Snyder’s Unit Hydrograph
To Plot snyder’s unit hydrograph we need value of basin lag (tpr), time
base(tb) , width of hydrograph at 50% discharge(W50) , width of
hydrograph at 75% discharge(W75)
The peak time is distance from centroid of effective rainfall to peak
of the discharge.
\LARGE t_p=5.5t_r \\ else \\ t_p=t_{pr}+\frac{t_r-t_R}{4} \\ t_p=C_1C_t(LL_c)^{0.3}
where,
tp = Peaking time in standard condition
tpr = Basin lag in general condition
C1=0.75
Ct=Watershed factor
\LARGE q_p=\frac{C_2C_p}{t_P}where,
qp is peak discharge per unit catchment area
Cp=Watershed factor
C2=2.75
\LARGE q_{pr}=\frac{q_pt_p}{t_{pr}}C3=5.56
The width of hydrograph at 50% of peak discharge and 75% of peak discharge is given as:
\LARGE W_{50}=2.14q_{pr}^{-1.08}\LARGE W_{75}=1.22q_{pr}^{-1.08}The time base of hydrograph is:
\LARGE t_b=\frac{C_3}{q_{pr}}