Question

) In the calculation of gradually varied water surface profiles; a. When should calculations be done in downstream to upstream order, instead of upstream to downstream order? b. What are some fundamental differences between the Standard Step vs Direct Step methods?

Answer 1

In gradually varied flow, the water surface profile can be calculated from downstream going upstream (backwater calculation) or from upstream going downstream (frontwater calculation). The direction depends on the classification of the water surface profile (hydraulic slope and type of curvature). For mild, critical, adverse, and horizontal slopes FishXing performs a backwater calculation beginning at the downstream boundary. Frontwater calculations are performed for steep slopes, beginning at the upstream boundary. If a steep slope culvert is backwatered (S1 curve), FishXing also performs a backwater calculation and identifies the location of the hydraulic jump (if one occurs).

Differences between Standard Step Method and Direct Step Method-

The standard step method is a computational technique utilizes to estimate one dimensional surface water profiles in open channels with gradually varied flow under steady state condition.

In Direct Step Method, the entire length of the channel is divided into short reaches and the computation is varied out step by step from one end of the reach to the other.