Hydropower is poised to play an increasingly important role to meet Malaysia’s energy and climate goals. Currently, the share of hydropower in the country’s electricity generation mix is around 16% according to latest statistics released by the Energy Commission of Malaysia.

However, the utility of hydropower does not just stop at being an efficient source of renewable energy. Progressively more, hydropower is being deployed in Malaysia as a method to mitigate floods in flood-prone areas of the country.

How hydropower helps flood mitigation

On average, Malaysia receives an annual rainfall of 2540 to 3850 mm, making it one of the countries with the heaviest rainfall in the world and is thus prone to monsoonal and flash flood. Floodplains in Malaysia are estimated to cover an area of 9% of the total landmass in the country which is home to some 4.8 million people. Add to that the effects of climate change and rapid urbanisation and the tendency for destructive floods to occur in the country only rises. As such, one of the ways to mitigate this issue as well as maximize water availability for human consumption is to construct hydroelectric dams.

According to Ts. Dr. Faizah Che Ros, Senior Lecturer of the Department of Chemical and Environmental Engineering and Associate Fellow of the Disaster Preparedness and Prevention Centre from the Malaysia Japan International Institute of Technology (MJIIT) and Universiti Teknologi Malaysia (UTM), hydroelectric dams capture floodwater in water catchment areas which store large volumes of water when a flood occurs. When the flood season is over, the water is then released under controlled circumstances back to the river or stored for later use.

The accumulation of large volumes of water in the reservoir make flood management a crucial part of hydropower plant

“Whereas non-structural measures such as monitoring of rainfall and river stages would require observation at several location at the upstream and downstream, damming allows the maintenance and monitoring of a single body of water where the accumulation of large volumes of water in the reservoir make flood management a crucial part of hydropower plant,” she added.

Ts. Dr Faizah pointed to the Kenyir dam as an example. The dam was mainly built for hydroelectric generation besides providing water regulation benefits and flood mitigation, succeeded in reducing flooding at the downstream area since 1986. The 155m high rockfill dam with eight earthfall saddle dams forms a reservoir spanning close to 370 km squared. Its ungated chute spillway has a discharge. capacity of 7,000 cubic metres per second making it an effective flood prevention dam especially during the monsoon season.

Another example is the Three Gorges Dam in China. It can hold the flow of water from Yangtze River and prevent rushes of water to its downstream branches. The water level in this dam must be kept below 165 metres in light of possible annual flooding. Nevertheless, there is enough room in its reservoir for the water level to rise up to 175 metres or approximately 22.1 billion cubic metres of water. Effectively, the Three Gorges dam acts as a superb defence against floods. It was reported last year that the dam restricted water discharge at 19,000 cubic metres per second despite a higher average inflow of around 40,000 cubic meters per second into the reservoir.

The case of the Nenggiri Dam

One such similar dam with flood prevention capabilities is the proposed hydroelectric dam in Nenggiri, Gua Musang, which, when completed is expected to solve the yearly flood woes in Kelantan. The dam would act as a flood-mitigating mechanism to halt the flow of water into the rivers thus reducing the risk of floods especially in upstream areas of the state.

Where undammed water systems require the observation of several waterways, the proposed Nenggiri Dam would require maintenance and monitoring of a single body of water which would ease the burden of flood mitigation. The water from the dam can also be used to aid agricultural drainage and other domestic uses.

According to Ts. Dr Faizah, while hydropower dams are indeed not perfect, using the Neggiri Dam as an example, the advantages far outweigh the disadvantages.

“The dam would minimize the impact of annual monsoon floods, especially at Kuala Krai and Kota Bharu. At the same time, it is a long-term investment designed to produce electricity for decades to come. Besides that, such impact can be mitigated by taking appropriate measures and further minimised by watershed management and environmental monitoring program,” she said.

Nevertheless, she also stressed that the economic benefits of the dam must be balanced with sound policies and good governance to ensure that the rights of affected indigenous population are taken into account in planning, construction and sharing of benefits.

Other success stories of flood mitigation

The Nenggiri dam project is not the first of its type as such initiatives have been proven successful in other countries.

In the Mekong River, dams have been a useful in flood mitigating tool for many years. A study found that that six Upper Mekong Basin mainstream dams and 71 Lower Mekong Basin tributary dams would decrease the river’s annually flooded area by up to 6.6%. Another research published in 2017 noted that flood reservoirs in dams alleviated flooding along the upper Lower Mekong Basin and predicted that the benefits of flood control outweigh climate-driven increases in flood magnitude through 2070.

Over in Japan, the Maruyama Dam has been integral to flood prevention since its completion in 1995. It is a concrete gravity dam, measuring 98.2 m high and 260 m long with an effective storage capacity of 4,028 cubic metres and a flood control capacity of 2,120 cubic metres. In addition to the classic method of using long continuous dikes to channel floodwaters to the sea as quickly as possible, the Japanese government employs such large dams to decrease peak flood discharges and reduce the load of river channels into the Kiso River Basin.

In the United States, it was reported that approximately 20 percent of its listed dams in its national inventory was primarily used for flood control. Estimates show that over US$5 billion of flood damage had been negated thanks to such dams in the Central Valley, Tennessee Valley and California. The Seven Oaks Dam, Castaic Dam and the Buchanan Dam are some examples of dams that have helped prevent floods thus reducing risks associated to loss of life and property to millions of US citizens. It is projected that investments in such flood control structures result in a sixfold return in terms of flood loss prevention.

It is projected that investments in such flood control structures result in a sixfold return in terms of flood loss prevention.

In terms of public policy, many countries have made hydroelectric dams a key pillar of their renewable energy and flood control.

Norway, for example published a parliamentary white paper on energy policy which highlighted the importance of hydropower plants in flood control as the impacts of climate change makes this perspective more important than before. According to a study from the Japan International Cooperation Agency (JICA), the Philippines, China, UK, and Indonesia are some of the countries that have increased their flood control budgets in the past years as a reaction to the enormous damage from recent disasters.

To Ts. Dr Faizah, these examples prove that the future of hydro dams serving as flood mitigation measures can be seen as a good strategy to reduce the negative impact of flood, especially downstream area with high populations.

Long term outlook

In the long term, innovations in dam technology would only improve the utility of new and existing hydropower dams. Their flood prevention capabilities offer a broad blanket of protection especially for those, who live close to rivers or large bodies of water.

Ts. Dr Faizah points out that the increasing variability in rainfall is expected to be a major consequence of climate change. With some predictions indicating intensified monsoons in the coming decades, hydroelectric dams can serve as a bulwark against any unexpected flooding.

“With the benefits of hydropower dams as flood control structures, the future of hydro dams serving as flood mitigation can be seen as a good option to reduce the negative impact of flood, especially downstream area with high populations,” she further explicated.

Already, many countries such as China and the United States have increased their investments in hydroelectric dams as a result of their electricity generation and flood mitigation benefits.

“The challenge of doing this successfully depends on engineering design, strategy (the seasonal planning for water level management at the reservoir), and to plan (the day-to-day or hour-to-hour) response by the dam operator during the flood event. Engineering calculations and design are extremely important, as well as the knowledge of the design team, and their ability to predict major flood events is crucial,” stressed Ts. Dr Faizah.

Ultimately, the benefits of such projects are far reaching and can potentially be live saving. Once a dam has been successfully operating for a few decades, the downstream inhabitants become used to the new flow regime. Buildings and other infrastructure are sometimes constructed in floodplain. This can also lead to ancillary economic benefits in terms of tourism, navigation and manufacturing which can boost the local economy.