Appendix A: A Practical Guide to Effective Discharge Calculations
Most Probable Annual Flood (Q1.58)
- The discharge corresponding
to the probability
of the modal annual flood event in a Gumbel extreme value type 1 (EV1) derived from the observed annual
maximum flow series. This event has a recurrence interval of 1.58 years. Papers reporting research
involving Q1.58 include Woodyer (1968) and Dury (1973).
- A stream which exhibits
a measurable surface discharge more
than 80%of the
(Osterkamp and Hedman, 1982).
Regime Theory - A self-formed alluvial channel is in regime if there are no net changes in discharge
capacity or morphology over a period of years. The concept was originally developed by engineers
designing canals to convey a steady discharge with neither erosion or siltation in India and Pakistan
(Kennedy, 1895; Lindley, 1919) and, later in North America (Blench, 1957).
Sediment Concentration - Concentration of sediment in the stream represented by the ratio of sediment
discharge to the water discharge. Usually expressed in terms of milligrams per litre or parts per million
(ppm). It is normally assumed that the density of the water-sediment mixture is approximately equivalent
to the density of the water.
Sediment Discharge - Mass of sediment that passes through a cross-section in a stream per unit time.
Usually expressed in kilograms per second or tons per day.
Sediment Rating Curve - Graphical representation of the non-linear relationship between discharge (x-
axis) and sediment discharge (y-axis).
Suspended Bed Material Load - A portion of the bed material load that is transported in suspension
within the water column.
Suspended Load - A component of the total sediment load made up of sediment particles moving in
continuous suspension within the water column. Transport occurs above the bed, with the submerged
weight of particles supported by anisotropic turbulence within the body of the flowing water.
Total Sediment Load - Total mass of granular sediment transported by the stream.
Unmeasured Load - A portion of the total sediment load that passes beneath the nozzle of a
conventional suspended load sampler, by near-bed suspension and as bed load.
Wash Load - A portion of the total sediment load composed of grain sizes finer than those found in
appreciable quantities in the stream bed. In sand-bed streams wash load moves as suspended load, but
in boulder-bed rivers the wash load may include gravel which moves as bed load. The sum of bed material
load and wash load makes up the total sediment load.