Project Implementation and activities:

The eco-restoration of Sembakkam Lake in Chennai is an ongoing project demonstrating science-based restoration approaches by TNC and its partners. The project involves the use of nature based solutions for conservation of urban wetlands.

Key Steps:

• 1,00,000 cum of silt removed from lake, resulting in improved water storage capacity by 36 % , increase in groundwater recharge of about 50,000 cum/ annum and improved flood mitigation capacity.
• Strengthening of the embankments of about 1.5 km length
• Construction of two numbers of flood regulators for flood mitigation
• Creation of ecofriendly landscape for community connectivity and improvement of biodiversity habitat is in progress
• Creation of constructed wetlands for incoming wastewater treatment is in progress. The treatment system aims to improve the lake water quality to category D of Central Pollution Control Board Standards. The constructed wetland system is aimed at providing evidence-based solutions for decentralised and nature-based treatment system with a reduced environmental footprint.
• Project demonstrates strong stakeholder engagement involving various government departments such as Water Resource Division – Public Works Department, urban local bodies, District Collectorate, local communities who are forthcoming to support the on -ground works in possible ways.
• The project involves long term monitoring, evaluation and maintenance and has incorporated plans on using IoT (Internet of Things) based lake water quality monitoring system to regularly monitor the water quality with reference to Central Pollution Control Board surface water quality standards.

The project involves restoration of the 100-acre urban lake for the following benefits,

• Improvement in storage capacity through silt removal that provides flood and drought mitigation benefits
• Improvement of lake water quality by treating incoming wastewater using nature-based solutions*
• Accrue flood mitigation benefits through strengthening embankments and construction of flood regulators,
• Improvement in biodiversity habitat and community connectivity through eco-friendly landscaping development
• Work closely with Government and other stakeholders such as local community, subject matter experts for a participatory restoration approach
• Build community ownership for long term maintenance.
• Showcase use of advanced monitoring techniques such as Internet of Things (IoT) for periodical monitoring of lake water quality during pre & post restoration

*The methodology adopts nature-based solutions such as constructed wetlands in a hybrid approach for decentralised treatment of incoming wastewater. The total treatment capacity is of 7 million litres per day, which is supposedly one of the largest treatment capacities using reedbed technology for wastewater implemented in India. The unconventional approach uses locally available materials that will help showcase the benefits of nature-based solutions including its cost effectiveness, clean energy solutions and ease of operation while also offering benefits of supporting biodiversity and improved aesthetics.

Implementing partners:

The Nature Conservancy- India – Provided the conceptual plan for an integrated wetland restoration model and mobilised funds for the project

The Care Earth Trust: Carried out the biodiversity assessment, community engagement and project execution on ground.

Indian Institute of Technology Madras: Provided technical assessment for the baseline survey for hydrology, hydrogeology and other limnological studies and recommendations based on the assessment results obtained. The partner was engaged in continuous review and project monitoring.

FINISH Consortia: Organisations comprising Indian Leather Institute Foundation, The Solutions Centre and the FINISH society designed the constructed wetland systems for the treatment of wastewater of 7 MLD capacity using a hybrid methodology.

Source of Finance:

The capex was mobilised by The Nature Conservancy from various donors and philanthropists and the OPEX is planned to be covered by the ULBs. However, the confirmation from ULB is awaited on taking up the OPEX part. The OPEX is required to maintain the wastewater treatment system using constructed wetlands which requires 1/3^rd of the OPEX compared to the conventional systems. CAPEX is approximately 10 crores. OPEX is estimated to be around 25 lakhs per year, which includes electricity costs to run the pumps for the waste water treatment system.

Challenges addressed:

As the project is on Urban Lake restoration, the process was dependent on climatic conditions of the city. An unexpected drought condition in 2019 delayed the dredging activity as the communities were apprehensive of losing water when water levels were lowered in the lake to facilitate dredging. Similarly, the extended monsoon and unexpected intense showers in non-monsoon months in 2021 and 2022 rendered the lake bed and embankments slushy which created a risky and non-conducive environment for machinery work. The unprecedented pandemic which occurred during 2020-2021 temporarily slowed progress as travel was restricted in most parts of the city.

However, the lost time was only adjusted by speeding up the work when site conditions improved and proceeding with due permission and support from the competent Government Authority.

Impacts:

The project involves restoration of the 100-acre urban lake for the following benefits,

• Improvement in storage capacity through silt removal that provides flood and drought mitigation benefits
• Improvement of lake water quality by treating incoming wastewater using nature-based solutions*. In comparison with the conventional grey infrastructure treatment method, the hybrid method adopted at Sembakkam lake based on semi -mechanized nature-based treatment system offers 30 % and 70 % lower construction and operation costs respectively , resulting in cost savings and ease of operation and maintenance.
• Accrue flood mitigation benefits through strengthening embankments and construction of flood regulators,
• Improvement in biodiversity habitat and community connectivity through eco-friendly landscaping development
• Work closely with Government and other stakeholders such as local community, subject matter experts for a participatory restoration approach
• Build community ownership for long term maintenance.
• Showcase use of advanced monitoring techniques such as Internet of Things (IoT) for periodical monitoring of lake water quality during pre & post restoration

*The methodology adopts nature-based solutions such as constructed wetlands in a hybrid approach for decentralised treatment of incoming wastewater. The total treatment capacity is of 7 million litres per day, which is supposedly one of the largest treatment capacities using reedbed technology for wastewater implemented in India. The unconventional approach uses locally available materials that will help showcase the benefits of nature-based solutions including its cost effectiveness, clean energy solutions and ease of operation while also offering benefits of supporting biodiversity and improved aesthetics.

Lessons Learnt:

Adaptive management for the restoration of land resources is key as any restoration project may throw unforeseen challenges during the restoration process.

Restoration of natural resources is not a one-time activity, but a process in itself starting from baseline assessment, followed by restoration planning, implementation and post implementation maintenance.

Stakeholder consultation formed a critical component of the process as getting a common consensus from different groups of people involved remained challenging. For example, while some people around the lake complained of ground water contamination due to lake pollution and welcomed green approaches for wastewater treatment there were others apprehensive of a treatment system in their neighhourhood. Similarly, while some people liked to have recreational spaces around the lake, there were some who raised objections that the serenity of the place would be disturbed if recreational spaces are built. Stakeholder consultation is therefore a must in any restoration process and the project implementation team should carefully evaluate people’s concerns and then take a decision based on actual facts and analysis. The basis of decision making addressing the concerns need to be documented as a part of decision-making process in consultation with the competent authority for the restoration process.

Scalability and replicability potential and conditions for success:

The Sembakkam Lake restoration project was aimed at demonstrating an integrated and holistic restoration process driven by science-based approaches.

Besides demonstrating the need to determine the optimal depth for any lake dredging process, this project adopts a green approach for treating incoming wastewater using a hybrid waste water treatment system including constructed wetlands. This methodology helps in keeping the lake clean with minimal requirement of electricity, chemicals or manpower which is both economic and eco-friendly. Hence, as the project is completed it has great potential to be replicated across other wetlands that face urban environmental challenges.

Author

Alpana Jain, Program Lead – Cities, The Nature Conservancy

Email: alpana.jain@tnc.org