Water flows from higher grounds to lower grounds.

The gradient map is the DEM (Digital elevation model) of Bangalore which represents the terrain of the city.

Red represents the higher grounds and blue represents the lower grounds.

The city lies within two sub basins of the Indian subcontinent: the Cauvery Basin and the Ponnaiyar Basin.

The city has 5 major catchment valleys, divided by the ridge line:
1. Hebbal Nagavara Valley
2. Koramangala Challaghatta Valley
3. Vrishabhavati Valley
4. Suvarnamukhi Valley
5. Arkavathi Valley

Sitting at 900m above sea level with no perennial rivers, Bangalore has relied on man-made tanks and other water-bodies as its primary water source since the city's establishment in the 16th century.

Categories of waterbodies identified in the city over the last few centuries:

1. Kere: Man-made tanks larger than 3 acres. Historically built as irrigation tanks.
2. Gokatte: small ponds used by cows for bathing and drinking.
   
3. Kunte: seasonal, small ponds used for domestic activities and recharging rainwater. Often between 1-3 acres.
   
4. Kalyani: stepped tanks

Head to the Filter & Find Section to explore the categories of waterbodies further.

Over the last 4 centuries, these waterbodies have been built over - they have reduced in size with most of them disappearing completely. We have identified 108 lost lakes of Bengaluru from historic maps and traced them from Historical maps of 1790, 1870, 1896 and 1969.

Historically, water used to travel from tank to tank through naturally formed low-lying stormwater streams - forming a cascading water-system. Most of these streams have been converted into concretised storm-water drains, locally known as 'Rajakaluves'.

Over time, some of these drains have been built over and disconnected from the cascading system. The map shows the existing rajkaluves. The image below is typically how primary drains with retaining walls look like around you.

Click on the drains for more information.

The secondary drains carry runoff, from road-side drains and tertiary networks, to the primary drains.

The image above shows a typical condition of secondary drains connecting to primary drains. These drains link tanks and eventually flow into rivers, forming the city's cascading stormwater system.

Notice how flood-prone zones overlap with lost lakes and constricted drains!

Encroachments have narrowed drains over the years, while tanks and marshes have been built over completely. This has blocked the city's natural drainage pathways.

Now, these vulnerable low-lying areas experience severe waterlogging and flooding during heavy rains. The map shows flood-prone locations as recorded by KSRAC in 2023.

Source: Open City

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