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Water Supply: Dams

Water Supply: Dams

Author: Jensen Morgan

Determine the benefits and impacts of dams.

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Video Transcription

Hi, I'm Jensen Morgan. We're going to talk about some great concepts in environmental science. Today's topic is water supply. So let's get started.

We're going to talk about global water supply, where our drinking water comes from, dams and their impacts, and why some people are working to remove them. Only 3% of all the water on Earth is freshwater, and of that only 1% is accessible by humans. That 1% comes from lakes, streams, and aquifers. Aquifers are underground sources of water. As human population increases, competition for that 1% of accessible freshwater will increase as well.

Pockets of groundwater can be found in aquifers underground. Groundwater makes up only 1% of the water on Earth, yet it provides the majority of drinking water humans consume, and also provides for a portion of agriculture and industry's water use. Commonly, wells are drilled or dug down to access the groundwater.

Usually such wells are lined to keep out contaminants, both biological and chemical. But if they're not, various microorganisms and chemicals can seep in and contaminate the water. Over time, if water consumption exceeds the ability for rainfall to recharge the groundwater, it could result in soil drying out.

This can be problematic for local vegetation. In some cases, so much groundwater has been removed that topography can sink and change, because it isn't supported by water underneath anymore. Salt water can also leak into freshwater aquifers as groundwater sources are depleted.

As human population has grown, we've decreased groundwater resources, and they're expected to continue declining in size. It is possible for groundwater to recharge through rainfall, but we've built impermeable surfaces, such as roads and buildings, that don't allow water to soak into the earth, and instead divert it far away. In addition, humans' activities have also contaminated groundwater resources, primarily through fertilizer runoff.

While groundwater provides the majority of drinking water, we do utilize rivers, lakes, and streams. We have built dams, like this small one here, to manipulate water flow so that we can obtain it when we need to, and release its flow when we want. The upstream body of water created by the blocking of a dam is called a reservoir. And doing so provides us with water for drinking, agriculture, hydroelectric power, and recreation.

Dams like the Three Gorges Dam, the largest dam in the world located in China, can have many negative environmental impacts. This is the upstream side of the Three Gorges Dam. It's so large that boats look tiny in comparison-- see that one there?

On the upstream side of things, dams can cause lots of problems. Flooding during construction or when in operation can cause problems for humans and ecosystems nearby. Whole villages had to be moved for the creation of the Three Gorges Dam.

Because dams disturb the natural flow of rivers and streams, it actually disrupts natural flood cycles that are important to adding nutrients to flood plains. The stagnant water on the upstream side also encourages disease, because insects like mosquitoes thrive in it. This is the downstream side of the dam.

Dams like this can negatively impact aquatic species, especially migratory ones, because it prevents mobility, fragmenting and altering their habitats. Salmon are a prime example. In the US, many dams have impacted salmon migration because they can't get upstream due to the dam.

As a result of impacts like this, there are growing attempts to remove dams from rivers and streams. There are a number of benefits from removing dams, such as restoring natural flow of the river, preventing future structural collapse of the dam which could cause catastrophic flooding, improving native aquatic species habitat, improving mobility for migratory fish species, improving biodiversity, restoring natural land habitats in the area, and restoring nutrients to natural floodplains.

Whew, that was a lot today. Let's have a recap. We talked about world water supply, and how we can use only 1% of 3% of freshwater on the planet. We talked about groundwater resources and aquifers, how we primarily source drinking water from there, and how these sources are declining and becoming contaminated. We talked about dams and their impacts, as well as the benefits of dam removal.

Well that's all for today. I hope these concepts of been helpful. Looking forward to next time. Bye.