Appendix A: A Practical Guide to Effective Discharge Calculations
Dominant Discharge (Qdom) - The single, steady discharge which would produce the same cross-
sectional morphology, alluvial features, planform geometry, and dimensions as those generated by the actual
flow regime (Inglis, 1949).
Effective Discharge (Qe) - Discharge class responsible for transporting the largest fraction of the bed
material load in a stable channel over a period of years (Andrews, 1980, pp. 311). Defined by the peak
in a histogram of bed material load (tons) versus discharge (cumecs) developed using the principles of
Ephemeral Stream - Watercourse in which channel processes and morphology are significantly affected
by the fact that the discharge of water is intermittent. To be comparable with the definition of a perennial
, this may
as a water course which exhibits
a measurable surface discharge less than
of the time (Osterkamp and Hedman, 1982).
Fine Material Load - A portion of the total sediment load composed of particles finer than those found
in the stream bed, and usually the fraction finer than 0.062 mm. Often synonymous with wash load.
Flow Doing Most Work - A steady discharge which performs the most geomorphic work, where work
is defined in terms of sediment transport (Wolman and Miller, 1960).
Flow Duration Curve - A graphical representation of the percent of time (x-axis) that a specific
discharge (y-axis) is equalled or exceeded during the period of record for which the curve was developed.
- A geomorphic expression introduced
by Leopold and Maddock
describe the morphology of an alluvial river as a function of dominant discharge. The concept is similar to
regime theory, but differs in the way that the dominant discharge is expressed. With respect to the
hydraulic geometry of an alluvial river, the dominant discharge is the single flow event which is
representative of the natural sequence of events which actually occur. Regime theory was developed for
canals, which do not experience a range of flows. Hence, the dominant discharge for regime theory is
the steady, operating discharge.
Mean Annual Discharge (Qma) - Yearly-averaged discharge. Papers reporting research involving Qma
include: Carlston (1965, 1969); Dury (1964); Leopold and Maddock (1953); Schumm (1971).
Mean Annual Flood (Q2.33)
- Discharge corresponding
to the probability
of the mean
annual flood event in a Gumbel extreme value type 1 probability distribution (EV1) derived from the
observed annual maximum flow series. This event has a recurrence interval of 2.33 years. Papers
reporting research involving Q2.33 include Brush (1961) and Ferguson (1973).
Measured Load - A portion of the total sediment load measured by conventional suspended load
samplers. Includes a large proportion of the suspended load but excludes that portion of the suspended
load moving very near the bed (that is, below the sampler nozzle) and all of the bed load.