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changes, i.e., the coastal fluvio-morphologic change 
and the river outlet and coastline change. 
4.1 Coastal Fluvial Morphologic Change 
It includes channel shifting change, channel 
geometric change, and channel pattern change. 
Both banks have been examined separately their 
shifting and erosion changes. The north bank showed 
extremely unstable by shifting northward and 
southward alternately during the first 66 months 
(May 1976 - Nov., 1981). The maximum shifting 
distance amounted to 6,458 m (northward) within 17 
months for Q4. It was becoming docile with the 
declining of shifting rate after 1981. But it still 
remained a moderate high migrating rate, ranging 
from -150 to -500 m per year. The south bank 
showed a similar change with the north bank during 
the first 66 months. The maximum shifting distance 
amounted to -3,728 m (southward) within six months 
for Q7. For the stage of 1982 - 1987, it tended to 
decrease its migrating rate. But it is becoming 
extremely unstable with the escalating moving rate 
after 1987. The difference of the shifting change 
between both banks after 1987 possibly results from 
the differential embankments. The northern 
embankment is stronger than that on the south bank. 
The channel thalweg is examined its change in both 
the (metric) shifting rate and the all-round spatial 
arrangement and orientation changes. The lateral 
shifting of the channel thalweg shows a similar trend 
in the south bank. The lineament analysis is used to 
characterize the orientation, sinuosity, and river fluid 
potential changes. 
Some aspects of the channel geometric change are 
examined. The channel length shows an increasing 
trend with an average of 1,650 m per year. But the 
increment tends to slow down. The channel tends to 
decrease its width and is becoming approximately 
equal wide as a whole. 
Channel pattern changing from braiding, straight, to 
slightly meandering has been well documented by the 
accompanying maps (Figure 2). As a whole, the 
channel bifurcation index" tends to decrease, while 
the channel sinuosity tends to increase. Two major 
stages can be well defined. The second stage can be 
further subdivideded, based on the degree of 
  
xs Bifurcation index is the ratio of total branching channel(s) 
length to the length of the river axis. 
artificial intervention. 
Braiding Stage (1976 - 1980): During this period, the 
river channel system was extremely unstable, 
showing the most significant change. The channel 
system changed from disorderly braiding, well- 
organized braiding, to generally straight. The 
channel system became relatively straight, with a 
decreasing trend of channel sinuosity. The channel 
bifurcation index tended to reduce and so for the 
longitudinal profile gradient. The channel stability 
index™ shows an obvious decreasing trend, and the 
channel tended to be more stable. 
Straight - Slightly Meandering Straight Stage I (1981 
 - 1987): During this period, the channel stability 
index tended to increase, and the channel became 
less stable. Due to the rapid vertical progration, the 
river longitudinal profile gradient became much more 
gentle. The capacity of the flow to transport its 
suspended bed-load diminished. This resulted in 
severe silting which caused the channel unstable and 
successive flooding events (twice within 1987). The 
situation in late 1986 - 1987 evidenced that the 
development of the channel entered the stage of 
wither or decay under a natural condition. 
Straight - Slightly Meandering Straight Stage II (after 
1987): As the channel sinuosity was increasing, the 
channel was gradually changing from straight to 
slightly meandering straight. The channle as a whole 
tended to become more stable. Human intervention 
was highly successful, especially during the first two 
years (1988-1989), in strengthening the mainstream 
to improve the capacity of the flow to transport its 
suspended bed-load. However, this may maintain the 
actual running state of the channel for several years, 
on the long run, a well-organized (artificial) 
diversion has to be carefully considered. 
4.2 River Outlet and Coastline Dynamic 
Change 
The temporal migrating change of the river outlet is 
presently examined (Table 1). The outlet 
displacement, a scalar without direction, represents 
the distance between two outlets. The outlet shift, a 
vector with the direction (negative value means a 
westward shift for x-shift, or a southward shift for a 
y-shift), characterizes the migrating change over 
  
Ex Channel stability index — B'?/M, where B is the width of 
main channel, and M is the average depth of river channel. 
803 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996