DIRECTSTEP will calculate the length
of the S3 water-surface
profile in trapezoidal, triangular, or rectangular
prismatic channels using the direct step method (Chow, V. T.:
Open-Channel Hydraulics, McGraw-Hill, 1959).
The depth increment is set at 1 mm (0.04 in).
Click the YES button if you are using SI units;
click NO if you are using U.S. customary units.
In SI units, use meters and cubic meters
per second; in U.S. customary units, use feet and cubic feet per second.
The program will prompt you
to enter discharge Q, bottom width B, side slope z, bottom slope S,
Manning n, and upstream depth yu.
The program will calculate the normal depth downstream.
To specify a triangular channel, enter bottom width B equal to 0.
To specify a rectangular channel, enter side slope z equal to 0.
Enter bottom slope S in dimensionless form (Example: 0.003).
The program reports the
normal depth downstream, the number of 1-mm (0.04-in) depth intervals,
and the channel length (m or ft)
to 50, 20, 10 and 1 mm (2, 0.8, 0.4, and 0.04 in) below normal depth.
The last value (1 mm) is taken as the length of the S3
water-surface profile.
Caution: Please make sure that your input data
makes sense from a hydraulic standpoint. The upstream depth yu should be smaller
than the downstream normal depth for the specified hydraulic conditions.