Repair of Leaks in Dams: Risk Assessment & Client Communication

Leaks in Dams: How to Save Water, Time and Effort

From large hydroelectric sites to private decorative reservoirs, dams are invaluable geographical areas. Given their various applications across industrial and agricultural settings, there’s no doubt that dam structures should be assessed and monitored on a regular basis.

Interestingly, one of the main problems that hydro engineers, contractors, and dam owners face is leaking. Even though dams are normally expected to lose water – often due to sedimentation, seepage, and evaporation – leaks in dams can be unpredictable. We should note that reservoir sedimentation is defined as the process of accumulating sediments or solid materials, which can lead to decreased storage rates and eventual abrasion of dam components. Seepage, on the other hand, is defined as the water movement from the upstream face of the reservoir to its downstream surface.

In contrast, leakages occur when water escapes through an opening, such as a hole or a crack. Leaks in dams can be caused by various issues, such as erroneous design principles, inappropriate cut-off trench under the embankment, use of unsuitable soils, failure to remove vegetation, aging, and poor maintenance. Leaking dams are detrimental not only to farm life and economies but people’s health. The collapse of the Whaley Bridge reservoir in the UK proves that dam leaks pose a threat to life.

Due to the uncertainties around dam leaks, professional help and on-site inspection are crucial. Because if one is unable to identify the cause of the problem, any experimental solution will be unsafe and wasteful!

Risk Assessment, Client Communication, and Investigation – Essential Steps to Fixing Leaky Reservoirs

Risk assessment and investigation are the first steps to treating leaks in dams. Sometimes the problem is obvious; the dam doesn’t fill in adequately, water is escaping through the walls, recent storm damage, and so on and on. In some cases, subtle markers, such as unusually healthy crops below the reservoir, might indicate leaks. Daily measures can also help owners calculate how much water is being lost, and how much of the daily losses are due to leaking.

Nevertheless, if leaks in dams cannot be identified easily, professional help and on-site investigation are mandatory to help earth dam owners to solve the right problem and find a balance between costs and effectiveness.

Thus, client-contractor partnerships should be based on trust. While contractors should always propose strategies that are economically sound and effective in the long-term, clients should be willing to provide transparent information and embrace new strategies.

Muchalinda Dam: Changing Direction and Strategy | A Case Study

The beautiful Muchalinda Dam is a powerful example of changing direction and strategy, a process in which dam owners and experts should build a relationship based on trust and transparency. Here we should mention that Muchalinda Dam, located near the Buddhist Monastery in Wilton, New South Wales, has a total area of 2404 square meters.

An initial assessment proved that the dam was leaking significantly. During a two-week inspection, experts noticed a loss of 800 mm or 1% of its total volume, as well as an increase in the sitting groundwater levels. Interestingly, the presence of such alarming markers often indicates that internal holes, such as pipes and tunnels, are increasing in size. Note that piping or tunneling occurs when seepage causes a line of weakness, which might create an opening.

Yet, the experts involved in the initial assessment of the Muchalinda Dam were not given comprehensive pieces of information. It became clear that the information regarding the clay content in the dam and its low-level mark were inaccurate, and the leak wasn’t caused by problems in the upper band. Further evidence showed that the Muchalinda Dam was originally designed to provide a road base, not to contain water. Not only the initial structure had a different use, but after a solid rock shelf had been hit, further activity was stopped and the rubble was pushed into what is now the leaking dam wall.

Additionally, experts detected the following errors:

• Use of heavy machinery on sandstone, which can cause cracks
• Rock spoil rolled into a dam wall
• Lack of soil compaction
• Use of porous non-clay materials

Furthermore, as the dam hadn’t been keyed into the rock, seepage-induced piping and saturation undercut were detected.

Based on the collected data and the Mohr-Coulomb Failure Theory used to analyze rock mechanics and failures, experts proposed three strategies to help to fix the leaks in dams:

• Demolish the dam
• Fix the leakage
• Leave it as it is and report the dam as a dangerous facility with structural flaws

In order to fix the Muchalinda Dam, though, experts insisted on changing direction. They suggested the following steps (as opposed to using a wet blanket):

1. Drain the dam (24 hours)
2. Spread bentonite and clay (7 days) to cut water supply to sub-surface pipes
3. Roll-in bentonite (5 days)
4. Refill the dam (24 hours)

Here we should note that, if left untreated, it’s expected that the wall of the Muchalinda Dam will collapse within 12 months.

Leaking Dams: Long-term Solutions and Safety

When it comes to leaks in dams, dam owners can decide to demolish their dam or tackle the problem. Neglecting a leak, though, can only endanger public and environmental safety.

As mentioned above, various causes and solutions to a leaking dam exist. Some of the common strategies to repair a leak in dams include the use of:

• A plastic membrane liner
• Concrete linings
• A local clay liner
• A bentonite clay liner
• Compacted earth clay linings
• Sealants, such as gypsum or sodium tripolyphosphate
• Bituminous sprays or coatings
• Polymer plugs

That said, building a new dam in a place with suitable soils can sometimes be cheaper and allow changed land use. 

Interestingly, bentonite, the material proposed for the repair of the Muchalinda Dam, is defined as an active liner, a type of flocculate clay. This type of white clay expands 400 times its weight by absorbing water and can be used to fill a void as a comprehensive seal. Moreover, the bentonite clay is eco-friendly and cost-effective; it absorbs different chemicals and can stop toxic materials from reaching crops and plants.

If dam owners decide to use bentonite clay as advised by experts, they can choose between two methods: wet blanket and dry blanket strategies. When employing the bentonite dry blanket method, the bentonite is spread over the dam area at a rate of approximately 15 kg/m2. If the dam contains rock, though, the rock should be covered with at least 300 mm of compacted clay mixed with bentonite.

The bentonite wet blanket method, on the other hand, does not require dams to be emptied. The bentonite is spread over the water surface at a rate of 30 kg/m2. Yet, this method can be unpredictable, with a success rate of 70%; and when it comes to water management, dam owners should aim for 100% effectiveness, especially in arid areas.

Risk Assessment, Client Communication, and Repair of Leaks in Dams: Conclusion

Water losses can have numerous negative effects on both local and global levels. Though many new dams are expected to lose water through evaporation, sedimentation, and seepage, leaks can be unpredictable and dangerous. While some leaks are obvious, some problems are difficult to detect. Thus, professional help and risk assessment are crucial to help dam owners to choose the right solution to their problem.

To repair leaks in dams, experts can employ various strategies, such as building a new dam, using polymer plugs, or applying bentonite clay. In fact, bentonite is considered one of the most effective and active materials to improve dam design, water management, and safety.

Many times problems are caused by erroneous design principles and poor maintenance, which can be embarrassing to workers, contractors, owners, and users at the same time. Thus, transparent communication becomes essential to help all the parties involved build a relationship based on trust. In the end, expertise and trust go hand in hand, so dam owners won’t spend their resources like water.