see our Primer on Safety and Legal Considerations for Rainwater Harvesting in the MMWD Service Area.

Berms, Basins & Swales

Berms, basins and swales can be dug by hand, can cost nothing to install, and can reduce the need for irrigation, saving you money on your water bill!

A berm is a raised mound of soil.  It can:
  • add visual height and interest to a flat or sloping garden
  • edge a basin to help temporarily hold stormwater and infiltrate it into the soil
  • be a planting bed for groundcover or other plants
  • act as a "high-and-dry" raised pathway through a garden
  • hold rocks or boulders to create a more natural look
  • be any shape, size and length, but is generally longer than it is high
A basin or swale is a low area or depression in a landscape. It can:
  • reduce erosion and flooding on your property
  • collect rainwater temporarily, allowing it to percolate slowly into the soil and recharge the aquifer
  • direct moisture into the soil in areas you want to hydrate (i.e.; trees, beds)
  • direct stormwater runoff away from areas with undesirable pooling (i.e.; your foundation) and into the landscape
  • become a fertile planting area as runoff water and nutrients and plant roots and decay improve the soil structure 

A few things to know about building berms:
  • They can be built with the soil you dig out to create a basin or swale.
  • The top of a berm should be level and gently tamped to avoid erosion.
  • They should incorporate an overflow spillway (a low point on the berm) for runoff during large storm events. 
A few things to know about building basins or swales:
  • They are one of the quickest, simplest ways to take advantage of the rainwater where it lands.
  • They can be located uphill from areas you want to hydrate, or downhill from areas with undesirable pooling.
  • They should have a level bottom so that water can percolate slowly and evenly into the soil.
  • They can be mulched and planted with native or climatically appropriate plants that like to have their "feet wet", or hidden altogether by filling them with wood chips or gravel. Swales can be disguised as a dry creek bed.
  • They can fill up with organic matter and debris, and may need to be cleaned out periodically to maximize the holding capacity.
  • Swales are built on contour, perpendicular to the grade, and shaped in a variety of ways, from a crescent to a long, narrow line. Basins tend to be more bowl-like in shape.
Here's a link to "How to Dig Swales". The method shown is for a contour berm and swale on a slope. It was designed to reduce erosion caused by runoff, and feed water to trees below it.

Diversion Swales

Diversion swales direct stormwater runoff to water-harvesting earthworks. They can be used to gradually drain and direct overflow water from one water-harvesting earthwork to another and help create fluid movement of rainwater runoff through a property. They are usually planted with native grasses, groundcover or other plants.

Infiltration Basins

Infiltration basins are shallow, bowl-like mulched depressions dug into the earth that collect rainwater and allow it to percolate into the soil. They are often placed next to roads to collect runoff that is then naturally filtered by plant roots and micro-organisms, or they can be dug around the diameter of tree canopies to deliver rainwater directly to the roots.

French Drains

A French drain is a trench or ditch filled with gravel, rock or rough organic material. It is designed to allow water to infiltrate quickly into the porous spaces in the trench, then slowly percolate into the root zone of surrounding soil. French drains provide a solid, stable surface at ground level that can be walked on and are often used around the perimeters of buildings. They can also be installed beside driveways, patios and other hardscapes to collect runoff.


The shelf-like nature of terraces slow water that would otherwise run down hill, and allow it to spread out and infiltrate the soil. They are built on contour to slopes or hillsides and can be planted. They can be built with or without retaining walls, depending on the soil and slope of the site.

Check Dams

Check dams are low, pervious dams often built with unmortared stone (sometimes in the form of wire-encased gabions) and situated across a minor channel of water to decrease the stream flow velocity, stabilize land and reduce gullies and erosion downstream.