On March 14, 2019 the Spencer dam on Niobrara river, located south of Spencer in Nebraska state in USA breached, killing four people in the downstream. The Investigation Report about the disaster has been made public now on April 24, 2020. The remains of Spencer Dam — a skeleton of concrete and steel amid a sea of sand — became one of the iconic images of the March 2019 “bomb cyclone” flood that caused billions of dollars in damage across Nebraska.
Less than four months later, on July 2, 2019, Tiware dam breached[i] in Chiplun taluka of Ratnagiri district of Maharashtra, killing 23 people. The then Maharashtra Chief Minister Devendra Fadnavis on July 6, 2019 announced a Special Investigation Team (SIT) to probe into the disaster, the SIT was to submit a report in two months, but the report was submitted in January 2020, but the report is not in public domain. When SANDRP talked with the chairman of the committee, he disclosed that the report has been submitted to the department in early Feb 2020 and it can only be made public by the department once they accept the report. He revealed that the SIT had found that there were issues with material of construction (masonry in place of Concrete) and design of the conduit of the dam. He agreed that the report should be made public promptly, but expressed his helplessness in face of the norms in India. SANDRP also called Secretary, Department of Water Conservation, Govt of Maharashtra, but got no response.
There is a lot to learn for us in India in comparing the two dam breach incidents and how both are treated.
Tiware Dam breach The then Maharashtra Chief Minister Devendra Fadnavis announced that a Special Investigation Team will probe the disaster. The SIT, to be led by Avinash Surve, Secretary, Water Resources department, will have to submit its report within two months, an official statement said on July 6, 2019[ii]. Other members of the SIT include Ratnagiri district collector, superintendent of police, and a chief engineer from the state’s Water Conservation department. The SIT was to probe the loss of lives and properties into the flood caused by the dam breach, the reasons behind breaching of the dam, fix responsibilities of the guilty persons concerned and also suggest ways to ensure that such incidents do not recur.
The Spencer Dam Investigation Report “The Spencer Dam Failure Investigation Report”[iii] (SDFIR) done by the Association of State Dam Safety Officials was made public this week on April 24, 2020. The report was done by the same group that investigated the failure of a spillway at the Oroville Dam in California in 2017. It says in Forward to the report: “The mission of ASDSO is to improve the condition and safety of dams through education, support for state dam safety programs and fostering a unified dam safety community. ASDSO undertook this project at the request of the Nebraska Deparatment of Natural resources, the state regulator, and the Nebraska Public Power District (NPPD), a dam owner, with this mission in mind and understanding the need for dam safety community to learn from this failure… The dam owner and state regulator cooperated completely in the investigation, and NPPD provided funding. However, neither entity was involved in the development of the scope of work, panel selection, or panel discussions, calculations, deliberations or decisions.”
The Spencer Dam Disaster The reports in March 2019 said that the Spencer dam played a major role in controlling the Niobrara River’s flow into the Missouri River near Niobrara. This breach forced the Army Corps of Engineers (a federal agency) to increase the water releases from Gavins Point Dam to 90 000 Cusecs, not seen since 2011. The dam breach and floods left two towns (Niobrara and Verdigre) without any water supply and poor road access. Another eight thousand people in Norfolk were evacuated due to fear of levee breach along Missouri River in Mississippi basin. The problems started with heavy rains on March 12 onwards.[iv]
Breath taking drone video footage of the breached dam two days after the disaster is available.[v]
The SDFIR report said that the dam’s failure was the first caused by an “ice run event” in the database of 380 dam failures kept by the national dam safety group.
Spencer dam failure scenario The SDFIR report included a dramatic recounting of the demise of Spencer Dam in a segment entitled “An Adverse Convergence of Factors.” Subzero weather had left ice 2 feet thick on the Niobrara River upriver from the dam. Then came a thaw, increasing flows into the river threefold, followed by a storm that turned into a “bomb cyclone” around March 12 with 2 inches of rain, followed by snow and blinding winds. The report says: “During the evening of March 13, dam operators opened all four of the dam’s tainter (radial) gates to their maximum six foot opening on the spillway crest. They later released stoplogs from some of the other bays to increase outflow, but were not able to open most of the stoplog bays due to ice… Around midnight on March 13, a major ice run came down the Niobrata River, failing the Stuart Naper Bridge and damaging Highway 11 (Butte) Bridge. Both bridges are upstream from Spencer Dam… One or more ice jams occurred upstream from the dam, backed up flood waters and burst sending a great amount of rubble and flood water toward the dam.”
An ice jam a half-mile long and 3,000 feet wide formed upriver at the Nebraska Highway 11 bridge south of Butte. That jam likely broke, the report said, sending a surge of ice and water downstream that might have jammed again, before releasing a torrent toward the 3,200-foot-wide earthen and concrete dam “with catastrophic results.”
The SDFRI says: “Ice rubble likely clogged the opened gates and stoplogs of the dam’s spillway and the reservoir rose to the dike crest. Continued inflow of ice and water into the reservoir pushed some ice rubble onto and over the crest and downstream slope of the dike (embankment). Ice pushed through the upstream brick wall of the powerhouse… Flow overtopped the dike, causing the downstream side of the dike to erode. The erosion led to headcuts, which grew in several locations along the dike’s downstream slope. The dam’s embankment dike breached in two locations, the first breach occurring around 5:15 AM. The breaches widened and discharged water and rubble downstream.”
Two operators described how the catwalk above the dam’s spillway was shaking from the pounding of ice chunks, and how they were unable to open all the dam’s “stoplog” spillways because they were frozen shut. With water rising and the catwalk impassable, the operators fled the powerhouse about 4:30 a.m. on March 14, 2019 and drove around to the other side of the spillway. The dam breached in two places at about 5:15 a.m., according to the report, which surmised that ice had clogged the spillway, causing a 10-foot rise in the water/ice level in about 37 minutes.[vi]
The 92-year-old dam was battered by a torrent of floodwaters and ice chunks — some weighing more than 2 tons and measuring 2 feet thick and 20 feet across. The chunks blocked the spillways of the dam causing water to back up and overtop the earthen and concrete structure, eventually washing it away. The Niobrara River tore holes in the Spencer Dam, creating two new river channels.[vii]
Findings SDFIR identified two key human factors that contributed to dam failure and consequences.
- “There is notable lack of knowledge about ice-run related potential dam failure modes generally in dam safety industry. Specifically, NebDSP did not know that Spencer Dam had previously failed and was damaged in ice run events. NPPD had limited knowledge of past ice run events at the dam… Current dam safety best practices do not include evaluating run of the river dams for stability during ice runs.”
– The dam’s past history included a breach caused by a spring “ice run” in 1935 and damage to dam gates and power house by two similar events in 1960 and 1966. The report found: “These incidents do not appear in ASDSO’s database as ice related failures. There was no consolidated history of the dam and important records were lost, unorganized or unavailable… Furthermore, NebDSP predominantly relied on its dam inspection program to bring dam safety issues to the attention of dam owner; latest vulnerabilities such as performance during ice run floods are not addressed in the state’s inspection reports.”
Mark Becker, a spokesman with the Nebraska Public Power District, the current dam owner, said that dam records were swept away by a flood in 1966, which was before the utility owned the hydroelectric dam. The officials could have reconstructed the history.
- “The Penal believes that NebDSP and NPPD underestimated the potential of the dam to cause life threatening flooding at the downstream house and property in the event of dam failure. There was a lack of recognition that the house, Strawbale Saloon and RV Camp ground situated just downstream from the dam would be at risk if the dam failued. One reason is that the Downstream Hazard Potential Classification (DHC) of the dam was “significant” when in the panel’s opinion, it should have been “high”. Its significant DHC rating resulted in less dam safety regulation including no requirement for an Emergency Action Plan (EAP). If the dam were designated a “High” hazard potential dam, there might have been a requirement to modify the dam to increase flood handling capacity” and ice run events. Such a rating also might have led to the removal of imperiled properties or a warning system for dam operators and downstream residents.
Baker said that he did not know why state regulators had not noted the existence of a house just below the dam, which would have elevated the dam’s rating to a “high hazard.” That would have led to better warning systems and possibly, removal of the house. Such classifications are done by the state.
Lessons to learnt from Spencer Disaster The SDFRI listed following among the lessons for future.
- More research needs to be done on the dynamic nature of rivers in cold weather regions, including ice run formation, frequency, movement, damage and how infrastructure like dams should be designed, maintained and operated to withstand ice run loading.
- Dam inspections, while valuable, are not adequate dam safety evaluations in themselves. Evaluations must include review of critical documentation and records. Potential Failure Modes (PFM) Analysis at an appropriate level should be conducted as part of dam safety review. Once the PFM are understood, inspection checklists should be modified to identify signs these PFMs are developing and/or the dam is vulnerable to them.
- Dam owners should maintain a complete and organised set of electronic records for their dam(s). A concise history of the dam with reference to key records and past incidents is invaluable.
- One of the most important responsibilities dam safety regulators have is to periodically assess the areas downstream of low and significant hazard dams to evaluate whether the hazard classification is appropriate. Documented formal procedures (including reviewing data such as aerial or satellite photography and verifying during site inspection should be adopted.
- For dams with people at risk downstream, Emergency Action Plans should be developed and exercised.
- Dams should have operation plans that include operations during extreme events.
- Engineers working on dams, bridges and other infrastructure facilities at rivers in cold weather regions need to assess whether the rivers are susceptible to period severe ice runs. If this susceptibility exists, it should be addressed in design. Dam facilities should be designed to be operated safely during these extreme weather events. Warning systems are one potential measure to reduce risk where ice runs form.
What we in India can learn from Spencer Disaster episode While the number of deaths due to Spencer dam disaster (4) is far fewer than the number of deaths (23) at Tiware dam disaster, we see that the probe report of the Spencer Dam disaster has been done by an independent organisation and and that organisation has also selected the people to be on the panel, not the government, even as the dam owner and state government’s NebDSP has provided funding, information and all the cooperation for the report. This is very different than the situation with respect to Tiware Dam disaster. Secondly, the report of the Spencer Dam probe has been PROMPTLY and AUTOMATICALLY been put out in public domain unlike in case of Tiware Dam SIT report, which remains wrapped in files. Thirdly, there is no element of secret about the dam, dam site or dam related information in USA, unlike the situation in India. Fourthly, the dams are given hazard classifications in USA, but we have yet to do it in India. Fifthly, the annual inspection reports of dam safety by independent team of experts is a reality in USA, whereas in India, it is not known to happen for all dams and even where it happens, it remains a secret. It may be noted that Spencer was a 92 year old dam when it breached in 2019. Tiware was possibly (there is no clarity as to when exactly it was commissioned) less than 20 years old, was a much smaller dam that Spencer dam and yet it created more deaths than did Spencer dam.
Clearly, India has a long long way to go before we can be confident about safety of India’s dams. But there is a lot we can understand from these episodes if we want to.