Urban drainage
- Created by: rchapman99
- Created on: 21-11-17 14:56
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- Urban drainage
- Infiltration is low and surface runoff is high in urban areas
- Urban areas are covered in impermeable materials. Many urban structures are designed to shed water quickly.
- Infiltration is low in urban areas, so replenishment of groundwater stores is slow. Groundwater feeds rivers, so during drier periods, river discharge in urban areas is low.
- Precipitation is higher in urban areas than in rural areas, and storms are more intense - increased surface runoff.
- Runoff is channelled through man-made pipes, which transport water to rivers and streams.
- Low infiltration rates, high surface runoff and channelling of water means that water enters rivers quickly. This gives a short lag time and high peak discharge, with a fast return to base flow.
- Catchment management aims to reduce urban drainage issues
- Catchment management is a way of managing rivers and improving drainage systems by looking at the whole river catchment, and the interactions between water and land.
- It aims to minimise issues such as flooding, drought, water pollution and erosion in sensitive areas, and to improve river ecosystems.
- There are two main methods that can be used to manage river catchments
- Hard engineering - man-made structures such as dams, floodwalls and reservoirs, which are often used to prevent flooding and ensure a constant water supply. However, these schemes are often expensive and can disrupt natural systems.
- Soft engineering - uses knowledge of the river basin and its processes to try to work with nature. It involves land use management. It can also involve river restoration and conservation. It is generally cheaper and it can improve the local environment. However, planning restrictions can limit the construction of new homes and businesses, and land use management is hard in areas that are already urbanised.
- Decisions about what methods to use are made by experts in water management rather than residents - what is best for the catchment as a whole may not be best for all individuals, so some residents and communities may feel ignored.
- Catchment management schemes can also be disruptive.
- SUDS can make urban drainage more sustainable
- Sustainable Urban Drainage Systems (SUDS) aim to imitate natural drainage systems, rather than channelling water through pipes and drains.
- They use several methods to decrease flooding, water pollution and drought in urban areas.
- Vegetated trenches increase interception of rainfall, and retention basins store water. They help to increase infiltration and water storage - decreases is runoff and channel flow, which lowers flood risk. Also decreases the amount of pollutants entering watercourses.
- Vegetated roofs intercept rainfall and increase evapotranspiration, which reduces flood risk.
- Containers on the roofs of buildings catch and store rainwater for reuse - helps to reduce drought risk.
- SUDS are more sustainable than traditional urban drainage methods because they work with the natural environment to improve drainage and water quality. Vegetated trenches and roofs also provide new habitats and increase biodiversity.
- Enfield is restoring its water systems
- River restoration and conservation aims to restore river systems to a more natural state. It can help to reduce flood risk, decrease water pollution, create new habitats and increase biodiversity.
- One are that is restoring its rivers is Enfield, north London. It has regular floods.
- The area is heavily urbanised - this has caused problems for drainage and water quality.
- The spread of urban structures has increased surface runoff and channel flow. This has increased the frequency and intensity of floods - over 9,000 homes at risk.
- Surface runoff from roads has increased levels of pollutants such as oil and heavy metals in watercourses.
- Water pollution also comes from domestic sources - up to 10% of houses in Enfield have wastewater pipes that feed directly into rivers.
- In 2012, a project began to restore rivers in the area, with the following aims
- Reduce flood risk and limit the impacts of flooding on habitats and residential areas.
- Reduce surface runoff from roads and pollutants entering rivers in order to improve water quality.
- Provide more habitats for wildlife and new recreational areas for residents.
- The project has used SUDS to help restore river systems and meet these aims.
- Vegetated trenches have been created around roads to absorb runoff and decrease flood risk.
- Rain planters have been installed in schools - these collect rainwater and manage the flow of water into drains, lowering flood risk. This also provided opportunities to educate children about water management.
- Wetlands have been constructed to improve water quality.
- Lots of groups have been involved in the project
- Defra and Thames Water are providing funding. In 2012, Defra granted £340,000 to the project to construct more SUDS.
- Local residents - reactions from the community have been very positive. Volunteers have been involved in water quality monitoring and litter pickups.
- Local schools - Thames21 offers education sessions for local schools to increase engagement. In 2015, 1,000 students were involved in litter picking and wildlife monitoring.
- The project is ongoing, but it's had some successes already.
- Flood risk seems to be reduced.
- SUDS have reduced ammonia levels in Salmons Brook by 67% and nitrogen levels by 43%.
- Populations of eels and some species of insects have increased.
- However, pollution and litter are still an issue in many rivers.
- Infiltration is low and surface runoff is high in urban areas
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