The hydraulic radius of a circular pipe of diameter 'd' flowing full is
A
$$\frac{{\text{d}}}{4}$$
B
$$\frac{{\text{d}}}{2}$$
C
$$\frac{{2{\text{d}}}}{3}$$
D
$$\frac{{\text{d}}}{3}$$
Correct Answer: $$\frac{{\text{d}}}{4}$$