ground water harvesting

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….!!!!