Estuary Processes and Managment - River Dynamics and Integrated River Management - page 465

Fig. 8.4 Development of the Jiuduansha Shoal: (a) Longitudinal section of the Jiuduansha Shoal (121°35ƍE,
31°16'N-122°25ƍE, 31°5'N, Fig. 8.3 as A-A N ) from 1959 to 2001; (b) Cross section of the Jiuduansha Shoal at 122°E
(shown on Fig. 8.3 as B-B N ) from 1953 to 2001
that consists of the West River, North River, East River, and Tanjiang, Suijiang, Liuxi, and Zengjiang Rivers.
Sediment from these rivers has deposited at the bay and has formed many islands. Channels connect with
each other like a spider web. The river water flows into the South China Sea through eight large mouths:
Humen, Jiaomen, Hengmen, and Hongqili from the east, and Modaomen, Jitimen, Hutiaomen and Yamen
from the west, as shown in Figure 8.5(c).
8.1.2 Effects of Human Activities
In general, male deltas develop if the sediment load/water ratio is high and the tidal current is weak, e.g.
the Yellow River delta. If the load/water ratio is not high and tidal current is strong a female delta develops,
e.g. the Yangtze River delta. Figure 8.6 shows the gender of the delta (thus gender of the river) as a
function of sediment load/water ratio and tidal range. Points of female deltas are in the upper-left zone
and points of male deltas are in the bottom-right zone. There is a transitional zone between the male and
female areas. The impoundment of a river can cause the river to change genders because dam construction
traps a lot of sediment,, resulting in a reduction of the load/water ratio by 70%-99%. The Nile River and
the Ebro River are changing from male to female due to remarkably reduction in the sediment load
transported to the deltas.