It is difficult to calculate accurately the minimum water depth for anchor gear to be braked effectively in weight dropping mode by Newton classical mechanical law.

Calculation on uniform flow depth and critical depth of open channel with iterative method;

The direct solution on critical depth of horseshoe section tunnel;

Approximate solution for the critical depth of a arched turnel;

Approximate formula for calculating the critical water depth at circular cross section;

The new algorithm of nonlinear constrained optimization calculation of critical water depth problem s new algorithm;

Calculating critical water depth of trapezoids open channel by real coding based on Accelerating Genetic Algorithm;

A new iterative method of calculating critical depth of water for ladder canal is presented in the paper.

The criterion of fissure water pressure causing landslides is discussed, then calculation method of critical depth of water is put forward when landslides of low dip slope fail.

Graphic method and trial-and-error method are the common methods that apply in computing the depth of water under the normal conditions and critical depth of water.