Rain garden

**1. Rain Garden History and Development:**
– Rain gardens were first created to mimic natural water retention areas before urbanization.
– Residential rain gardens were developed in 1990 in Prince Georges County, Maryland.
– Rain gardens in Somerset subdivision replaced traditional BMP ponds and proved cost-effective.
– Rain gardens reduced stormwater runoff by 75-80% during regular rainfall events.
– Rain gardens have been used as LID tools before being recognized by professionals.

**2. Urban Runoff and its Effects:**
– Urban areas cover natural water pooling areas with impermeable surfaces.
– Stormwater runoff causes pollution, erosion, and flooding in waterways.
– Redirected stormwater is warmer and leads to upset in aquatic ecosystems.
– Pollutants in stormwater runoff include VOCs, pesticides, herbicides, and metals.
– Urban watersheds are affected by greater quantities of pollutants due to anthropogenic activities.

**3. Stormwater Management and Bioretention:**
– Bioretention facilities treat urban runoff, stormwater, groundwater, and in some cases, wastewater.
– Environmental benefits of bioretention include increased wildlife diversity and habitat production.
– Bioretention controls stormwater quantity through interception, infiltration, evaporation, and transpiration.
– Soil quality and microorganism activity are key components of bioremediation.
– Stormwater quality is controlled by settling, filtration, assimilation, adsorption, degradation, and decomposition.

**4. Rain Garden Design and Maintenance:**
– Rain gardens must be designed based on peak runoff rates during severe storms.
– Rain garden plant species should match site conditions and infiltration capacity.
– Bioretention soil mixture typically contains 60% sand, 20% compost, and 20% topsoil.
– Regular maintenance is essential for optimal bioretention system performance.
– Pruning, weeding, and monitoring water levels are key maintenance tasks.

**5. Global Implementation and Research:**
– Rain gardens are part of China’s strategy to slow down stormwater retention in urban areas.
– The Wildfowl and Wetlands Trusts London Wetland Centre features a rain garden in the UK.
– The 12,000 rain garden campaign for Puget Sound aims to build 12,000 rain gardens in Western Washington by 2016 in the US.
– Dr. Allen P. Davis and his team at the University of Maryland have conducted extensive research on rain garden effectiveness.
– Rain gardens play a crucial role in water-sensitive planning and design, as outlined in various publications.