As the marine actions are relatively weak, the
active delta can be doubtless classified as a fluvial-
dominated delta. Linear fit analysis shows that the
general change trends of the channel length and
deltaic area are highly synchronous. The position
change of the river outlet determines the
configuration of the delta. As the yearly total amount
of the sediment discharge decreases, the increment of
the channel length tends to decrease, and also for the
increment of the deltaic area. As the action of the
fluvial process declines, the prograding of the (front)
sand bar and the coastline tends to slow down.
Marine actions, however, are becoming more
important, particularly when the river channel was in
dry. For example, in 1992, the river was in dry for
150 days (April - August). No sediment load was
carried to the delta. Consequently, the mouth
sand/silt bar suffered from an escalatingly strong
marine erosion. That is why the channel length as
well as the deltaic area showed a noticeable loss in
1992.
Human activities, in the form of building of
embankments, artificial diversion, channelization,
dredging, and pumping of ground fluids, have posed
a very important effect on the development of the
delta. Before May 27, 1976, a canal of a length of
8.75 km, together with about 95 km embankments,
has been constructed for the latest artificial diversion
project. These embankments have played a
significant role in limiting the channel shift as well as
bankful flooding, and the guiding of the prograding
orientation of the delta. Since 1988, an intensified
dredging programme has been carried out around the
river mouth. The development of the mouth channel
has been effectively controlled, especially during the
first two years (1988 -1989).
The reason for the southward shifting of the river
channel (thalweg as well as both banks) , river
outlet, and the delta (siltbar) is very complex.
Although this southward shifting can be logically
explained by the principle of the Coriolis force, the
involvements of the marine hydraulic effect, the
tectonic activities, and the differential embankments
should be carefully considered. In the delta, the
dominant northeastern-oriented wind tends to
transport silts and sands southward. Statistically the
strong tidal currents move southward, which can
contribute to a dominated southward transports of
silts. Recent study shows that the southern part of the
present Yellow River Delta is a tectonically
depressing area with an average subsiding rate of 4.2
- 8.3 cm per year (Li, 1993), which surely favours
the southward shifting of the delta (channel, mouth
siltbar). Considering that most of the oilfields are in
the north of the actual channel, the embankments
consequently would have to be stronger on the north
than that in the southern bank. As a result, the
northward shifting of the north bank is relatively
stopped compared to the southward shifting, which
may affect the shifting change of the channel
thalweg.
6. CONCLUSIONS
This study firstly reveals a comprehensive macro-
evolution of a large river delta, the active Yellow
River Delta, by integrating multitemporal image data
with field observations. This delta, developed
initiately since May 27, 1976, has displayed a very
complicated environmental changes, both in fluvial-
morphodynamics and coastal dynamics. Since 1986,
the tenth year of running, the present river channel
has entered a stage of wither under a natural
condition. It is the human intervening that
maintaines the actual running state of the river course
up to now. However, on the long run, an artificial
divertion has to be carefully considered and carried
out. The results demonstrate that satellite remote
sensing in the context of a GIS is very useful for
documenting the time-sequential ^ dynamic
environmental changes and analyzing the
contemporary processes involved.
7. ACKNOWLEDGMENTS
This project was supported by the Dutch
Government, the International Institute for Aerospace
Survey and Earth Sciences (ITC), the University of
Utrecht, and the Institute of Marine Geology
(MGMR). Dr.A.van Gelder, Dr.J.H.van den Berg,
Drs. M.C.J. Damen , Dr. R.van Zuidam, and Prof.
Guodong Cheng are greatly acknowledged for their
contributions to the project. I am very grateful to
Jayne Atienza, N.C.Kigma, Aiko Mulder, and
Zhang Z., who helped me in more ways than one.
8. SELECTED REFERENCE
Yang, X., 1995. Monitoring Morphodynamic Aspects
of the Present Huanghe River Delta, China.
Enschede, The Netherlands, 192p.
806
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
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