ENVE-205 Environmental Engineering Hydrology

CHAPTER VI: Hydrographs

In this chapter, streamflow and runoff hydrograph general properties will be discussed.  Perennial, intermittent, and ephemeral stream properties will be introduced.  The deailed mathematical derivations for both rising and falling limbs of runoff hdrographs will be performed.  The unit hydrograph formation from a given streamflow hydrograph will be presented.  The lagging procedure for obtaining a longer duration unit hydrograph from given two or more shorter duration unit hydrographs will be discussed.  A convolution-superposition procedure will be presented for producing runoff hydrographs using unit hydrographs for precipitation events with non-uniform intensity distribution.  Synthetic hydrograph use and their various types for Rational and NRCS models will be discussed.

Study Plan:

·        Learning hydrograph properties such as rising and falling limb behavior, the concepts of lag time, time to peak, time of concentration, recession time, and base time.    (Section 6.1).

·        Learning the stream types (perennial, intermittent, ephemeral) according to their streamflow behavior.    (Sections 6.1.2).

·        Deriving the mathematical formulations for rising and falling limbs of a hydrograph.  (Sections 6.2.1, 6.2.2). See formula derivations in Fig. 6.2.1.A1 and Fig. 6.2.2.A1. Example problem 6.1 (see the additional information in Fig. Ex. 6.1.A1).

·        Learning the unit hydrograph formation from a given streamflow hydrograph in four steps.  Learning the lagging procedure for obtaining a longer duration unit hydrograph from given two or more unit hydrographs with shorter duration.  (Section 6.3). See Fig. 6.3.A1.

·        Learning a convolution-superposition procedure for producing runoff hydrographs using unit hydrographs for precipitation events with non-uniform intensity distribution.  (Section 6.3.1).  See Fig. 6.3.1.A1.

·        Learning the concept of synthetic hydrographs.  Constructing synthetic hydrographs for Rational model with D=tc and D> tc and derivation of peak flow rates.  Constructing synthetic hydrographs for NRCS model with D=tc and D< tP and derivation of peak flow rates.  (Section 6.4.1, 6.4.2).

·        Learning the concepts of water quality such as pollutant load, event mean concentration, and loading rate (Section 5.5).

·        Homework problems 1, 2, 4, 5, 10, 11, 12.