Geography Reference
In-Depth Information
100%
8
Flagogna reach
Cornino reach
90%
7
80%
6
70%
5
60%
50%
4
40%
3
30%
2
20%
Flagogna reach
Cornino reach
1
10%
0%
0
0
0.5
1
1.5
2
2.5
3
0
0.5
1
1.5
2
2.5
3
Water surface elevation at Villuzza [m]
Water surface elevation at Villuzza [m]
(a)
(b)
25%
Flagogna reach
Cornino reach
20%
15%
10%
5%
0%
0
0.5
1
1.5
2
2.5
3
Water surface elevation at Villuzza [m]
(c)
Figure 15.11
Inundation dynamics in two study sites on the Tagliamento River: a) water proportion, b) braiding index and c) ratio
between upstream disconnected and connected water bodies, in the two study sites.
The effect of river morphology on river ice growth
was recently documented using a long series of pic-
tures taken during the freeze-up period on the Rimouski
River, Canada (Dube, 2009). In rivers where riffles
and pools are present, the spatio-temporal ice growth
varies according to complex interactions between river
morphology, hydro-meteorological conditions and flow
discharge. Dube (2009) aimed to quantify ice cover
growth rates at a riffle and pool scale to examine the
effect of river morphology and of hydroclimatic condi-
tions on ice cover growth. To achieve these objectives, 24
digital ground based photos were taken manually on a
daily basis at 8 locations along a riffle and pool section of
the Rimouski River from the 30/11/2005 to the 9/03/2006
(100 days). Figure 15.12a-f shows two series of pictures
(for the pool and riffle) taken on the same days. The
pictures clearly reveal differences in the ice cover growth
between the pool and the riffle but also identify differ-
ences in ice types and the processes that lead to complete
ice cover.
A challenge with ground based photographs is to
convert the visual observation into quantitative mea-
surements that can be used to compare sites or processes.
Here, we used the daily pictures to compute daily ice cover
growth rates. Because of the obliquity of the picture, the
pixel ground size varied within the images. Instead of
orthorectifying all of the pictures, we produced a rating
curve to determine the daily width of the ice cover. Ten
ground control points were used to compute a rating
curve between the pixel rows and the ground distance for
each morphology. The rating curves followed exponential
models with R
2
above 0.99 in both cases. These models
were then used to estimate the daily width of the ice cover.
The change in ice cover width between two consecutive
days was then used to compute the proportion of river
closed by ice on a day by day basis.
Figure 15.12g presents the ice growth curves for the pool
and the riffle that were extracted from the photographic
time series. The curves reveal that the early growth of
the ice cover is synchronous in pools and riffles and that
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