Ground 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 borewells/Open wells that it is unsustainable to pump out water from wells without recharging the same from the rain water. To reverse the trend or to reduce the effect of over exploitation, ground water recharge needs to be taken up on a large scale at residential and institutional buildings.
There are many methods of ground water recharge. Following are few methods for recharging groundwater using rain water from rooftop of buildings and other sources:
Step 1: Dig the Pit of size 1.2 to 1.5 m. Depth: 2.5 to 3.0 m.
Digging of pit to a depth of minimum of 2.0m (Dimensions are variable, site specific))
Step 2: Fill with 40 mm metal (50%)
Step 3: Fill with 20mm metal (25%) and construction of brick wall
Step 4: Fill with coarse sand (10%) and construction and plastering of brick wall with opening
Step 1:Drilling of bore well to a depth of 60m (200’)
Lowering of Casing (6 to 10m based on collapsing)
Digging of pit to a depth of minimum 2.0m around the drilled bore well (Dimensions are variable)
Step 2: Drilling of 10 to 12mm holes to PVC Casing (up to 1.0m from the bottom of the pit)
Fixing of rabbit wire mesh (SS) around casing at holes portion)
Filling of pit with metal as per specification (50% of the depth with 40mm and 25% with 20mm metal)
Step 3: Construct a brick wall and link with roof top pipes into the pit
Step 4: Filling the coarse sand of 15% and rest 10% is vacant (as per sketch)
Close it with perforated removable slabs
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 ¾ 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.
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. 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.
Step 1: Excavation for infiltration gallery
Step 2: Aggregate layers in infiltration gallery
Step 3: Perforated Pipe in infiltration gallery
Step 4: Plastic mesh layer in infiltration gallery
Step 5: Sand layer on plastic mesh
Step 6: Perforated pipe connection to the bore well
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:
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.
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 infiltration gallery.
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.
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 Hyderabad. Consequent to this, the rainwater run-off has increased, and ground water recharge has declined.
Harvest rainwater through your walk paths.
In Hyderabad, a kilometer of walk path with porous pavements has a potential to harvest 30 lakh liters of rainwater per year. With moderate percolation efficiency of 75%, around 15 families of Hyderabad can depend entirely on recharged ground water all through the year.
Can we bring in this change?
Porous foot paths are cheaper to build and easy to maintain compared to conventional foot paths.
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.
Greater Hyderabad Muncipal Corporation has on area of around 825 sq.km. in the city limits. The civic amenity open area includes bus-stops, play grounds, educational institutions, recreation parks etc. There are around 1060 parks in Hyderabad. The total land cover dedicated for 1017 parks is 694.4 acres. Total water requirement of these parks at the rate of 2 litre per sq.m. for around 325 non-rainy days is 56.20 Million Liters.
The rainwater harvesting proposed for parks in Hyderabad is mainly planned to harvest water from the open area including the paved walk paths and the structures inside the park. It is planned to allow the rainwater to percolate mainly in the green areas which are not paved and cemented. During heavy rains, the excess flow from the saturated soil of the green area will flow into the walk path which is paved. The rainwater which is flowing in this paved area is guided to go out to the nearest storm water drain (following the natural gradient).
The rainwater harvesting interventions will intercept the outlet of the rainwater channel which is carrying the storm water from the park (at the exit point of the park). A silt trap is designed to collect the debris and the silt flowing along with the rainwater. The relatively clean water flowing out of the silt trap is systematically diverted into the infiltration gallery/ Recharge Pit. The accelerated infiltration galleries are the structures which are open wells created using pre-cast cement rings.
The accelerated recharge wells are the dug wells inside the park at the lowest level (gradient). These wells are typically 1.5m, 2m and 3m in diameter with depth of around 3 to 6m and Rainwater harvesting Pits of size 1.5 m*1.5 m. Pre-cast cement rings which are of appropriate diameter and height of around 0.3 to 0.5m. These rings are placed one above the other without any cement mortar in between joints. Loose aggregates (stones) are packed in the annular place between the cement rings and the excavated well. The entire well inside the cement rings is kept empty without any filler material. These cement ring wells will have a safety metal grill at the ground level. The last cement ring of the well is placed over the safety grill to prevent easy access into the well. These accelerated infiltration galleries – cement ring wells are closed at the top with a cement slab. The silt traps which are harvesting surface flow of rainwater from the parks will discharge rainwater through a pipe into these wells. Most of the water percolates into the soil and joins the ground water underneath.
A shallow bore well / tube well is drilled closer to these accelerated infiltration galleries to collect the harvested water underground. These bore wells will supply water for the plants in the parks during the non-rainy days.
Some of the parks which have larger paved areas, playgrounds or structures are provided with underground sumps to harvest rainwater directly. The harvested rainwater is used for the toilet blocks and for watering the plants.
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.
Creation of water harvesting ponds in concave depression and low-lying areas.
Natural flow of water
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.
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.
City storm water drains to recharge ground water!
The drain in front of your house can harvest precious rainwater and recharge ground water.
Ground water is exploited beyond the limits and is declining in alarming speed in our cities. Simple interventions can reverse the trend.
Create a rainwater recharge trench in front of your house:
Open up one of the stone slab at the bottom of the storm water drain.
Dig a pit of rectangular shape to a depth of one meter or 3 feet.
Fill the trench with pebbles or stones or aggregates or broken bricks to 2 ft depth.
Add a layer of smaller stones or aggregates (Jelli) for a depth of 6 inches over the pebbles.
Place a mosquito net over the layer of small stones.
Fill the balance top portion of the trench with river bed coarse sand.
Rainwater from the road, from your house or from your neighbours will flow in to the trench and the sand will arrest all the silt before the rainwater percolate in to the ground. Once in a while the sand layer may be removed, washed in water to takeout all the silt and relayed to activate.
A very effective and low cost option to harvest rainwater for ground water recharge.
Roofs made of corrugated iron sheet, asbestos sheet or tiles, RCC can be utilized for harvesting the rainwater. Gutters and channels can be fixed on the edges of roof all around to collect and transport the rain water from the roof to the storage tank. Gutters can be prepared in semi-circular and rectangular shapes. Locally available material such as plain Galvanized Iron sheets can be easily folded to required shapes to prepare semi-circular and rectangular gutters. Semi-circular gutters of PVC material can be readily prepared by cutting the PVC pipes into two equal semi-circular channels. Bamboo poles can also be used for making gutters if they are locally available in sufficient quantity. Use of such locally available materials reduce the overall cost of the system.
Step 1: If the roof is thatched, polythene sheets can be used for collecting the rainwater.
Step 2: he collected rainwater is filtered through a filter filled with pebbles in the bottom and coarse sand on the top.
Step 3: The filtered water is collected either in storage tank of existing sump and the overflow water may be diverted to percolation pit nearby.
FOR SLOPING/TILED ROOFS: STEP BY STEP APPROACH :
Step 1: In a slopped/tiled house the rainwater from the roof is collected through the gutter in the roof.
Step 2: The collected water is filtered through a filter filled with pebbles in the bottom and coarse sand on the top.
Step 3: The filtered water is collected either in a storage tank or existing sump. Over flow water may be diverted to an existing open well/bore well or percolation pit.
Step 1: In houses with sloping roofs the rain water may be collected to the half cut PVC pipes fitted along the sloping sides and it may be directed to either sump/open well/bore well or recharge well.
Step 2: Check the weather the rain water drain pipes extend up to the bottom of the building.
Step 3: Interconnect the rainwater drainpipes if there exist more than one.
Step 4: To collect rainwater in a sump construct a filter champer of size 2/1/2′ * 2/1/2′ * 2/1/2′
Step 5: The bottom half of the filter chamber has to be filled either with broken bricks/bluemetal/pebbles and followed by one feet of coarse river sand. A nylon mesh has to be provided in between the two layers. The top portion of the filter chamber should be convered with RCC slab.
Step 6: The inlet rainwater drain pipe should be on the top of the filter chamber and the outlet pipe connecting the filter chamber to the sump should be at the bottom.
Step 7: Surplus spill over water from the sump may be connected with the existing open well/borewell or to the recharge well.
Step 8: In the absense of sump,filter champer may be connected to the existing open well/borewell.
Step 9: In the absense of sump,open well and bore well the rain water may be recharged through percolation pits and the bottom of bit should be in the sandy formation.
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.
Step one: Select down water pipes carrying most of rain water from your roof
Step two: Inter connect these pipes
Step three: Attach a rainwater filter at the end
Step four: Connect the filtered water out let of the filter to your underground sump / tank
Normally, debris, dirt and dust get deposited on the roof during non-rainy periods. When the first rains arrive, this unwanted material will be washed into the storage tank. This may cause contamination of water collected in the storage tank thereby rendering it unfit for drinking and cooking purposes. Therefore, a first flush system can be incorporated in the Roof top Rain Water Harvesting Systems (RRHS) to dispose of the first flush so that it does not enter the tank.
There are two such simple systems. One is based on a simple manually operated arrangement whereby, the down pipe is moved away from the tank inlet and replaced again once the first flush water has been disposed. In another simple and semi automatic system, 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 the first flush pipe the valve is closed to allow the water to enter the down pipe and reach the storage tank.
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.
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.
PopUp Filter for Roof top Rainwater Harvesting
How PopUp filter works?
The “PopUp Filter” has three components (rainwater receptor, flush valve and filter element). Rainwater receptor is where the rainwater is allowed to flow from down pipes in to the filter 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 is relatively cleaner and flows out through an outlet, which can be led to storage device.
Filter element is mounted on a vertical stabilizer barrel with a friction fit. Filter element need to be cleaned periodically during the rainy season to remove the impurities trapped and there by keep the filtration system clean. In the event filter is not cleaned and the filter element is getting clogged, “PopUp Filter” has a safety feature built into it. The water pressure pushes out the clogged filter element from the stabilizer barrel and allows 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.
PopUp Filter Maintenance:
Flush the first rainwater by opening the flush valve on the filter for few minutes, close the flush valve after all the dirt on the roof is flushed. When the rain stops, flush the filter and 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 the clean filter element back to its place by gently inserting it in the barrel. Take care not to press it too hard at the end. If pressed too hard, filter element gets locked inside the barrel 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 us.
First Flush Lock and Sand Bed Filter
The function details of automatic first flush separator and sand bed filter.
Rainwater collected from the roof top will enter the first flush lock, which will allow only the initial rainwater with all the dirt and contaminants of the roof to flow in to the flush tank and automatically divert the subsequent flow in to the sand bed filter chamber. The filtered water from the sand bed filter will flow in to the sump for future use. The stagnant water in the first flush tank and sand bed filter chamber is allowed to in filter in to the ground (the bottom of these tanks are not cemented to facilitate ground water recharge). This arrangement automatically keeps the first flush and sand bed filter chambers dry during the non rain days.
Clean the first flush chamber once in a month during the rainy season by scraping the bottom and removing all the silt and other material collected in the chamber.
Physically remove any floating elements trapped on the filter bed periodically.
Filter bed of aggregates or sand need to be taken out of the filter chamber once in three months and washed in fresh water, dry in sun and refill them back in the filter chamber.