Water flows in a trapezoidal channel where the bottom width is 6 m and side slopes are 2 : 1(H : V). The channel lining has an estimated Manning's n of 0.045, and the slope of the channel is 1.5%. When the flow rate is 80 m³/s, the depth of flow at a gaging station is 5 m. Classify the water-surface profile, state whether the depth increases or decreases in the downstream direction, and calculate the slope of the water surface at the gaging station. On the basis of this water-surface slope, estimate the depths of flow 100 m downstream and 100 m upstream of the gaging station.
a. Normal, increases, 0.015, 4.85 m, 5.15 m
b. Steep, decreases, 0.015, 4.85 m, 5.15 m
c. Mild, increases, 0.015, 4.85 m, 5.15 m
d. Steep, increases, 0.015, 4.85 m, 5.15 m