Using Hydro Power Plants for Flood Prevention

Overview

Hydro power plants provide clean and affordable electricity in large quantities. They are often the main renewable energy technology choice for governments due to its ability to deliver reliable baseload energy with very minimal fluctuation. Hydro power plants are also able to accommodate changing demand and suited to large scale network response. Hydro power plants require damming a water supply which in the process often affects a catchment area’s environment. The accumulation of water in turn change the flow of water, consequently its temperature and the migration of fish living along the affected water path. Water damming for Hydro power plants has further effects on local ecologies due to flooded vegetation, changing water depth and chemical composition, and effects on siltation.

Hydro power plants can be used to regulate and reduce the risk of flooding. However, due to the large quantities of water stored in the dam of the Hydro power plants, they also bring with them a new risk of flooding. This article will examine the advantages and disadvantages in of Hydro power plants  for flood prevention. For more information on hydro power plants in general, have a look at the Hydro Power Basics article.

The Impact of Flooding on People

Flooding can have severe impacts for the effected population. These include the destruction of homes and agricultural land, the loss of property and above all the risk of people drowning in the floods. The damage caused by a flood can often have long term negative effects and it can take many years for the flooded area to recover, potentially leading to large economic losses.

The history of  Hydro power plants has been filled with stories of dams failing, giving way to flood-inducing volumes of water and in turn causing flooding disasters. The recent failure of Oroville dam’s main spillway forced led authorities to allow overflow via the auxiliary spillway, putting in danger the ground on which the dam stands. This has caused the evacuation of thousands of people in California, who lived in regions at risk of flooding.

The Impacts of Hydro Power Plants on Flooding

Hydro Power Plants Causing Flooding

The United Nations (UN) estimates that over 60% of the world’s largest river systems have been disturbed by dams and other man-made diversions, signifying a huge impact on local ecology and the water cycle within the area. Some of these effects may include loss of habitat in the catchment area (both for communities and animals), plain flooding and subsequent loss of endemic vegetation, and deviation in fish population.

Hydro power plants can cause an increased risk in flooding. The plain flooding caused by hydro power plants are controlled to form the power plant’s reservoir dam. The issue of uncontrolled flooding in relation to hydro power plants however are often due to a build-up of sediment, as was the case in the 2013 floods in North India "As small Hydropower Expands so Does Caution on its Impacts”, published by Yale Environment. Further studies confirm this, stating that sedimentation in the reservoir leads to a reduction in the available reservoir volume. Thus the reservoir is no longer able to control large inflows—such as those brought on by unusually heavy rainfall. This can then lead to unforeseen discharge/overflowing of the dam.

Events like these demand different methods of mitigation. An example of non-structural amendments includes more conservative level control by gradual discharge through spillways, implemented in parallel with sedimentation monitoring. Additionally, structural methods such as reservoir deepening or dredging to increase retention volume, and longer operation times can prevent flood risk. Alternative methods include altering the discharge flow to be dissimilar to rainfall or inflow times and mobilising the sediment build-up.

India’s Environment ministry reports that ill-managed hydro power plants in Northern India had a partial role in the floods the region saw in 2013. Specifically, they highlight the build-up of sediment in rivers due to these badly managed dams, displacing and raising water levels. Effectively, these waterways became more prone to overflow.

Another incident occurred in 2016 in central Vietnam where hydro power plants discharged up to 2,000 cubic meters of water per second after heavy rainfalls. This resulted in floods which killed several people and submerged many houses. It was found that poor operation of the hydro power plants was to blame for this flood and that the hydro power plants operator had failed to issue a warning to the local population about the unexpectedly large discharge.

Hydrop Power Plants Preventing Flooding

However, often hydro power plants are actually used to control and prevent floods. The accumulation of such large volumes of water in the reservoir make flood management a crucial part of hydro power plants. Whereas undammed water systems would require observation of several waterways, damming allows for the maintenance and monitoring of a single body of water. Even the smallest of retention volumes reduce the likeliness of flooding. For example, the Kaprun Ache, in Austria, had a natural probity of experiencing a flood every 10 years, however now, after the construction of a hydro power plants with a reservoir, the probability of a major flood occurring has dropped to once every 75 years.

In Brazil hydro power plants, in conjunction with a matrix based monitoring system, are also used to control flooding. The system is based on a waiting volume in the reservoir, a volume of water retained to allow optimal energy production, but also to safeguard from potential flood-inflow. This statistic is calculated using mathematical models of recurrence time, flood probability, inflow period characteristics, operational constraints and other factors. These are all considered in the planning stage of the hydro power plants to ensure that any hydro power plants built can control potential flood events.

Micro Hydro Power Plants

Micro and mini hydro power schemes are often run of-the river, which do not directly interfere with the natural flow of the river, or they have small dams/wires/catchment area to store some water above the turbine. Due to the small scale of the power plants they are general considered less environmentally intrusive than large scale hydro power plants. However, some studies have found that, some studies have found the micro hydro power sites increase the risk of flooding in an area. This is because the power site introduces a barrier into the river system, which can lead to a build-up of sediment which in turn can result in an increased risk of localised flooding. This is especially the case for micro hydro schemes which include a small catchment area. The 2013 floods in Uttarakhand, India, serve as a prominent example for this. The floods where cause by especially strong monsoon rainfalls, however, a government-commission claimed that the many micro hydro dams in the area contributed to the floods. They caused “fragmentation of the river habitat”  and changed the sediment flow. While individual small scale hydro plants do not have “the measurable impacts you have with bigger dams … a study in the Nu River area in China found that the cumulative impacts of small hydropower can actually outweigh those of larger dams.”

However, micro and mini hydro power plant can also be designed so that they contribute to flood prevention, for example by providing additional flood plain storage. For more information on the different design features for flood prevention have a look at the article Micro-hydro Power (MHP) Projects - Mitigation and Intervention Techniques - Flood Control and Improved Drainage for example micro hydro sytems which include a penstock can “reduce the risk of erosion and flooding in a stream because they route some of the water through a pipe instead of having it run down the streambed, and because they reduce the speed of the water.”

Conclusion

The maturity of hydro power plants technology as a way of harnessing cleaner energy means that a lot of experience has been gathered in this area. If designed and operated correctly this allows modern hydro power plants to control and prevent flooding as well as produce energy simultaneously. Smaller schemes still meet multiple challenges and have been shown to contribute towards flooding. This is possible due to small hydro’s effect on the bodies of water in the catchment area, changing their sedimentary flow and their cross-sectional areas in turn allowing flooding events to occur more easily. However, when carefully designed small scale hydro power plants do not necssarily have to increase the risk of flooding and can in fact even be used to mitigate the risk.

Related Studies

Hydropower Reservoir for Flood Control: A Case Study on Ringlet Reservoir, Cameron Highlands, Malaysia

• The study highlights the effect of sedimentation on hydro power plants reservoirs and their retention capability.
• It uses numerical simulation—backed by field tests—to estimate the discharge parameters needed in the event of reduced retention and increased sedimentation.
• The study recommends additional safety measures to prevent flooding from the Ringlet reservoir.

As Small Hydropower expands, so does caution on its impacts

• The article highlights the effects of small hydro on the local ecology
• This also shows how small hydro has contributed towards the flooding incidents in North India

Cumulative biophysical impact of small and large hydropower development in Nu River, China

• This study investigates the environmental and social impacts of large and small scale hydro power plants, comparing the effects by normalizing them per megawatt of power produced.
• Results from this study indicate that biophysical impacts of small hydropower may exceed those of large hydropower.

A Socio-Cultural Appraisal of Developing Micro-Hydro Power Generation at the Fulling Mill

• This study discusses the impacts of micro-hydro on localized flooding and its wider impact on the body of water itself

The Methodologies for the Flood Control Planning using Hydropower Reservoirs in Brazil

• The study showcases Brazil’s innovative take on hydro power plants control both as an energy producer and a water management asset.
• This study explains the methodology behind obtaining the critical values such as ‘Waiting volumes’ in flood control and demonstrates the computational tools in planning for flood control.
• These are applied to the Paraná River basin to highlight the methods’ value.

Flood Control Challenges for Large Hydro-Electric Reservoirs Examples from the Nam Theun - Nam Kading Basin, Lao PDR

• The study presents two cases in which hydro power plants may respond to excessive runoffs that may produce flooding later on, the Nam Theun 2 reservoir is used an example for these two simulations.
• It also highlights the value of management to a hydro power plant’s responsibility in a flooding event, whether it be as a contributing factor, or as a prevention tool.
• The study emphasises the value of research on climate periodicities and runoff behaviour to aid in flood prevention.

The contribution of hydropower reservoirs to flood control in the Austrian Alps

• The study indicates the duality of hydropower reservoirs and their role in flood control.
• This is achieved by comparing several flood events in different areas under the influence of an hydro power plants.

Further Information

• Hydro Power Portal on Energypedia
  
• Hydropower Basics
• Micro-hydro Power (MHP) Projects - Mitigation and Intervention Techniques - Water Harvesting
• Micro Hydro Power (MHP) – Pros and Cons
• Micro-hydro Power (MHP) Projects - Mitigation and Intervention Techniques - Flood Control and Improved Drainage
  
• Causes and Features of Watershed Degradation related to MHP Projects
  
• Socio-economic and Environmental Impacts of MHP
  
• UN study on the ecological impact of hydro power plants[JH1] 
• ECCR overview of the link between hydro power plants and river restoration
• Reuters news report on the findings of the Environment Ministry of India in relation to flooding in the previous year