Tidal Characteristic Numbers of Bed Load Transport

Graphical representation of characteristic numbers of bedload transport (with German text only). This graphical representation is also available in Encapsulated PostScript format

Motivation

The calculation as well as the graphic visualization of various tidal characteristic numbers of bed load transport contributes to an improved understanding of tidally dominated transport processes in estuaries. Spatial variations of bed load transport by means of flood and ebb currents can be highlighted for areas like coastal seas and estuaries.

• The calculated characteristic numbers of bed load transport do allow for a separation between the amount of bed load material transported by means of the flood current as well as by means of the ebb current. Differences in between the two transport rates are mainly due to different hydrodynamic regimes during ebb and flood tide (e.g. maximum and/or mean current velocity, duration of ebb/flood current).
• The asymmetry between ebb and flood current transport can be at best demonstrated using the ratio between flood- and ebb-induced transport rates. But also the calculated residual transport is a good measure for these differences. Zones of convergent or divergent residual transport indicate depositional or erosional areas, whereas zones with a mostly homogeneous residual bed load transport rate are related to a dynamically stable bed.

An automatic analysis of all tidal characteristic numbers of bed load transport is carried through by the computer programs TDKLF and NCANALYSE.

Definitions for the Tidal Characteristic Numbers of Bed Load Transport

Program NCANALYSE

Flood Current

Mean Bed Load Transport due to Flood Current

Mean value (computed from magnitude) of bed load transport during flood current. Vector quantity. The magnitude corresponds to the mean value computed from the magnitude of all individual vectors (given for different dates). Mean direction follows from vectorial addition of the individual vectors.

Residual Bed Load Transport due to Flood Current

Residual bed load transport during flood current. Vector quantity. Magnitude as well as (mean) direction follow from vectorial addition of the individual vectors (given for different dates). In case all individual vectors point into the same direction mean and residual value are identical. The residual can never be larger than the mean value.

Integral Bed Load Transport due to Flood Current

Integral (over time) bed load transport during flood current. Vector quantity. Follows from vectorial addition of the individual vectors (given for different dates).

Ebb Current

Mean Bed Load Transport due to Ebb Current

Mean value (computed from magnitude) of bed load transport during ebb current. Vector quantity. The magnitude corresponds to the mean value computed from the magnitude of all individual vectors (given for different dates). Mean direction follows from vectorial addition of the individual vectors.

Residual Bed Load Transport due to Ebb Current

Residual bed load transport during ebb current. Vector quantity. Magnitude as well as (mean) direction follow from vectorial addition of the individual vectors (given for different dates). In case all individual vectors point into the same direction mean and residual value are identical. The residual can never be larger than the mean value.

Integral Bed Load Transport due to Ebb Current

Integral (over time) bed load transport during ebb current. Vector quantity. Follows from vectorial addition of the individual vectors (given for different dates).

Tidal Cycle

Mean Bed Load Transport within a Tidal Cycle

Mean value (computed from magnitude) of bed load transport during a tidal cycle (here this corresponds to the period between two subsequent ebb slacks). Scalar quantity. Magnitude corresponds to the mean value computed from the magnitude of all individual vectors (given for different dates).

Residual Bed Load Transport within a Tidal Cycle

Residual (computed from vectorial addition) bed load transport during a tidal cycle (here this corresponds to the period between two subsequent ebb slacks). Vector quantity. Magnitude and direction are computed from vectorial addition of the individual vectors (given for different dates).

Integral Bed Load Transport within a Tidal Cycle

Integral (over time) bed load transport during a tidal cycle (here this corresponds to the period between two subsequent ebb slacks). Vector quantity. Follows from vectorial addition of the individual vectors (given for different dates).

Ratio of mean Bed Load Transport during Flood Current : mean Bed Load Transport during Ebb Current

Quotient computed from the magnitude of mean bed load transport during flood current and mean bed load transport during ebb current.

Ratio of mean Bed Load Transport during Flood Current : mean Bed Load Transport during Tidal Cycle

Quotient computed from the magnitude of mean bed load transport during flood current and mean bed load transport during the tidal cycle.

Ratio of mean Bed Load Transport during Ebb Current : mean Bed Load Transport during Tidal Cycle

Quotient computed from the magnitude of mean bed load transport during ebb current and mean bed load transport during the tidal cycle.

Program TDKLF

Flood Current

Bed Load Transport due to Flood Current

Amount of Bed Load Material which is transported by means of flood current through a cross section

Ebb Current

Bed Load Transport due to Ebb Current

Amount of Bed Load Material which is transported by means of Ebb Current through a cross section

Tidal Cycle

Residual Bed Load Transport during a Tidal Cycle

Residual amount of bed load material which is transported by means of ebb and flood currents through a cross section (the different transport directions are taken into account). If the transport by means of flood current is equal but in opposite direction of the ebb current transport this will result in a zero advective residual transport of bed load material.

Bed Load Transport, Flood-Ebb-Ratio

flood to ebb ratio for the different amounts of bed load material which are transported by means of flood and ebb currents

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