Pond Boss Forums POND CONSTRUCTION Building a dam Keyway drawings/pictures

I'm gonna crawl into the pigpen all the way.

I agree with TNHB & D.I.E.D. that the amount (height) of water determines the pressure on the dam. But it seems like a keyway increases the vertical cross-sectional area of the dam (by going deeper than the bottom of the pond), thus lowering the ... let's say strain ... on an individual area of dirt in the dam.

To use a firearms analogy, a blowback action uses only the mass of the bolt to hold the cartridge being fired in place, thus limiting pistol-sized bolts to relatively weak cartridges (9mm Makarov about the maximum power) or requiring massive bolts for more powerful cartridges (like .45 ACP in a Thompson submachinegun). This is analogous to (as Eddie stated) a normal-sized unkeyed dam holding back a shallow pond, or a inordinately massive dam being needed for a deep pond.

But if we add a keyway to the dam (or a locking mechanism to the bolt) the same sized dam (or bolt) can hold back a deeper pond (or fire a more powerful cartridge - how .45 acp can be safely fired in a gun the size of a 1911 instead of a Thompson).

If water leaks through the dam, this has the effect of weakening the dam - lowering it's shear point. This is like using soft, weak steel on a bolt's locking ribs. A good keyway also helps waterproof the dam to prevent this.

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I think most misunderstandings (which may appear to be disagreements) we can have on this issue are the result of not correctly understanding terms like pressure and force wrt ponds and dams. I'm pretty sure I'm personally screwed up some on these words.