A small dam

[eTraxx]

I'm building this small dam for my O scale module. It's 24ft wide in full size. This is where it's at right now .. sandstone texture paint, A/I wash and drybrushing with FolkArt Linen.  I'm at the point I need to take a good look at some photos of old dams to see where to go from here .. pin washes I think, weathering powders. That white thing is the intake for the pentock. A pipe will connect there to deliver water to the turbine. Still need NBW .. but that's for tomorrow. (that funny looking top is blue painter's tape covering the area where the 'water' will go)

[finescalerr]

Effective. -- Russ

[artizen]

So I am looking at the spillway?

Would the pipe (the white thing) not be better slightly lower to allow for varying levels of water behind the dam? Because I live in Australia our dams vary from 100% and overflowing to only 10% and pumping mud for drinking water.

[eTraxx]

Yes, that's the spillway.

- if the purpose of the dam is to supply drinking water then the intake could be lower to allow using all the available supply. That though would mean that the demand exceeds the supply. Once the community lowers the water level to the bottom of the intake they would then have to depend on the rate of flow of the water supply to refill the dam .. not very appealing.
- if the purpose of the dam is to raise the water high enough to power a turbine then the higher the better. If you take the flow volume of the stream .. cross-section of stream - 1 foot x height x width .. x .. rate of flow (like 1 ft per second) then .. x .. 60 you get cu.ft. per minute. Water weighs 62.5 lbs per cu. ft. That's your power source .. that weight raised. The higher you raise it the more work you get from it. Just calculating that .. lbs per minute without any head (raising the water up) you divide by 33,000 and get hp from that water.

The interesting thing about this is that you can take a stream that might not have enough energy to power a turbine at ground level can be successful simply by raising it up via damming. That's from a book titled 'Power development of small streams' published in 1920. Example .. a 12 inch Hunt-Francis turbine (No.2 wheel) would produce only 1.15 hp with a 4 ft head requiring 187 cu.ft. min of water. If you raised the head to 87 ft that jumps to 119.24 hp requiring 873 cu.ft. min water flow. 873 cu.ft. min isn't really that much .. that would be for example a stream 7 ft wide and 2 ft deep flowing at 1 ft. per second.

Ok. Sorry for all the numbers .. but I've been happily calculating the requirements for my little dam to make sure all the 'bits and pieces' are the right sizes

[Malachi Constant]

Well, I was right with you till you went all techno-wiz there ... but the dam looks good!    -- Dallas

[eTraxx]

Well, I was right with you till you went all techno-wiz there ... but the dam looks good!    -- Dallas

That's what happens after I have a couple of beers and post! .. and thanks Dallas.

[artizen]

I think I understand the principles of weight and volume to create force (and therefore power). Unfortunately, it was all in feet and pounds which I haven't used for over 40 years. Going metric while at school was something we jumped into with great enthusiasm because it was all so easy! One litre of water weighs one kilo... etc. Once you get used to the funny words used to describe things (never understood kilopascals for example) you can do most calculations by using your fingers and toes. 

So now I understand that this dam represents one that has its water level maintained within a very narrow range to be able to run a power house downstream. One of my favourite dams using penstocks to drive turbines that I have come across in this part of the world is Manapouri in Fiordland in New Zealand. There, the turbines are driven by vertical pipes 180 metres below the lake level. You can take a bus tour of the turbine hall through a 2.1 kilometre access tunnel (all underground below the mountains). And remember, NZ is the Shaky Isles!