# Snyder’s Unit Hydrograph

To Plot snyder’s unit hydrograph we need value of basin lag (t_{pr}), time base(t_{b}) , width of hydrograph at 50% discharge(W_{50}) , width of hydrograph at 75% discharge(W_{75})

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,

t_{p} = Peaking time in standard condition

t_{pr} = Basin lag in general condition

C_{1}=0.75

C_{t}=Watershed factor

\LARGE q_p=\frac{C_2C_p}{t_P}

where,

q_{p} is peak discharge per unit catchment area

C_{p}=Watershed factor

C_{2}=2.75

\LARGE q_{pr}=\frac{q_pt_p}{t_{pr}}

C_{3}=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}}