Friday 27 November 2015

Green Drainage for Urban Area

An urban area must have robust water drainage system. The rainwater seeps into the soil but the excess rainwater goes into the drainage system. With proper techniques and maintenance of the drainage system, the risk of flood can be reduced. Otherwise after mild to heavy rainfall, the excess rainwater flows towards low level areas and causes safety risks. A perfect water drainage system for any urban area includes small drainage systems in residential and commercial units for effective water drainage of that urban area as a whole. Water drainage techniques and processes are discussed here with an example of a house in England where the drainage system was efficiently applied.  In addition to such kinds of small drainage systems, utilization of the green spaces of an urban area as drainage areas increases the efficiency of water drainage. Maintaining proper water drainage of an urban area is discussed with an example of using vegetated areas in China.    
Water Drainage System for a Residential Unit
A water drainage system was designed and maintained for a house that was reported by Scholz (2004). The residential unit was in Sandy Lane (Bradford, West Yorkshire England) and the rain water drainage system was built using the technique of pond system. The drainage system included a vegetated attenuation pond and a vegetated infiltration basin. These both were small ponds to store and maintain the runoff rain water. There was aquatic vegetation in the infiltration basin to improve its infiltration properties. There was a separate sedimentation tank in which the rainwater was to be drained. The sedimentation tank and attenuation pond together could carry up to 1.9m3 of the runoff water and the additional infiltration basin had a capacity of 1.8m3. That was a reasonable amount that this system could manage before letting the runoff water escape. The depth of infiltration basin was 40cm. Two rain gauges were fitted between attenuation pond and infiltration basin. Infiltration rates were found out to determine the infiltration properties of the runoff water that is going into the infiltration basin. Sampling and evaluation of the runoff water was done weekly. The runoff water was evaluated for temperature, BOD5, total and suspended solids, water conductivity, turbidity, dissolved oxygen, pH, many nutrients analysis, and total concentration of elements. After sometime of this setup, there was algal growth in the infiltration basin which was removed manually from time to time as required. This algal growth was reduced using barley straw, zooplankton and tadpoles to improve the workability and life of this design.
The benefits of this water drainage system included tackling of the excess rainwater runoff as well as recycling of the collected water. The attenuation pond had the water quality that could be used for irrigation and other recycling purposes.   
Application of Ecohydrology Technique for Water Drainage
When the vegetation areas of a city are used properly as a part of water drainage system, the rainwater can be controlled to a large extent. Ecohydrology is the system of finding the solution of problems such as rainwater drainage by utilizing the potentials that are embedded within the ecosystem itself. Analysis of these potentials and balancing them with societal objectives can result in cost-effective and capable water drainage system. In Beijing, China an ecohydrology technique was evaluated by Li (2012) to tackle the water drainage and water logging. A vegetated area that was concaved down was used for rain water infiltration. The concaved down area was at lower elevation than its surroundings. The concave surface was totally permeable as it was constructed using porous bricks and porous concrete. That permeable layer was allowing rainwater infiltration. The design was perfect to absorb rain water that was running off towards it. Furthermore, along with addressing water drainage the system was enabling evotranspiration and balancing the water cycle. The benefits of using this system is that it is aesthetic, creative, cost-effective, it can be applied to small area, and it offers optimum solution to water drainage problem.
Due to heavy rainfall and inadequate water drainage systems urban areas are at risk of casualties, overall economic fall and traffic jams. Management of rainwater drainage is important for sustainable and risk free urban areas. When there are good urban designs that are addressing the problem of water drainage then the quality of life automatically becomes better. Importance of water drainage is discussed with two examples. One example is of water drainage system of a house. The rain water that was collected through that technique could be recycled such as in car wash. The other example explains the usage of green spaces of a city as a water drainage system which also provided environmental benefits like evotranspiration. These both systems if used in combination to one another can give long lasting and cost-effective results in solving water drainage related issues.

Li, C. (2012). Ecohydrology and good urban design for urban storm water-logging in Beijing,           China. Ecohydrology and hydrobiology, 12(4), 287-300.

Scholz, M. (2004). Case study: design, operation, maintenance and water quality management of       sustainable storm water ponds for roof runoff. Bioresource Technology, 95, 269–279.

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