Fundamentals of Engineering Design
when siting grade control structures in unstable reaches. An example relationship is shown in Figure 5.26.
For example, the drainage area of a particular reach is 100 square miles. The stable channel slope for that
reach from Figure 5.26 is approximately 0.0010. Therefore, the grade control structures will be designed
for a slope of 0.0010.
Figure 5.26 Equilibrium Channel Slope Versus Drainage Area for Hickahala Creek,
Batupan Bogue and Hotopha Creek are Shown. The 95 Percent
Confidence Intervals are Plotted (from USACE, 1990b).
The slope-drainage area curve is a valuable relationship for initial understanding of an unstable
watershed. However, the relationship is empirical and extrapolation to other watersheds, beyond the range
of size in the same watershed, or to different times is risky. Constant field verification is necessary for