Dam if we do, dam if we don’t

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AS civilisations developed, the need for quality water increased in tandem.

To meet this need over time, reservoir or dam development began taking on a progressively important role as a supply infrastructure, freeing up raw water to end-users with a minimum risk of non-compliance or failure.

The reservoir impounds storm-generated run-off during the wet season and releases the stored water during a period of low-flow regimes or dry spells. The construction and implementation process involves meticulous engineering planning and precision.

There are dams all over the world. In Sarawak alone, at least four are found, including one raw water regulating dam — the Bengoh Dam — in Kuching.

The Bengoh Dam is built to provide adequate water to meet current as well as future demands of the city and the greater Kuching and Samarahan areas until 2030.

The existing water supply at Batu Kitang consists mainly of ‘run-of-river diversion’ which may not be able to sustain unabating demand in the years to come.

Already Kuching has begun experiencing inadequate water sources that, at times, led to serious shortage and hardship issues over the past few years.

Environmental experts believe one of the reasons for water shortage nowadays is the uncertainties spawned by the twin weather phenomena — climate change and global warming.

Whether or not the Bengoh Dam will be able to supply adequate quality raw water to the people in Kuching is still debatable. But in terms of implementation, it’s indubitably a successful project.

The 63-metre high by 267-metre long structure is the second roller compacted concrete (RCC) dam in Malaysia after the Kinta Dam in Ipoh, Perak, which offers a projected service life of 100 years.

The already impounded Bengoh Dam is believed to have carved out a lake with a surface area of about 10 square km.

According to the affected residents in Kampung Taba Sait, the impoundment has completely submerged their previous longhouse.

A study published in the International journal of Hydrology Science and Technology considers the Bengoh Dam safe based on the probable maximum precipitation (PMP) series.

The study also states the roles of surcharging volumes above the top water level of the reservoir are demonstrated via their respective flow attenuation capabilities.

From its physical outlook, the dam structure has undeniably been designed with engineering prudence. It is a fact that every dam may face an acceptable risk and probability of failure. And dams can pose risks, especially to those living downstream if they are not maintained and operated correctly.

Possibilities of failures

The possibility of dam failure could be attributed to various catastrophic events, including slope and embankment collapse, extensive piping or internal erosion and the over-topping of the dam body by enormous land mass movement within the reservoir water bodies.

The worst case scenario is an earthquake, which may cause complete bursting. This is the least expected but once the reservoir bursts, it spells disaster for the downstream communities. The aftermath clearance and reconstruction usually involve prohibitive costs.

Bengoh Dam is only about 40km from Kuching and large populations and infrastructures are located downstream of it. Kampung Bengoh itself is located about 2km from the dam. Coming after it are kampungs Danu, Semadang, Giam and Git, all situated on riverbanks.

Although dam failures are infrequent, their impacts can be catastrophic, often far exceeding typical stream or river flood events and can adversely affect people, their livelihoods and properties.

In fact, any dam has the potential to affect downstream areas and lives in a negative way. Many dams — should they fail — can also affect the delivery of essential utilities or flood control.

During periods of extreme flow, dams may fill to capacity, necessitating emergency releases that can flood downstream areas. Therefore, people swimming and fishing downstream of dams could be caught in planned spillway releases which may lead to tragic results.

Dams which occasionally break up because of engineering errors, enemy attacks or natural disasters, are considered ‘installations containing dangerous forces’ under International Humanitarian Law due to the massive impact from a possible destruction on the civilian population and the environment.

It’s true dam failures are comparatively rare but if it happens, the consequences are dire — like immense damage and loss of life among the communities downstream.

In 1975, the failure of the Banqiao Reservoir Dam and other dams in Henan Province, China, caused more casualties than any other dam failures in history. About 171,000 people perished while 11 million were rendered homeless.

In 2012, a dam in the northern Brazilian state of Rio de Janeiro, failed, forcing thousands from their homes. The water broke through the dam protecting the town of Campos de Goytacazes.

Officials described the situation as ‘a race against time’ to evacuate people before the area became flooded.

Since the incident, the Brazilian government has set up an early warning systems to ensure people evacuate before floods strike.

Common causes of dam failure worldwide include sub-standard construction materials and techniques (Gleno Dam); spillway design error (South Fork  Dam, near the failure of Glen Canyon Dam); geological instability caused by changes to water levels during filling or poor surveying (Malpasset Dam); sliding of a mountain into the reservoir (Vajont Dam — not exactly a dam failure but causing nearly the entire volume of said reservoir to be displaced and overtop the dam)and poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava dam collapse).

Among other conspicuous causes are extreme inflow (Shakidor Dam); human, computer or design errors (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant); internal erosion, especially in earthen dams (Teton Dam) and earthquakes.

No idea of risks

While it has been proven the impact of dam failure can be catastrophic, many people living downstream of the Bengoh raw water reservoir have no idea they are at risk.

I spoke to several people who would possibly be affected by any dam disasters, and many said they hadn’t a clue of the downstream risks.

I was also surprised to note even those living near the riverbanks were totally unaware of the dam-failure flood zone or the ‘high-hazard’ area.

High-hazard is a classification, meaning if the dam fails, the floods will likely kill people.

Most people living downstream also have no inkling of what a high-hazard dam’s flood zone means, claiming they have never been notified of any emergency-response plan for imminent failures.

Moreover, there are no flood maps of the ‘inundation zone’ — the area that will be impacted downstream of the dam in the event of a failure or uncontrolled release of water generally much larger than the normal river or a stream flood event.

Therefore, based on a random survey of downstreamers, it’s important for the dam administrators to come up with a booklet to help answer questions about dams — such as what purposes do a flood map and a high-hazard zone serve and what are the dams-associated risks?

State officials and the dam administrators should be able to provide information on the dam’s hazard potential classification — when was it last inspected — and also the dam’s condition on a regularly basis.

There’s a need too for the dam administrators to have in hand an Emergency Action Plan (EAP) to show people what to do during a crisis. The EAP has to be a formal document, identifying potential emergency conditions at a dam site, and specifying actions to reduce property damage and loss of life, including actions the dam administrators should take to mitigate on-site problems and issue warnings to the emergency management authorities.

As for downstreamers, especially those near a dam-break inundation area, it’s important they realise they and their loved ones live, work or recreate in areas that may be affected by the presence of a dam and what to do if this is the case.

It may be not be necessary to some but most need to find out their evacuation route to ensure a quick way out of harm’s way in the event of a dam incident.