Janemba said:
You're completely missing the point of an engineering process. You're trying to say that anything can just be built using an iterative process of refinement if it deosn't work. That's how backyard tinkerers make things (and why they usually fail), not engineers. For any engineering project, trying to "just build it" is a recipe for disaster.
Building a dam is a good example, you can't "just build it" because you have to make a lot of
calculations and do a lot of design work
first! This way you first of all know it will work and how strong it is before you even build it. Going through an iterative process of building dams until you get it right would be ridiculously expensive, and would be terribly dangerous considering there is a lot of engineering that goes into building a dam, let alone the dam's design itself. By designing it you can also guess at what it will look like and how much it will cost for an engineering and construction proposal.
Things like this would have to calculated: how thick it will have to be, what shape it will need to be, how much flow is anticipated through it, what size turbines can be used in it for power generation, how much power generation is anticipated for the surrounding community, how will it be anchored in its surroundings, what kind of materials will be used, will the dam have traffic present on it, will the dam withstand events that could compromise its structure possibly putting people in danger downstream, how will you redistribute flow while the dam is being built, how will the dam be built, how long is its predicted lifetime, what will maintinence costs be... and a lot more.
All of the above examples in a dam would have to be calculated using knowledge in statics, dynamics, structures, mechanics of materials, material science, industrial engineering, reliability engineering, heat transfer, and thermodynamics. In each case, calculations would be made using knowldedge in mathematics and the applicable subject.