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Rainfall results in the formation of stormwater. Stormwater that is not absorbed by the ground due to impermeable pavement or hard surface, spills over to the road or hard surface, is collected by the underground drainage system, called stormwater drainage system.
The purpose of civil drainage is to collect rainfall runoff from all across the city and discharge it slowly to the downstream river or natural water catchments. Stormwater drainage systems frequently collaborate with the environment, channelling, attenuating, and discharging stormwater through natural features such as lakes, ditches, ponds, swales, streams, etc.
Water rushes off hard surfaces such as roads, parking bays, rooftops, pathways, and driveways into stormwater drains. In an urban setting, stormwater drains out to the smaller pipes that connect to larger stormwater pipes, and that finally connects to oversize drains or pipes that transport the water to the outfall points such as streams, and creeks, rivers, and/ or the ocean.
The storm system is distinct from the sewage system and just caters to rainwater and groundwater. It also prevents flooding by attenuating surface water. The storm sewer system that drains surface water directly to the nearest outfall such as stream or pond or river, is connected to the drainage system that you usually see on the roads, footway, and parking bays”.
The sewage water that comes from the household such as the kitchen sink or toilet in your home, is untreated water and therefore goes first for the treatment and then discharges to the nearby outfall points. Stormwater is normally not significantly contaminated, so they need a relatively simpler treatment process before discharging to the outfall points such as streams, lakes, rivers, or the ocean.
When rainwater does not drain away through typical drainage systems or does not trickle down to the permeable ground earth, but instead lies on or flows over the ground, surface water flooding occurs. The responsibility of managing or controlling the risk of surface water flooding comes under the purview of the lead local flood authority or agency.
The poor drainage system can cause flooding, resulting in property loss and possibly causing people to relocate to avoid the floodwaters. Flooding can also wreak havoc on water supply infrastructure and pollute home water supplies. Following are some well-known common causes of poor drainage systems:
A sustainable drainage system (Suds) is a natural way to manage surface water that can be employed in any form of development:
Here are four programs that change stormwater from a waste to a resource, ranging from building thriving wetlands to reducing the demand for potable water supplies:
Stormwater is water that drains into a street drainage system from rain and other sources and discharges to the downstream river or pond or creeks. Flooding and bank erosion are prevented by stormwater drainage systems.
Water from households and businesses is the main source of wastewater. Before wastewater is discharged to the nearby streams or creeks, it is very important to treat them.
Stormwater management is the attempt to limit rainwater or melted snow runoff into streets, open ground, and other locations while also improving water quality. Stormwater is filtered when it is trickled down to the existing ground soil and eventually fills the aquifers or runs into nearby streams and rivers.
When heavy rains fall, however, the saturated earth produces surplus moisture that seeps across the ground and then to the storm drains and finally to the downstream ditches. It caters to debris, eroded soil mass, bacteria, chemical substances, and other forms of pollutants and is therefore treated (by the downstream defender) before discharging to the stream or river just before the outfall point.
In urban settings, impervious surfaces like road pavement, footways, rooftops obstruct the rainwater from naturally soaking into the existing ground. Instead, the stormwater rushes into the storm drain system, through gully & pipe network, drainage ditches, etc, and its causes flooding, contamination, turbidity (or muddiness), sometimes overflowing storm and sanitary sewer systems, and finally damages the infrastructure and properties.
Stormwater management and green infrastructure, on the other hand, aim to collect and reuse stormwater in order to preserve or reinstate natural hydrologists. Stormwater management is primarily concerned with retaining stormwater and eliminating pollutants.
Stormwater management includes porous surfaces that allow rain to trickle down into the ground soil. It also manages grey infrastructures such as culverts, orifices, storm sewers, and traditional piped drainage networks, and aims to restore or mimic the natural water cycle.
Integrated water management (IWM) of stormwater helps to minimize or eliminate various potential issues such as the health of rivers or waterways and challenges of the water supply system due to the rapid urban agglomeration. IWM is commonly associated with green infrastructure management and prefers to be involved during the early stages of the design process.
It helps to identify and mitigate major roadblocks at the early stage of design and a well-integrated infrastructure can be developed. Infrastructure development and urban growth result in increased demands for robust surface water drainage systems.
Although climate change and reduction in the green field are two very important factors to consider while designing the proposed drainage system. It is recommended to consider a 20% uplift in surface water quantity due to the climate change factor and maintain the greenfield runoff rate at the outfall location.
That means provision of an attenuation system, stormwater harvesting (to decrease the amount of water that can cause a potential for flooding), infiltration (to reestablish natural groundwater recharge), bio-retention or biofiltration (e.g., rain gardens) to accumulate and treat runoff and discharge it at a controlled rate (by flow control devices) to lessen the impact on the down streams, and wetland treatment solutions are some non-exhaustive solutions to be explored by the designers.
The most common solution is to provide land-based treatment such as attenuation ponds, infiltration trenches, bioswales, permeable paving, etc to reduce stormwater runoff. Engineered, manufactured items can also be used to accomplish comparable, or possibly better, effects than land-based systems.
The ideal LID solution balances the anticipated outcomes (runoff and contamination management) with the associated costs. IWM, is still in its early days, bringing together components of drainage, hydrology, ecology, and the recognition that old-style drainage solutions only push issues downstream, putting the environment and natural water supplies at risk.
I hope this blog will help you understand the stormwater drainage system and its associated advantages, disadvantages, etc.
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