6. overview of category C interventions
6.1. Land Drainage for Cultivation
This intervention was reported for all regions.
In Austria and Denmark, for example, land drainage, either for flood control or land reclamation, is probably the single most important measure which has adversely affected the landscape (loss of wetlands, small scale structures in the landscape), the biodiversity and the hydrological cycle.
Between 1980 and 1990 more than 37 % of wetlands of Austria have been destroyed. In Denmark it is estimated that about 49 % of the agricultural land has been drained, mainly in the 19th century.
The main benefits of this intervention are reclaimed land for cultivation, increase agricultural production (economical benefits) and a reduction in the risk of floods.
Land drainage causes the loss of important wetlands with their biodiversity and nutrient retention capacity as well as the loss of important water retention areas. Because of the removal of water from drained areas, runoff and high-flow peaks will increase as well as the risk of downstream floods which may lead to river channelisation. The groundwater table and renewal rate will then further decrease in the drained area/catchment.
Nowadays in Austria the drainage of
land is no longer supported by government and programmes to recover drained land and
restore rivers, including riparian wetlands, have been started to re-establish their
natural hydrological features. Thus it is expected, that land drainage will decrease.
6.2. Land Sealing
This intervention refers to chapter
6.1 (land drainage due to cultivation) and was reported in all biogeographic regions. It
is caused by urbanisation, infrastructure for traffic and tourist facilities such as
skiing grounds in mountainous areas.
6.2.1. Urbanisation and Infrastructure
This intervention is closely connected to, and illustrated by, demographic trends and the increasing mobility of the population by individual transport.
Land sealing causes an increased and accelerated runoff, which causes problems in local flood control. In addition, sealed land prevents groundwater recharge by preventing the slow infiltration of water in particular during snow/frost thaw. Runoff water from sealed housing and traffic areas is normally unfiltered and contaminated with chemicals. This does not include major pollution caused by accidents.
Intimately related to this
urbanisation and construction of buildings in zones former flood plains is the extensive
flood control and sealing of river banks.
6.2.2. Tourism - Skiing Grounds
Land sealing for tourism purposes is reported in mountainous regions and especially concerns skiing grounds. Skiing tourism is one of Austrias most important economic factors. Skiing pistes cover about 250 km2 (0.28 %) of the Austrian territory.
The more severe environmental
impacts are normally associated with downhill skiing. Forest clearance, construction of
infrastructure (access roads, parking, hotels, lifts) and increased incidence of
avalanches (mudslides) are major negative effects as well as water pollution due to sewage
and chemicals caused by tourists outnumbering the local population many times over short
periods. In some areas an extensive use of water due to snow cannons is a further impact
in the water cycle (Stanners and Bourdeau, 1995).
6.3. Wet Cuts - Mining of Alluvial Gravel
Especially in the French Atlantic and Continental regions wet cuts in floodplains for mining of alluvial gravel as well as dredging in river beds has been reported as an important and economically useful source of high quality aggregates. It causes a massive intervention in the hydrological cycle. Also lakes will be created which sometimes may have better water quality for fish production than the rivers.
This intervention may affect
groundwater quality as a result of the decreased filtering capacity and the frequent use
of the created quarries as waste dumping grounds (especially illegal operations). It was
also reported that the concentration of nitrate or pesticides increases due to pumping
during quarry operations.
6.4. Agricultural Activities - Increase in Intensity of Agriculture
An increase in the intensity of agriculture is a pan-European problem and was reported for the northern and south-western part of the Atlantic region of France and the Continental region of Austria. As a result and benefit, for example, Austria has reached a high degree of self-sufficiency in agriculture.
Such activities include land improvement, land consolidation, land drainage, merging of small areas, removing of hedgerows as well as the type of tillage, type of crop cultivated, simplification of crop rotation, single-crop farming, etc. It disturbs the water balance of rural areas (decrease in the groundwater renewal rate, decrease in the groundwater table, increase of water discharge, etc.) and increases the risk of erosion (erosion caused by precipitation, wind-erosion, mudflow, flooding (inundation), slumping).
The main causes of increased erosion
are seen as single-crop farming, simplification of crop rotation, soil compaction (caused
by wheel tracks), deterioration of the soil structure, changing from grassland to arable
land and land drainage. This will reduce the water storage capacity and the filtration
capability of the soil, and the surrounding surface waters may become eutrophic. Soil
compaction and deterioration of the soil structure increases the surface runoff and,
therefore, will reduce the groundwater renewal rate of this area. The increase of biomass
of the crops increases the water consumption and as a consequence reduces the soil
moisture and the groundwater renewal rate. In some regions often the associated irrigation
completes the increased water demand.
Forestry activities in catchments were reported as significant in Norway and Portugal. In Norway deforestation was a drastic intervention during the 17th until the middle of the 19th century. The last century was characterised by afforestation which has strongly influenced the runoff regime in Norwegian rivers.
In Portugal deforestation is still a serious problem especially caused by urban development, agriculture, tourism and fires.