Contact No. : +91-936-950-3625
Welcome to Rain Water Harvester

Water is one of the most commonly used substances on our earth. We need water for all our activities in day-to-day life. Water supply in urban area is always short against the total demand. Surface water is inadequate to meet our demand and we have to depend on ground water. Due to rapid urbanization, infiltration of rainwater into the subsoil has decreased drastically and recharging of ground water has diminished. This scenario requires an alternative source to bridge the gap between demand and supply. Rainwater, which is easily available and is the purest form of water, would be an immediate source to augment the existing water supply by "catching water wherever it falls".
Rainwater Harvesting has emerged as a viable alternative to traditional perennial sources of water in hilly areas, in places where the level of fluoride and arsenic is above permissible limits and in urban areas facing water shortage and flooding during monsoons.
Rainwater Harvesting (RWH) is the process of collecting and storing rainwater in a scientific and controlled manner for future use. Rainwater Harvesting in urban areas include

  • Roof top rainwater harvesting
  • Rainwater harvesting in paved and un-paved areas (open fields, parks, pavement landscapes etc.)
  • Rainwater Harvesting in large areas with open ponds, lakes, tanks etc.

Benefits of Rainwater Harvesting

  • Environment friendly and easy approach for water requirements
  • RWH is an ideal solution for water requirements in areas having inadequate water resources
  • Increases ground water level
  • Improves ground water quality
  • Mitigates the effects of drought
  • Reduces the runoff, which other wise flood storm water drains
  • Reduces flooding of roads and low-lying areas
  • Reduces soil erosion
  • Cost effective and easy to maintain
  • Reduces water and electricity bills

Rainwater Harvesting

  • Traditional Water Harvesting in India underlines the importance of step wells, lakes, tanks, channels etc., as water storage bodies, the basic purpose of which was to establish a chain of water storage structures. However, a vanishing "Lake Culture" due to urbanization and industrialization has caused these systems to be neglected.
  • To make Rainwater Harvesting (RWH) a success, we should have a thorough knowledge of the following:
    geographic location; climate; geology; soil; land use; water requirements; existing water supply system; cost of water; systems & forms of RWH and the potential of harvesting rainwater.
  • RWH has the following unique advantages
    • Capturing rainwater in-situ and augmenting supply water at a marginal cost
    • Replenishing groundwater through recharging of rainwater by using the soil column
    • Reducing pollution and contamination
    • Reducing the water bill for the state exchequer
    • Providing clean and safe water
    • Least capital investment with maximum benefits to households and the city as a whole
  • The demerits of RWH
    • It is dependent on the monsoons and intensity of rainfall.
    • It depends on intensive participation from house level to the city level.
    • It is only a supplementary source and cannot replace the existing supply system completely.

Quality of rainwater harvested
As the primary source of water, rainwater is the purest form of water. Rainwater harvesting not only solves the problem of availability of water, but also provides good quality water.
However, certain precautions need to be taken to ensure that the stored water is not polluted.

  • Keep the roof or the water collection area clean before the rains.
  • Flush the rainwater collected in the first few minutes.
  • Store the collected rainwater in a closed container (avoid sunlight).
  • The quality of water deteriorates in the presence of sunlight and air.
  • Water can be kept clean over a period of five to six months in a clean container stored in an enclosed area protected from sunlight.

Who can harvest rainwater and where?

  • People planning construction of house, modification of house, existing house, etc.
  • From rooftops of Govt. buildings, Institutions, Hospitals, Hotels, shopping malls etc.
  • From rooftops and open areas
  • Farmlands, Public Parks, Playground, etc.
  • Paved and unpaved areas of a layout/city/town/village

Need for rainwater harvesting
Water harvesting is an activity of collection of rainwater and storing in containers for direct use or can be recharged in to the ground.

  • As water is becoming scarce, it is the need of the day to attain self-sufficiency to fulfill the water needs
  • As urban water supply system is under tremendous pressure for supplying water to ever increasing population
  • Groundwater is getting depleted and polluted
  • Soil erosion resulting from the unchecked runoff
  • Health hazards due to consumption of polluted water

Methods
Rainwater Harvesting
Rainwater stored for direct use in tanks above ground or underground sumps or overhead tanks and used directly for flushing, gardening, washing etc.
Ground water recharge
Recharged to ground through recharge pits, dug wells, bore wells, soak pits, recharge trenches, etc.
Rainwater Harvesting potential
Rainwater harvesting potential in urban areas is huge. Considering the availability of rainwater in a residential site of 40 x 60 feet (an area of 2400sq.ft./223 sq.mts.), around 2,23,000 lts of rainwater can be harvested in a location where the rainfall is around 1000 mm or 39.4 inches (Bangalore receives around 1000 mm of rainfall annually). The amount of rainwater that can be harvested from the available rainwater in the plot depends on potential rainfall, catchment area available, collection methods and its efficiency etc.
Rainwater Harvesting for Domestic Applications
Water requirement of a house can be broadly classified into

  • Drinking
  • Cooking
  • Bathing
  • Washing
    • Vehicles
    • Utensils
    • Clothes
    • Floor cleaning
  • Gardening
  • Flushing in toilets

For washing, gardening and flushing toilets, relatively less clean water can be used (secondary use).

Rainwater Harvesting (RWH) can meet all these above needs with suitable RWH techniques.

Water requirement in a house is throughout the year. However, rainwater availability without having facilities to store is limited to number of rainy days and the quantity of rainwater available during the rainy days. Several interventions can be made to enhance the number of days of use of rainwater from number of rainy days to 365 days a year. Parameters, which support rainwater harvesting, are availability of space, willingness to invest, technical suitability of soil structure and geological parameters.

Rainwater Harvesting for Rooftops
Roof Top Rainwater Harvesting
In urban areas, buildings are usually constructed with rooftops of Reinforced Cement Concrete (RCC), Mangalore tiles, Asbestos / galvanized iron / zinc sheets etc. Construction of buildings with the above mentioned material requires roof top rainwater to be removed from building tops and currently been let off into storm water drains outside the plot area (which eventually goes away from the city).
The rooftops being built significantly with hard material, large quantities of rainwater runoff and loss due to evaporation and percolation are very minimal. Thus, rooftop rain water harvesting can be put to good use by storing rooftop water on (a) roof itself (b) ground level (c) below the ground, by using storage devices like masonry tanks / ferro cement tanks / plastic or metal containers.
1. Roof area calculation
Roofs are of broadly two categories - flat roofs and sloping roofs.
Flat roofs when made with reinforced cement concrete normally have waterproofing course on the surface as a finish. The waterproof course is done with a small slope towards the downtake pipes. Usual practice is to use lime surkhi, in recent times a rich cement mortar is used ("muddy" in local parlance), weatherproof tiles are also laid on cement mortar. These types of roofs are ideal for rooftop rainwater Harvesting.
Effective roof area for Rainwater Harvesting
Flat roof:
Calculation of Effective roof area

Divide the roof area into convenient grids and calculate
the area of each grid.

Example A1= X x Y

Add the individual grid area to get the total roof area.
i.e. A1+A2+A3+A4+A5+A6+A7+A8... = A (Total area).

Effective roof area is excluding the peripheral wall thickness
and any other opening.
Sloping Roof:
Calculation of effective roof area

Divide the roof area into convenient grids and calculate each grid area by taking projected length & breadth. Actual surface area i.e. x x y is not considered for the calculation of roof area but the projected area i.e. a x y is considered.

 

Example:

(A1) Area of one part of the roof = a x y

(A2) Area of other part of the roof = a x y

Total area = 2 x a x y

2. Channelisation
Down water pipes made out of PVC, HDPE or cement pipes can be used for transporting rainwater collected from roofs to the filtration system before storing. The size of the down take pipe varies depending on the roof area, which is connected to the down pipe.
3. Filtration
Rainwater collected on the roof is very pure and clean. However, there are many substances, which get mixed up with this pure water on the roof (leaves, bird droppings, dust etc.). These contaminants need to be filtered before the rainwater is stored. There are many filtration systems.
a. Sand bed filter
b. PopUp filter
c. Stabilization tank
a. Sand bed filter:
Sand bed filter is the traditional method where coarse riverbed sand, pebbles and aggregates are filled as layers one above the other in a confined masonry structure. Rainwater is allowed at the top from one end and filtered water is drawn from the other side.

b. PopUp filter:
A simple "PopUp Filter" designed by A.R. Shivakumar of KSCST and it is effectively working for residential buildings and smaller institutional or industrial applications. The "PopUp Filter" has three components (rainwater receptor, flush valve and filter element) rainwater receptor where the rainwater is allowed to flow from down pipes and a flush valve is provided to flush the first flow of the rainwater along with leaves, dust etc. Water received in the receptor flows upwards against gravity through a filter element to filter most of the floating elements and allow water to stabilize in this filtration zone. Rainwater passing through this filter element (which is relatively cleaner), flows out through an outlet, which can be led to storage device. Filter element is mounted on a vertical stabilizer pipe with a friction fit. In the normal course, rainwater gets filtered and flows through outlet into the storage device. Filter element needs to be cleaned periodically during the rainy season to remove the filtered material and to keep the filtration system clean. In the event where the filter is not cleaned and the filter element is getting clogged, The "PopUp Filter" has a built-in safety feature it to push out the filter element from the stabilizer pipe and allow the water to flow out freely. This safety feature will avoid flooding of the rooftop because of clogged filter. The first indication of the filter getting clogged is rainwater flowing out of a vent hole provided on the top of the filter element.

These PopUp filters are simple in design and are very flexible to install in verifying field conditions.
An important feature in filtering is the separation of first flush of rainwater from relatively cleaner and purer subsequent rain.
c. Stabilization tank:
For large volume of rainwater a unique design has been developed by the author to trap light and heavy impurities with out having any filter media. Rainwater is allowed to flow through a series of small tanks and by providing an entry and exit for water at strategic positions, impurities can be trapped in the stabilization tanks for subsequent cleaning. Heavier impurities will get trapped in the first two tanks as the water flows out at the higher level. Lighter and floating impurities get trapped in the third and fourth tanks as the water flows out at the bottom or lower level. Periodic cleaning of these tanks is required to remove the impurities.

4. Storage
Storage of harvested rainwater is possible at various levels
The storage structures may vary from permanent masonry tanks, ferro-cement tanks to plastic or metal tanks. The capacity of storage device can be decided by considering parameters such as roof area, water usage and space availability. Water consumption in a house is throughout the year and water availability from rainfall is for a limited period restricted to number of rainy days in a year. To make rainwater available in non rainy days, storage device need to be designed with an optimum capacity to suit the need / requirement. In Rainwater Harvesting system, storage device is the single most expensive component. Optimum size of the storage device and cost effective methods to store water are the key issues for a viable roof top rainwater harvesting system.


Collection surface
Larger the roof area available for rainwater collection higher is the quantity of rainwater collected. Cleaner and better the quality of rooftop, cleaner and better will be the rainwater collected. Maintenance of the roof surface and keeping it clean has a direct bearing on the quality of water collected.
Rainwater Harvesting Storage facility and Capacity
Rainwater collected on the roof and guided through the down water pipes gets filtered in the filtration system and is available for direct use. Rainwater coming out of the filter may be guided to a storage device for future use. Positioning, size and capacity of the storage container may be decided considering the roof area and the requirement of raw-water. Higher the storage capacity more will be the rainwater availability during the non rainy days. In urban areas, like Bangalore, total rainwater storage capacity of around 8,000 to 15,000 lts would suffice for the requirement of secondary usage (gardening, vehicle washing, cleaning etc.).
Roof yield or potential rainwater from a roof
Roof yield or the potential rainwater from a roof is normally referred to the annual yield from a given roof area. Annual yield is the quantity of water in liters collected from a given roof over a period of one year covering all the rainy days. It is the product of roof area and the annual rainfall.
Example:
a. Roof area of 100 Sq. meters with annual rainfall of 1000 mm (milimeters)
Roof yield = 100 X 1000 = 1,00,000 liters/year
b. Roof area of 1000 sq. feet with annual rainfall of 40 inches
Roof yield = 1000 X 40 X 2.36 (constant) = 94,400 liters/year
Cost of Rainwater Harvesting:
Examples to illustrate, rainwater harvesting can be many and the cost involved also vary from case to case. The parameters that influence the cost of rainwater harvesting are:
� How much rainwater to collect
� Type of surface from where rainwater is collected
� Existing structure and fittings for rainwater collection and flow
� Type and capacity of harvested water storage device
� Method and system of rainwater retrieval system for use from storage device
Considering the above facts, rainwater harvesting can cost as little as Rs. 1000/- and may go up to Rs. 50,000/- for a residential building.
Rainwater Harvesting for those who does not have proper roof
Rainwater can also be harvested by those who does not have proper roof by creating temporary collection surface by using a clean cloth piece (Sari or Doti or Panche)
Four corners of the cloth piece may be tied with separate threads and stretched three feet above the ground and tied tightly to four supports (poles / supports / walls etc.) during a rainy day. As the rainwater falls on the outstretched cloth depressions in the middle will be formed and all the water will get collected at the center. Since the cloth is pours water will start getting filtered through the cloth and starts dripping / flowing down at the center. A vessel or a can be placed to collect this pure rainwater for further storage in an enclosed tank or a larger container for future use.

Illustrations for Rainwater Harvesting at Residential Buildings
Case - I: Keep a water storage tank or a structure below down water pipe, which carry rainwater from roof. Guide the overflow of the tank to the drain on the road side/recharge ground water. Use the collected water for gardening, vehicle washing etc. when required. This water cannot be stored for many days since organic matter coming from rainwater will start decaying in the storage tank and will contaminate water.
Case - II: Rainwater flowing from the roof through down pipes has to be filtered for removing organic/inorganic substances. This filtered water may be allowed to flow directly to a storage device kept on the ground. The overflow of this tank may be connected to the drainage on the rode side/recharge ground water.
Steps involved:
a. Connection from down water pipe to rainwater filter
b. Installation of �PopUp Filter� to tank
c. Installation of storage tank
d. Piping connection from filter to the tank and
e. Overflow of the tank to outside drain/ground water recharge
Process: Flush the first rainwater by opening the flush cap on the filter for few minutes, close the flush cap after all the dirt on the roof is flushed out and clean water starts flowing. Remove the filter cartridge gently from its place and wash it thoroughly under a running tap by gently tapping the filter element with a stick on all sides. The dirt sticking in the filter element gets released and washes off. Replace clean filter element back to its place by gently inserting it in the vertical pipe. Take care not to press it too hard at the end. If pressed too hard, filter element may get locked inside the pipe and may require greater force to retrieve it back and also may not PopUp when the filter is clogged or choked. Allow the filtered water to get stored in tank for future use.
Case - III
In a building having a roof at differential levels or where more than one floor building is involved, rainwater may be allowed to flow from the top most roof through down pipes to roof next below it. Here rainwater has to be guided to flow through the filter to remove organic/inorganic substances. This filtered water may be allowed to flow directly to a storage tank kept on the intermediate roof (may be ground floor roof). Overflow of this tank may be connected to an underground sump or to the drain on the roadside or to recharge ground water.
Steps involved
a. Connection from down water pipe to rainwater filter
b. Installation of "PopUp Filter"
c. Installation of storage tank on the ground floor roof/intermediate roof
d. Piping connection from filter to the tank
e. Connection of overflow from the tank to underground sump or to the out side drain or recharge ground water
Process: Flush the first rain water by opening the flush cap on the filter for few minutes, close the flush cap after all the dirt on the roof is flushed out and clean water starts flowing. Remove the filter cartridge gently from its place and wash it thoroughly under a running tap by gently tapping the filter element with a stick on all sides. The dirt sticking in the filter element gets released and washes off. Replace clean filter element back to its place by gently inserting it in the vertical pipe. Take care not to press it too hard at the end. If pressed too hard, filter element gets locked inside the pipe and may require greater force to retrieve it back when required for cleaning and also may not PopUp when the filter is clogged or chocked. Allow the filtered water to get stored in tank for future use.
Water stored in the tank can be used for gardening, vehicle washing, toilet flushing etc. Since water is stored on the rooftop, there is no need for a pump to pump-up water. Water can be allowed to flow by gravity. The overflow of this tank is connected to a secondary storage at underground sump. Water from the overhead tank can be used first and on using up all water in the overhead tank, water stored in the underground sump can be pumped up for use during subsequent non rainy days.

Ground water recharge
Underground water is one of the important sources of water in urban areas. With increasing urbanization, underground water has been indiscriminately exploited causing depletion in water table and water availability. It is very evident from the number of failing bore wells / open wells that it is unsustainable to pump out water from wells without recharging the same from the rainwater. To reverse the trend or to reduce the effect of over exploitation, ground water recharge need to be taken up in large scale at residential and institutional buildings.
There are many methods of ground water recharge. Following are few methods for recharging ground water using rainwater from rooftops of buildings.
a. Reused plastic barrels method
b. Direct recharge through Open wells and Bore wells
c. Infiltration Gallery for large buildings
d. How to build an Infiltration Gallery?
e. Roads / Trenches
f. Parks and Open spaces
g. Layouts
a) Reused plastic barrels method
This cost effective and simple method has been developed by A.R. Shivakumar. In this method, Overflow of rainwater from the storage structure and water from the roof other than the roof connected to the storage structure may be allowed to flow through a �PopUp Filter�. This filter will filter floating elements and to some extent the silt coming in the water. Relatively cleaner water comes out of the filter and is allowed to flow into ground water recharge gallery.

The ground water recharge gallery is created by using reused plastic oil/chemicals barrels (blue colored drums sold on the road side for construction activities etc.).
These barrels are of around 200 to 220lts. capacity each and are quite strong in their construction. One side of the barrel (top or bottom), which is circular in shape, is cut open.
Depending on the total roof area connected to this infiltration gallery, more number of barrels are used for ground water recharge. The barrels are buried underground with their sides cut open facing down wards.
These empty barrels are buried without filling anything into them. The top of the barrel, which is intact, should be two feet below the ground level. These barrels are placed one beside other and they are connected to each other at the top by a pipe. By doing so, these barrels are placed up side down under the ground at a depth of two feet from the surface. Outflow of the PopUp filter is connected to the first barrel in the row by a pipeline.
Rainwater flowing from the filter flows into the first barrel, which is underground and its bottom cut open. Since the ground below the barrel is porous, water flowing into it infiltrates into the ground. During heavy rainfall, more water stores temporarily in the first barrel and over flows in to the next and later to subsequent barrels. As the height of the water increases in the barrels, percolation level also increases because of water head inside the barrels. In a system of barrels, first barrel in the row receives water and subsequent barrels are interconnected at the top to receive excess rainwater. Last barrel carries the overflow (if it happens) through a pipe into the storm water drain outside the plot. To facilitate the air trapped in the barrels to escape out, an air vent is provided at the last barrel by fixing a vent pipe (Overflow pipe can also act as an air vent).
In the normal situation, where house is not located in low-lying area, (water stagnation during rainy season), one barrel is required to percolate water from a roof area of around 400 sq. ft. However, the percolation from each barrel depends on many other parameters like water table, soil structure, rainfall in the site etc.
Process: Identify an open space around a building to create barrel system of infiltration gallery. Excavate earth to a depth of 6ft. from the ground level. The width of excavated pit must be slightly more than the diameter of the plastic reused oil barrel (around 1 � ft. or 21 inches).
Length of the excavated pit must be equal to number of barrels used multiplied by diameter. For example a four barrels infiltration gallery will have excavated pit of 21inch X 4no. = 84 inch or 7ft. length.
Take required number of plastic barrels (each of around 200lts.) and cut open one side of all the barrels.
Drill two holes at the bottom end on opposite sides with diameter slightly more than that of rainwater down pipe (4 or 5 inch as the case may be). Install empty barrels so prepared in the excavated pit with their cut open side facing downwards. Align all the barrels in one line with the side holes facing each other. Insert a pipe of 12inch length to interconnect two neighboring barrels.
Guide the rainwater pipe connected to the outlet of the Popup filter to the first barrel. Connect a similar pipe as overflow to the last barrel and leave the outlet of this pipe to the drain outside the building. Make sure a cap with perforations is fitted to prevent rats or insects from entering the overflow pipe at the drain. Also make sure that the over flow pipe end is at a level above the normal water flow level in the drain.
Fill up the excavated pit with soil leaving the barrels and the connecting pipes undisturbed. Once the soil over these barrels stabilizes, activities like gardening, cement flooring, light vehicle parking etc. can be taken up.
Rainwater flowing from the Popup filter flows in to these barrel system of infiltration gallery and recharges ground water.
Direct recharge through open wells and bore wells
Rainwater from the roof may be allowed to flow through PopUp filter and recharge ground water from an existing open well or a bore well. In case of an open well, filtered rainwater may be directly let in to the well through pipe from any one side of the well. Make sure the water pipe is slightly projected in to the well and a bend at the end of the pipe will guide the water downwards. This arrangement will avoid the water flowing on the wall of the well and subsequent damage to the wall. During heavy rainfall water level in the well raises and subsequently descends to maintain the ground water level. Wells can be built by digging the ground to the required depth (15 to 30 feet) and building the retaining wall around (preferably round) or by inserting cement rings to avoid caving in of the sidewall. It is advised not to allow the filtered rainwater from the PopUp filters in to the bore well (live or failed). Fine silt or dust from the roof may pass through the filter and block the micro pores or aquifers in the bore well causing permanent damage to the bore well. Rainwater from the filters may be allowed to stabilize in a storage facility or an infiltration gallery specially designed to inject rainwater in to the borewell. Infiltration gallery may be built next to the bore well, as explained in the section "Infiltration gallery for large buildings". The size of infiltration gallery can vary from 300 cft. to 800 cft. depending on the roof area. A perforated pipe needs to be installed in the second layer from the bottom from one end to the other. Farther end of the perforated pipe needs to be blocked with an end cap and the other end of the pipe is inserted in to the borewell by drilling the casing pipe of the bore well to the outside diameter of the perforated pipe. Make sure the perforated pipe is not projecting too much in to the borewell which will cause hindrance to install pump in to the bore well. At the same time if the pipe is not properly and firmly fixed to the casing pipe chances of silt/sand or other material may get an entry in to the bore well. Size of this pipe can be of 40mm or 1.5� diameter having 6mm holes (at an interval of 150mm or 6�) all along the bottom side of the pipe. It is important to have holes only at the bottom side of the pipe as shown in the figure to avoid fine silt entering the bore well.
How does the direct injection of rainwater works?
As the rainwater descends in the infiltration gallery, most of it gets in to the subsoil and recharges ground water. During heavy rainfall, rate of infiltration will be slower than the inflow of rainwater and the rainwater starts accumulating in the gallery. As the level of water increases in the gallery and rises above the perforated pipe level, clear and stabilized water enters the pipe from the small holes provided at the bottom of the pipe to reach the bore well. In this process fine silt, which escapes PopUp filters and sand bed at the top of infiltration gallery descends to the bottom of the infiltration gallery and settles down permanently. Clear and safe rainwater recharges the bore well aquifers to increase the yield and availability. It is advised to consult a professional before attempting to inject rainwater into bore wells.
Infiltration Gallery for large buildings
Infiltration Gallery is to store rainwater temporarily and allow the stored water to infiltrate into underground aquifers. When the rainwater from the roof is allowed to flow on the ground infiltration (water percolating into the ground) is less, causing more of runoff, thereby majority of rainwater quickly reaches drains or storm water drains or streets and flows away from the building. To artificially increase infiltration, two parameters are important:
(a) increasing the surface area of the soil / earth in contact
(b) creating water head on the soil / earth
Increase in any of the above or both will influence greater infiltration of rainwater into ground. The level of infiltration also depends on the structure of the soil.
How to build an Infiltration Gallery?
Identify an open area around the building, and excavate earth to the required size, the excavated pit can be of rectangular or circular in shape. To support better infiltration and for convenience of excavation, the infiltration gallery can be of minimum 5 ft. and maximum 10 ft. depth and of similar width. Length of the Infiltration Gallery can vary to accommodate runoff water from the roof during heavy intensity rains. The excavated pit has to be filled layer by layer with material like pebbles, gravel, sand etc. These layers of different material will allow the rainwater to flow gently without much of turbulence and accommodate storing of rainwater temporarily. The sand layer will arrest silt coming in along with rainwater. To have a greater effect of the layers of different material, fill the excavated pit with soling or aggregate of large size to a depth of two feet. Fill the second layer with 40mm aggregate to a depth of one foot and the third layer with 20mm aggregate to a depth of one foot. Repeat the combination of 40mm and 20mm aggregate till 2ft. short of ground level (leaving 2ft. depth of pit empty from the top). Over the layer of the aggregate, spread a sheet of plastic / nylon mesh or net (mosquito net). Fill the balance of the infiltration gallery (top 2ft.) with coarse river sand. Build a boundary rim around the infiltration gallery with brick and cement masonry structure. This will avoid flow of water from the surrounding along with other impurities directly entering into infiltration gallery.
Important

  1. All the material used in infiltration gallery like aggregate and sand need to be thoroughly washed to remove all silt and finer particles before filling into the infiltration gallery.
  2. Infiltration Gallery created underground should not be lined with plastic or brick and cement masonry or any other material, which will block the rainwater entering into underground aquifer.
  3. The bottom of the infiltration gallery should not be lined or rammed to create hard surface. All these attempts will block the rainwater entering into underground aquifer.

Process
The rainwater flowing from the building roof will be filtered in popup filter and canalized through pipes or cement lined channels to reach infiltration gallery. At the point of enter of rainwater in the infiltration gallery, splash pad may be laid to avoid splashing of water. Splash pad may be of rubber or plastic with perforation to hold water from flowing directly into sand. Water entering the infiltration gallery through sand bed will reach different layers of aggregates and start infiltrating into ground. The popup filter on the down comer pipe will arrest most of the impurities. The sand layer in infiltration gallery will arrest finer silt or dust coming along with rainwater. Different layers of material in the infiltration gallery will facilitate flow of rainwater gently into infiltration gallery without having much turbulence. During heavy rainfall, water flowing into infiltration gallery will be more than the water infiltration into the ground, thereby the water temporarily gets stored and the level of water in the infiltration gallery rises. With increase in the water head percolation level also increases.

Rainwater Harvesting from Roads
In the recent past, rapid growth in the urban areas has led to asphalted roads and stone slabs or pavers for footpaths. This accounts for nearly 10% of the total area of Bangalore. Consequent to this, the rainwater run-off has increased and ground water recharge has declined.
As the roads are built sloped towards the sides, rainwater falling on the road is guided to the side drains. When it rains, water flows from the apex to the sides and collects in the sidewalk area and subsequently flows to the storm water drains.
To increase ground water recharge by percolation and decrease the flooding of storm water drains, an infiltration trench could be built by the side of the drain all along the road, wherever possible. The infiltration trench can be 2 feet wide and 2 feet deep and filled with pebbles or aggregates with a top layer of coarse river sand.
As the rainwater from the road flows into the infiltration trench, water percolates into the ground. During heavy rainfall, excess water spills over to the storm water drains. The infiltration trenches store water temporarily during rainfall and later for infiltration. These infiltration trenches may be exposed as walk ways or paved with inter-locking pavers, specially designed with gaps in between for water to flow into the infiltration trenches.

Parks and Open Spaces
Water harvesting methods in parks and open spaces involve micro-watershed management methods that allow rainwater infiltration and percolation into the ground. The runoff has to be minimized by providing adequate number of percolation pits and dispersion trenches. In large parks, storage of rainwater in small ponds is also possible since the ponds can be integrated with the landscape of the park. Mapping of the contours, planning for rainwater outflow in consonance with natural drainage patterns, identifying appropriate areas for percolation pits / dispersion trenches will be required.
Recharge of pits or trenches
Ground water recharge in parks can be enhanced by a simple technique of providing recharge pits or a trench.

  1. Width of pit: 1.2 to 1.5 m. Depth: 2.5 to 3.0 m.
  2. Material: 40-60 mm coarse gravel followed by 20 mm aggregates and 2 mm sand. Pits are conveniently made at suitable low-level micro-watershed locations as collection centers of surface runoff.
  3. A splash pad is provided on top of the sand layer to cut off the velocity of entry of water to the pit.
  4. The number of such pits is based on the park area and the small rivulets dissecting the landscapes into micro-watersheds.

Requirements
Creation of water harvesting ponds in concave depression and low-lying areas.
�    Allowing groundwater recharge by the creation of seepage pits.
�    Allowing surface runoff to enter into existing wells or artificial water bodies.
Natural flow of water 

  1. Surface runoff water should be trapped in ponds, tanks and lakes when available, so that it can be used for maintenance during dry periods.
  2. This practice is similar to dry land technology of agricultural belts.
  3. Low-lying areas and drainage channels are earmarked and convenient micro-watersheds are prepared.
  4. Water harvesting is followed based on natural flow and surface accumulation of the runoff water.
  5. Water follows the lowest contour gradient available for that area.
  6. These structures not only provide water for the park, but also increase groundwater recharge.
  7. Providing a bore well in these areas will enhance the availability of water in its vicinity.

Rainwater run-off from open space and paved areas can be stored in underground sumps by filtering through sand-bed filters and guiding the filtered water through channels.
Layouts
Layout refers to a geographical area encompassing sites, roads, drains, civil amenities and parks. Rainwater Harvesting in layouts can be done using the 'Cascade Capture Method'.
In this process, rainwater can be harvested on a plot or through recharge of ground water. The run-off from the plot could be captured by storm water drains and directed into artificial infiltration or percolation pits. The overflow from the storm water drains and infiltration system could be captured in lakes and tanks. The method of rainwater harvesting involves contour mapping, drainage pattern, determining a storage point / ground water recharge   and ensuring segregation of sewage / sullage from storm water run-off.

 

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