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The Science

How the Restored Pond Works

A pond is a simple piece of infrastructure: a basin that catches monsoon rain, holds it, and lets it soak slowly into the ground. These diagrams show the mechanism. They are schematic and not drawn to scale.

Part 1

How it works

Where the monsoon rain goes

The same piece of land, before and after restoration. Buried, it sheds water into the streets. Opened up, it stores water and passes it down to the aquifer.

Buried under wasteBefore
Cross-section of the buried pond Rain falls on a basin filled with compacted waste. Water runs off sideways into the streets and very little reaches the groundwater below. Groundwater 1 2 3
  1. A buried basin. Years of household waste and construction rubble filled the pond and were compacted flat.
  2. Rain runs off. With nowhere to collect, monsoon rain runs across hard ground into streets and drains, adding to waterlogging (Dev, 2017; Shuster et al., 2005).
  3. Little recharge. Very little water soaks through the compacted fill, so the groundwater below is not replenished.
Restored as a pondAfter
Cross-section of the restored pond Rain and runoff collect in the excavated basin. Water is stored, seeps down to raise the groundwater, evaporates to cool the air, and is filtered by plants at the edge. Groundwater 1 2 3 4 5 6
  1. Catches the rain. The open basin collects rain and runoff from the ground around it. About 77% of the district's annual rain arrives in the monsoon months (Dev, 2017).
  2. Holds stormwater. Water held in the pond is water kept off the roads and out of the drains at the peak of a downpour (Balasubramanian, 2023).
  3. Recharges groundwater. Stored water seeps slowly through the bed into the aquifer, the same principle as a percolation tank (Raj et al., 2024).
  4. Plants clean the water. Vegetation on the banks and in the shallows traps sediment and takes up nutrients and pollutants (Fletcher et al., 2024).
  5. Cools the air. Evaporation from open water lowers the temperature of the air around it (Jandaghian & Colombo, 2024).
  6. Makes habitat. Open water and planted margins give insects, amphibians and birds somewhere to live (Hill et al., 2021).
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A year in the life of the pond

The pond will not look the same all year. It fills in the monsoon and draws down through the dry months, and that cycle is how it does its work.

Late June to September
Monsoon

Rain and runoff fill the basin. Most of the year's rain arrives in these months (Dev, 2017).

October to November
After the rains

The pond holds its water, and the water seeps slowly into the ground (Raj et al., 2024).

December to February
Winter

Planted margins take hold, and the standing water becomes habitat for insects, amphibians and birds (Hill et al., 2021).

March to June
Summer

Evaporation is at its highest and the water draws down. Like many water bodies in Gurugram, the pond may dry out before the next monsoon.

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How planting keeps the water clean

The research the project draws on describes three planting zones, each doing a different job, from the top of the bank to the open water.

Planting zones from bank to open water A cross-section showing trees and shrubs on the bank in zone A, reeds in the shallows in zone B, and a floating planted raft and submerged plants in open water in zone C. Runoff flows through zones A and B before reaching the water. A B C
  • AThe bank. Trees, shrubs and grasses form a buffer that slows runoff and filters it before it reaches the water (Mishra et al., 2025).
  • BThe shallows. Reeds and other plants rooted at the water's edge trap sediment and take up nutrients (Fletcher et al., 2024).
  • COpen water. Planted floating rafts and native aquatic plants treat the water itself (Addo-Bankas et al., 2022).
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Part 2

What the design has to manage

A pond that works on paper can still fail in the ground. These are the processes that decide whether Badshahpur Pond keeps holding, cleaning and recharging water over the years, and what each one asks of the design.

The water budget

Every pond keeps the same account. Water comes in as rain and runoff, and leaves by seeping into the ground, evaporating or overflowing. Only the share that seeps down recharges the aquifer.

The pond's water budget A cross-section of the pond with five numbered flows: rain falling on it, runoff entering from paved ground, water percolating down to the groundwater, water evaporating, and surplus water leaving through an overflow. Groundwater 1 2 3 4 5
  • 1Rain. Falls straight onto the pond. About 77% of the district's annual rain arrives in the monsoon months (Dev, 2017).
  • 2Runoff. Hard surfaces increase both the volume and the speed of the water running off them (Shuster et al., 2005). The area draining to the pond decides how much arrives.
  • 3Percolation. Water seeping through the bed, the useful output. It depends on permeable soil beneath the pond (Bouwer, 2002).
  • 4Evaporation. Water lost to the air, at its highest in the hot months before the monsoon.
  • 5Overflow. Once the basin is full, the surplus has to leave by a safe route.
The account

Change in stored water = rain + runoff − percolation − evaporation − overflow

The terms in blue add water and the terms in brown remove it. Of the three losses, only percolation reaches the aquifer.

What one measured tank did with its water
  • Percolated into the aquifer: 57 to 63%
  • Evaporated: 37 to 43%

A percolation tank in hard-rock terrain in South India, monitored for two years. About 80% of the water that percolated was later pumped out again by neighbouring boreholes (Massuel et al., 2014). Badshahpur's soil and climate are different, so its own figures have to be measured.

What the design needs
  • The area that drains to the pond and the volume the basin can hold.
  • A record of the water level through the year.
  • The rate at which water soaks into the bed, tested on site (Bouwer, 2002).
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Silt: why a pond needs upkeep

Runoff carries soil with it, and ponds are very good at trapping that sediment (Verstraeten & Poesen, 2000). Left alone, a pond slowly fills itself in and seals its own bed.

Left aloneWithout upkeep
A pond silting up Runoff carries sediment into the pond. A layer of silt covers the bed, the water is shallower, and little water seeps down to the groundwater. Groundwater 1 2 3
  1. Sediment arrives. Soil washed off the surrounding ground enters with the runoff and settles in the still water.
  2. The bed clogs. A layer of fine material builds up on the bed and blocks the pores of the soil beneath, so less water seeps through (Bouwer, 2002).
  3. The basin shrinks. Each year the pond is shallower and holds less water.
MaintainedWith upkeep
A maintained pond Runoff first passes through a small silt trap where sediment settles. The banks are planted, the bed is clean, and water seeps freely down to the groundwater. Groundwater 1 2 3
  1. A silt trap at the inlet. Letting sediment settle out before the water reaches the pond limits clogging (Bouwer, 2002), and a small trap is far easier to dig out than the whole bed.
  2. Planted banks. A buffer of grasses, shrubs and trees slows runoff and filters it before it reaches the water (Mishra et al., 2025).
  3. Desilting in the dry season. Drying the bed and scraping off the clogged layer restores the rate at which water soaks in (Bouwer, 2002).
What the design needs
  • An inlet where silt can settle and be dug out.
  • Stable, planted banks.
  • A desilting routine for the dry season, with someone responsible for it.
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What lies under the bed

This pond was used as a dump. Water that passes through buried waste dissolves what is in it and becomes leachate, which can carry dissolved organic matter, salts, heavy metals and synthetic chemicals (Kjeldsen et al., 2002). Around the Gazipur landfill in Delhi, leachate was found to have contaminated the groundwater (Mor et al., 2006).

Waste left under the bedThe risk
Water seeping through buried waste A shallow pond sits on top of buried waste. Water seeps down through the waste, picks up contaminants and carries them into the groundwater. Groundwater 1 2 3
  1. Water seeps down. The pond does what it was built to do and sends water into the ground.
  2. It passes through the waste. On the way it dissolves contaminants out of whatever is still buried there.
  3. The aquifer receives them. Recharge turns into a source of pollution.
Waste removedThe requirement
Water seeping through clean ground The waste has been excavated down to natural soil. Water seeps from the pond through clean ground into the groundwater. Groundwater 1 2 3
  1. Excavate to natural soil. The dumped material has to come out across the whole bed, not only where the water will stand.
  2. Water seeps through clean ground. The ground beneath a recharge basin has to be free of polluted material (Bouwer, 2002).
  3. The aquifer gains clean water. Recharge adds to the groundwater without degrading it.
What the design needs
  • Excavation that reaches natural soil across the whole bed.
  • A soil test of the finished bed.
  • A water quality test once the pond holds water.
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Three more things to manage

Standing water in a city brings its own problems and its own opportunities.

Nutrients
Algae

Runoff and sewage bring nitrogen and phosphorus. Too much of either feeds algal blooms, which strip oxygen from the water (Smith et al., 1999). Keeping sewage out comes first: about one water body in five in Gurugram is at risk from it (GMDA, 2019).

Public health
Mosquitoes

Still, shallow water choked with plants breeds mosquitoes. Research on constructed wetlands points to design and upkeep: areas of open, deeper water, vegetation that is kept in check, and conditions that favour the natural predators of the larvae (Walton, 2012).

Ecology
Life arrives on its own

New ponds are colonised quickly. A group of new ponds in England, monitored for seven years, came to hold more plant and invertebrate species than established ponds nearby, helped by clean water and other wetlands close by (Williams et al., 2008).

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What still has to be measured

These are the mechanisms the restoration relies on. They are not results yet. How much water the pond holds, how quickly it seeps into the ground and how clean that water is will be assessed once the pond has been through a monsoon. Measurements of this kind are scarce: a review of rainwater harvesting in India found surprisingly little field evidence of how much individual structures recharge (Glendenning et al., 2012).

References on this page19 sources
  1. Addo-Bankas, O., Zhao, Y., Gomes, A., & Stefanakis, A. (2022). Challenges of urban artificial landscape water bodies: Treatment techniques and restoration strategies towards ecosystem services enhancement. Processes, 10(12), 2486. https://doi.org/10.3390/pr10122486
  2. Balasubramanian, I. (2023). Strategies to mitigate urban flooding and build climate resilience: Lessons for Indian cities. International Society of City and Regional Planners. https://isocarp.org/app/uploads/2023/08/Indumathi-Balasubramanian.pdf
  3. Bouwer, H. (2002). Artificial recharge of groundwater: Hydrogeology and engineering. Hydrogeology Journal, 10(1), 121–142. https://doi.org/10.1007/s10040-001-0182-4
  4. Dev, A. (2017). Urban cannibalism: A self-destructive decay – the duality of ecological dismay; Gurgaon. International Journal on Emerging Technologies, 8(1), 297–303.
  5. Fletcher, J., Willby, N. J., Oliver, D. M., & Quilliam, R. S. (2024). Multi-pollutant removal dynamics by aquatic plants in monoculture or mixed communities. Environmental Research, 263, 120041. https://doi.org/10.1016/j.envres.2024.120041
  6. Glendenning, C. J., van Ogtrop, F. F., Mishra, A. K., & Vervoort, R. W. (2012). Balancing watershed and local scale impacts of rain water harvesting in India: A review. Agricultural Water Management, 107, 1–13. https://doi.org/10.1016/j.agwat.2012.01.011
  7. Gurugram Metropolitan Development Authority. (2019, May 2). Water bodies in district Gurugram [Compliance report in O.A. No. 325 of 2015, Lt. Col. Sarvadaman Singh Oberoi v. Union of India & Ors.]. National Green Tribunal. https://www.greentribunal.gov.in/sites/default/files/all_documents/GMDA-Compliance%20Report%20In%20O.A.%20No.%20325%20of%202015.pdf
  8. Hill, M. J., Greaves, H. M., Sayer, C., Hassall, C., Milin, M., Milner, V. S., Marazzi, L., Hall, R., Harper, L. R., Thornhill, I., Walton, R., Biggs, J., Ewald, N., Law, A., Willby, N., White, J. C., Briers, R. A., Mathers, K. L., Jeffries, M. J., & Wood, P. J. (2021). Pond ecology and conservation: Research priorities and knowledge gaps. Ecosphere, 12(12), e03853. https://doi.org/10.1002/ecs2.3853
  9. Jandaghian, Z., & Colombo, A. (2024). The role of water bodies in climate regulation: Insights from recent studies on urban heat island mitigation. Buildings, 14(9), 2945. https://doi.org/10.3390/buildings14092945
  10. Kjeldsen, P., Barlaz, M. A., Rooker, A. P., Baun, A., Ledin, A., & Christensen, T. H. (2002). Present and long-term composition of MSW landfill leachate: A review. Critical Reviews in Environmental Science and Technology, 32(4), 297–336. https://doi.org/10.1080/10643380290813462
  11. Massuel, S., Perrin, J., Mascre, C., Mohamed, W., Boisson, A., & Ahmed, S. (2014). Managed aquifer recharge in South India: What to expect from small percolation tanks in hard rock? Journal of Hydrology, 512, 157–167. https://doi.org/10.1016/j.jhydrol.2014.02.062
  12. Mishra, A., Hamby, J., Cepeda, A., & Tufail, M. (2025). Restoring Najafgarh Jheel: An ecohydrological approach to ecosystem restoration. Taylor & Francis. https://www.taylorfrancis.com/cw/10.4324/70f89840-6d56-45df-a1d9-6bbd9abc32e5
  13. Mor, S., Ravindra, K., Dahiya, R. P., & Chandra, A. (2006). Leachate characterization and assessment of groundwater pollution near municipal solid waste landfill site. Environmental Monitoring and Assessment, 118(1–3), 435–456. https://doi.org/10.1007/s10661-006-1505-7
  14. Raj, A., Yadav, B., Patidar, N., Krishan, G., Deka, B. J., Jeong, S., Pandey, A., Matsuno, Y., & Singh, R. D. (2024). Artificial recharge initiatives in India: Challenges and future scope. APN Science Bulletin, 14(1), 93–109. https://doi.org/10.30852/sb.2024.2568
  15. Shuster, W. D., Bonta, J., Thurston, H., Warnemuende, E., & Smith, D. R. (2005). Impacts of impervious surface on watershed hydrology: A review. Urban Water Journal, 2(4), 263–275. https://doi.org/10.1080/15730620500386529
  16. Smith, V. H., Tilman, G. D., & Nekola, J. C. (1999). Eutrophication: Impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems. Environmental Pollution, 100(1–3), 179–196. https://doi.org/10.1016/S0269-7491(99)00091-3
  17. Verstraeten, G., & Poesen, J. (2000). Estimating trap efficiency of small reservoirs and ponds: Methods and implications for the assessment of sediment yield. Progress in Physical Geography, 24(2), 219–251. https://doi.org/10.1177/030913330002400204
  18. Walton, W. E. (2012). Design and management of free water surface constructed wetlands to minimize mosquito production. Wetlands Ecology and Management, 20, 173–195.
  19. Williams, P., Whitfield, M., & Biggs, J. (2008). How can we make new ponds biodiverse? A case study monitored over 7 years. Hydrobiologia, 597(1), 137–148. https://doi.org/10.1007/s10750-007-9224-9

Every source used on this website is listed on the References page.