ground water harvesting
TRANSCRIPT
WELCOME
WELCOME
LWM 608 GROUND WATER ENGINEERING (2+1)
NAMITHA M RID. No: 2015664502
M.Tech. (Land & water management engg.)
AEC & RI, KUMULURTamil Nadu Agricultural University
GROUNDWATER HARVESTING
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
SUB-SURFACE DYKES
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
Main advantages of groundwater dykes
Submergence of land can be avoidedLand above reservoir can be utilizedNo evaporation loss from the reservoir
takes placeNo siltation in the reservoir takes placeCollapse of dams can be avoided.
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)
GROUND WATER SHAFTS
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
www.youtube.com/watch?v=c8BAXP5aibI
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
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
How to harvest rainwater?
Broadly there are two ways of harvesting rainwater:
(i ) Surface runoff harvesting
(ii) Roof top rainwater harvesting
Surface runoff harvesting:In urban area, rainwater
flows away as surface runoffThis runoff could be caught
and used for recharging aquifers by adopting appropriate methods.
Roof top rainwater harvesting:System of catching rainwater
where it fallsRainwater is collected from the
roof of the house/buildingIt can either be stored in a tank
or diverted to artificial recharge system
contd…Less expensive and very effectiveHelps in augmenting the ground
water level of the area.
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
Roof catchment
Catchment for collecting the rainwaterStyle, 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
Drain pipes
Pipes of suitable size, made of PVC / Stoneware
To drain off the roof top water to the storm drains
GuttersChannels 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
Rectangular gutters
Semi-circular gutters
Down pipePipes that carries the rainwater from
the gutters to the storage tankDown 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
Most Common Arrangement of Down Pipe
Down Pipe
First flush pipeDebris, dirt and dust collect on
the roofs during non-rainy periodsA 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
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.
First flush pipe
Filter unit Filtration forms the most important
process in the purification of waterIt involves allowing water to pass
through a filter media e.g. sand.Filtration involves removal of
suspended and colloidal impurities present in water
Depending on the type of filtration, the chemical characteristics of water may be altered and the bacterial content may be considerably reduced
Storage tankUsed to store the water that is
collected from the Roof topsSmall-scale water storage:
Plastic bowls, buckets, jerry cans, clay of ceramic jars, cement jars, old oil drums etc.
Large scale water storage: Bigger tank with sufficient strength and durability
Construction materials: RCC, masonry, Ferro-cement, PVC
Collection sumpSmall 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
Pump unitHand 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.
TYPICAL ROOF TOP HARVESTING SYSTEM
Methods of Roof Top Rainwater Harvesting
Storage of Direct useRecharging ground water
aquifers
Storage of Direct useRain 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
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
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
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
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 coversBottom of pit should be filled with
filter media.
contd…Capacity of the pit can be designed on the basis of catchment area, rainfall intensity and recharge rate of soilDimensions of the pit: 1 to 2 m width and 2 to 3 m deep depending on the depth of pervious strata
Suitable for recharging of shallow aquifers, and small houses
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.
contd…Usually made for harvesting the
surface runoffLength of the trench is decided as
per the amount of runoff expectedSuitable for small houses,
playgrounds, parks and roadside drains.
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
f) Percolation Tanks
Artificially created surface water bodies, submerging a land area with adequate permeability to facilitate sufficient percolation to recharge the ground water
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
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
contd…Nesting of birds on the roof should be preventedTerraces should not be used for toilets either by human beings or by petsProvide gratings at mouth of each drainpipe on terraces to trap leaves debris and floating materials
contd…Provision of first rain separator
should be made to flush off first rainsDo not use polluted water to
recharge ground waterGround water should only be
recharged by rainwater.
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
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
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
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
Just remember…
THANK YOU….!!!!