296
R.H. Charlier and Chr. P. De Meyer
Chapter III : Sediment Budget Analysis
1
The Sediment "Bank Account"
Sand available for accretion, erosion or transport makes up a "bank" in which
quantities are deposited or from which the)' can be withdrawn. One can also
speak of supply. While we commonly refer to "sand", it often is rather "sediment"
which can be of various nature, origin, size, texture and so on. The study of
marine sediments and marine sedimentation is a discipline in itself. The
elementary traditional view is that sediments are brought to the sea from inland
or on-shore coastal sources, and then deposited according to size in a succession
of ever diminishing grain "diameters" from shallow to deep waters. Things,
however, are not that simple as local phenomena and morphology sometimes give
the impression that the pattern has been "inversed" (e.g. tangue).
Sediment transport occurs by dragging over the bottom, or by saltation (bedload
transport) or in suspension (suspended-load transport). They occur in general
concurrently. Transport zones are the offshore (wave-induced motion over
ripples), and the surf (most induced by the passing breaker).
Grain diameter size has been "measured" subjectively and according to several
quantitative scales (e.g. Wentworth, Atterberg, AFNOR). For Wentworth, sand
has a diameter > 0.074 mm (or 3.75 ~o) to < 2 mm (or - 1.0 ~o). His "name
classes" for sands differ from the Unified Soils Classification in that the USC
coarse sands (- 1.0 ~o to - 2.25 ~o) are considered gravel (- 1 to - 2 ~o) and "small
pebbles" (- 2 to - 2.25 ~o), his very fine sand (3 to 4 ~o) is already silt for the USC
(upper limit 3 ~o). Incidentally ~o = log2, a diameter value expressed in mm (4 ~o
- 0.062 mm).
In a preceding chapter the removal agents have been listed, natural and manmade. P.D. Komar calls these the debits. In the credit column appear longshore
transport into area, river transport, sea cliff erosion, onshore transport, biogenous
deposition, hydrogenous deposition, eolean transport onto beach zone, beach
artificial recharge and/or nourishment.
R.H. Charlier and Chr. P. De Meyer
Chapter III : Sediment Budget Analysis
1
The Sediment "Bank Account"
Sand available for accretion, erosion or transport makes up a "bank" in which
quantities are deposited or from which the)' can be withdrawn. One can also
speak of supply. While we commonly refer to "sand", it often is rather "sediment"
which can be of various nature, origin, size, texture and so on. The study of
marine sediments and marine sedimentation is a discipline in itself. The
elementary traditional view is that sediments are brought to the sea from inland
or on-shore coastal sources, and then deposited according to size in a succession
of ever diminishing grain "diameters" from shallow to deep waters. Things,
however, are not that simple as local phenomena and morphology sometimes give
the impression that the pattern has been "inversed" (e.g. tangue).
Sediment transport occurs by dragging over the bottom, or by saltation (bedload
transport) or in suspension (suspended-load transport). They occur in general
concurrently. Transport zones are the offshore (wave-induced motion over
ripples), and the surf (most induced by the passing breaker).
Grain diameter size has been "measured" subjectively and according to several
quantitative scales (e.g. Wentworth, Atterberg, AFNOR). For Wentworth, sand
has a diameter > 0.074 mm (or 3.75 ~o) to < 2 mm (or - 1.0 ~o). His "name
classes" for sands differ from the Unified Soils Classification in that the USC
coarse sands (- 1.0 ~o to - 2.25 ~o) are considered gravel (- 1 to - 2 ~o) and "small
pebbles" (- 2 to - 2.25 ~o), his very fine sand (3 to 4 ~o) is already silt for the USC
(upper limit 3 ~o). Incidentally ~o = log2, a diameter value expressed in mm (4 ~o
- 0.062 mm).
In a preceding chapter the removal agents have been listed, natural and manmade. P.D. Komar calls these the debits. In the credit column appear longshore
transport into area, river transport, sea cliff erosion, onshore transport, biogenous
deposition, hydrogenous deposition, eolean transport onto beach zone, beach
artificial recharge and/or nourishment.