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Storm water management

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calculating run off flow ,,,,, Various methods of managing STORM WATER

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Storm water management

  1. 1. By Vivek (15BCL0153) Varun(15BCL0139) NATARAJAN
  2. 2. Why we need to manage storm water • Because impervious surfaces do not allow rain to infiltrate into the ground, more runoff is generated than in the undeveloped condition. Due to this reduction of level of water table advances and depletion of ground water resource occurs which is a key factor to severe drought and scarcity conditions .
  3. 3. • To avoid flooding in transportation corridors and to control damage to properties • Both cases can cause severe damages and contamination of the environment if sanitation facilities are flooded. This results in high costs and notably massive suffering for the local communities.
  4. 4. He divided special tropical rainfall into the following four classes: (i) Negligible falls: All rainfalls under 12 mm a day unless continuous for several days; also rainfalls 12 to 40 mm a day, when there is no rain. (ii) Light falls: All rainfalls up to 25 mm a day followed by similar or heavier falls. Steady pours of 25 to 40 mm a day, when there is no rain of similar or greater amount before or after that. (iii) Medium falls: Rainfalls from 25 to 40 mm a day when preceded or followed by any but light falls. (iv) Heavy Falls: (a) All rainfalls over 75 mm a day or continuous falls at 50 mm a day. (b) All rainfalls of an intensity of 50 mm or more per hour. Average rainfall for 3 months has been recorded as 916.3 mm
  5. 5. Here F/S=0 P=average rainfall
  6. 6. Total area of VIT is 370 acres, in which urban spread occupies an area of 220 aces. Discharge for concrete floors :- Runoff coefficient[k]=0.85 Avg rainfall i Area = 140 acres = 54 hectres average rainfall = 0.00042 m QP=1/36*K*PC*A Q = 1/36 * 0.85 * 54 * 10000 * 0.00042 = 5.355 cub.m = 5355 litre/hr = 1,15,66,800litre/3 months This is the discharge for normal rainfall.
  7. 7. Dicharge for a peak rainfall , i.e all time record per day = 170.9 mm Q = 1/36 * 0.85 * 0.007 * 56 = 89.25 cub.m/hr = 89250 litre/hr = 192780000 litre/3 months Dicharge for area including grassland and woodland forests :- According to the type of soil present in vellore the Runoff coefficient is taken as [k] = 0.1 Area = 150 acres = 60 hectre Q = 1/36 * 0.1 * 60 * 10000 * 0.00042 = 0.7 cub.m = 700 litre/hr = 1512000 litre/3 months {Discharge for normal rainfall}
  8. 8. Q = 1/36 * 0.1 * 60 * 10000 * 0.007 = 11.66 cub.m/hr = 11660 litre/hr = 251858600 litre/3 months Avg Discharge in pavements = 2613 lt/hr = 5644080 lt/3months
  9. 9. Infiltration trenches are shallow excavations that are filled with uniformly crushed stone (similar to soak pits) to create underground reservoirs for stormwater runoff. The runoff gradually exfiltrates through the bottom of the trench into the subsoil and eventually into the water table. • As the percolation of water depends on the soil conditions also some time some soils are not porous in that case infiltration trenches can be used
  10. 10. Grassed Swales
  11. 11. Pervious paths Pervious pavement is a permeable pavement surface with a stone reservoir underneath. The reservoir temporarily stores surface runoff before infiltrating it into the subsoil or sub‐surface drainage and in the process improves the water quality. Porous materials such as ancient lime mortars and pervious pavements are made using relatively mono graded materials. In the case of pervious pavement this translates as a lack of "fine" materials. Pervious pavement is also sometimes also referred to as “no fines concrete”
  12. 12. Places Where the runflow is more then storage vault systems are adopted . The water settles in a tank and are infiltrated through the gravel and geotextile sheets.
  13. 13. • Perforated pipes use a combination of pipe storage and gravel storage to provide detention and promote infiltration.
  14. 14. Permeable pavers installed
  15. 15.  Blue roofs, also known as controlled flow roof drain systems, provide temporary ponding on a rooftop surface and slowly release the ponded water through roof drains.  Blue roofs have weirs at the roof drain inlets to restrict flow.
  16. 16.  Green roofs consist of a vegetative layer that grows in a specially-designed soil that may sit above a drainage layer.  Green roofs detain stormwater in the void space of the soil media and retain stormwater through vegetative uptake and evapotranspiration.
  17. 17. Weirs with predetermined flow rates at various ponding depths control the release rate from a controlled flow roof drain
  18. 18. Gutters Gutters are channels fixed to the edges of roof all around to collect and transport the rainwater from the roof to the storage tank. Gutters can be prepared in rectangular shapes and semi-circular Strom drains
  19. 19. TREATMENT OF STORM WATER Contaminants in water may include algae, air pollution, bird excrement, and leaves, sand, and dust. Local wells have dealt with these problems for decades. Installation of filtration and purification equipment can remove these contaminants at home as well. First, take measures to keep foreign matter out of the incoming rainwater,flush devices, gutter screens and other screening mechanisms keep the rainwater as clean as possible before it enters the conveyance system. Using screens and filters will greatly reduce maintenance and lengthen the life of the pump and filtration/purification system.
  20. 20. One of the more expensive but effective purification treatments for rainwater is that of a combination of filtration and UV treatment. Physical filters “remove particulates, and the UV-light chamber…kills bacteria and other organisms by exposing them to high-energy ultraviolet light.”  These systems are expensive to install, but also cost quite a bit annually. The UV light stays on all year, so electricity costs are, relatively, quite high.
  21. 21. People commonly use household bleach for this process, which is of concern to some due to the chemical factor. wind up boiling the water first, then adding several drops of chlorines into a quart of rainwater. you should “allow at least 30 minutes for the chlorine to disinfect your water if the water is 70 degrees F or above. Allow up to an hour if the water is near freezing.
  22. 22. This is one of the more labor-intensive purification processes, but it also winds up being a bit more natural in leveraging the sun for purification.  A one-quart Ziploc bag be filled with water, and that the bag be placed on two feet of aluminum foil, shiny side up in a very sunny place. The bag needs to heat for several hours and the water should remain at 160F or higher for at least that long so that waterborne pathogens can be successfully eliminated.
  23. 23. A treatment-train approach to stormwater management involves a range of measures (primary, secondary, and tertiary) that work together to enhance water quality. Primary treatment The aim is to remove gross pollutants and coarse sediment (>5mm in size) and help in the downstream treatment of smaller pollutants. Secondary treatment These measures aim to remove fine particles, sedimentation, and attached pollutants. Tertiary treatment Third-stage treatment measures remove very fine/colloidal particulates, dissolved nutrients, and heavy metals.