in method 4 i have set my 'target WS change' at the state's regulated increase of 0.2ft. After running the program with the 100 yr storm elevation, my water level has increased beyond the target WS change of 0.2 at a some stations.
I am not understanding why this is happening? Isn't that 'target change' the maximum increase at which the water can increase?
A target is a target, not an absolute. Remember that whatever changes occur in your downstream cross-section will affect the water surface elevation at cross-sections upstream.
The following is copied from page 9-8 of the HEC-RAS Hydraulic Reference Manual:
"Recognizing that the initial floodway computations may provide changes in water surface elevations greater, or less, than the "target" increase, initial computer runs are usually made with several "target" values. The initial computer results should then be analyzed for increases in water surface elevations, changes in velocities, changes in top width, and other parameters...
"The increase in water surface elevation will frequently exceed the "target" used to compute the conveyance reduction and encroachment stations for the section. That si why several target increase values are generally used in the initial floodway computations.
"After a few initial runs, the encroachment stations should become more defined. Because portions of several computed profiles may be used, additional runs with method 4 or 5 should be made with varying targets along the stream. The final computer runs are usually made with encroachment Method 1 defining the specific encroachment stations at each cross section."
