How a Dam Reports on Itself

A dam under load is never silent. It is reporting on itself every hour, through the instruments embedded in its body and foundation, and each instrument is the early warning for a different way the structure can fail. The point of a monitoring programme is not the instruments. It is the failure mode each one is watching.

Start with the cheapest. A V-notch weir measuring the water that seeps through and under the dam is, by the assessment of the Indian Standard itself, the most telling instrument on the structure. IS 7436 Part 2, the BIS guide for measurements on concrete and masonry dams, puts it plainly.

Seepage is, undoubtedly, the best indicator of the overall performance of a dam because this reflects the performance of entire dam and not just the condition at discrete instrumented points.

IS 7436 (Part 2):1997, Clause 4.2.1.

A sudden rise in seepage with no rain to explain it, or seepage that turns cloudy, is the earliest signature of internal erosion carrying soil out of the foundation. The rest of the suite watches narrower failure modes. Piezometers and uplift cells measure the water pressure under the base, which buoys the dam up and reduces the effective weight holding it down against sliding and overturning; when uplift climbs past a threshold, the stability calculation no longer closes. Plumb lines and pendulums hung in vertical shafts measure how far the dam is deflecting, and the Indian Standard says the first years of those readings will reveal any dangerous tilt or movement. Joint meters and crack meters measure whether two blocks are moving relative to each other, which is usually the foundation settling unevenly beneath them. Thermometers track the heat of hydration while the concrete is young and the seasonal thermal cycling for the rest of the dam's life. Strong-motion accelerographs wait for the earthquake.

None of these instruments reads a verdict off a single number. What matters is the trend. A baseline is established from the first readings, and an anomaly is a departure from that established trend, in either the magnitude or the rate of change. An instrument with no baseline, or a data series with a gap in it, cannot tell you whether today's reading is normal or the start of something.

Which is the problem. An instrument only warns you if someone reads it, and on India's ageing dams a great many have gone silent. The clearest evidence is not commentary. It is a statutory document. The Telangana State Dam Safety Organisation, in its 2023-24 annual report filed under the Dam Safety Act, recorded the condition of the instrumentation at Nagarjuna Sagar, one of the largest dams in the country.

Nagarjunasagar dam has instrumentation to measure uplift and pore pressure monitoring but this equipment is not active. Same is the case with equipment related to crack and joint movement, and stress and strain measuring of the structure.

Telangana State Dam Safety Organisation, Annual Report 2023-24, as reported by Deccan Chronicle, 27 January 2025.

The same report noted that many of the state's 174 specified dams lack even basic instrumentation, down to devices for water level, seepage, and uplift. A dam whose uplift, joint-movement, and stress instruments are all inactive is not reporting on itself at all. It is being watched by eye alone, which is exactly the condition instrumentation exists to improve on, because the most dangerous distress develops inside the structure where no inspection can see it.

The law has now closed the option of leaving it that way. The Dam Safety Act 2021 requires the owner of every specified dam to install and maintain a minimum set of instrumentation under Section 32, to carry out pre-monsoon and post-monsoon inspections under Section 31, and to prepare an emergency action plan under Section 36. These obligations run on the same five-year clock as the first Comprehensive Dam Safety Evaluation under Section 38, which expires on 30 December 2026. The CDSE reviews the performance and maintenance record of the structure, and a dead instrumentation system is precisely the kind of gap it is designed to surface.

What the live version looks like is on display at Idukki, India's first arch dam. Under the Dam Rehabilitation and Improvement Project, Idukki was fitted with a real-time structural health monitoring system carrying tilt meters, crack and joint meters, uplift gauges, a plumb line, and geodetic prism targets on the dam's curved face read by robotic total stations, all reporting continuously rather than waiting for a technician with a clipboard. That is what a dam sounds like when its instruments are alive.

The lesson: A dam reports on itself, but only through instruments that are read, and only against a baseline that has not been allowed to lapse. Seepage is the master indicator; uplift is the stability warning; the plumb line is the movement warning; the joint meter is the differential-settlement warning. Before December 2026, the dam owners who have let their instrumentation go dark have to revive it, re-establish the baseline from a fresh set of readings, and restore the data series, because an unread instrument is not a safety margin. It is a blind spot that the paperwork records as if it were a margin. The cheapest weir, read every week, is worth more than the most sophisticated sensor that no one has logged since 1990.

Read more: Thermal Instrumentation for Mass Concrete Dams →