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To Build a Dam…or Not to Build a Dam?
Balancing the Natural and Built Environment in Dam Construction
There’s no silver bullet when it comes to the question, “to build a dam…or not to build a dam?”. Dams are one of the largest superstructures ever built by mankind. They’ve provided drinking water, agricultural irrigation, flood control, and hydropower to hundreds of millions of people throughout our history.
When constructed in the wrong place, however, the impacts of dams on natural river systems and watershed health, fish passage and wildlife habitats, and the livelihoods of ecosystems can be catastrophic.
So, how can you assess the positive and negative effects of dam construction to best answer the question, “to build a dam…or not to build a dam?”. What are the factors that should be taken into account when making this critical decision? And why should you not ask these questions on a site-by-site, dam-by-dam basis; but rather, master plan for the entire fluvial (i.e. river system) behavior and dynamics and where the dam is located within that system at the watershed level?
Benefits of Dams & When to Build
There are currently close to 50,000 dams in operation and more being constructed around the world at an increasing rate each year. So why do we have so many? There are numerous advantages to dams that help sustain basic human needs.
Historically, dams have been constructed as a means of water management and supply (for both drinking and irrigation), hydropower and renewable energy, and transportation. They’ve helped control the flow of water, prevent famine, and mitigate floods. Today, dams are usually constructed for hydropower generation. In fact, in 2015, hydropower produced approximately 17% of the electricity and 70% of the renewable electricity in the world. This is an astounding figure that’s supposed to increase each year for the next few decades.
In areas with irregular rainfall distribution or high precipitation, dams may be a necessity to store drinking and irrigation water, control floods, and mitigate streambank erosion. Dams are also modular and don’t consume water or emit carbon dioxide. Large, fascinating dams, such as the Hoover Dam (the largest reservoir in the U.S.) for example, have been tourist attractions for decades that represent a staple of progress and modernity.
When Dams Do More Harm Than Good
Ever heard of the boomerang effect? When something does more harm than good and comes back to bite you? Well, this can certainly be the case when you build a dam in the wrong area within a river system. In fact, inappropriate dam construction within a river basin can lead to incalculable human, environmental, and economic life cycle costs.
Rivers are one of the most biologically diverse and productive ecosystems on the planet,
but they only take up less than 1% of Earth’s surface.
So when deciding whether and where to build a dam, it’s imperative to master plan at the entire watershed scale. Why? Improper dam construction can hinder necessary alluvium and sediment transport and deposition processes, which impacts critical riparian and floodplain habitats downstream. In turn, this can lead to coastal erosion, land degradation, poor water quality, increased flooding, sea level rise, and other compounding factors.
What makes matters worse is that nearly half of all fish stocks can be found in free-flowing rivers. Thus, large dams present a major obstacle for fish and the various wildlife species that rely on fish migration and reproduction for survival. Many regions have already experienced a disappearance of aquatic species (e.g. leading salmon and trout) as well as birds in floodplains, forests, wetlands, farmlands, deltas, mammals (e.g. Yangtze river dolphins, orcas, Tapanuli Orangutans, etc.) and other wildlife populations from dam construction.
Large dams also have the capacity to flood entire regions downstream and prompt evacuations, as we’ve seen countless times. They also require millions of tons of concrete to build the superstructures, the roads to them, and their grid connection technologies.
Climate and Dam Removal Considerations
Construction of ground dams (i.e. dam reservoirs, not underground dams/aquifers) is typically a no-go in arid areas with high evaporation rates. Although water storage is needed in these particular climates, building new dams and reservoirs can be a major waste of resources. In fact, they can actually increase the price of irrigated water for farmers in these regions.
So should old and/or obtrusive dams be removed? While removing outdated dams can help restore a river and threatened or endangered fish and wildlife populations, the sediment and silt that can accumulate behind a decades-old dam can be disastrous. That is, of course, if it’s not removed properly.
Alternatives to Dam Construction
Do we have viable water supply, energy production, and flood protection alternatives to dams? What are the options to meet those needs sustainably and in a world of changing climate and hydrology? By strategically considering how to better plan for current and future development, innovative techniques can be implemented to balance nature and reduce our reliance on dams and river diversions.
Some studies support groundwater recharge and reuse as an effective and environmentally-friendly alternative to dam construction. Others argue against this alternative however because of economic and bottom-line factors and recommend relying on dams until more conducive technologies come to fruition. Other water management options for water storage and flood management include groundwater aquifers, wetland restoration, green infrastructure and LID, restoring river meanders, constructing bypass channels, and more.
Today, most dams are built for the purpose of hydropower generation. But there are a variety of cheap, local, and decentralized alternative technologies available. Unconventional solutions, such as floating solar technology Flotovoltaics, are also making waves in water- and energy-intensive industries. Other hydropower dam alternatives include wind power, solar power (e.g. microgrids), fuel cells and microturbines, geothermal power, biogas, ocean power, more energy efficient facilities and homes, and others.
To Dam…or Not? How to Decide
So, the question remains: to build a dam…or not to build a dam? What’s a reasonable price to pay for dams in terms of the economic, social, and environmental impacts?
The pros and cons of dam construction have been highly debated in recent years. But because every river system and region are different, it’s important to assess the negative and positive impacts of dams in comparative situations. It’s also critical to master plan at the watershed scale in order to determine the best water management, energy generation, and environmental solution for your community. If not, a dam can wreak havoc on the environment and communities that can amount to substantial, recurring losses every year.
What are your opinions on the “hot topic” debate: to build a dam…or not to build a dam? Help us start a larger dialogue amongst the engineering community about how we can best manage our limited resources. Get in on the discussion!