In February 2017 an overflow spillway on a major dam, the Oroville Dam in California, collapsed and disaster was narrowly averted.
Here in Zambia we also have an ageing dam with structural problems not envisaged when the dam was planned and built. Can the Zambezi River Authority who is responsible for Kariba dam learn some lessons from this incident? A report investigating why this failure to prevent disaster on the Oroville Dam occured has just been published. This should be required reading for the ZRA, ZESCO, and all relevant people in the Ministry of ENERGY, especially the Minister.
A summary of the reports findings has been written by Elizabeth Ingram of Hydroworld.com –
Below are some telling statements surrounding the spillway incidents in the US that occurred. “The Oroville Dam spillway incident was caused by a long-term systemic failure of the California Department of Water Resources (DWR), regulatory, and general industry practices to recognize and address inherent spillway design and construction weaknesses, poor bedrock quality and deteriorated service spillway chute conditions.”
“The incident cannot reasonably be ‘blamed’ mainly on any one individual, group, or organization.”
Nonetheless, “Challenging current assumptions on what constitutes ‘best practice’ in our industry is overdue.”
Final report released
In its final report, officially released yesterday (from which the quotes above were taken), the Oroville Dam Spillway Incident Independent Forensic Team said there was no single root cause of the incident, nor was there a simple chain of events leading ultimately to the necessity of the evacuation order. “Rather, the incident was caused by a complex interaction of relatively common physical, human, organizational, and industry factors, starting with the design of the project and continuing until the incident.”
Physical factors were placed in two general categories:
1.Inherent vulnerabilities in the spillway design as-constructed and subsequent chute slab deterioration
2. Poor spillway foundation conditions in some locations
Human, Organizational and Industry factors were cited as:
“Normalization” of drain flows and cracking in repeated inspections (starting in the early 1970s after initial slab cracking and high drain flows in the late 1960s)
Decision (in February 2017) to accept use of emergency spillway against civil/geological advice.
In the end, the team determined “There were many opportunities to intervene and prevent the incident, but the overall system of interconnected factors operated in a way that these opportunities were missed.”
Specific to DWR, the report says:
“The dam safety culture and program within DWR … was still relatively immature at the time of the incident and has been too reliant on regulators and the regulatory process.”
“… DWR has been somewhat overconfident and complacent regarding the integrity of its civil infrastructure and has tended to emphasize shorter-term operational considerations … [resulting] in strained internal relationships and inadequate priority for dam safety.”
In the end, the lessons learned are probably the most important take-away from the incident and provide a way forward for dam safety worldwide. They are:
1. Dam owners must develop and maintain mature dam safety management programs which are based on a strong “top-down” dam safety culture. There should be one executive specifically charged with overall responsibility for dam safety, and this executive should be fully aware of dam safety concerns and prioritizations through direct and regular reporting from a designated dam safety professional, to ensure that “the balance is right” in terms of the organization’s priorities.
2. More frequent physical inspections are not always sufficient to identify risks and manage safety.
3. Periodic comprehensive reviews of original design and construction and subsequent performance are imperative. These reviews should be based on complete records and need to be more in-depth than periodic general reviews, such as the current FERC-mandated five-year reviews.
4. Appurtenant structures associated with dams, such as spillways, outlet works, power plants, etc., must be given attention by qualified individuals. This attention should be commensurate with the risks that the facilities pose to the public, the environment, and dam owners, including risks associated with events which may not result in uncontrolled release of reservoirs, but are still highly consequential.
5. Shortcomings of the current Potential Failure Mode Analysis (PFMA) processes in dealing with complex systems must be recognized and addressed. A critical review of these processes in dam safety practice is warranted, comparing their strengths and weaknesses with risk assessment processes used in other industries worldwide and by other federal agencies. Evolution of “best practice” must continue by supplementing current practice with new approaches, as appropriate.
6. Compliance with regulatory requirements is not sufficient to manage risk and meet dam owners’ legal and ethical responsibilities.
Bottom lineAs the report succinctly states:
“The fact that this incident happened to the owner of the tallest dam in the United States, under regulation of a federal agency, with repeated evaluation by reputable outside consultants, in a state with a leading dam safety regulatory program, is a wake-up call for everyone involved in dam safety.
By Adrian Piers
Agriculture, Fisheries and Aquaculture Consulting
East African Community and SADC Region