Rain Garden
Type of Development
New Development
Topography
Hills, Valley
Longevity
Short Term
Environment
Urban
Maintenance
Medium
Cost
Fairly cheap, easy to implement on a community level.
Overview
Rain gardens are shallow to deep depressions filled with flood resistant, native plants that detain and slowly filter stormwater runoff for up to two days. In order to efficiently capture and store rainwater, these gardens are best suited to be a bowl or horseshoe shape. The size of a rain garden can vary widely and can be implemented on a large or smaller, residential scale. California rain gardens often look different than their counterparts in areas with more precipitation, and consist of rocks, shrubs, and native plants that do not require irrigation after their roots have settled. California rain gardens should be designed to be dry most of the year.
Function
Rain gardens reduce runoff in stormwater management systems by directly filtering water into the ground.
Benefit
Rain gardens store storm runoff and filter pollutants so that groundwater is uncontaminated. Not only will groundwater be fresh, it will be recharged through natural percolation and over time reverse compaction and sinking. Rain gardens can be implemented at a city or individual level in backyards and around neighborhoods. Native and ecologically suitable plants will provide strength in the soil and have a higher capacity to filter and store water in the ground. Rain gardens can be built to divide pedestrians and cyclists from vehicular traffic, increasing safety. They are visually appealling and positively impact natural environments.
Dependency
Sunlight, high percolation rates, access to water runoff
Development Considerations
The placement of rain gardens will determine the success of the development. The area must be somewhat flat, with a slope of no more than 15%. The ideal depth will depend on size, with bigger sites being deeper, but no site deeper than 3 ft. If gardens are placed in urban areas, curbs and gutters must be removed or changed to be applicable. For example, curbs should have cuts to allow water to flow into gardens instead of into storm drains. Gardens should not be placed over septic tanks, pipes, or drains. Gardens should be placed at least 5 ft away from buildings or 25 ft if the building has a basement. Areas with limited drainage, like clay soil, require additional elements such as gravel beds and underdrains to prevent waterlogging.
Environmental Considerations
The type of plants depend on how frequently the area will be flooded. Soil percolation is the most important consideration. If soil is too dense and dry, water will not be able to flow through gardens and instead will runoff completely. Water table needs to be considerably below the depth of the garden. Most effective on a small scale.
Maintenance Consideration
Maintenance is minimal due to native plants ability to self regulate. However, invasive plants need to be removed regularly and underdrains become clogged frequently. First years of implementation requires regular maintenance to ensure effectiveness.
Cost Considerations
Fairly cheap, easy to implement on a community level.
Case Studies
Cathedral Park Rain Garden
Portland's Biggest Rain Garden: Portland, Oregon has redeveloped their city to include a multitude of nature based solutions on large scales. One of their most successful implementations was developing 3,600 rain gardens throughout the city. Cathedral Park houses Portland's biggest rain garden.