Question

The total observed runoff volume during a 4 hour storm with a uniform intensity of 2.8 cm/hr is $25.2\times {10}^6{m}^3$ from a basin of $280k{m}^2$ area. What is the average infiltration rate for the basin?

• A. 3.6 mm/hr
• B. 4.8 mm/hr
• C. 5.2 mm/hr
• D. 5.5 mm/hr

Answer 1

The correct option is D 5.5 mm/hr

The average infiltration rate is also called W-index.
Thus
$W=\frac{P-R-I_a}{t}$
where,
P = Total storm precipitation depth
R = Total storm runoff depth
t = Time of rainfall excess
$I_a$ = Initial losses in terms of depth

$\therefore P=2.8\times 10\times 4=112mm$

$R=\frac{25.2\times {10}^6\times {10}^3}{280\times {10}^6}=90mm$
$t_c=4hr$
$I_a=0$

$\therefore W=\frac{112-90}{4}=5.5mm/hr$