Wednesday, January 27, 2021

Devanahalli and its water: Then and Now

The Devanahalli town located very close to the Bangalore International Airport (34 km from Bangalore) is home to around 30,000 people. It is also 

the main town of Devanahalli Taluk in the Bangalore Rural district. The town is of historical significance. The town is still a sought after location for

 its old temples, forts dating back to the 15th Century. The town is also the birthplace of Tipu Sultan, an erstwhile ruler of the Kingdom of Mysore 

from 1782 to 1799.

Locating Devanahalli

Traditionally, Agriculture has been practiced in Devanahalli and it is the main livelihood to many communities in the town. Devanahalli is also home

 to a number of Keres, open wells and step wells/Kalyanis which are of cultural and heritage value. They were also the traditional water systems locally. 

This region has historically been dependent on the network of cascading tanks, step wells and open wells to tap local groundwater for different water 

needs. Tanks served the purpose of both groundwater recharge and as irrigation reservoirs. All domestic needs and agriculture needs are served by 

Open wells and step wells/kalyanis used for religious and cultural purposes. 

 

Within the town Shineeru kere or “Sweet water lake” and Doddadda ammani kere or “very big lake” are two major water bodies. These water bodies 

serve the drinking, domestic and agriculture needs indirectly. The two lakes recharge the groundwater as well. To access this groundwater, almost 

every household and farmers built open well as a decentralized water management system. Devanahalli also had few public open wells to serve the 

needy. These public open wells also had a kundi/small tub adjacent to it to withdraw water from well and pour into the tub to use for their day needs. 

In few of the public places/places of importance, a traditional water distribution system/ Silendra near the dargah is places which served water for

 travelers who waited here to board a vehicle or for rest.

Identified open wells in Devanahalli

Open well

Step well

Kundi/ Tub

Silendra/ Water distribution system for travellers

With a new wave of urbanization proposed by Bangalore International Airport Area planning Authority (BIAAPA) in the last decade, Devanahalli is 

planned to be the centre of new developments. It would be surrounded by large Software, Hardware, Financial Services and Aerospace special 

economic zones (SEZs). Today, its municipal boundaries cover an area of around 16 sq km but it's set to expand in the coming years. This 

development will also lead to transition from agricultural lands to real estate – currently mostly into residential properties. Along with the 

landscape transition, the region will also experience transition in its water scape. The catchments of the lakes are already disturbed affecting inflows 

into the lakes. Groundwater tables have also fallen drastically in the region, and in general this area experiences water scarcity.  

 

Farmers therefore have invested in drilling deeper bore wells in many places, often without adequate yields. Beautiful open wells with masonry stones 

dot the landscape, but are mostly dry and filled with solid waste today. The area has also seen investments by farmers in drip irrigation systems to 

conserve the water. The town is managed by local municipality i.e. the Town Municipal Council (TMC). The individual households of the town are now 

connected with water pipes to receive municipal supply from public bore wells dug by the TMC or from tankers and few are connected with their own 

borewells, changing the water paradigm from decentralized water management to centralized water supply. Eventually, to sustain the growing water 

needs, deeper aquifers replaced traditional systems as a primary driver for irrigation and domestic consumption. Though, these sources provided 

short term relief  but drastic exploitation of groundwater was soon visible. Every year 8-10 new borewells are dug to meet the growing water 

demands of the town putting shallow aquifers out of the imagination. This is the best time for Devanahalli town to realise the role open wells have 

played over the centuries in management of water. Can we look at bringing back this water heritage of the town which were crafted exquisitely to be 

called work of art? Stories are already emerging from the town of formal and informal enterprises realising the importance of shallow aquifer. 

 

In the next few blogs we will talk about small stories on the impact of urbanization on shallow aquifer in Devanahalli. 



Monday, January 25, 2021

Puttenahalli-Yelahanka Lake Report 2020

  

Summary

Puttenahalli-Yelahanka Lake is spread over 34 acres in North Bangalore.  Known for its bird population and bird diversity it was declared as a “Bird Conservation Reserve’ in 2015.  For a long time, with heavy inflow of sewage into the lake water quality had deteriorated. The Forest department, Citizens, Institutions and Ornithologist came together to design and rejuvenate the lake to help restore the lake to its original glory.  When we visited the lake in August 2020 the rejuvenation process was complete.


The lake's main source of water was a combination of rain and treated sewage.  It receives runoff from its upstream source, Attur Lake.  However, due to urban growth this source had become a trickle and very little run-off reached the lake from 2012.  Instead, wastewater, predominantly sewage began flowing in and filled this Lake.  From 2013 plans were initiated first, to remove the sewage sludge from the lake and second, provide for an alternative source of water to keep the lake filled throughout the year.  To achieve this, a diversion drain for sewage was designed and executed to divert incoming sewage into a 3m wide diversion drain that runs along the South and East side of the lake.  In this way primary sewage is prevented from directly entering the Lake.  A runoff diverting sluice was designed and built upstream at the mouth of the lake so that only storm water or heavy runoff can enter the lake upstream.  Whereas the daily flow of sewage continues to flow in the diversion drain.  The stormwater or runoff entering the lake through this sluice is allowed to flow on a boulder and reed bed so as to trap the plastics and other floating wastes and thus allowing only clean water to enter the lake during the rainy season.  The work on restoration began in 2016 and was completed in July 2018.  As a part of the above restoration, a ‘Passive Conditioning Plant’ was constructed at the South East corner of the lake and commissioned with a capacity of providing one million liters of good quality water into the lake to compensate for evaporation losses and fall in the water levels in the Lake.  Wastewater from the diversion drain is channelled into this plant which then gets treated before it enters the lake. The quantity of wastewater entering the plant can be controlled by the balancing weir and a sluice gate.  Water is treated and let into the lake to replenish the water lost due to evaporation, mainly in summer while also allowing a defined quantity of nutrients for supporting primary algal biomass to grow and support a high fish density for the birds’ food.


Location with series of the lake


Plan of the lake

 A                                                                                                        A’

Conceptual Section AA’



Overview and Observations


Puttenahalli lake is located in North Bangalore in Yelahanka, on the way to Doddaballapura, near KPTCL office.


Puttenahalli Lake

  

Custodian

Forest Department

Lake Area

34 acres

STP 

Passive Conditioning Plant

Wetlands

Yes

Upstream lake

Attur Lake

Downstream lake

Yelahanka Lake


The Forest department which is the custodian of the lake, in partnership with YPLBCT (Yelahanka Puttenahalli Lake and Bird Conservation Trust) lake group overlooks the maintenance of the lake in consultation with water experts from IISc and Bird experts from GKVK. The entire lake is imagined as an urban forest, designed to keep human interference to the minimum.  The walking path covers only the northern part while the Southern and Eastern and Western boundaries do not have public access.  There are benches placed and gazebos planned for photographers and birdwatchers to pursue their interests.  The lake is designed to be generally shallow in nature with a maximum depth of 8 feet with three depth zones keeping in mind different types of birds will inhabit and benefit from the shallow (waders), mid-depth (swimmers) and two metre deep (diving birds) zones. The depth of the lake increases gradually from 2ft to 8ft West to East. 


YPLBCT is an active citizen lake group.  They have various activities like Idol making for Ganesha festival, Kere Habba, Bird census at the lake to encourage citizens to get involved with the lake.


Inlet


There are two sources of water for this lake.  As sewage flows along the run-off channel, there is a need to separate the daily flow of sewage from the rain-water entering as run-off from upstream.  Upstream of the Lake, the daily flow of sewage is let into a diversion drain that flows along the southern boundary for nearly a kilometre and then flows past the eastern bund towards the Yelahanka Lake.  At the mouth of the Lake, there is a diversion system such that when the flow is low and the water level in the run-off channel is low, it flows into the diversion channel.  However, when there is heavy runoff from heavy rain and the water level in the drain is high, a large part of the runoff flows past the barrier into the shallow end of the lake over a boulder trap that arrests silt and debris.  On the other hand when there is no rain and the water levels in the lake is low due to drying up, the sewage is let into the PSTP (passive sewage treatment plant), gets treated to bath water quality and then flows into the lake at the deep end.  A balancing weir is built slightly downstream of the PSTP inlet such that water is taken into the lake only if the water level in the lake is low.  When the Lake is full, no sewage enters the PSTP and all the sewage flows down the diversion drain.  Thus fresh water from run-off enters the Lake upstream at this mouth at the shallow end while sewage is taken in only when the Lake water level is low through the PSTP at the deep end of the Lake.  The diversion drain prevents the sewage directly entering the lake. There are sluice gates at both the inlets to control the inflow of water that may be needed during maintenance of Lake.


Sluice gate at the Southwestern side of the lake


Passive Sewage Treatment Plant (PSTP)


A passive conditioning plant with a capacity of one million liters per day (1MLD) is constructed in the lake at the deep end on the Southeast corner of the lake abutting the diversion drain.  A balancing weir helps control the intake of sewage into the plant. The balancing weir lets sewage to flow into the PSTP only if the water level in the lake is low and the Lake is drying up.  The passive conditioning plant has 3 zones or tanks.  In the first zone incoming sewage is subject to anaerobic digestion and most of the organic matter in the sewage is converted to biogas while a small part of the digested material, predominantly anaerobic bacteria settle down as sludge.  The treated supernatant stripped off the digestible organic material, now flows to the next zone where it is treated with algae in two stages for further purification.  In the second tank, specialized algae called Euglena are allowed to grow and these feed on the suspended bacteria still remaining in the water coming out of the anaerobic digester.  After a day of treatment by Euglena in this tank, the clarified water enters the second algal tank.  This tank permits a high growth of algae and in bright light, due the rapid photosynthesis, the pH of the water rises to about 9.0 and supersaturating the water with photosynthetically derived oxygen.  These two phenomena of high pH and supersaturated dissolved oxygen in water firstly kill most of the potential pathogens (if found) and second remove a large part of the nitrogen and phosphorus from the water.  The treated water at this stage reaches recreation quality or wild-life quality and after this the water enters the lake.  The treatment and filling up the lake with treated sewage is necessary to replenish water lost due to evaporation and during summer and prevent the lake going dry. This will ensure water at the lake all through the year and helps to recharge the groundwater level in the vicinity.  The water quality is so managed so as to provide for food for the higher levels of fish numbers maintained to attract more water birds.


Passive Sewage Treatment Plant

Outlet


There is one main outlet or spillway at the Northeast of the lake.  Lake water overflows from an overflow weir.  The diversion drain diverts sewage flowing into Puttenahalli lake and flows along its boundary without allowing it to mix up with the freshwater in the Lake.  The excess water from the lake falling over the spillway as well as the diversion drain join after crossing the lake and flows into a reed bed before entering the Yelahanka lake. 


Outlet


Islands and Bird Nesting Sites


There are 4 mini islands created at the lake. Two islands existed prior to restoration and two more were created during the restoration process.  The islands are planted with trees for creating bird habitats keeping in mind the roosting and nesting activities.  A gazebo is being built opposite these islands for photographers and bird watchers for their activities. There is no direct access to the island and therefore birds roosting and nesting remains undisturbed.


Island

There are seatings provided along the pathway. 


Benches


Livelihood Activities


Various livelihood activities are being added slowly to sustain people dependent upon the Lake.  Grass cutters are allowed into the lake to cut grass and Alternanthera and take it for feeding their cattle. This helps keep the weed level low in and on the banks of the Lake and also reduce human-snake encounters.


A Grass cutter at the lake

Fishing


The lake has been seeded with four kinds of fishes while catfish has inadvertently entered this lake from upstream lakes.  Controlled fishing has been taken up to reduce the population of large fish (more than half kilo), so as to maintain fish at sizes appropriate for birds to feed on.  Only large fish are allowed to be removed from the Lake through use of large nets and any small fish caught are returned to the Lake.  Large fish usually prey on smaller fish as their main food and thus need to be selectively removed.  Some extent of emergent weeds need to be maintained as fish shelters to maintain the fish population especially of the fingerlings and hatchlings.  However, there is a need for a more scientific management of the fish population and types in the lake to favour bird feeding.  Studies are on to show that fish are breeding and growing the lake. 


Biodiversity at the lake


Puttenahalli lake was declared as a ‘Bird Conservation Reserve’ in 2015.  The rejuvenation and design for the lake was planned and executed with this in mind.  After the rejuvenation, the lake sees many birds roosting and nesting.  Bird Surveys are carried out twice a month and species sighted are recorded and discussed with the management group as well as interest groups.  There are a lot of insects such as butterflies and dragonflies, beetles and wasps that supplement various other bird feed such as Myna, bee-eaters, etc.  One could also see different species of plants around the lake. For a complete list please visit YPLBCT website.


Below are few pictures of the biodiversity that we noticed


  1. Birds


Coots


Purple Swamphen


There are over 120 species of birds spotted at the lake; Coot, Purple moorhen, Spot billed ducks, Pond heron to name a few.  We observed Coots nesting near the island.


  1. Flora




Few plants that we observed are Kadamba tree, Canon ball, Ficus, Acasia, Rain trees, Jamoon tree, Honge, Bamboo.  Some of the wetland species were Alternanthera (alligator weed), Typha, Ipomea (morning glory), Vetiver, Colocasia, Cyprus, duckweed, Knot weed, Wolffia, Bamboo to name a few.  Wolffia size depends on the amount of ammonia in the waterbody. Less ammonia encourages Wolffia-major to grow and more ammonia encourages wolffia-minor to growThe same plant behaves differently on soil and on water.  Taking knotweed as an example, the stem of knotweed is hollow when in water and solid/filled when on soil.


There are date palm trees on the island which have mile-a-minute creepers covered over it with beautiful pink flowers. 


Duckweed at the outlet

As indicated earlier, the Lake was designed to have three depths to meet the needs of three types of birds.  At the shallow end, it was observed that the alligator weed was growing in abundance and has created a niche for various types of swamp hens (purple moorhen, etc).  On any given day there are over a hundred swamp hens to be sighted.  They also created nests among these weeds and are breeding extensively.  The occurrence of these alligator weeds is due to the legacy sludge and the difficulty during lock down for Lake maintenance and weed removal.  We were told that this excess growth will slowly subside once the sediment stabilises and submerge vegetation sets up, which then takes care of the weeds.  It can take up to 2 years to see the effect of the restoration.


  1. Fishes- 

The fishes have been reported to include Catla, Tilapia, Rohu, Snake head fishes, Guppies and Cat fishes.


  1. Insects

Grizzled Pintail



Common Picture Wing

Many butterflies were observed. A picture of one of the Blues is below.


Blues