Surveys were carried out in 2010 and 2011 at three times in
each year representing low loading (May), medium-loading
(August) and high-loading (November) periods. Water depth
and velocity were measured using a current meter at each 2-m interval along three
transect lines of 10-m interval. The three transect lines
covered the area of the most apparent aquatic plant patches
in the study site. For comparison among river subareas, the
data on water depth and velocity along each transect were
used for area zonation into the ‘shallow’ and the ‘deep’
zones. In this study, the shallowzone (always found on the left
side of the river) generally had lower water velocity because
of a denser growth of submerged plants. At the centre of the
shallowand deep zones, a comprehensive study ofwater and
sediment quality and aquatic plant abundance was carried
out.
In order to assess the flow impacts on persisting aquatic
plants, the average water velocity (V; m/s) for 3 months prior
to each sampling time was approximated using equation: