Let me explain it with a famous saying

Where there is a will, there is a way. Where there is a will, there is a way.

There is a way It is the main clause, where there is a will is an explanation of There, and it is an appositive clause of There; there is a will is an explanation of where, and it is an appositive clause of where

So this famous saying is superimposed Double appositive clause

The example sentence you gave does not have the first there, you can reorganize the sentence

Where there is enough water, the plan lies.

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Where here can only be interpreted as a directional adverb that modifies lies, and the entire sentence where there is enough water is considered an adverbial clause; and there is enough water is an explanation of where, which is considered an appositive of where

< p> So the example sentence is an adverbial clause superimposed on an appositive clause