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  • Hi. It's Mr. Andersen and this is environmental science video 5. It is on water resources.

  • Our body is filled with over 60 percent water. And this does not seem like a big deal because

  • the earth is covered with over 70 percent water. The problem with that is that most

  • of that is sea water that we cannot use. And the freshwater that remains, most of it is

  • going to be frozen in ice caps and glaciers. And so the percent that is really fresh water

  • on the surface is a small percent of the water on our planet and it is finite. The amount

  • of water we have on our planet has never changed. Now as the sun provides energy to the earth

  • the water will move around through the hydrologic or the water cycle but we have a finite amount

  • of water. And most of it is going to be sea water. We have a little bit of fresh water.

  • The sea water moves around through ocean currents. The fresh water could be divided into ground

  • water, water underneath the surface and then surface water which is on the surface. Now

  • we need that water. We need it domestically in the home to take a shower or to drink.

  • But we also need it in industry to make our goods. And most of it actually goes to agriculture

  • to make the food that we eat. The problem with water on our planet is that it is unevenly

  • distributed. In some areas there is lots of water. In some areas however there is going

  • to be scarcity. And so humans have had to learn how to store water, move it around and

  • in the future we may have to desalinate some of that sea water so that we can use it as

  • fresh water. Now where is that ground water stored? It is underneath the ground in aquifers

  • that we can deplete. What about the surface water? Well it can be stored in reservoirs

  • that occur naturally or ones that are created as we produce dams. And then we can move it

  • around through aqueducts and even to the planet itself through irrigation. But we have a finite

  • amount and so conservation is incredibly important. And economics have contributed to water loss

  • and could help us to actually solve this water conservation problem. And so the hydrologic

  • cycle works like this. Anywhere there is water on the surface we can have evaporation. That

  • gets cooled and eventually leads to condensation and precipitation. Once it is on the surface

  • we call that surface water. It is running over the surface. That could be lakes and

  • swamps and rivers. After we have that water hit the ground it can however be infiltrated

  • into the soil and the ground itself. To give you an example of that imagine I have a beaker

  • here. Is it full? Well maybe full of air. If I put marbles in it, is it full? No you

  • can see there is spaces in it. What if I fill it up with sand? Is it full? No. There is

  • still spaces in there. If I fill it up with water now we are starting to fill up that

  • beaker. And that is what infiltration is. As the water flows down into the soil we call

  • that now ground water. Let's say it is not filling that whole beaker. It is right here.

  • That point at which we have saturation in the ground water is called the water table.

  • Most of our planet is covered with water, unfortunately it is seawater. It has salt

  • dissolved in it. If you drink it you will die. If we put it on our fields the crops

  • are going to die. Now it moves around using currents. We talked about that in the last

  • video on the atmosphere, it is cells in the atmosphere and coriolis effect. So we have

  • these general trends in circulation. But also salinity affects it. And so if we look at

  • an area right here it is a high salt concentration because we have a lot of evaporation. But

  • up here we have a lot of melting of that glacial ice. And so we are going to have a low salt

  • concentration. And so the salt concentration and differences in heat create these thermohaline

  • circulations that really make that whole ocean on our planet one system. Now if we look at

  • fresh water it can be divided into water that is above the surface, we call that surface

  • water and then ground water. But what is interesting is if we look to the sides of that stream

  • you can see the water table in the ground water. And so if you dig a hole right here

  • it is just going to fill in with water because of all of that ground water around it. Now

  • this is an aquifer. It is storage of that water in the ground water. We call this unconfined

  • aquifer because the water can move between the surface and the aquifer itself. If I were

  • to dig down a little bit we could find what is called a confined aquifer. And that is

  • going to be stuck between this impermeable rock down here and above it. Now let's say

  • we want to get to that ground water on the surface. If we want some of the surface water

  • we simply pump it out of the stream. But if we want to get water out of that ground water

  • we could dig a well. Now the water, we could either pump out the water or sometimes we

  • will have what is called an artisan well where there is either enough gravity above it or

  • enough pressure in the ground water so it actually comes out. But as we use that well,

  • just like using a stream the water table is going to drop. And so we are going to start

  • to deplete that aquifer. Now an important term in filling an aquifer is something called

  • recharge. So as we get water and infiltration we are going to fill up that aquifer. But

  • if the outputs, in other words if we pull out more water then we are putting in, we

  • are going to deplete the aquifer. And what are we using all of this fresh water for?

  • Well if we break it out using a pie chart most of it is actually for agriculture. The

  • growing of our food. We use some of it for industry. And then some of it domestically

  • in the house. The problem again is that it is unevenly distributed on our planet. Brazil

  • is going to have plenty of water. But if we look in the desert southwest of the US or

  • in the Sahara there is not going to be any water right there. And so what have humans

  • done? We have started to store water. So reservoirs are an example of that. A big example would

  • be the Three Gorges Dam that was built in China. It was finished in 2006. And so this

  • is what that river, the Yangtze River looked like before they built the dam. And then they

  • built the dam, finished in 2006. You can see what it looks like then. So we are storing

  • the water behind the dam. What is nice about that, now we have water that we can use at

  • will. We also can get energy from it, as we run that water through a generator. We can

  • control flooding downstream. And also we can use that for irrigation. Or the Three Gorges

  • Dam they are using to increase shipping on the Yangtze River. So it sounds great. What

  • is the problem? Well there is going to be destruction wherever that water went. So we

  • are decreasing 20 percent of the forest in this Yangtze River. We are displacing over

  • 1,000,000 people that used live there. We also have evaporation of the water off the

  • surface. And then we are going to have nutrients that start to deposit there that would have

  • normally moved their way down the river. And that is going to disrupt wildlife. And so

  • fish obviously cannot spawn, move up and down in the stream. But it is also going to change

  • the temperature of the water. An example. There is a freshwater dolphin that went extinct

  • in the Yangtze River and the Three Gorges Dam may have contributed to that. We can also

  • store it underground. That is naturally stored in what are called aquifers. One of the largest

  • ones on the planet is the Oglala Aquifer. It is going to be found in the midwest. And

  • so here it is in Nebraska. But it goes all the way down to Texas and up into South Dakota.

  • It is a huge aquifer. So if we look at the amount of water stored underground it is over

  • 1000 feet of infiltrated saturated water underneath the ground that we can use. And you can see

  • right here that there is tons of irrigation going on. This is in Kansas. They are using

  • center pivot irrigation so they can grow their crops. It seems great but what happens again

  • is that we can deplete that. So if we look at, this is during a 15 year period of time,

  • there is an increase in the aquifer in certain areas but most of the time we are seeing depletion.

  • And sometimes that aquifer has kind of disappeared. And a lot of scientists think in the next

  • 100 years the Oglala Aquifer is just going to disappear. Why is that a problem? It could

  • take another 6000 years to fill it up again through natural recharge. Now we also have

  • to move water around. So looking to California is a great example of that. So if we look

  • in California they need a lot of water in the central valley and then in the south,

  • Los Angeles and San Diego. So they built this huge system where they can move water where

  • it is, in the mountains, and they can move it through these aqueducts to where it is

  • needed. Now you can see that is controversial. So people in this area are saying you are

  • depleting our rivers. In this area we are saying we have more population. We are growing

  • your food so we need more of that water. And this conversation becomes more heightened

  • when we move into drought. And California is in an awful drought right now. Drought

  • occurs when you receive way less then the normal amount of water. And so as we use that

  • for agriculture, irrigation movement is super important. So how do we move the water actually

  • to the plant. The easiest way to do that is using furrow irrigation. You can see it is

  • easy. You just dig a trench. What is the problem? We have efficiency rates of around 60 percent.

  • What is that? That is how much of the water is actually going to the plant without being

  • evaporated and infiltrated into the soil. So we could move to flood irrigation. Higher

  • efficiency but it is going to damage the plant a lot of the time. We could move towards a

  • spray irrigation, high efficiency, but what are we doing? You can see we are adding equipment.

  • This is the center pivot. So that costs money. Or we could move to drip irrigation. And you

  • can see that it is going to 95 percent efficient but it is going to cost the farmer a lot more

  • money to do that kind of irrigation. As we move into drought situations desalination

  • becomes an option. We can remove the water from sea water. One way to do this is through

  • distillation. What you do is you heat up the water and it evaporates. It is kind of like

  • the hydrologic cycle. You then cool it down usually through pipes and what you do is you

  • remove the water. What is a problem? It costs a huge amount of money. We could also do that

  • through reverse osmosis. This is a reverse osmosis plant over on the side. What you do

  • is put a membrane right here and then we squeeze the water and as you squeeze the water you

  • move the water through but you leave the salts behind. Now we have fresh water. What is the

  • problem. It costs a lot of money. About 1 percent of the people on our planet are using

  • water that is created through desalination. But by 2025 we should have 14 percent of the

  • people on our planet in water scarcity and so desalination may be an issue. Now how did

  • we get to this problem? It seems like we have an unlimited amount of water? And remember

  • our model the earth provides the life support for society and the economy on the inside.

  • And so the economy got us to this point. The decisions that we as governments made got

  • us to this point. Where is the big mistake we made? Well water does not cost enough.

  • It is low cost water. In other words governments are subsidizing the cost of water so farmers

  • and industry and you are not really paying the amount that water costs. And as a result

  • you are not going to conserve it because it is just pennies on the gallon. It is incredibly

  • cheap. And so how could we solve this problem? People might not like it but if we increase

  • the price of water people are going to start to conserve. And we can also use incentives.

  • In other words we can pay people, pay farmers for example to use irrigation that is going

  • to be more efficient or to conserve water. That is another way that economics can start

  • to solve this problem of water conservation. And so did you learn the following? I would

  • pause the video at this point and try to fill in all the blanks. But let me do that for

  • you. Remember the water resources move through the hydrologic cycle. We have sea water. We

  • have fresh water. Ocean circulation and desalination could help us solve this problem. The fresh

  • water can be ground water or surface water. We use it for domestic, industry and agriculture,

  • would be what is here. We can store the surface water through reservoirs, aquifers is ground

  • water. And then we are going to use aqueducts and irrigation to help us move that water

  • around. But again, conservation is incredibly important. Economics are going to drive that.

  • And I hope that was helpful.

Hi. It's Mr. Andersen and this is environmental science video 5. It is on water resources.

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B1 US water aquifer irrigation surface ground fresh water

Water Resources

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    Joseph Hsieh posted on 2020/02/08
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