These turbines are installed on Conduit #3, which is one three conduits bringing water from the Bull Run Watershed into Portland. I believe the water is diverted at the outlet of Bull Run Reservoir 2, which is at about 850’. Portland itself is at 50’, so there is a natural downward flow.
In terms of affecting tap pressure, it’s not really an issue. The water from the conduits goes into reservoirs and storage tanks within the city, and those are what mainly supply tap pressure. So as long as the flow is enough to keep the local reservoirs supplied, I don’t think there’s a problem.
You are going to to ruin internet commentary by posting a well thought out expert comment on a topic you are actually explicitly qualified and experienced in.
That was very informative, and answered a lot of my questions about water pressure in lines.
I wish my job title had the power to shut up stupid people like yours typically can. Even if I’m an expert on something people question me without engineer in front of my name.
In a world full of know-it-alls, the title of engineer still gets people to listen to you. The only people who question engineers occasionally are machinists who have to make occasional questionable items from design engineers.
The short answer is “the laws of thermodynamics” – it takes energy to make water gush out forcefully, you can’t harvest that energy with a turbine and still have it available for gusheration. However, I wasn’t considering (or aware of) @DrDave’s point that the turbine isn’t installed on a terminal stretch of pipe feeding taps, but rather between a reservoir and a storage tank. In that context I don’t think my observation applies, so I recant.
There is a water pipe under the Bass Strait, about 100km long. It feeds fresh water from lakes in Tasmania, to Victoria, where water is in high demand. I was surprised to learn that the entire system is fed by gravity. No pumping required.
Its a strange thing to have in a generally flat city where even some storm water has to be pumped to avoid flooding.
Short summary of the Portland Water System – it’s all gravity fed except in parts of West Portland where there is some pumping involved. Yeah, you lose some pressure, but I’m guessing they must have enough.
Whether this is the best place to put dollars for clean energy I can’t say, but there’s plenty of precedent for it. t’s a very cool thing, and not really different than many “Run-of-the-River” power plants (just stick your paddle wheel in the river and you get what you get) you see all over the world.
Micro hydro has come into favor in Oregon for farmers that irrigate. Piping instead of using open ditches has been a common upgrade due to its advantages in eliminating evaporation and absorption losses (with the downside of taking away a source of open water and infiltration for the local ecosystem), and putting in some hydro generation is a nice add-on.
Gaviotas, Colombia has had some interesting approaches to irrigation infrastructure.
Some of that infrastructure is described in this book:
It’s a good layman’s book, with minimal diagrams and technical details.
The scenario you describe…
… had to be addressed because fresh water, at the start of the project, was not something the village had in abundance.
Basically, the farmers worked out a way to re-use the existing ditches in the fields by carving “forms” of the lower half of irrigation pipe profiles into the soil, pouring in the requisite-yet-minimal concrete mix or whichever (it’s been a while since I read this book, I am sorry I don’t have the correct pozzolan on the tip of my tongue right now), laying in a flattened plastic tube-shaped bag down the middle tied off at one end, filling the tube with water to take on the interior shape of the pipe, then pouring concrete mix on the top half of the pipe form, letting the whole works cure.
Once the concrete is set and cured to the right amount of hard, the tied end of the plastic bag-tube was loosened, the water exits as the plastic is pulled out, to be used again (I guess, assuming the plastic was intact enough).
I am omitting a lot of steps here, but the gist of basic procedure is here. The cast-in-situ irrigation pipes worked, according to the book.
Back in 2000 when everyone was terrified of the Y2K bug, a lot of crackpots were saying civilization was going to grind to a halt. DH and I did some research, among other things our local power station and water supply. We get our water either from groundwater falling on mountain slopes on the windward side and siphoned out of streams (whole 'nother issue about who gets dibs on that water), or by sticking a straw in the aquifer under the mountain. The water board explained that they could supply up to 40 gallons per person per day even if all their pumps shut down, because the system was just that robust.
When I lived in Portland (60 years ago) their main water supply came from Bull Run Reservoir, up on the side of Mt. Hood. They fed from that into multiple reservoirs on the highest hills around town. Overall, a very gravity-oriented system.
This reminds me of the wide-eyed blog posts you see every few months suggesting that we wear special sneakers to charge our phones, or build roads that “generate” energy from cars driving on them. And some of those posts are based on someone seriously proposing it for real (it’s usually a design student of some description).
Um, actually – no, yours is a great explanation of how this works. Water utilities are huge electricity users. Respectfully, I would just like to add that there are a couple of viable applications for hydroelectric generation systems in water supply and distribution processes – that are much more practical than mere PR ploys.
The first is when water is taken from an aqueduct by way of a turnout facility. Imagine a pair of 12-foot diameter aqueducts snaking across undulating hills and valleys. The water carried therein is under significant pressure from boosting over many miles of mountainous terrain into desert valleys. There are water retail outlets along the aqueduct that need the water. This water is of great value to desert communities, where surface water is scarce, and supplies are otherwise made available by pumping from deep within the ground. The water conveyed by an aqueduct is considered raw, or non-potable. Conventional water treatment processes must be employed prior to distributing it to users in these parched communities. These treatment processes will require that the energy of 10,000 GPM of flow be dissipated prior to entering chambers, where sediment and other solid impurities contained in the raw water are settled out. This energy is dissipated by a hydroelectric turbine that generates enough electricity to power the other treatment processes required to filter and clean the water, in order to render it potable.
The next application is when water is similarly transmitted across the city distribution system. From one end, say, from a Superfund treatment system that is cleaning groundwater polluted by a generation of improper disposals of spent jet fuel, booster pumps consume electricity to empower the water through a dedicated pipeline to a way station, where the water is stored temporarily in a ground-based tank. When the water enters the tank, the head is broken, or the pressure becomes 0 psi. From there, the water is boosted by energy-intensive pumps further to the other end of the City. When enough flow exists from the Superfund treatment system, a hydroelectric generating station can be inserted just prior to the tank, where the remaining pressure in the pipeline is converted to electricity, which provides power to the pump station in order to boost it to its destination. This entire process can take place at the same elevation, by the force of booster pumps, even if the source and destination are many miles away from one another. And yet, the energy of the boosters required to move the water from Point A to Point B can be recovered by a hydroelectric generating station. The recovered energy can then be used to boost the water again to its final Point C destination.
Without these hydroelectric generating stations, water users would be paying higher rates for their water. With the cost of electricity and the benefit of offsetting this cost, the hydroelectric generating stations pay for themselves within several years. What’s more, you will probably hear that the cost of water will not go down if less water is used. However, these sustainability improvements do help keep the cost of water from going up too quickly.
Oh, yeah, all those are excellent projects; they overlap the well-understood job of pulling energy out of gravity flow of water, with the job of getting water to treatment facilities for use as potable. My comments were limited to extraction of water from distribution pipes already full of potable water.
The Portland project actually is more than the stuff I was talking about, because it has some gravity-fed pipes, even though they only have the elevation drop of the river slope itself, there’s no dam or cliff or anything for really serious energy gains.
The final line of the City Lab article on it is " While Portland’s hydropower project cost about $1.7 million, it is expected to produce [$2 million] in clean energy over its 20 year contract." … which, given the time-cost-of-money, is not payback. My horseback estimate of “maybe in thirty years” turns out to be about correct. If the equipment lasts 30 years. If it doesn’t make payback, then, sorry, that particular project had to have P.R. value, or research value, to make up the difference, or they wouldn’t have approved it.
Your discussed projects were on a larger scale, with transmission mains, and were proposed based on an under-10-year financial payback, which gets them approved like any other engineering project proposal, and those will always go forward.
That general type of hydroelectric generation will be showing up in coming years, more as “run-of-river” hydroelectric plants along the river - but if the ecology does not complain at having a chunk of river abstracted way upstream, and if the need for potable water along the way pays for the pipe anyway, then putting the transmission pipe together with turbines is going to become very common. It won’t make a huge difference in continental energy strategy, but it doesn’t have to, it just has to make that payback.
