Monday, April 11, 2022

Basement seepage and lakes

The unseasonal rains of 2021 have brought out several seepage issues in underground basements around the city due to ill-conceived modifications in and around these areas. Given the number of lakes in Bengaluru, this issue is especially aggravated on sites that are close to one.

The water table is naturally high around a lake. Hence, it becomes crucial to consider the natural slopes of the land as well as the drains and canals (and Raja Kaluves) that connect to the lake. The relatively recent practice of raising the land of a particular plot to avoid seepage can further aggravate the issue for its neighbours if not planned properly.

Flooded basement

This blog post aims to address these very issues with practical and easy-to-implement solutions.

1. The seepage problem

The high groundwater table around a lake leads to seepage issues in the monsoon. The best way to deal with this is to dig wells at the points of seepage and pump water out from it. This would push the groundwater table below the level of the basement.

Continuous withdrawal of water from the well will encourage more subsurface flow into the well, thus diminishing the flow towards the building basement. Water that is being withdrawn can be tested for quality and put to appropriate uses.

Depending on the depth of the water table, it is recommended that a 3-6 feet wide and a 15-30 feet deep open well to be dug for this purpose. Digging one well at a time and observing its performance will give a good idea of if/how many more such wells would be required.


Recharge / withdrawal wells

2. Harvesting rainwater, storing and using it

The presence of any building (residential/commercial) benefits the scope of rainwater harvesting and its storage. Depending on the rainfall and the space availability, enough rainwater for at least a few months can be harvested during the monsoon in Bengaluru. If not stored and used, this water would add to the runoff water and aggravate seepage issues. Pavement water should be directed into recharge wells, which could also act as withdrawal wells in case of seepage issues.

Basic rooftop RWH system

3. Installing an STP system

Installing an STP system in any residential/commercial building is a must according to the BWSSB rules. It becomes doubly important when the property is near a lake to avoid water contamination issues.

There are great ways to use this STP-treated water as well. The most common is to circulate the treated water back into the flush tanks in the building. It can also be used for gardening purposes. Depending on its treatment, many individuals and communities are successfully using the STP-treated water for other domestic purposes (like cleaning, washing, etc.) as well.

4. Long-term sustainability plan

The most sustainable solution is to make sure that the water is allowed into the lake in the long run. Any blockages in drains and canals (or Raja Kaluves) should be cleaned up to open water passages.

Reopening a drain, however, is not always possible. Especially if some sort of a structure has been built on it. In such scenarios, creating an alternative drain/culvert under or near the original drain is recommended. This would ensure that the water would have a path to the lake.

Culvert under connecting road

Finally, instead of buying water from a government/private agency, relying on the water that reaches the site naturally (either through rainfall or by natural flow) is always more economical and avoids flooding and water scarcity issues.

Helpful contacts

Well diggers:

Rainwater harvesting vendors:

Water quality testing labs:

STP vendors:

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