Environmental Engineering Reference
In-Depth Information
Table 11.2
The main human activities that have influenced river systems.
Activity
Reason
Impact
Land drainage
Agricultural
Loss of floodplains and wetlands; increased sediment supply
to the river; increased flood peak through decreased storage.
Isolation/loss of floodplains; loss of biodiversity.
Ecological deterioration downstream; increase in
contamination; disruption to the transfer of sediment.
Prevents fish passage to upstream reaches; reduced access to
spawning grounds.
Disrupts the physical equilibrium of the watercourse; impact
on riparian vegetation and water temperature; increase in flow
velocity and hence reduces habitat and biodiversity.
Flood protection
Reservoirs/dams
Urban/economic
Water supply/
hydroelectric power
Mill systems
Weirs
Channelization
Erosion prevention; flood
control; drainage of
surrounding land;
navigation; infrastructure
Gravel/sand extraction;
increased capacity
Drinking water and
agriculture
Increased populations
and economic growth
Dredging
Over-widening and -deepening of the river; instability and
bank collapse; removal of natural bed material.
Lowering of river-water levels and the floodplain water table.
Water abstraction
Urban expansion
Increase in hard surfaces, greater/faster runoff; loss of riparian
corridor and floodplains; poor water quality; sewage; spillages.
external factors including climatic conditions and
human activities such as afforestation, deforestation,
urbanization, land drainage, pollutant discharges and
flow regulation; it is the combination of the natural
river processes that occur over time (Schumm &
Litchy 1965, Brunsden & Thornes 1979, Schumm
1979) and the external influences that ultimately
determine the form of a watercourse.
From a geological point of view the continent of
Europe is relatively young and this has resulted in river
catchments that tend to be numerous, but small,
compared with much of the rest of the world. Only
about 70 rivers in Europe have catchment areas ex-
ceeding 10,000 km
2
. Of these the largest is the Volga
at 1,360,000 km
2
(compared with 3,349,000 km
2
for the
Nile) and this, together with the Danube and the
Dnepr, drains one quarter of continental Europe.
Furthermore, the rivers of Europe account for only 7%
of the world's rivers with a total annual discharge of
about 3100 km
3
(8% of the world's discharge) of fresh
water into the sea each year (Kristensen & Hansen
1994); although a relatively small amount of the total
discharge the overall impact is not insignificant. The
temperate humid climate together with a high per-
centage of highly erodible limestone means that the
amount of dissolved solids in European rivers is con-
siderable. This is exacerbated by a heavily populated
continent and associated agriculture resulting in an
intense concentration of minerals within the rivers.
The concentration of pollutants varies between
European countries. In those where coastlines are
dominant (e.g. UK, Norway, Sweden, Denmark, Italy
and Greece) there is tendency towards small catch-
ments and short rivers. Thus population tends to con-
gregate towards the coastline and hence waste water
is often discharged into the coastal areas rather than
into the river systems. In these instances water qual-
ity of the rivers upstream is often relatively good and
therefore restoration efforts are able to concentrate on
ecological habitat initiatives. Conversely, combating
river pollution tends to be the main rehabilitation driver
in countries with no coastline (e.g. Switzerland)
where waste water has, historically, been pumped
directly into them.
11.3.1 River flow
River flow varies during the year and this is deter-
mined by the seasonal variation in weather conditions
