Biome Trust: TG Halli Reservoir Report

Summary

TG Halli Reservoir(TGR), also known as TG Halli Dam or Chamarajsagar, is a man-made reservoir built by constructing a dam in the year 1933. The reservoir lies at the confluence of Arkavathy River and Kumudvathy River 35 kms west of Bangalore^[^2].

The size of the TGR is as follows:

Catchment area	1453 sq. km	Covers parts of Doddaballapur, Nelamangala, Devanahalli, Magadi and Bangalore taluks.^[^3]
Depth	75 ft
Storage capacity	3.345 tmcft(Approximately 280,00,000 cum) 1 tmcft= 2.83168466×10¹⁰ litres

During our visit to TG Halli on 18/01/2018, we observed that there isn’t any walking path around the lake, however, the reservoir has multiple entry points to reach close to water body. There is no STP at the reservoir, but during our visit to the reservoir, we were told that the treated water from Nagasandra STP joins the Arkavathi river before it enters the reservoir.

While there are no constructed wetlands throughout the reservoir, we observed natural growth of wetland species such as Water Hyacinth at certain points in the reservoir.

TG Halli Catchment area^[4]

Overview and Observations

The water from TGR is currently being used for irrigation purposes. However, until about 2012, the water was being used for drinking purposes as well. Because the water quality was found to be substandard and the water quantity reducing significantly, its usage for drinking purpose stopped^[1].

There have been numerous articles on the water quality of TGR which mention that the TDS was beyond 500 ppm and both BOD and COD were way higher than acceptable levels. But, due to heavy rains Bangalore has witnessed this year, it was said that the water quality has improved to an extent that the TDS, BOD, and COD levels of inlet water at the confluence of Arkavathi and TGR were 450 ppm, 5 ppm, and 120 ppm respectively. The BOD and COD of the water at the outlet after the TGR water has been treated using WTP are 4 ppm and 30 ppm, respectively. The current level of the water is 66 ft and it was said that the water level has significantly increased in the last 6 months owing to heavy rainfall.

Water Hyacinth is found to grow in certain parts along the edges of the reservoir.

We observed significant algae buildup on the sides of the reservoir and the water colour seemed to be greenish.

Fishing is done in TGR. However, more information about who is allowed to fish is not available.

The Reservoir

Two inlets from which water would enter TGR are summarized below.

Inlet	Name	Description	Photos
1	Arkavathy River	Mix of storm, sewage, treated STP water and effluent from various industrial estates enter the TGR through Arkavathi river. The engineer incharge of TG Halli informed us that Arkavathi river flows through Harekyathnalli, Kithnalli Bridge and Varthur Bridge before entering the TGR near Naganalli.
2	Kumduvathy River	We were told that currently, no water enters TGR through Kumduvathy river as the river has dried up.		Pictures not available

There is one reservoir outlet which flows through a channel after the TGR water is treated using WTP. This water is being used for agricultural purposes and further flows into Manchinabele and Mekedatu Rivers.

The STP

The Nagasandra and Chikkabanavara STPs which are of 20 and 5 MLD capacities are upstream of TGR. It was said that the Nagasandra STP treated water is let into the Arkavathy river which enters TGR. However, we believe that treated water from various STPs could enter into Arkavathy river.

The Wetlands

Currently, there are no constructed wetlands in TGR. However, we observed floating wetland species along the edges at some parts of the lake.

It was reported in Deccan Herald on 30th Jan 2018 that the ambitious project to treat sewage in Arkavathi river flowing into TG Halli has been awarded to Hyderabad based Akhil Infrastructure Pvt Ltd. The cost of the project is 11.49 crore rupees and the technology that would be adopted is Natural Biological System(NBS) which uses engineered wetlands to treat wastewater.