How humans interact and effect river
processes:
Three ways
humans can influence the natural processes a river carries out are by
1) Shortening the Rivers course
2) Construction of dams
3) Building of artificial
levees/dykes/embankments
1) Shortening of the Rivers course:
·
As
the river Rhine is such an important artery of trade it was decided to shorten
its course by approx. 100km.It is an important waterway as it connects the
North Sea, Mediterranean Sea and the Black Sea.
·
Meanders
have now been bypassed and new channels created and as a result the Rhine is
now shorter, straighter and deeper.
·
The
impact of this is that it has doubled the speed of the waters flow from Basle
to Rotterdam. Thus its rate of erosion has increased and caused water to
cascade down when there is heavy snow or rain upstream.
2) Construction of dams:
·
Since
the 1950’s HEP stations have been built along the upper section of the River
Rhine and this has increased the problem of flooding. Thirteen HEP stations
were built along the French-German border under the ‘Power Project’ and this
involved the construction of a new section of the river parallel to the old
Rhine. Countries are investing heavily as HEP is a renewable energy source and
as fossil fuel continue to be depleted.
·
These
dams cause sediments to be trapped and this reduces the rivers load. As a
result the water after the dam is rejuvenated and is flowing faster which in
turn transfers water downstream at a quicker pace.
·
In
China the Three Gorges dam was built along the River Yangtze. This dam is 185
km high and 1.6km wide. It is used to generate power to some of the major
cities such as Shanghai and to prevent flooding.
·
However
as a result it has stopped the transportation of fertile alluvium downstream
and now farmers have had to buy expensive fertilisers instead.
·
Also
the natural habitat has been affected and as a result in 2007 the Yangtze
dolphin was declared extinct.
·
In
Ireland the Ardnacrusha (HEP) Scheme on the Shannon and the Blessington Lake-
reservoir Co. Wicklow have been built and these have impacted numerous fish
such as the salmon.
3) Artificial levees/embankment/Dykes
·
Previously
when the Rhine flooded it spread across the floodplains however now over 85% of
its natural floodplains have been lost due to agriculture and buildings and so
embankments needed to be built in order to protect these.
·
However
this has closed off the natural floodplains and has simply moved the flooding
downstream this previously wouldn’t have been at risk of flooding.
·
This
has also resulted in more sediments being deposited in the river bed. As this
has raised the level of the river then the embankments also need to be raised
which in turn continues to cost the countries effected money to do so.
·
As
the size of ships using the river increased in size stretches of the river were
narrowed to create a deeper channel and so the river began to flow faster and
the rate of erosion increased.
·
If
floods pushed to towards the mouth then Dutch polders at serious risk of
submergence.
·
The
River Rhine flooding is now almost an annual event and in January 1995 Cologne
ended up 2 metres underwater due to this, Also in the Netherlands 250,000
people and animals/poultry had to be evacuated and this seriously affected both
sides of the Ijssel which is a highly intensive horticulture and agricultural
area.
