“The Unit Hydrograph Model for Hydrograph Separation” Ninghu Su Landcare Research, New Zealand Ltd. Environment International, 21, #5, 509-515

Article Summary Introduction to Hydrographs Nash Instantaneous Unit Hydrograph (IUH) Model Parameter Equation Development 3 Time Points for Parameter Estimation Time of Concentration from Slope-Channel Relations Recession Limb Used for Baseflow Calculation Estimate Baseflow for Rising Limb (63%)

Key Hydrograph Features Initial Loss – rainfall that does not affect hydrograph Lag Time of Total Storm Hydrograph Lag Time of Baseflow Hydrograph Point A – Flow at Time = 0 hr Point B – Time when Discharge Increases Time of Duration for Effective Rainfall Time of Concentration = Last of Overland Flow Flows Point C – Time when Baseflow Begins Point D – Time when Overland Flow Ceases

Hydrograph Calculations Slope-Channel Empirical Equation for Time of Concentration Time of Rainfall – Lag Time is Time of Effective Rainfall To Draw in Points C & D Rising & Recession Limbs are Determined