Module 3: Hydrologic Analysis

Lecture 4: Introduction to unit hydrograph
 

Unit hydrograph (contd..)
Example Problem (contd..)
  • Empirical unit hydrograph derivation separates the base flow from the observed stream flow hydrograph in order to obtain the direct runoff hydrograph (DRH). For this example, use the horizontal line method to separate the base flow. From observation of the hydrograph data, the stream flow at the start of the rising limb of the hydrograph is 100 m3/s
  • Compute the volume of direct runoff. This volume must be equal to the volume of the effective rainfall hyetograph (ERH)
                   VDRH = (200+600+900+700+500+300+200+100) m3/s (3600) s = 12,600,000 m3
  • Express VDRH in equivalent units of depth:

VDRH in equivalent units of depth = VDRH/Abasin = 12,600,000 m3/(315000000 m2) = 0.04 m = 4 cm