Forest Service Peak Flow Calculator
Estimated peak flow for burned areas using Curve Number technology

Manual entry
From ERMiT
From WEPP Online GIS
Run Description
Storm runoff, Q   mm  in
Storm precipitation, P   mm  in       if Q > P use P ~ 2 Q 
Watershed area, A   ha  ac
Watershed flow length, L   m  ft
Avg watershed gradient, Sg   m/m  ft/ft
Curve number, CN             CN estimate from ERMiT:   (forest)  
Time of concentration, Tc   hr  hr      Tc ~ hr (flat watershed; dry soil)
Ponding adjustment factor, Fp         0% pond: 1.0; 1.0%: 0.87; 5.0%: 0.72
Surface storage, S   mm  in
Initial abstraction, Ia   mm  in
Unit peak flow rate, qu   m3/s per ha/mm x 10-3  ft3/s per acre/in x 10-3
Estimated peak flow rate, q   m3/s  ft3/s
Culvert diameter, D   cm  in    h   m    ft 
use Mica Creek example | clear |
Curve Numbers for Forests



Elliot, William J.; Hall, David E.; Robichaud, Peter R. 2010. Forest Service Peak Flow Calculator. Ver. Moscow, ID: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. Online at <>.