Wetlands in River Valleys as an Effect of Fluvial Processes and Anthropopression - Wetlands and Water Framework Directive: Protection, Management and Climate Change - page 74

Fig. 5.7 The curvature comparison of the natural (blue) and regulated (red) river channel

Table 5.2 Expected change of parameters characterizing the river channel fl ow and the fl floodplain

inundation
Parameter River

width (m)

River
depth (m)

Flooded area
(Q1 %)
(mln m 2 )

Valley capac-
ity (Q1 %)
(mln m 3 )

Water depth in the
valley during flood
(Q1 %) (m)

Current
state

25 0.6 7.6 4.7 1.2

After
restoration

14 - 50 0.4 - 0.8 11.2 8.7 0.8

transportation and instability of the bed during flood events. The curvature of the

natural channel differs dramatically in comparison to the regulated ones (Fig. 5.7 ).
The multichannel system is well developed. To provide calculations of the

fl

fl ow

distribution within the modi ed or restored river channels, the HEC-RAS calcu-

lation has been performed. The parameters of regulated and restored river channels
are gathered in Table 5.2 .
The comparison of width and depth of the Nida branches shows that the
expected width of the natural bed is about 34 m and the depth should vary from
0.5 to 1 m.
As long as the river was natural within the broader valley, it used to redistribute
water periodically within the different parts of

. The restoration works should
start from rebuilding proper connections between the old channels as well as ini-
tiating the water redistribution within the whole channel system. There is no cer-
tainty that on the sandy substratum of the valley the in

“ delta ”

ltrated water could be

limited to the acceptable level. In the past within the region Nida had

naturally hold one or two main channels (Fig. 5.1 ). For this reason, only part of the

“ delta ”