What is hydropower: the bigger picture

What is hydropower?

Ask any eel you know: there’s a lot more to hydropower than just what goes on at the power station – plenty of people (aquatic or otherwise) have a stake in the water involved. So, I called on a bunch of experts at our parent company, Hydro Tasmania, and sister company, Entura, to see how everything works together.


What is hydropower?

First up, hydropower (also known as hydro energy) doesn’t necessarily mean hydroelectricity – in reality it’s power, in any form, that comes from harnessing the movement of water. Personally, I like to think of a brutish 10th century wheat-crushing gristmill. But for the sake of this article, you can safely assume hydroelectricity is what I’m on about.


How does hydropower work?

Hydropower uses moving water to turn a waterwheel or turbine (if you know a thing or two about wind power, think of water as wet wind). Once you’ve got movement, all you need to do is connect it to the machine that needs powering. Back in the day you might’ve hooked it up to the saws in a sawmill or the grinders in a gristmill. The world was your early-machinery oyster.

Watermill
Water is a conscientious employee at the local mill.

‘Sounds a little archaic for me’ I hear some of you say. Well, not for long.

Since electricity got popular, we’ve also used hydropower for that – we call it (you guessed it) hydroelectricity. So instead of using the water turbine to power machinery, it’s hooked up to an electricity generator instead. Easy.


How hydropower dams are built

Without getting into the nitty gritty details (sorry, nerds), here are some basics on how a hydropower system comes to watery life.

First, we choose where to put it. While investigating this work I spoke with geomatician Inga (real area of expertise, real name) who likens her role to being the Google Maps of Hydro.

When there’s a question of where something should go, she and the rest of the spatial team (once again, real name) look at all the factors that make a spot right for the job – weather, terrain, infrastructure, you name it. The team also advises if a spot should be avoided for cultural or environmental reasons.

But if you can’t find an Inga, here are a few things to think about:

  1. Make sure there’ll be enough water. You’ll need rainfall data, and some idea of how climate change is set to affect the area.
  2. Check the foundations. You don’t want there to be any chance the earth is going to crack under the (literal and very real) pressure of a dam.
  3. Work out how much you need to generate – now, and in the future.
  4. Figure out where your power station will go, and how far electricity will need to travel (the further it goes, the more you lose).
  5. Find out about potential social and environmental impacts. This is usually done with the help of specialised teams who advocate for the land and people affected by a project.
  6. And of course, make sure you have the funding.

Now, it’s time to build a dam. Here are some of the most common types used for hydroelectricity.

Arch
Built into surrounding rock. Curves upstream so that pressure from the water causes it to push into the rock, which strengthens the structure. Good for narrow canyons and gorges.

Gravity
Built from the ground up from concrete or stone, designed to be so heavy that the pressure of the water upstream can’t move it.

Arch-gravity
A combo of (surprise!) arch and gravity dams – they use both the weight of the fill and pressure against the surrounding rock to stay in place.

Embankment
Like gravity dams, only made from compacted earth. They can be either rock-fill, or earth-fill.

Rock-fill
An embankment dam with a core of dumped and compacted rock. Sometimes that rock is impermeable, otherwise a watertight layer (like concrete) is built onto the upstream face.

Earth-fill
An embankment dam made of compacted earth, sometimes fitted with a drain layer for seep water. Like rock-fill dams, they might also have a watertight layer.

The next step is in the building. And since we humans can’t build a permanent dam directly into water (you win again, beavers), here’s how we usually do it.

  1. Divert the river upstream to stop water flowing to where you need to build. Sometimes a cofferdam (a temporary barrier) is set up to help with this.

    As well as diverting water, cofferdams can be used to create dry spaces directly in a river (imagine above-ground pool, but the water’s on the outside). Sometimes builders will do this in one half of a river, build half the dam, then do the same on the other side and connect them in the middle.
  2. Cofferdam
    Cofferdams provide a water-free in-river experience.
  3. Get your foundation ready. If there are any cracks and fissures in the earth below the dam, pumping grout in from above will make sure they’re solid.
  4. If you’re building a concrete dam: you’ll have batching plants on-site, which are like on-site concrete factories.

    Then there are two options: either pour the concrete into formwork (which is engineer for ‘moulds’) to make stackable blocks, or pour an entire concrete layer at a time, compacting each with rollers. Stack blocks, or pour layers until you have the height you need.

    As for how the concrete gets up as the dam gets higher, I learned of two possible approaches: on conveyor belts (orderly, low-key), or in skips lifted by cranes (chaotic, exciting).

    If you’re building an embankment dam: the materials that will make up your dam wall are either brought to the site, or (if the area is rich in those resources) they’ll already be there. Then it’s a matter of adding and compacting layer after layer until your dam is the size you need.

  5. How does a hydropower plant work?

    Once you’ve got the dam (and the water), you’re halfway there. The next step is running the water through a power station, which is where the electricity is generated.

    You could put a power station right by your dam, but sometimes it makes more sense to build it further away. This might be because:

    • you want the power station closer to existing transmission lines. This saves on building costs and reduces the amount of energy you lose in transmission, or
    • it lets you generate more electricity. Building your power station much lower than your dam means water gains more speed (and therefore power) before reaching the turbines.

    Of course, you’ll need something to help you get the water from the reservoir to the power station. Depending on the terrain, you can move it using pipes, tunnels, or flumes (which are like open-top canals, on stilts).

    Once water gets to the power station, it moves through a water turbine that’s hooked up to a generator. As the turbine spins, electricity is generated. That electricity moves via power lines away from the power station and where it needs to be.

    Did you know? When we think of dams, we often imagine water spilling over the top of them. This isn’t necessarily a good thing though – in those cases, water doesn’t move through turbines, so it’s not being used to generate electricity. Sometimes spills are necessary though, especially to prevent flooding when excess rainfall is expected.


    The best way to use water

    Once you’ve got a hydropower system up and running, it’s a good idea to get onto someone who can tell you how to use it. Senior resource modeller (and, as a colleague put it to me, ‘knower-of-things’) Roger talked me through how the modelling team helps do that.

    For hydroelectricity, they use modelling to try and mimic what’s going to happen with water (you and I might call it ‘telling the future’). That involves looking at things like water inflow, lake capacity, generating capacity and electricity demand, then using that information to decide how much to generate, and when. That way, you can generate enough to meet people’s needs, while using your resources as efficiently as possible.

    The job also involves what’s called scenario analysis, which means testing ideas about how to best use water and assets. That means if someone says ‘could any of these ideas make our station more efficient?’ or ‘should we do our planned outage in January?’, the modelling team helps them figure it out. It left me wishing there was a modelling team for some of my ideas.


    Keep those turbines turning

    Hydropower systems are like any other piece of machinery – you need someone to take a look at all the parts every now and then. Particularly when that part is a 100-tonne water turbine that can take 3 years to upgrade.

    That’s what the Assets and Infrastructure team does, for two reasons: to make sure dams and power stations are safe to operate, and that they’re fit to work efficiently for as long as possible (which is a big part of having a truly renewable outlook).

    Sometimes, it means taking things apart to check how they’re going, while others are checked by inspecting and measuring. And (because we live in the future) some even have tech built-in so they can just send a status update digitally – like texting mum to tell her you’re safe instead of her breaking in to check you got home ok.


    The fun stuff: water for recreation

    You probably know from the last time you washed your hands that water isn’t just used to generate electricity. So part of Hydro’s job is to make sure people still get to use it for other things – like fishing, water sports, or just having a nice place to go walking. Given Tasmania’s reputation as an outdoor-activity wonderland, there are huge cultural considerations they need to take into account when managing land and water.

    I spoke to Sarah who explained how part of Hydro’s job is balancing the needs of all different types of water users. So if a group needs rapids for rafting, or the right water levels for rowing or fishing, they can move water around for them. It’s a bit like event planning – only you want your venues to be full of water. Even fish.

    Fishing
    Responsible water management is as important as choosing a sensible hat to wear fishing.

    It’s not just the humans that need taking care of either. Fish and other aquatic critters also rely on water for their day-to-day.




    Monitoring the environment

    Unlike eels, there are some creatures who spend a lot of time in the same place. That means if their watery world changes too much, there can be problems. I spoke a bit more about this with Cameron (a different one), an environmental planner at Entura.

    The main thing Cam talked about was macroinvertebrates – tiny organisms that typically live in the sediment between larger rocks. Because they don’t migrate, they’re a good indicator of the health of a river (the more there are, the less likely the environment has been changed).

    The increased water flows caused by hydropower systems can be a problem for macroinvertebrates. That’s because the sand and silt that makes up their habitat can be easily washed away – which has the usual follow-on effects for the local food chain.

    So, how do you avoid that erosion? Mainly by monitoring the environment so you can change what you’re doing if it’s having unexpected consequences. Here’s an example from the Gordon River:

    When water levels at the riverbanks suddenly decreased, Hydro found it caused a lot more erosion than expected. The good news was that the level-drops were being caused by a system upstream that they could control. So, they put in a ‘ramp-down’ rule, that says if they need to stop the flow, they have to do it more gradually. So far, it’s been effective at limiting erosion at those riverbanks.

    This kind of monitoring happens regularly to reduce the impact that hydro energy systems have on the environment.


    Where to from here: pumped hydro

    One of the big advantages of hydro energy is what’s called pumped hydro, which is kind of like turning hydropower systems into giant rechargeable (watery) batteries.

    It starts out the way you’d expect – water falls, turbines turn, hey presto, electricity. But instead of letting the water flow on, they catch it in another reservoir below the first. That way, they can pump water back up to the reservoir it came from and start the process again.

    The clever thing about the system is that the pumping process uses excess electricity – usually during the day when demand is low, and more electricity is coming from solar and wind power. Then, when those other renewable resources aren’t available, they’ve got water at the ready to make hydroelectricity.

    Pumped hydro is the next big thing on Hydro Tasmania’s list as part of their Battery of the Nation project. Having water stored this way means that even when solar and wind power can’t be generated, we’ve still got a way of generating renewable energy.

    Hydro’s also put together a video that explains the pumped hydro process:

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