Rwh presentation

02/05/2023Training Module for MBSE AMBAJOGAI COE 1


WHAT IS RAINWATER HARVESTING??


Rainwater Harvesting


The scarcity of water is a well-known fact. In spite of higher average annual rainfall in India (1,170 mm, 46 inches) as compared to the global average (800 mm, 32 inches) it does not have sufficient water.

Most of the rain falling on the surface tends to flow away rapidly, leaving very little for the recharge of groundwater. As a result, most parts of India experience lack of water even for domestic uses.

Surface water sources fail to meet the rising demands of water supply in urban areas, groundwater reserves are being tapped and over-exploited resulting into decline in groundwater levels and deterioration of groundwater quality.

This precarious situation needs to be rectified by immediately recharging the depleted aquifers. Hence, the need for implementation of measures to ensure that rain falling over a region is tapped as fully as possible through water harvesting, either by recharging it into the groundwater aquifers or storing it for direct use.

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WHY RAIN WATER BE HARVESTED?

To conserve & augment the storage of ground water

To reduce water table depletion

To improve the quality of ground water

To arrest sea water intrusion in coastal areas

To avoid flood & water stagnation in urban areasTraining Module for MBSE AMBAJOGAI COE

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WHAT IS RAIN WATER HARVESTING ?

It is the activity of direct collection of rain water

Rain water can be stored for direct use or can be recharged into the ground water aquifer

Training Module for MBSE AMBAJOGAI COE


RWH IS MOST SUITABLE WHERE ...

groundwater is scarce groundwater is contaminated terrain is rugged or mountainous seismic & flooding events are common the aquifer is at risk of saltwater

intrusion population density is low electricity & water prices are rising water is too hard or mineral laden


HOW TO HARVEST RAINWATERBroadly there are two ways of

harvesting rainwater

(i) Surface runoff

harvesting

(ii) Roof top rainwater harvesting


METHODS OF RAINWATER HARVESTING – Broadly there are two ways of

harvesting rainwater Surface runoff harvesting Roof top rainwater harvesting


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


ROOF TOP RAINWATER HARVESTING

It is a system of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchments, and the rainwater is collected from the roof of the house/building. It can either be stored in a tank or diverted to artificial recharge system. This method is less expensive and very effective and if implemented properly helps in augmenting the ground water level of the area.


2. Roof catchment systems

System componentsDomestic rainwater harvesting system consist of:

• a collection surface,• a storage tank, and• guttering or channels to transport

the water from one to the other.

Peripheral equipment sometimes incorporated:

• a first-flush system,• a filtration equipment, and• settling chambers


TYPES OF FILTERS USED FOR RAIN WATER HARVESTING

1. Sand Gravel Filter

These are commonly used filters, constructed by brick masonry and filleted by pebbles, gravel, and sand as shown in the figure. Each layer should be separated by wire mesh.


2. Charcoal Filter

Charcoal filter can be Made in-situ or in a drum. Pebbles, gravel, sand and charcoal as shown in the figure should fill the drum or chamber. Each layer should be separated by wire mesh. Thin layer of charcoal is used to absorb odor if any.


3. PVC- Pipe filter This filter can be made by PVC pipe of 1 to 1.20 m length; Diameter of pipe depends on the area of roof. Six inches dia. pipe is enough for a 1500 Sq. Ft. roof and 8 inches dia. pipe should be used for roofs more then 1500 Sq. Ft. Pipe is divided into three compartments by wire mesh. Each component should be filled with gravel and sand alternatively as shown in the figure. A layer of charcoal could also be inserted between two layers. Both ends of filter should have reduce of required size to connect inlet and outlet. This filter could be placed horizontally or vertically in the system.


3. Ground & rock catchment systems

Large (top) and small (left) ground and rock catchment (bottom right)Source: MBUGUA unknown; http://www.irc.nl/redir/content/download/128508/350879/file/TP40_7%20Rain%20water%20harvesting.pdf [Accessed 1.6.2010]

System componentsGround & rock catchment systems consist of:

• a collection surface,• a storage tank, and• guttering or channels


CONTOUR TRENCHES


Gully plugs and nala bunds help to control the flow of water, sedimentation and recharge ground water aquifers

Gully plugs and nala bunds4. Watershed management


DIFFERENT TYPES OF RAINWATER HARVESTING IN INDIA• Tankas

Tankas (small tank) are underground tanks, found traditionally in most Bikaner houses.

• KhadinA khadin, also called a dhora, is an ingenious construction designed to harvest surface runoff water for agriculture. Its main feature is a very long (100-300 m).

• Vav / vavdi / Baoli / BavadiTraditional stepwells are called vav or vavadi in Gujarat, or baolis or bavadis in Rajasthan and northern India

• Ahar Pynes This traditional floodwater harvesting system is indigenous to south Bihar.

• ZingsZings are water harvesting structures found in Ladakh. They are small tanks, in which collects melted glacier water.


RAIN WATER PATTERN IN INDIA Total annual rainfall in India: 400

million hectare-meters (area x height) India’s area: 329 million hectares If evenly spread, average height:

1.28m Actual distribution:

Highly skewed area-wiseThar desert receives less than 200mm

annually, while Cherrapunji receives 11,400mm

But almost every part of India receives at least 100mm annually

Key: even 100mm annual rainfall sufficient if harvested properly and where it falls


TANKA

Tankas (small tank) are underground tanks, found traditionally in most Bikaner houses.

Built in the main house or in the courtyard. Circular holes made in the ground, lined with fine polished lime, in which raiwater was

collected. Tankas were often beautifully decorated with tiles, which helped to keep the water

cool. The water was used only for drinking. If in any year there was less than normal rainfall and the tankas did not get filled,

water from nearby wells and tanks would be obtained to fill the household tankas. The tanka system is also to be found in the pilgrim town of Dwarka where it has been

in existence for centuries. It continues to be used in residential areas, temples, dharamshalas and hotels.

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KHADIN (OR DHORA) Practiced in Jaisalmer area

Not enough rain to fulfill crop requirements

Designed to harvest surface runoff water for agriculture.

Its main feature is a very long (100-300 m) earthen embankment (khadin bund) built across the lower hill slopes lying below gravelly uplands.

Sluices and spillways allow excess water to drain off.

The khadin system is based on the principle of harvesting rainwater on farmland and subsequent use of this water-saturated land for crop production.

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KUI 10-12 m deep pits dug near tanks to

collect the seepage. Kuis can also be used to harvest rainwater in areas with meagre rainfall.

The mouth of the pit is usually made very narrow. This prevents the collected water from evaporating.

The pit gets wider as it burrows under the ground, so that water can seep in into a large surface area.

The openings of these entirely kuchcha (earthen) structures are generally covered with planks of wood, or put under lock and key.

The water is used sparingly, as a last resource in crisis situations.


NADIS, TALABS, LAKES Nadis

Natural surface depression which receives rain water from different directions

They receive their water supply from erratic, torrential rainfall.

Can lead to heavy sedimentation and siltation Trees can prevent some of this Dredging out the sediment before monsoon can

also helpCan lose water by evaporation

Talabs, lakes are similar Toba is similar as well – natural

depression with a natural catchment area


BAVDI Traditional stepwells are called vav or vavadi in

Gujarat, or baoris or bavadis in Rajasthan and northern India.

They were secular structures from which everyone could draw water.

Most of them are defunct today. Stepwell locations often suggested the way in which

they would be used. Within or at the edge of a village - utilitarian purposes

and as a cool place for social gatherings. Outside the village, on trade routes - resting places.

When stepwells were used exclusively for irrigation, a sluice was constructed at the rim to receive the lifted water and lead it to a trough or pond, from where it ran through a drainage system and was channeled into the fields.


SCHEMATICS OF A DUG WELL


METHODS OF RECHARGING SUBSURFACE AQUIFERS 1. Through recharge pit. 2. Recharge through abandoned hand

pump. 3. Recharge through abandoned dug

well/open well. 4. Through recharge trench. 5. Recharge through shaft. 6. Recharge trench with bore.


Catchment Area

• Rooftop• Land surface

Collection Device

• Storage tanks• Rain barrel • Water cistern

Conveyance System

• Gutters• Down-pipes• Pumps

WHAT DO WE NEED TO DO WITH WATER?

Slow it, Spread it, Sink it!



Catchment Area/Roof- the surface upon which the rain falls

Gutters and Downpipes- the transport channels from catchment surface to

storage Leaf Screens and Roofwashers

- the systems that remove contaminants and debris Cisterns or Storage Tanks

- where collected rainwater is stored Conveying

- the delivery system for the treated rainwater, either by gravity or pump Water Treatment

- filters and equipment, and additives to settle, filter, and disinfect

RWH System Components


Rainfall quantity (mm/year) Rainfall pattern Collection surface area (m2) Runoff coefficient of collection (-) Storage capacity (m3) Daily consumption rate (litres/capita /day) Number of users Cost Alternative water sources

Factors affecting RWH system design


Catchment Area/Roof- the surface upon which the rain falls

Gutters and Downpipes- the transport channels from catchment surface to

storage Leaf Screens and Roofwashers

- the systems that remove contaminants and debris Cisterns or Storage Tanks

- where collected rainwater is stored Conveying

- the delivery system for the treated rainwater, either by gravity or pump Water Treatment

- filters and equipment, and additives to settle, filter, and disinfect

RWH System Components


ROOF TOP RAINWATER HARVESTING


Diameter Of pipe (mm) Average rate of rainfall in mm/h

50 75 100 125 150 200

50 13.4 8.9 6.6 5.3 4.4 3.3

65 24.1 16.0 12.0 9.6 8.0 6.0

75 40.8 27.0 20.4 16.3 13.6 10.2

100 85.4 57.0 42.7 34.2 28.5 21.3

125 - - 80.5 64.3 53.5 40.0

150 - - - - 83.6 62.7


DO'S AND DON’TS

Harvested rainwater is used for direct usage or for recharging aquifers. It is most important to ensure that the rainwater caught is free from pollutants. Following precautionary measures should be taken while harvesting rainwater:-

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.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……… continued


References1.Texas Guide on rain water harvesting

2. “A Water Harvesting Manual for urban areas” issued by CentreFor Science and Environment

3. Paper on “Rain Water Harvesting” written by Sri. KaushalKishore , Materials Engineer, Roorkee published in CE&CR ,May 2004

4. Indian Standard Guidelines for Rain Water Harvesting in hillyareas by roof water collection system” IS 14961:2001

5. Indian Standard “ Drinking Water Specifications” IS 10500 :1991

6. Indian Railway Works Manual 2000

7. www.rainwaterharvesting.org

8. www.aboutrainwaterharvesting.com

http://www.rainwaterharvesting.org/


Happy rainwater harvesting

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