Topographical characteristics of the study area
The study site possessed two distinguishable zones: ‘shallow’
and ‘deep’ water (Fig. 3). The shallow zone, located on the
left side of the river, consisted of finer deposits and dense
patches of aquatic plants. The deep zone, which covered the
middle region to the right side of the river channel, consisted
of larger deposits such as coarse sands and gravels. Generally,
fewer rooted plants were found in this area.
Ratios of the depths of the ‘deep’ to the ‘shallow’ zones
slightly varied over time, and had an average of 1.95 : 1. Thus,
the deep zone was about twice as deep as the shallow zone.
The greatest difference in depth between the two zones was
found during the first survey of May 2010 (Fig. 3a). Thereafter,
the river’s topographical characteristicswere varied. Ratios of
water depth in 2010 that were in the ranges of 1.55 : 1 to
4.36 : 1 decreased to 1.01 : 1 to 1.72 : 1 in 2011. Such
changes reflected the impact of large flood-induced discharges
during late 2010. Additional differences in water
depth were noted along the three transects (10-m interval),
particularly during the survey of August 2010. At that time, the
depth ratios of transect lines 1, 2 and 3 were 3.50 : 1, 2.87 : 1
and 1.55 : 1, respectively. The deep zones upstream were
comparatively deeper than those downstream. Impact from