if D is D hours unit hydrograph and T relates the equilibrium discharge approximately at the end of the base period T hours of the unit hydrograph, then the number of unit hydrographs needed to produce the S-curve hydrograph is given by:
1
\(\frac{T}{D}\)
2
\(\frac{D}{T}\)
3
\(\frac{{\left( {T + D} \right)}}{D}\)
4
\(\frac{D}{{\left( {T + D} \right)}}\)