A fundamental characteristic of water in the game is its tendeny to flow downward due to gravity. The water will flow to the most accessible low point. When the water has no where to go but through the dam? The water will only flow through the dam if its surface meets very near the height of the dam. When it does meet and the water on the other side of the dam is near the base? #Cha-ching!

Until the water reaches about the same height of the dam, you will not produce any hydroelectricity. It's somewhat like a straw that you place above the surface of the fluid in your glass. You're not going to get any pressure to draw the fluid into your mouth. Similarly, if the water surface is not sufficiently above the dam intake, then the dam is not yet operational. #Pressure!

The second thing to keep in mind is that length does not matter as much as height. It's all in the height. Again, gravity! The farther the water falls, the more potential energy your dam will harness.

The real trick is placing your dam at a height and length so that water upstream does not find a path through terrain that is at a lower elevation than the height of the dam. Rule of thumb: always place the height of the dam at an elevation lower than the terrain surrounding the upstream water. In other words, the dam should not exceed the highest elevations of the upstream terrain! #Always!

Gravity! Height Vs. Length! Terrain Elevation! #Don'tForget

When considering a hydroelectric dam, ask yourself:

• Are there any deep rivers going between cliffs on this map?
  
• Is the river's inflow at the edge of the map?
  
• Can you place a hydroelectic dam as close to the map's edge as possible?
  
• Is there a waterfall on the map that you can exploit?

Upon finding a potential location, check the area with plans of dams using the dam tool and consider:

• Will the currents sufficiently raise the banks, meet the dam's height, and feed water to the dam continuously?
  
• Will the dam be cost effective?
  
• Will the dam and the resulting reservior of water it holds take up more space than your power alternatives?
  
• Will the water find an easier route down past the dam?
  
• Will this cause a flood that drowns your citizens? #Sadface!
  
• Are there better power alternatives for your city right now?

If your answers to these questions do not correspond to implenting your proposal, then I advise you consider other options. Otherwise, build the damn thing! #Didyougetit?

You should always keep in mind the cost effectiveness of your power grid when planning to expand upon it. Think about cost per MW!

• At 427MW, a dam is better than a solar plant.
  
• At 321MW, a dam is better than any wind plant.
  
• At 257MW, a dam is better than a nuclear plant. (Not considering 1.92k m³ water / week!)
  
• At 229MW, a dam is better than a coal plant. (Not considering cost of resource burned!)
  
• At 201MW, a dam is better than an oil plant. (Not considering cost of resource burned!)
  
• At 27MW, a dam is better than an incineration plant. (Just burn garbage with it!)

This considered, the goal of your city should be fusion power! But you need plenty of power until you get there. A fusion plant produces 16GW for only 8,000€. 1/2€ per MW!

To get the most out of your power plants, you should budget your grid at 150% if needed. Conversely, you can conserve power and money by lowering the budget. Roughly 108% - 115% is most cost-effective in the budget panel.

The budget is not linearly proportional to power production.

Fusion Power is your primary goal. Once you have it, forget dams, wind, solar and nuclear. Nothing compares to the supremacy of fusion power!

To unlock fusion, you need 6 unique buildings (in bold, prerequisite in regular) and 65k population:

3 Full Cemeteries -> Plaza of the Dead
1 Full Lifetime -> Fountain of Life and Death
3 Water Pumps for 1k Days -> Tax Office
1k Abandoned Buildings for 5 Weeks -> Observatory
5k Full Lifespans Over Time -> Science Center
50% Highly Educated -> Modern Art Museum

Uh, good luck, you are on your own in this endeavor!

Failure should not be an option! On some maps and playthroughs, you and your city will be better off if you just take an alternative path of power production. Do what is most cost effective per MW, but what also delivers. Sometimes, hydroelectric dams just are not damn practical. Go solar or wind until you can get fusion!

If you want a go with a city-building and damn-building map, try Islands! #ILoveComments!

Did you like my dam puns and #hashtags?

Guide to Dams, Levees, and Water Control

PROtips for Skylines

Electricity and the best power plants [1.2]

Why don't these dams work[forum.paradoxplaza.com]

A in-depth Guide on Hydro Power Plants[forum.paradoxplaza.com]

Hydro-Dam Fail in Cities: Skylines

Cities Skylines: The Great Flood

Cities: Skylines Dam Placement Epic Failure

Cities: Skylines Lets Play Part 29 ► Hydro Electric Dam and Airport Parking! ◀ Gameplay / Tips