Which one of the following is not a factor in controlling times of concentration of watershed runoff?

(a) The drainage density,

(b) the roughness of the flow surface,

(c) the rainfall intensity,

(d) the flow lengths,

(e) all of the above are factors (Figure 3. 17).

Figure  3. 17

Rate (cm/h) 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 Rainfall excess Rainfall Infiltration. 0.1 0.0 20 40 60 80 50 Time (min)