When Silt Fills Your Water Reservoir 

I simply had no idea how interesting dirt could be. Dude you rock!

Absent dredging, all lakes, reservoirs, etc, are temporary. A lot of meadows start as lakes - get filled up, filled in, etc.

No idea silting claimed that much of a reservoir capacity each year…

Jon slowly working their way to making a video about everything that has the word yield associated with it

I would like to add that there is a fourth option: just live with the fact that the dam has silted up. In Africa there are many 'sand dams' purposely constructed. They build a simple dam which in a few years completely silts up. The sediment behind the dam will still hold groundwater which can be used for irrigation and drinking water. The advantage of a silted-up dam is that the groundwater will not evaporate like the water in a reservoir.

This video essay superseded my Dam engineering class back at the college, can't be more didactic than that! Kudos to you

The news clip about record low water levels in Germany has nothing to do with sedimentation or silt. The picture shows an iconic part of the Rhine river, which does not have dams. The nearest dam is app. 200 km upstream. The reason why commercial shipping had massive problems in the years since 2018 are the enormous summer droughts in western Europe. At this particular part, the river cuts through a mountainous region, the valley is narrow, the riverbed is solid rock. (The scenic valley is a tourist hotspot, btw). There is no silt. Interestingly there is the opposite of a sedimentation problem upstream. In the 19th century the river's meanders were cut off, creating shortcuts to prevent flooding and convert swamp into farmland. Since then, the river has cut deeply into the soft ground (there the riverbed is sediment), causing the groundwater table to drops significantly.

Australia developed a problem with agricultural land erosion.....which began to be addressed with the "land care" program to arrest erosion with trees and land contours. Land erosion really came into its own during the 1930's drought conditions, combined with economic hardship led to sever over grazing, which deprived entire regions of their top soil, which were thin and fragile.

An Archimedes screw set at the dam on the upriver side can lift silt from the base and dump it out on the downriver side. This would need to be set up during dam construction and it would likely take a number per dam not just one but it would help with the removal by constantly removing silt. Since at the dam itself is where the silting first starts by keeping it low there you keep it dropping there so the rest of the catch basin doesn't get as silted.

One of the other consequences of silt accumulation in dams is that they create "hungry rivers" downstream. Flowing waters have a certain amount of stream power, which carry sediments. If the water flowing out of a dam no longer holds sediment (because it got dropped behind the dam), it's going to pick up sediment downstream of the dam. This increases erosion downstream, which can have serious knock-on effects to anything that is near the river downstream. So siltation is not just a problem at the dam. It's also a problem downstream of the dam.

Another problem is that the silt is very fertile when it is spread out on the land during floods but is useless sitting on the bottom of a reservoir. The Aswan dam comes to mind.

4:07 "A cargo ship passes sandbanks near Kabul, Germany during historically low water on the river Rhine." The nearest "Kabul" is a kebab restaurant an hours drive away. The photo is from a village called Kaub

Unless your dam is very poorly designed, silting up does NOT affect how much power can be generated. Only the storage capacity of the damn is affected. And so the only effect it can possibly have is running out of water to generate power with. Low water levels at a dam DO affect power generation, as the water pressure in the turbine is lower.

A lot of the causes of siltation are also causes of eutrophication, where a water body is essentially made unfavorable to life through a combination of vastly increased nutrient levels and algal blooms

Small point, Pressure waves travel long distances underwater very quickly, meaning underwater explosions can injure susceptible sea life far the explosion. So Air bubble curtains are used for acoustic dampening, not to drive away sea life.

Why not use underwater vacuum hoses powered by the hydraulic head, especially when the opportunity to leverage all the excess energy and capacity during storms that will overfill the Dam. During construction a network of pipes with a grid of inlets that can be selectively opened one at a time could be used later to clear silt. If there isn't enough suction, a venturi powered by dam outlet flow could boost it. What is the economic value of all the silt, and quit it be used for something?

Matilija Dam, located in the Ventura River watershed on Matilija Creek near Ojai, was built in 1947 and silted beyond use by 1960s. A notch was cut in the dam for safety reasons but total removal remains beyond available funds. PS - Blocking river sediment has been blamed for a lack of sand replacement on local beaches. PS2 - Los Angeles retention dams mentioned as having been cleared of silt are specifically designed to catch water from extreme rainfall events and debris to prevent flooding downstream. Basins have to be cleared on a routine basis to maintain capacity.

Another issue with dams stopping silt from moving down the river, that you didn't talk about as much, is it causes high erosion downstream from the dam.

@Asianometry We too have a problem with reservoir silting in Pakistan. Our major rivers carry a lot of silt for example the Indus and Jhelum. Our 2 biggest dams (Tarbela and Mangla Dams) have been continuously silting hence their reservoir boundaries have to be periodically raised to keep up the storage capacity.

Silt is what is missing in agriculture on the fields quite often due to methods used. Not sure if it might be viable to prep dredged/dugg out silt with rotten plant cellulose to create humus for aggriculture. It would be i guess more cost effective to have better aggriculture methods in the first place that prevent fields to be washed away.

Your videos are the equivalent of a 3am Wikipedia deep dive about a random yet highly interesting topic.

The forest fire, followed by flash flooding, filled the riverbed, and now the water goes wherever it wants in the Santa ynez water Reservoir Canyon, Pacific Palisades, California

The flip side of this situation is the fact that dams increase coastal erosion. The silt and sand that would go to building beaches and marshes is trapped behind the dams and causing problems with them.

Thank you for this uncommon type of information about civil engineering. I appreciate your work in educating your followers on critical pieces of infrastructure - industrial, civil, or otherwise. Greetings from the UK, Anthony

If you look at satellite photos of Lakes Mead and Powell on the Colorado you can see all the silt since they are so low.

you can never stop sedimentation of dams. you can mitigate, but physical removal will always be a necessity

Super interesting, Lake Okeechobee in Florida is also facing siltation though for a different reason. Historically the lake was ringed by shallow seasonally submerged grass flats. The shallow lake would accumulate silt but in heavy storms the winds would push water and silt into the grass flats where it would get trapped. The silt is heavy in organic matter and has created some of the richest most fertile tropical peat lands. The lake is now rimmed with a levy that prevents the silt migration and the grasslands are now all agriculture mostly Sugar Cane.

Our small local dam is empty once every few years. Then they dig out all the soil. Thought that happens everywhere😮

Having rafted in the Green River in Utah in spring some years ago I saw first hand the silting going on. I went for a swim and in a half hour the pants pockets were full of silt. Gave me some reflection on how much was going downstream to Lake Powell. I can only speculate how much silting is going on there as the Green and Colorado both go thru many miles of sedimentary rock before hitting the reservoir. It would be interesting to find out form people managing the reservoir how full of silt it is. (If they will admit to it).

Interesting topic. I don't know how accurate the claim is, but allegedly, China's huge 'Three Gorges' dam on the Yangtze river will become silted within ~50 years due the high degree of silt coming from upstream. What's worse is that the silt contains a LOT of pollution.

One solution would be to have a pre dam dam that lowers the speed of water and is designed to be easy to clean of sediment. But it is expensive and long term

Shout out to Cogswell Reservoir on the West Fork San Gabriel River in southern California! I love riding my bicycle up there: the roadway in is closed to normal vehicle traffic and is a lush, tranquil place year-round.

The finest silts make it all the way to the dam and you can see it seeping in through the gaps in the lower galleries.

i would expect a dam to have smaller gates on the bottom that would open for a short period of time once every few years to wash the silt out and then close

Silt can also block harbours. Specially older harbours founded in a time when depth was not the primary driver, and storm shelter often was more important. A famous example in Europe is Belgian Bruges, a medieval prosperous town with a harbour. It lost a functional harbour that routed a high percentage of Northern European trade due to silting. Because of that however, the architecture survived and now it is is tourist town. In modern times, even the North Sea is dredged to allow Brazilian iron ore vessels to reach Rotterdam. (these largest class of ships only go to certain Chinese deep sea harbours and Rotterdam)

Dams may provide renewable-resource services (water storage, flood control, hydroelectricity), but dam SITES are not a renewable resource.

The speed at which you create quality content is amazing. Take good care of your self.

Very cool video, I was not expecting such a subject to be tackled on this channel. For anyone else who might have been pleasantly surprised by how interesting this video was, I can suggest the channel Practical Engineering. The host Grady offers some very interesting material about everything concerning our constructed environment.

Yep, silt fill in reservoirs is a problem everwhere, but regular dredging can mitigate that problem.

Another first class video. Awesome channel! 😃

Asianometry Another cool topic about silt is how it makes clay! You could do a whole video about clay pottery history in asia, briefly tied in with the composition of clay. Love your videos, keep them coming!

I once camped atop a silted dam for a back country project. We drank filtered water from a pit we dug in the silt. It was the worst water I had ever tasted, full of tannins and who knows what, clogged our filters almost instantly. We were finally relieved by a storm that caused some streams to flow. Now I work at a mine where I see this effect on a fractally small scale on a daily basis.

I don't think dredging is that expensive, especially if it's just once per 50 years. You can do it from floating riverboats to reach everywhere in the reservoir bed. I think the real problem with this stuff is that most dams are the small cheap versions that exist at almost every river, often unregistered and old, and they piled up with crap that made them useless by now. Will take massive re-industrialization effort to go fix up all those.

Not mentioned here is the role of silt in the prevention of coastal erosion. The Amazon dumps around 3 cubic kilometers of silt in to the ocean every year. Prevent that silt from flowing and you change the entire east coast. Recent coastal flooding in Asia for example was made worse by the lack of silt transported in the decades earlier. It has to be said however, that there had been very little done to mitigate the problem of siltation. Bottom line: We want that silt downriver, not in the dams.

Underrated subject. It won't be as popular, but thanks for doing this.

I first became aware of the silting problems when watching reports about an experiment with Glenn Canyon Dam in Northern Arizona. They conducted an experiment to see if a carefully managed release could restore some of the flood runoff benefits to the soil around the river channel. Turns out that this didn't go as planned but it did lower the level of the reservoir enough that you could see that there were large volumes of sediment in some areas of the reservoir. One of the most effective areas for sediment control in this area seems to me to be the Salt River system of dams outside Phoenix. The water flowing into the reservoir comes from two sources. One of these is dry two-three months out of the year. The other takes a pretty lazy path downhill from the eastern part of the state so doesn't really have a chance to pick up much velocity anyhow. The big concern, before the dams were built. was flood from rain and snow runoff on the watershed. A half inch of rain on the watershed could push the river beyond its banks as it passed through Phoenix because it would load washed and draws that were normally dry and that's where a lot of the silt came from. Otherwise, now, first, this river has to pass over a weird dam originally used to divert water into a power plant at the Roosevelt dam. This slows the water heading into the reservoir considerably so most of it comes out fairly clean. The water then has to make its way down to to Roosevelt dam's outlet, several miles away further on down. Then it passes into a second reservoir, then a third, then a fourth, then finally a diversion dam at the northeast edge of town that feeds water into the local irrigation canals, typically claiming all the water released upstream from that and a second system. So before the downstream dams were built in the 1920s and 30s, and before concrete lining of these canals, cleaning out the canals and irrigation ditches was an ongoing process. Now, there are occasionally rocks about 6-12 inches around that find their way into the canals but the water normally carries nothing more than algae and other growth rather than silt and that's the only reason the water isn't actually clear. So it was serendipitous that the way the system of reservoirs were constructed resulted in very clean irrigation water and reduced silting of everything, allowing it to last for 100 years with no reports that there are any real problems with capacity.

I like how varied your content is, I use to watch your videos about industrial topics, but now I enjoy your videos even though I can’t predict what the next topic is

I would suppose that is why Norwegian Hydro power is so effective. The dams are in the highlands where there is very little soil. There is quite a bit of mineral accumulation that probably does some damage to the turbines. Quite a lot of silica due to the bare mountains I believe.

I suggest you take a look at The Loess Plateau and how it has been recovered. Also, investigate the Paani Foundation's Water Challenge in India.

Excellent job - on-par with Grady @Practical Engineering!

At 5.59 or have a pre settling reservoir to trap the majority of the silt before it reach the main dam and easier to get rid off....yes I know it will not clean the lot but it will increase the use of the dam by decades.....then every so often empty the dam and truck out the silt to start another cycle to prolong the dam utility...

"Dead Storage". I just thought applied to the Hoover Dam and Lake Mead, near Las Vegas. Last year, due to the prolonged drought, they found quite a few dead bodies there. You know Las Vegas & the mob connection.

What about them benifits? A silted dam becomes a piece of flat land with deep and very fertile soil. As for a hydro electricity dam, a silted dam will effectively always be high.

Janos Silt: I HAVE SEDIMENTS! POWERFUL SEDIMENTS!

There is a simple, inexpensive fix for this problem that would decrease silting by one or two orders of magnitude (10 to 100 times less). Simply ensure that beavers occupy as much of the catchment of these dams as possible. Their ponds collect the sediment and turn it into valuable 'bottom land'. And they do so much more. They a) reduce flood peaks and increase low water flows, b)direct water underground where it is save from evaporation, c)store much more water than is in the pond itself by raising the water table in the surrounding area, d) greatly increase biodiversity in their area, e) remove nutrients from the water and on and on it goes.

I like that at the beginning of every video there's a map (almost) showing where my home is.

Have we considered simply exploding the silt? On a more serious note, I wonder if, keeping this in mind, it would make sense to build dams in pairs, with the expectation that only one would be fully operational at a time. Then, when the one in operation needs to be desilted, the other one can 'take up the slack' by being put into operation. I mean, there are no silver bullets, but just something that came to mind. Edit: That's what I get for not waiting until the end of the video!

Silt is really a problem called a loosing battle in the dam. In my region there is a river with 8 power plants and 2 flood dams. At first nobody really payed attention to silt, but 30 years ago a major drought revealed that there is no storage anymore. Since then there is constant work on the silt problem, and no matter what they do, they barely maintain the level or maybe advance by little bit year over year. Last estimate was they restored around 5% of the storage capacity.

I guess videos about sediment buildup in reservoirs is topic that more people than I had previously assumed would enjoy.

That is some obscure knowledge to impress your buddies at a drinking session!

This is a major problem in my state (MS) in the US. MS has several large flood control dams and deals with a lot of rain and lots of fine alluvial sediment. It keeps the army corps of engineers here who manage these quite busy.

Every time I see a new video from you it makes the day better

another grrrreat video. thank you for all the work, and then sharing.

I don't think of it as silting, I think of it as very efficient mud storage.

Agriculture has been dealing with the issue of silting for over 100 years in Australia, possiblity many hundreds in other countries, we use smaller settling ponds that catch water and gradually let's it flow into the main reservoir via channels or pipes, the smaller ponds dry up quickly and are easily cleaned in a day or 2 with heavy machinery. In the case where it is not dry you can transfer the water via diesel pumps.

Practical Engineering has a very different presentation style than I remember (j/k nice video)

In Pasadena CA there are two dams that are heavily silted. Both are on the Arroyo Seco. Not a river (only when it rains), but more like it's Spanish name suggests; arroyo: stream/brook. There's the Devil's Gate Dam, it's been dredged for the last few years. Mind you that Southern California doesn't get much rain. During the summer there's hardly any water. Making it easier to haul away all that silt. But when it does rain there is so much silt that comes down the mountain. Then a few miles upstream is the Brown Mountain Dam, built in 1943, according to it's website. It's a rather small dam. The website says that it's 81ft high. If you hike up to the dam now you will see that it's silted all the way to the top. If you're from the area do yourself a favor and make the hike. There's not much of an elevation gain, I think it's only 500ft over 2 to 3 miles. It's hardly felt.

I spent a summer hiking in the canyons of Utah. I got to see, first hand, the damage silting does to a number of small reservoirs. Take into account that many of the places that are good for dams are not very accessible to heavy machinery. It's a complex problem.

Yep, there was a recent job done to prevent silting at the Zengwen reservoir. It also has a connection to another reservoir, I guess it is the Wushantou?

Finally a video on a topic I find oddly interesting! Great stuff

Oh I just saw a short video demonstrating this whole video. Someone was showing how a dam works but after putting a sponge into a clear container that had water flowing from left to right, they added in small sedimentary sand after the water levels changed. I wasn’t sure it would be that bad on a larger scale but it looked like it wouldn’t be good even on a scale as big as your hand. First everything slowed down (mind you the initial flow of the water and sand was fast already) then it all slowed down, flooded till it was level, and as he added more sand, it all flushed out and even went faster than before. I feel like it’s a video someone found and just said “this is how a dam works” but I don’t think that was the original purpose of that video now. Wish I had the link from Instagram, I’d post it here.

I had no idea this was a effect, very interesting, good video!

Hadn’t heard of this before. Now I’ll be waiting for a Practical Engineering video on the topic

I wonder... I saw one of the dams open spillway and spew tons of mud. What would happen if near the bottom of the dam we would make an optional spillway that opens on a regular basis, but just a thin flat thing, not very big. Open it just enough, so silt goes, close when you see water. Repeat every few days. With enough level difference, water would fill the hole with new silt, and you should reach some kind of equilibrium state. especially if currents would be engineered to pass over that thing, and leave all the silt incoming. Anyone knows any issues with that ?

I look forward to every new video. Such a wide range of interesting topics.

You should read Cadillac Desert. People need to watch the videos about removing the dams on the Elwa River....silt and wood are critical to near shore habitat where the rivers enter the oceans....off river channel storage is probably the best solution.

This was very interesting. I know absolutely nothing about dams, nevermind the silting of said dams. With that said, the creator made a video that was still interesting and easy for a layman to follow. Good work all around.

Seems like silt could be useful material for construction.

Thanks for another dam wonderful video. You’ve helped me change my hopeful career path towards more infrastructure

Elk river Minnesota opens up the dams every several years to drain the lake and dig silt out and put it back in the fields. Usually only takes the summer, but not more than a year.

I remember cleaning our basement's sump pump well from silt, before it got to reach the impeller, on a regular basis as a teenager.

Build small continuous flow tunnels at the bottom of new dams, with maybe some larger ones that can be open as needed.

You didn't mention the biggest hurdle. Pumping and the power for it. Everything is uphill from sea level. Pumping cost can make desalination more desirable.

By Louisville Kentucky they used to have a incline belt for mining gravel out of the river perhaps that could help replenish farm lands if not to polluted

Near Angkor temple in Cambodia, there're 2 large man made reservoir built a thousand year ago: east Baray & west Baray. The east Baray is 90% filled with sediment while the larger west Baray is not. Wonder why they don't behave the same way.

I knew I wasn’t the only one who worried about this type of stuff. Super educational. A master class in reservoirs and siltation.

This presentation was absolutely educational. I am more aware more about the sediment problems behind Dams. I was always aware of the Hoover Dam silting up but did not consider the rest of the world's dams. The various silt removal methods, some better than others. What about bottom release instead of top water release, how well would that help, and how far from the Dam's bottom release area have a decent silt removal zone? Being retired from Drilling and Blasting, I'm leaning on explosives but after the bottom is loosened up how would that material be removed other than a slow, suspension flow to the outgo at the Dam. Thank you for this subject affecting all Dams, hopefully, some newly built Dams have engineered methods into the construction that deal with this problem. Constant erosion. Constant silt depositing.

Oh yeah that makes sense. Usually during springs our local reservoir opens the gates to let through the copious amounts of water from melting snow, at the same silt gets moved too I assume.

That was excellent. As an Antipodean that used to have to deal with hydrology and land management, I really appreciated the Australian examples to illustrate your points. Bonus, I learnt something about the climate, geography, and hydrology of both South America and Taiwan.

I love this channel, so interesting.

Seems to me that a side tunnel at the exit height of the dam should be installed with a huge barge on the other side with movable pipe work that systematically traverses the bottom of the pond. This acting like a GIANT vacuum cleaner . Simply lifting the pipe out of the water would stop the flow. no valves needed. About 2000mm in ID should be sufficient. A heavy steel / Stainless steel pipe capable of rotating up and out of the water so that the flexible sections could be changed out would be needed.

A small point, but the cost to LA county was not per square meter, but (worse) per cubic meter.

Seeing that thumbnail i misread it at first glance as "when shit fills your water resevoir"

Really feeling satisfied that the Palmyreans (lived in central Syria) had achieved something!

3:23 check your source. The picture on the left is Tourtemagne Reservoir in Valais, Switzerland, with glacier in the background (Hauenstein 2005)

We have a major issue with silting on the lower parts of the Columbia River caused by volcanic ash still coming down the tributaries from the 1981 Mt St Helens eruption. They have to hydraulically dredge the river yearly to keep the shipping channel open.

Running a large diameter pipe along the bank to where water enters the reservoir and connecting it to a floating dredge

The fact we know about it and implement nothing to get rid of the problem. Like why cant we add a door at the bottom or multiple doors that we open 1 or 2 times a year for a short time to get rid of extra dirt behind dam walls.

What is the economic value of all the silt, and quit it be used for something?

You don’t know until you know. Good job enlightening this old man who thought he knew enough.👍