1 Introduction
A river is regarded as a whole system in the principle of river
continuum, and the channel connectivity is the basis of judging the
regional continuity (Robin L, et al, 1980; Leigh C, 2009). The
connectivity of the water system refers to the smoothness of the
interconnection between water system units, which is the basic attribute
of river systems and plays an important role in the ecological
environment, material transport and energy cycle of rivers (Pringle C,
2003; Pringle C, 2001). Rivers with good connectivity are conducive to
the development of various functions, such as hydrological regulation
and storage, water and sediment transport, and ecological environment
(Michaelides K,2009; Williams, C. J.,2015).
Due to the influence of reservoir construction or soil and water
conservation, the sediment load of the Yichang hydrological station is
greatly reduced, which leads to significant changes in the channel
connectivity of the Jingjiang River. In particular, the impoundment of
the Three Gorges reservoir (TGP) in 2003 has a great impact on the
runoff, sediment load and channel erosion of the Jingjiang River. The
average annual runoff and sediment load of the Yichang hydrological
station were 395.8 billion m3 and 46.6 million t from
2003-2013, which were 9% and 90% smaller than before operation of the
TGP project, respectively. After the operation of the TGP, the sediment
concentration decreased by 75%, the suspended load and bed load
became coarse quickly (Zhu, 2012), and the water level changed
significantly in the Jingjiang River (Geng, 2012). In addition, the
Jingjiang River was in a balance of erosion and deposition basically
before the impoundment of the TGP, while the erosion-accretion variation
was severe after that (Xia, 2016; Chang, 2010; Chen, 2010; Xu, 2007;
Dai, 2013; Yang, 2014). The scour amount of the Jingjiang River accounts
for 78.9% in the Yichang-Chenglingji reach, and the scour intensity is
relatively large.
At present, the study of the Jingjiang River mainly focuses on sediment
variation, riverbank failure or channel evolution, but a comprehensive
study of channel connectivity is still lacking. Therefore, combined with
the river’s basic functions, we set up an evaluation model of the
channel connectivity using the AHP method described in this paper. Based
on data of the runoff, sediment load, cross-section morphological
parameters, and volume of scour and fill, the variation in processes of
the channel connectivity of the Jingjiang River was evaluated and
analyzed from 1955-2015.
In addition, there are some problems with channel connectivity in other
basins; for example, human activities and climate change cause river
channel cut-off in the Rhone, Rhine, Ain and Doubles rivers (Bornette,
2002). Due to the changes in the forest landscape pattern, landscape
connectivity decreased by an average of 54.74% in the Manwan Basin
(Yang, 2014). In addition, the dam is a strong disconnecting factor in
the longitudinal sediment connectivity in the Kaja river (Bertsch R,
2012). The flow connectivity, water discharge, and flood pulse changed
in the Paraná River after closure of the Porto Primavera Dam (José C,
2009). After the implementation of the water-sediment regulation by the
Xiaolangdi Reservoir, the lower reaches of the Yellow River are scoured,
which leads to a change in boundary connectivity (Liu, 2013). The
evaluation of the channel connectivity and the analysis of the
influencing factors in this paper can also provide useful information
for the connectivity of other rivers in the world.