Geology Reference
In-Depth Information
Fig. 7.5
Physiographic maps of four major tide-dominated
delta systems, including the (
a
) Changjiang, (
b
) Fly, (
c
) Amazon,
and (
d
) Ganges-Brahmaputra. Note the variable scale but similar
funnel-shaped morphology of the rivermouths, each with char-
acteristic channel-margin bars that are many tens of kilometers
long. Each delta system is also characterized by a large muddy
clinothem deposit that is forming off the rivermouth, at a similar
length-scale of many tens of kilometers offshore (Compiled
after Hori et al.
2002a
; Harris et al.
2004
; Nittrouer et al.
1986
;
Goodbred and K
uehl
2000
)
tide-dominated deltas as it is at many less energetic
river mouths. As with any complex natural system,
though, partially mixed stratifi cation and weak estuarine
circulation may develop locally within tide-dominated
deltas given spatiotemporal differences in tidal energy
(spring vs. neap) and river discharge (seasonality and
fl ow splitting amongst the distributary channels).
hydrodynamics. First, the fl ux of freshwater from the
river relative to the incoming tidal prism determines
the position of sediment transport convergence within
the rivermouth or on the shelf. Sediment convergence
occurs where sediments are trapped by outfl owing river
discharge and onshore tidal transport, causing a high
concentration of suspended sediment, often referred to
as the turbidity maximum, and high deposition rates on
the underlying seabed. In general, high river discharge
relative to the tidal prism forces the location of this
sediment convergence further seaward and defi nes an
important location of dynamic-scale sediment accretion
7.3.2.1
Sediment Transport Convergence
Although stratifi cation is not generally important in
tide-dominated delta systems, river discharge plays at
least two other key roles in defi ning system-scale
