Water surface profiles are computed from one cross-section to the next, beginning at the most downstream section, Section 1, along with the Starting Tailwater Elevation, working upstream. It solves the Energy equation using an iterative procedure known as the Standard Step method. Here’s how it works:
- The program assumes a water surface elevation at the next upstream cross section (or downstream cross section if a supercritical profile is being calculated).
- Based on the assumed water surface elevation, determine the corresponding total conveyance and velocity head.
- With values from step 2, compute the Friction Slope (Sf) and then the energy loss, he.
- With values from steps 2 and 3, solve the Energy equation for the water surface at point 2, WS2.
- Compare the computed value of WS2 with the value assumed in Step 1. Steps 1 through 5 are repeated until the values agree to within 0.015 feet (0.004 m).
Channel Studio assumes water surface elevations by taking the average of the computed and the assumed elevations. In other words, W.S. new = W.S. assumed + 0.50 * (W.S. computed – W.S. assumed). The very first trial, however is set by projecting the previous cross-section’s water depth onto the current cross-section.
Channel Studio will use up to a maximum of 25 trials to obtain a balance. If a solution cannot be found, it assumes critical depth and moves onward to the next section. If the calculation option “Supercritical Profiles” is checked On, then Channel Studio will automatically compute a supercritical profile.