Tuesday, December 12, 2017

Rachenahalli Lake Report

Summary
Rachenahalli Lake is on approximately 104 acres and is located in the north of Bangalore near the Embassy Manyata Business Park. The lake lies within the Yellamallappa Chetty Lake series within the Hebbal Valley. It is frequented by local residents who enjoy the provided walking path and park. During our visit on 7 November 2017, we observed that no STP exists in this lake; however, a well-demarcated area of wetland exists to the north of the lake. There are seven inlets - one into the wetland area, four from the wetland area into the main lake, and the other two directly into the main lake through naala overflow structures - and two outlets from the lake. The inlets carry a mixture of storm and sewage water. The volume of inflow through the inlets could not be determined.



Map 1





Overview and Observations
Rachenahalli Lake is located in Thanisandra, Bangalore.


Lake Area
104 acres
STP & Wetlands
No STP exists in the lake premises, however a 2.5 acre natural wetland exists to the northern side of the lake.

In 2016, Rachenahalli Lake was transferred from BDA to BBMP jurisdiction. Both prior to and after this change, the community group Jalamitra (founded in August 2015) has been active in the rejuvenation efforts.

It was observed that there is one inlet into the wetland and six inlets into the lake. From the wetland, there are four overflow inlets into the lake. The other two inlets are both naala overflows which will carry a mix of stormwater and sewage into the lake during flood events.

In the mornings and evenings, local residents use the path around the western, northern, and eastern edges of the lake for walking, jogging, or other workouts while also visiting the park along the western side of the lake. The park was under construction at the time of our visit and includes the following amenities: a gazebo, toilets, an office, a yoga platform, and a kalyani, as well as several benches.


The Lake
One wetland inlet and six inlets where water would directly enter Rachenahalli Lake were identified and are summarized below.

Wetland Inlet
Name
Description
Photos
1
Wetland Inlet
Overflow of storm and sewage water from Naala 1 enters into the wetland area in the north of the lake.
Lake Inlet
Name
Description
Photos
1
Wetland Overflow 1
After entering the wetland, any remaining flood water overflows across the bund and enters the lake. 

2
Wetland Overflow 2
After entering the wetland, any remaining flood water overflows across the bund and enters the lake.
3
Wetland Overflow 3
After entering the wetland, any remaining flood water overflows across the bund and enters the lake.
4
Wetland Overflow 4
After entering the wetland, any remaining flood water overflows across the bund and enters the lake.
4
Naala 1 Overflow
Naala 1 will also overflow into the lake through a structure under the walking path to the north of the park.

6
Naala 2 Overflow
Naala 2, carrying water from the area west of the lake, will pass through an overflow structure during flood events and enter into the lake


The two outlets from the lake are both overflow systems under bridges in the south of the lake. At both outlets, particularly outlet 1, there was noticeable green hue to the water exiting the lake (see photos below). We also observed what appeared to be raw sewage mixing with the water just beyond lake outlet 1.





Pictured above: Overflow Outlet 1 from Rachenahalli Lake





Pictured above: Overflow Outlet 2 from Rachenahalli Lake

There was minimal buildup of algae on the water surface, though there was a noticeable green hue to the water near the outlets. In the center of the lake, the depth may reach about 10-11 feet.

Along the walking path, there is a park on the western side of the lake. Within the park are various amenities such as benches, toilets, a gazebo, a kalyani, and a yoga platform (see Map 1 for locations).


The STP
At present, no STP exists at Rachenahalli Lake.


The Wetland
There is a 2.5 acre natural wetland at Rachenahalli in the north corner of the lake which  accounts for about 2.4% of the total lake area. The wetland is separated from the main lake by a bund, through which is a bridge under which water will flow from the wetland into the lake.

The wetland also has a large number of wetland plants throughout.

Wetland pictured above


 References

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