4.1 Boundary index
The average stability coefficients of the Zhicheng, Shashi, Jianli and
Luoshan hydrological stations in the Jingjiang reach are 0.34, 0.29,
0.27 and 0.28, respectively, which are higher than the critical value of
the stability coefficient of the curved reach. There is a great
difference in the change process of each hydrological station (Fig. 3a).
For example, the stability coefficient of the Zhicheng hydrological
station decreased slightly from 1991 to 2012, and this decrease was
caused by river channel sedimentation. The stability coefficient of the
Jianli hydrological station has an obvious increasing trend after 2007,
which is caused by channel erosion and changes in cross-section
morphology.
The Jingjiang River section belongs to a classical meandering river in
the plain area, and there is no dam. Therefore, there is continuity
along the river boundary, and the longitudinal connectivity index
displays little change as a whole. Fig. 3b shows the variation in the
stream gradient along the Jingjiang River in recent decades. The stream
gradient has a significant decreasing trend after 2003.