RAIN WATER HARVESTING

RAIN WATER HARVESTING

1. WELCOME WELCOME

2. LWM 608 GROUND WATER ENGINEERING (2+1) NAMITHA M R ID. No: 2015664502 M.Tech . ( Land & water management engg .) AEC & RI, KUMULUR Tamil Nadu Agricultural University GROUNDWATER HARVESTING

3. Ground water dykes (Sub-surface dykes) Subsurface dyke is a barrier impermeable to water, placed underground to control the groundwater flow in an aquifer, and to raise the water table Also known as ground water dams

4. SUB-SURFACE DYKES

5. Contd … Main purpose - Arrest the natural flow of ground water and increase the storage within the aquifer Water levels in upstream of ground water dam rises and saturate the otherwise dry part of aquifer

6. Main advantages of groundwater dykes Submergence of land can be avoided Land above reservoir can be utilized No evaporation loss from the reservoir takes place No siltation in the reservoir takes place Collapse of dams can be avoided.

7. GROUND WATER SHAFTS Most efficient and cost effective technique to recharge unconfined aquifer overlain by poorly permeable strata Surplus water can be recharged to ground water. Diameter: 0.8 m (drilling) to 2m (manually excavated)

8. GROUND WATER SHAFTS

9. Shallow shafts: backfilled by inverted filter boulders, gravel and sand Deeper shafts: lined, not necessarily completely backfilled Shafts ends in more pervious strata below confining layer, without touching water table

10. www.youtube.com/watch?v=c8BAXP5aibI

11. WATER HARVESTING MEASURES Conscious collection and storage of rainwater to cater to demands of water, for drinking, domestic purpose & irrigation is termed as Rainwater Harvesting  

12. Why harvest rainwater ? To arrest ground water decline and augment ground water table To beneficiate water quality in aquifers To conserve surface water runoff during monsoon To reduce soil erosion To inculcate a culture of water conservation  

13. How to harvest rainwater? Broadly there are two ways of harvesting  rainwater: ( i )  Surface runoff harvesting                  (ii)  Roof top rainwater harvesting

14. Surface runoff harvesting : In urban area, rainwater flows away as surface runoff This runoff could be caught and used for recharging aquifers by adopting appropriate methods.

15. Roof  top rainwater harvesting : System of catching rainwater where it falls Rainwater is collected from the roof of the house/building It can either be stored in a tank or diverted to artificial recharge system

16. contd … Less expensive and very effective Helps in augmenting the ground water level of the area.

17. Components of the roof top rainwater harvesting system Roof catchment Drain pipes Gutters Down pipe First flush pipe. Filter unit Storage tank. Collection sump. Pump unit

18. Roof catchment Catchment for collecting the rainwater Style, construction and material of the roof determine its suitability as a catchment Roofs made of corrugated iron sheet, asbestos sheet, tiles or concrete can be utilized as such Thatched roofs are not suitable

19. Drain pipes Pipes of suitable size, made of PVC / Stoneware To drain off the roof top water to the storm drains

20. Gutters Channels fixed to the edges of roof all around to collect and transport the rainwater from the roof to the storage tank Shape: Rectangular or semi-circular Made of either plain Galvanized Iron sheets or cut PVC pipes or split Bamboo

21. Rectangular gutters Semi-circular gutters

22. Down pipe Pipes that carries the rainwater from the gutters to the storage tank Down pipe is joined with the gutters at one end, whereas the other end is connected to the filter unit of the storage tank PVC or GI pipes of 50mm to 75 mm (2 inch to 3 inch) diameter are used

23. Most Common Arrangement of Down Pipe Down Pipe

24. First flush pipe Debris, dirt and dust collect on the roofs during non-rainy periods A first flush system can be incorporated in the roof top rainwater harvesting systems to dispose off the ‘first flush’ water so that is does not enter the tank

25. Contd … A separate vertical pipe is fixed to the down pipe with a valve provided below the ‘T’ junction After the first rain is washed out through first flush pipe, the valve is closed to allow the water to enter the down pipe and reach the storage tank.

26. First flush pipe

27. Filter unit Filtration forms the most important process in the purification of water It involves allowing water to pass through a filter media e.g. sand. Filtration involves removal of suspended and colloidal impurities present in water

28. Depending on the type of filtration, the chemical characteristics of water may be altered and the bacterial content may be considerably reduced

29. Storage tank Used to store the water that is collected from the Roof tops Small-scale water storage: Plastic bowls, buckets, jerry cans, clay of ceramic jars, cement jars, old oil drums etc.

30. Large scale water storage: Bigger tank with sufficient strength and durability Construction materials: RCC, masonry, Ferro-cement, PVC

31. Collection sump Small pit is normally dug in the ground beneath the tap of the storage tank for collecting water form the storage tank Constructed in brick masonry Size of collection pit shall be 60 cm x 60 cm x 60 cm

32. Pump unit Hand pump or a power pump fitted to the storage sump facilitates lifting of water to the user Size of the pump has to be decided depending upon the consumption of the stored water.

33. TYPICAL ROOF TOP HARVESTING SYSTEM

34. Methods of Roof Top Rainwater Harvesting Storage of Direct use Recharging ground water aquifers

35. Storage of Direct use Rain water collected from the roof of the building is diverted to a storage tank Water from storage tank can be used for secondary purposes such as washing and gardening etc Most cost effective way of rainwater harvesting

36. Recharging ground water aquifers Commonly used recharging methods are:- a)          Recharging of bore wells                 b)         Recharging of dug wells. c)         Recharge pits                                    d)         Recharge Trenches e)         Soak ways or Recharge Shafts     f)          Percolation Tanks

37. a)  Recharging of bore wells       Rainwater collected from rooftop is diverted through drainpipes to settlement or filtration tank Filtered water is diverted to bore wells to recharge deep aquifers Optimum capacity of settlement tank/filtration tank is designed on the basis of area of catchment, intensity of rainfall and recharge  rate

38. b) Recharging of dug wells. Dug well can be used as recharge structure Rainwater from the rooftop is diverted to dug wells after passing it through filtration bed Cleaning and desalting of dug well should be done regularly  to enhance the recharge rate

39. c) Recharge pits     Recharge pits- Small pits of any shape constructed with brick or stone masonry wall with weep hole at regular intervals Covered with perforated covers Bottom of pit should be filled with filter media.

40. contd … Capacity of the pit can be designed on the basis of catchment area, rainfall intensity and recharge rate of soil Dimensions of the pit: 1 to 2 m width and 2 to 3 m deep depending on the depth of pervious strata

41. Suitable for recharging of shallow aquifers, and small houses

42. d) Recharge Trenches Provided where upper impervious layer of  soil is shallow Trench excavated on the ground and refilled with porous media like pebbles Size: 0.50 to 1.0 m wide and 1.0 to 1.5 m deep.  

43. contd … Usually made for harvesting the surface runoff Length of the trench is decided as per the amount of runoff expected Suitable for small houses, playgrounds, parks and roadside drains.

44. e) Soak ways or Recharge Shafts Provided where upper layer of  soil is alluvial or less pervious Bored hole of 30 cm dia. up to 10 to 15m deep, depending on depth of  pervious layer Bore should be lined with slotted/perforated PVC/MS pipe to prevent collapse of the vertical sides

45. f) Percolation Tanks Artificially created surface water bodies, submerging a land area with adequate permeability to facilitate sufficient percolation to recharge the ground water

46. Built in big campuses where land is available and topography is suitable Surface run-off and roof top water can be diverted to this tank Water accumulating in the tank percolates in the solid to augment the ground water

47. Precautionary measures for harvesting rain water Roof or terraces uses for harvesting should be clean, free from dust, algal plants etc. Roof should not be painted since most paints contain toxic substances and may peel off Do not store chemicals, rusting iron, manure or detergent on the roof

48. contd … Nesting of birds on the roof should be prevented Terraces should not be used for toilets either by human beings or by pets Provide gratings at mouth of each drainpipe on terraces to trap leaves debris and floating materials

49. contd … Provision of first rain separator should be made to flush off first rains Do not use polluted water to recharge ground water Ground water should only be recharged by rainwater.

50. contd … Before recharging, suitable arrangements of filtering should be provided Filter media should be cleaned before every monsoon season During rainy season, the whole system should be checked before and after each rain

51. contd … At the end of the dry season and just before the first shower of rain is anticipated, the storage tank should be scrubbed and flushed off all sediments and debris

52. STREAM FLOODING Least costly surface water spreading methods Surface spreading method: Infiltration of water from the surface of the soil through the vadoze zone to the saturated part of the aquifer

53. Surplus water from the canal or stream is diverted to the adjoining areas through a delivery canal Embankments are made on two sides of the area to ensure proper contact time and water spread

54. Just remember… THANK YOU….!!!!