August 16, 2021

[Case Study] Monitoring One of the Highest Arc Dams in Asia – Idukki Dam.

Various factors influence the healthy working of the structure, including hydrological, geotechnical, structural, and other power-related issues. Avoiding dam failure requires several dam monitoring instrumentations. 

Dams have been constructed through the many centuries to fulfil the needs of humankind as well as save them from many disasters. Dams not only provide water for society but also protects us from the river and marine floods, provides hydroelectric power, irrigation water, and a pleasant environment. As we see the old dams ageing and the new ones being constructed, dam monitoring becomes more significant than ever. 

Various factors influence the healthy working of the structure, including hydrological, geotechnical, structural, and other power-related issues. Avoiding dam failure requires several dam monitoring instrumentations. 

In this article, we look at the case study of Idukki Dam Monitoring, one of the highest arc dams in Asia, by Encardio Rite.

Idukki Dam – An Overview

Idukki Dam

Idukki Dam is a thin arc dam located across the Periyar River in a ravine between two granite hills known as Kuravan and Kurathi in Kerala, India. The concrete, double curvature parabolic dam is one of the highest arc dams in Asia with a height of 168.91m. Completed in 1973, the dam currents measure 365.85m at its top with 7.68m width at the top and 19.81m on the bottom.

Idukki Dam is owned by the Kerala State Electricity Board (KSEB) and constructed with two other dams at Cheruthoni and Kulamanu. The three dams create an artificial lake. 

Together, they harness a major portion of the power potential of Periyar, the largest river in Kerala. They do so by creating a reservoir, diverting water through a conductor system consisting of a power tunnel and two underground pressure shafts to an underground powerhouse in Moolamattom. 

The installed capacity of the powerhouse is estimated to be 780 MW with 6 units of Pelton-type turbines that have a power generation capacity of 130 MW each. The water of the Periyar river falls through a drop of about 669.2 m, producing power in the underground powerhouse. 

Idukki Dam – Purpose of Monitoring

Downstream side of Idukki dam

Encardio Rite was assigned the contract for Real-Time Early Warning Structure Health Monitoring & Data Interpretation (RESHMI). RESHMI plays an essential role in dam safety and risk management. It is a part of the Dam Rehabilitation and Improvement Project (DRIP). The essential purpose of RESHMI is as follows: 

  • Improve the reliability of the dam by looking after its safety and longevity.
  • To identify any early signs of failure or potential danger to the dam and implement corrective measures without resulting in a complete shutdown or failure.
  • Acquire data on the dam’s performance in the real world to improve future designs.
  • Study the impact of any natural event on the dam’s structural integrity.
  • To propose the maintenance of the dam in an effective & efficient manner. 

| Also Read: Instrumentation & Structural Monitoring of Dams |

Encardio Rite’s Scope of Monitoring Work

Encardio Rite was entrusted with the following responsibilities during the monitoring of the Idukki Dam.

  • Supply and Installation of Geotechnical, Geodetic, and Hydro-meteorological sensors.
  • Monitoring the existing working sensors installed in the structure.
  • Programming and authorizing data loggers with wireless data transmission and robotic total stations with in-house developed control boxes
  • Providing seamless data storage and backup servers
  • Setting up Drishti, Encardio Rite’s in-house data management software for real-time monitoring and prompt alerts. 
  • Lightning surge protection and earthing

Idukki Dam Monitoring – Instrumentation

Tilt meter and crack gage in vault copy

InstrumentInstallation AreaPurpose
Uplift pressure meterDam Galleries(Drilled Drains)Monitor the uplift pressure on the dam
Crack meterCrack Joints in dam galleriesMonitor opening of existing cracks/joints between different blocks of the dam.
TiltmeterVault at the top of the dam & other areasMonitor the tilt of the dam structure
Concrete Temperature MeterGalleries in inclined holes, towards downstream side of the damMonitor the concrete temperature
Water Temperature MeterSuspended in water at different depths towards the upstream side of the damMonitor water temperature close to the dam’s face
Flow MeterDam drains in galleries along with V-notchMonitor the rate of water seeping through the dam’s foundation.
Water Level SensorTop of nearby dam (Cheruthony)Monitor the water level of the reservoir.

Flow meter in gallery drain 1

Apart from the above mentioned sensors, the following instruments were employed.

  • Weather Station comprising air temperature, wind speed & direction, relative humidity, solar radiation, barometric pressure, and rain gauge. 
  • Data Loggers were installed to accumulate data from the sensors. The data loggers have GSM/GPRS modem for wireless data transmission to the central server. 
  • Prism targets were installed at the downstream intrados (concave surface) of the arch dam. For the monitoring of the prism targets, two robotic total stations were set up.
  • An extensive earthing & lightning protection system was set up on the site as the location of the Idukki Dam was prone to thunderstorms and lightning. 

Instrumentation Challenges

The prism target installation on the concave side of the double arch dam proved to be very challenging. There was much preparatory work and arrangement to be carried out for the installation. The location was difficult to reach due to the double curvature-parabolic surface of the intrados of the dam and the huge height of the dam. 

Geotechnical Sensors

A trained and qualified person with a proper license to work at heights carried the installation for the sensor. A rope access technician controlled and assisted the movement of the person in charge of the installation. 

An experienced surveyor was situated at the robotic total station to ensure the correct direction of the prism target. In the end, the successful installation of the prism target was quite an achievement.

| Also Read: A Guide on Geotechnical Instruments: Types, & Application |

Data Collection & Presentation

Encardio Rite ensured that all the data from the sensors were readily available to the concerned people. Real-time monitoring from Geotechnical, Geodetic, and Hydro-meteorological sensors was accessible to the consultant/contractor at their desk. 

Drishti Sensors

The data was collected from Geotechnical and Hydro-meteorological sensors by the compact data loggers and data acquisition system with suitable interface unit and BusMux. 

Robotic total stations collected and transmitted data from prism targets at desired frequencies. The station was managed remotely with the help of an in-house control developed control boxes with suitable software. The collected data is then transmitted to a central server in the control room. 

The Drishti database management system of Encardio Rite makes the data accessible to all the stakeholders in near real-time with advanced alerts and warning systems. It helps to precisely evaluate the field data and implement corrective actions when required. 

Training provided by Encardio Rite

Training by ER team to KSEB team on instrumentation

An extensive training program was conducted for the geotechnical, geodetic, hydro-meteorological, seismic sensors, and data acquisition systems installed. The Encardio Rite expert team provided a training program to the KSEB site team. Extensive training was also presented on the Drishti database management system, data presentation, evaluation, interpretation etc. Both classroom and field training were included in the training.

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