Rapid urbanization of cities have resulted in reduced infiltration of precipitation (rain, melted snow etc. also known as “Storm-water”) in the ground. Before land is developed with buildings, railways roadways and agriculture, majority of the storm water soaks into the soil or evaporates. The storm water runoff occurs when the storm water falls over the infiltration surfaces that prevent the infiltration to the ground. The runoff volume increases and causes flooding when it starts accumulating sedimentation, oil/grease, trash, waste material and other matters present in the Environment. This pollutes the storm water in the urban areas which ultimately drains into the lakes and rivers polluting these water bodies. The Storm water management practice comes in place to control and use the storm water runoff.
The primary goal is to manage the water quantity and perform analysis of problems associated with storm water impact. Effective storm water management provides Environmental, social and economic benefits to local communities. When storm water management is effective, water bodies get cleaner, flood risks are reduced, costs due to flood damage are decreased thereby increasing the community quality of life. Green infrastructure practices are considered as the most effective storm water management practice, since it implements low impact development (LID) controls to manage runoff. Some of these techniques may also have important advantages for pollution reduction.
Certain Green Infrastructure Techniques are listed Below
Rainwater collected from roof, driveway, or street is collected & rain gardens are depressed areas that enable it to seep into the ground,that are filled with grasses, flowers, and other plants.
Bioretention Cells (or Bioswales)
Bio retention cells are depressions containing vegetation grown in an engineered soil mixture placed above a gravel drainage bed that provide storage, infiltration, and evaporation of both direct rainfall and runoff captured from surrounding areas.
Vegetative swales are ditches or depressions with sloping sides that are covered with grass and other plants to delay the conveyance of collected runoff and give it more time to infiltrate the native soil beneath it.
Narrow gravel-filled ditches called infiltration trenches are used to collect runoff from impermeable surfaces that are higher up a slope. They offer storage space and more time for runoff collected to infiltrate the native soil beneath.
Green roofs are a variation of a bio retention cells that have a soil layer atop a special drainage mat material that conveys excess percolated rainfall off of the roof. They contain vegetation that enable rainfall infiltration and evapotranspiration of stored water.
Rooftop (Downspout) Disconnection
This practice allows rooftop rainwater to discharge to pervious landscaped areas and lawns instead of directly into storm drains. It can be used to store stormwater (e.g., in a rain barrel) and/or allow storm water to infiltrate into the soil (e.g., into a rain garden or lawn).
Rain Barrels or Cisterns (Rainwater Harvesting)
Rain barrels and cisterns store roof runoff during storms and then release or reuse the water during dry spells. Cisterns offer more storage space than rain barrels and can be either above or below ground.
Continuous Permeable Pavement Systems
Rainfall can instantly flow through permeable pavement and into the gravel storage layer below, where it can slowly seep into the native soil of the location. In block paver systems, rainfall is captured in the open spaces between the blocks and conveyed to the storage zone and native soil below.
Storm water management through Green Infrastructure practices also helps curb the tendency for flash flooding and reduces the risk for flooding.
Through flood risk assessment, flood risk management examines the relationships between physical systems and socioeconomic contexts and works to increase awareness of and response to the dangers of flooding.
The major management tools utilized are Flood mapping and Flood modelling using Softwares such as MODLFOW to perform prediction models in areas with a high risk for flooding. The model is performed utilizing the historical data and current Socio-environment activities in the area to predict the risk for flooding over a time period by providing conceptual models with flood hazards. Flood maps are a form of risk maps and are useful to create documentation that allows policy makers to make informed decisions about flood hazards. Stakeholder engagement is also a useful tool for flood risk management that allows enhanced public engagement for agreements to be reached on policy discussions. Different management considerations can be taken into account including emergency management and disaster risk reduction goals, interactions of land-use planning with the integration of flood risks and required policies.