hey everybody it's mr smeeds and today we'll be covering topic 6.9 which is hydroelectricity our objective for the day is to be able to describe the use of hydroelectricity in power generation and also to be able to describe the environmental effects of hydroelectricity the skill that we'll practice at the end of today's video is to be able to justify a proposed solution so the first thing we'll do today is look at some hydroelectricity basics so hydroelectricity comes from the movement or the kinetic energy of moving water and in this case water is going to move past the turbine which will spin the turbine and then of course that turbine can power a generator which will generate electricity again this water could be moving with the natural current of a river or the tides of the ocean going in and out or it could be water that's falling through a channel an intake channel in a dam so we'll talk about those systems here shortly it is by far the largest renewable energy source globally so if we take a look of a graph here of global renewable energy generation we'll see that hydro power is uh you know far and away the biggest source of renewable energy globally and then we should also know that china brazil and the united states are going to be the three biggest producers of hydroelectricity globally so first we'll talk about by far the most popular way of generating hydroelectricity which is water impoundment and water impalement is just a fancy word for a dam so we're going to store water behind a dam this is going to basically create an artificial lake which we know as a reservoir and so then what happens is when we dam the river it's going to enable us to control the flow of the water and so that channel that allows the water to flow through the dam can either be opened wider to allow more water in or be closed to allow less water in so this allows us to also control the rate of electricity production so this is really convenient so we look at a image here to kind of help us understand again this dam this big concrete structure is built across the river we get this huge reservoir and artificial lake and this is basically stored energy at any time this channel down here can be opened water can flow through to spin the turbine which powers the generator to make electricity and so again really important to note that we can control the rate of electricity production by controlling the rate of water that flows through the intake channel it's also going to allow us to control the flooding that happens oftentimes in rivers seasonally so you'll get snow melt or you'll get especially heavy rains and that will cause downstream flooding but with a dam we can control the rate of flow downstream from the dam and so that allows humans to build settlements that are closer to the river because they don't get periodically flooded it's also going to be a really big source of tourism or recreation dollars that happen that flow into a local economy when you have a huge reservoir so people can go boating they can go fishing and so there's some really big you know economic impacts from a dam two issues we have to be aware of are the fact that the flooding behind the dam displaces a lot of ecosystems that used to be there and we get something called sedimentation sedimentation is where your sand and your silt and you know your dead organic matter is going to be building up behind the dam instead of naturally flowing downstream past the dam we'll talk about the impacts from an ecological standpoint of this but one of the impacts from an economic standpoint is that the dam becomes less efficient as more sediment builds up behind it and we'll also talk about a solution to kind of alleviate or reduce sedimentation later next we'll talk about a less common system of generating hydroelectricity which would be run of river systems and tidal energy so in a run of river system we have a smaller dam and instead of creating a huge reservoir it's just going to divert water through a man-made channel that runs parallel to the river in that channel there will be a turbine which gets spun by the natural current of the river and of course that is going to power generator to make electricity it's less impactful on the surrounding ecosystem because you don't flood the area behind the dam and you also allow the natural movement of sediments downstream so that's an important point to point out if we take a look at a diagram we can kind of understand we have a dam and there's still some accumulation of water but it's not going to be flooding to the same degree as a water impoundment system and so it just kind of diverts this water on this man-made channel and that's going to run through eventually a powerhouse which will have the turbine and the generator in it and then it runs back into the stream so again less impactful on the hydrology or the flow of the stream another thing we should know though is that it doesn't generate nearly as much electricity because it's just not going to be as much stored water and it also can fluctuate with the river level so if you have a year where there's less rainfall or less snowmelt that contributes to the water level that can decrease the amount of power you generate in this run of river system we also have something called tidal energy tidal energy is where the ocean ties which move in and out predictably each day are going to spin a turbine under water and generate electricity that way so if we take a look at a diagram here when the ocean is at high tide it's going to be moving closer to the land and so we'll get this water kind of accumulating behind this sort of dam of sorts and then when the tide flows back out it will flow past the turbine and spin it and vice versa you know when it comes when the tide moves in and one limitation of this though is that it's only really available in coastal areas that are very close to the ocean and so this is not something that can necessarily be an energy solution for everyone really again limited to coastal you know societies now we'll look at some of the ecological environmental and economic impacts of dams so first we have to know that dams flood habitats behind the dam so forests and wetlands could become completely submerged and basically no longer exist as habitats and then rivers which are kind of shallow fast-moving bodies of water become lakes which are vastly different ecosystems so if we look at a picture here we can understand the magnitude of this flooding and we can see that again what used to be forest and perhaps wetland or even grassland is replaced with a lake which again is a very different ecosystem so organisms that rely on the forest or the wetland no longer have a home or they have to migrate another important thing to know is that sediment buildup is going to change both the upstream and the downstream ecosystem we'll talk about why this happens here in a second and then another thing is that it's going to deprive the ecosystems downstream of the nutrients that come with the sediments that flow along the bottom of the water remember sediments can be broken down bits of organic matter which contain a lot of nutrients like phosphorus and nitrogen and wetland ecosystems especially depend on that really fertile organic matter flowing into them so a dam prevents those downstream wetlands from receiving those nutrients they need this is a graphic that will help us understand both the upstream and downstream impacts of a dam so we can see in a free-flowing river that does not have a dam we have fast-moving water we have water that's a little cooler because it is shallower and it's not kind of soaking up the sunlight because it's moving so fast we also have what's called a spawning habitat or kind of a rocky stream bottom this is an important place one for fish to layer eggs but two for organisms like macroinvertebrates which are basically big aquatic insects to live in and that's a really valuable habitat for them within the stream when we put a dam in place what happens is we get this buildup of sediment so we have all this sand and organic matter and debris and it's going to cover up that rocky stream bed so that we no longer have that streambed ecosystem that's so vital for fish spawning and for macroinvertebrates we're also going to get warmer water behind the dam and that's because it's sitting there and it has a higher surface area so it's absorbing more sunlight warmer water means less oxygen so it can support fewer aquatic species then we also have all these debris and all this organic matter that's trapped and that deprives the downstream ecosystem of some of those sediments which again contribute to that habitat on the bottom of the stream but also the nutrients that flow into those downstream ecosystems so it really changes the hydrology you know the flow of the water but also the transfer of nutrients for environmental impacts we have the increase of fossil fuel emissions just while we're building the dam so it is temporary but that's something we have to know it requires a lot of concrete we're gonna have increased evaporation as well because that reservoir is such a large surface that it comes into contact with more sunlight it takes in more heat so more water is going to evaporate and then finally we're going to have some methane release because all of that organic matter flooded by the reservoir is going to break down or be decomposed in anaerobic conditions meaning low oxygen conditions and that produces methane so that's a greenhouse gas when we look at economic impacts we have human homes and businesses that have to be relocated from the reservoir zone which will be flooded so that's a consequence initial construction is going to be very expensive so the upfront cost is very high electricity is very efficient to produce after this initial cost but someone has to fund that huge cost to start up a positive impact is going to create a lot of jobs so people need to be needed to run the dam to operate it to maintain it so that's a benefit and then also all of that sediment buildup will eventually lead to something called dredging which is where large cranes have to be brought in to basically grab and pull that sediment out of the reservoir and that's an economic impact another one is going to be the loss of ecosystem services that happen especially in those down stream ecosystems like wetlands which are going to be less productive and less stable due to their deprived nutrient flows from that dam blocking all those sediments so one consequence of dams that i kind of breezed past on the last slide is the disruption of fish migration so fish have a hard time migrating upstream past the dam because obviously they can't swim through the dam and they can't jump over it so a solution to that that's really common is a fish ladder a fish ladder is basically a series of cement steps or pools that the salmon can use to swim over the dam so they can flop and jump from pool to pool and then this you know diagram can kind of help you visualize that more and eventually they move up and over the dam to the other side now this is really beneficial because it enables migratory species like salmon specifically to swim upstream to their spawning grounds which is where they will reproduce and maintain their population this is beneficial for the salmon themselves of course it's beneficial for the predators of salmon like eagles and osprey and bears and anything else that can get its paws on a salmon and then it's also beneficial for humans because humans really utilize salmon as a recreational and you know food source and then another alternative to this which is kind of a fun thing this is like one of the cool apes concepts that you learn in this class is a salmon cannon it's a real thing it sounds made up but it's an alternative to fish steps or a fish ladder where basically they catch the fish and they feed them in this big tube so we have a gif of this here where you know the fishermen catch the fish and then they feed them into basically this big suction tube almost like when you go to the bank and you send in your little deposit tube and they feed the fish in and it just shoots them right over the dam to the other side so some pretty ingenious ways that humans have come up with to still help migratory species like salmon migrate past the dam to get upstream and then finally we'll look at some benefits of hydroelectric dams so some benefits include that there are no greenhouse gas emissions released when producing electricity so of course fossil fuel combustion produces a lot of carbon dioxide and all sorts of other air pollutants but once the is actually constructed when we're generating electricity there's no air pollutants released and there's no greenhouse gases released that reservoir can also serve as a really big source of tourism dollars so people come to boat and to fish it's also going to be a source of jobs so you need a lot of jobs to build the dam and to maintain it it's going to be really reliable consistent electricity so we don't have to worry about water running out we don't have to worry about the rate of electricity production because we can store water behind the dam so it's very reliable and it's an affordable source of electricity and again as i alluded to earlier uh no air pollutants released when generating electricity so we're not going to get socks and knocks and particulate matter like when we combust coal and that's a great you know alternative source of energy for the people that live there they get better air quality and for global warming as well another benefit is this idea that we can control the seasonal flooding of many rivers and so in the united states it's actually only three percent of all dams that are used to generate electricity the number one use for dams in the us or the number one reason they're built is actually recreation or sort of increasing property values the second reason is flood control and so dams are actually more so utilized for again controlling floods and building recreational reservoirs and one thing that we do have to know is that this flood prevention is really good for humans you know we get to have a reservoir we get to build our homes and our cities closer to rivers because we don't have to worry about them flooding but there's consequences especially to wetland ecosystems downstream of the dam so if we look at this diagram it can help us understand the hydrology of a river and what happens when we damn the river so the way this works is that mountains you know our rainfall somewhere or you know melting ice is going to contribute to the river it's going to flow and as it flows we have a flood plain on either side so this periodically floods with water which adds both water and nutrients to the surrounding ecosystem and especially when we get out to estuary habitats or wetlands like the salt marsh we deposit a lot of sediments here this makes this a really rich productive biome because so many plants can be supported by the nutrients in those sediments and so many organisms but the problem is when humans develop this area by building a dam we take away that floodplain so now there's no flooding periodically that means we can build our irrigation systems and our agricultural systems so much closer to the river because we don't have to worry about the flooding we can also build our cities and our towns right up to the edge of the river because we don't have to worry about them flooding what that does though you notice is we've removed the salt marsh the estuary habitat and so that is a big impact of this dam we don't get the same sediment we don't get the same nutrient deposition in the delta where the river opens out into the ocean and so it really alters the ecosystems that we typically find in these estuary areas so our practice frq for topic 6.9 today is to practice explaining two benefits other than agriculture and recreation that people gain from constructing dams on rivers