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You are here: Home / Publications / Human Interventions in the Hydrological Cycle / appendix b3 activities in the catchment (cat.c)

appendix b3 activities in the catchment (cat.c)

B3. ACTIVITIES IN THE CATCHMENT (CATEGORY C)

B3.1. Land Drainage Due to Cultivation

Information about this intervention has been received from Austria for the Alpine region, from Denmark and France for the Atlantic region, from Denmark for the Continental region, from France for the Mediterranean region and from Norway.

Austria: Land drainage, either for flood control or land reclamation, is an important measure which has adversely affected the landscape (loss of wetlands, small scale structures in the landscape), the biodiversity and the hydrological cycle.

It is estimated that for Austria as a whole about 250,000 ha have been drained during the last decades. Between 1980 and 1990 more than 37 % of wetlands of Austria have been destroyed. The drainage of land had been supported by the Federal Government and the Provinces since 1954. It is not supported any more and in some provinces, programs to recover drained land have been started. Thus it is expected, that land drainage will decrease.

The main benefits in Austria are land reclamation for cultivation, increase of the agricultural production (economical benefits) and reducing the risk of floods.

The effects of land drainage in Austria include:

  • Loss of important wetlands, loss of biodiversity

  • Lowering of the groundwater table, decrease of the groundwater renewal rate in the drained area/catchment

  • Loss of water retention areas

  • Increase of runoff and high-flow peak, increase of river peak flow and increase of the risk of downstream floods

Denmark: This is probably the single most important measure, which has affected the Danish landscape, the overall biodiversity and the hydrological cycle.

It is estimated that 15,000 km2 (49 % of the agricultural land) has been drained. These areas include the moraine soils (12,400 km2) in the Continental region and previous wetlands (2,600 km2) all over Denmark.

The main drainage of moraine soils took place in the 1850-1900. The main drainage of previous wetlands took place in the period 1920-40. The last big drainage project in the downstream part of the River Skjern valley included 39 km2 in 1965. Recently river restoration projects have included riparian wetlands as well, re-establishing their natural hydrological features. The River Skjern Restoration Project planned to be implemented 1997-98 will restore about 20 km2 of the 39 km2 previously drained.

The positive ecological benefits are extremely few, but it cannot be excluded that some terrestrial species/populations have increased. The economical benefits concern agricultural production. See chapter A.2.2.

The main effects of land drainage in Denmark include:

  • Water is removed faster from drained areas

  • Increase of river peaks, increase of the risk of downstream floods

  • Destruction of wetlands

  • Loss of nutrient retention / removal capacity (Typical values for Danish wet meadow are a nitrogen removal of 400 kg N ha-1 year-1 through denitrification)

  • Loss of their characteristic flora and fauna

  • Leaching of Fe++, acid water and ochre especially in the Atlantic region


France: The benefit in France is an intensification of agriculture (e.g. Poitevin area, Brittany).

The main problem is river channelisation to receive draining waters.

B3.2. Land Sealing

Information on land sealing has been received from Austria for the Alpine region and from France for the Atlantic, Continental and Mediterranean region.

The most important causes for land sealing are due to:

  • Urbanisation

  • Infrastructure for traffic

  • Tourism (skiing grounds)

B3.2.1. Urbanisation

Information on land sealing due to urbanisation has been received from Austria for the Alpine region, from France for the Atlantic, Continental and Mediterranean region and from Norway.

Austria: Land sealing causes an increased and accelerated runoff, which causes problems in local flood control. In addition, sealed land prevents the groundwater recharge by preventing the slow infiltration of water in particular during thaw. Runoff water of sealed housing and traffic areas is normally unfiltered and polluted with chemicals. This does not include major pollution by accidents.

Land sealing due to housing and traffic areas covers only 3 % of Austria. However, due to the unpopulated areas in the Alpine regions it consumes about 7 % of the populated area. In some valleys in the Alpine region the percentage is considerably higher (NUP, 1995). Intimately related to this urbanisation and construction of buildings in zones formerly reserved for inundation areas is extensive flood control and sealing of river banks.

The constructions of more houses and of more and larger streets follows the obvious desire to increase the size of flats (plus weekend houses) and to increase the mobility of the population by individual traffic.

France: There are particularly large areas of hypermarket development in the northern part of the Atlantic region and urbanisation especially in important alluvial aquifers of the Continental region (e.g. Rhône/Saône valleys, Rhine valley). Land sealing due to urbanisation is also a main intervention to the hydrological cycle in the Mediterranean region, shown on important demographic trends.

The main effects in the Mediterranean region of France are:

  • Pressure for expansion into areas vulnerable to flooding risk (drained areas)

  • Increasing water demand

  • Increased runoff-coefficient which causes an increasing flood risk

B3.2.2. Infrastructure

Information about land sealing due to infrastructure has been received from France for the Continental and Mediterranean region.

For a description refer to chapter 9.2.1 (Land sealing due to urbanisation).

B3.2.3. Tourism - Skiing Grounds

Information about land sealing due to tourism - skiing grounds has been received from Austria for the Alpine region.

Austria: Skiing pistes cover about 250 km2 (0.28 %) of the Austrian territory. Most of them are concentrated in few skiing centres and have been constructed during the last 20-30 years (ÖSTAT and Umweltbundesamt, 1994).

Skiing tourism is one of Austria’s most important economic factors.

The more severe environmental impacts are normally associated with downhill skiing. Following negative effects have been reported (Stanners and Bourdeau, 1995):

  • Forest clearance, construction of infrastructure (access roads, parking, hotels, lifts) and increased incidence of avalanches (mudslides).

  • Water pollution due to sewage and chemicals caused by tourists outnumbering the local population many times during short periods.

  • Use of water due the extensive use of snow cannons.

 

B3.3. Wet Cuts - Mining of Alluvial Gravel

Information about wet cuts for mining of alluvial gravel has been received from France for the Atlantic and Continental region.

This intervention is related to dredging in river bed as well as gravels mined in alluvial floodplain (e.g. Loire, Rhône/Saône valleys and the Rhine valley) and is an important and economically useful source of high quality aggregates.

The proportion of national aggregate requirement met by alluvial gravel extraction was 67 % in 1975 and 51 % in 1994 (Martin, 1996).

The main benefits in both regions are:

  • Increases capacity for biological processes in alluvial aquifer;

  • Creation of lake following closure of quarry;

  • Sometimes better water quality in these lakes for fish production than in rivers.

The main effects in both regions are:

  • Loss of filtering capacity for recharge to alluvial aquifer - may affect water quality;

  • Have often become sites for illegal waste dumping in the past, leading to groundwater pollution;

  • Acceleration of nitrate or pesticide groundwater pollution due to pumping carried out during quarry operations;

  • Possible denitrification of water in lakes created after quarrying - slow evolution of chemical composition of water due to contact with air.

Aggregate extraction from the alluvial plain of the Rhine - Continental region - throughout this century (about 1000 quarries in total). Currently 150 quarries (3,500 hectares) in operation producing 25 Mt/year of which more than a quarter is exported. The alluvial aquifer represents 80 % of water supplied in the region, currently with minimal treatment. A dozen of public water supply wells have been affected by pollution related to backfill of old quarries.

B3.4. Agricultural Activities - Increased Intensity of Agriculture

Information has been received from Austria for the Continental region and from France for the Atlantic region.

a) Atlantic Region

France: Intensification of agriculture is primarily a main intervention in the northern and south-western part of this region with a drastic increase in irrigated land and cultivation of high water demand crops. This is a driving force for the construction of irrigation reservoirs and an increase of water abstraction. Drainage of wetlands is a further effect of this intervention.

b) Continental region

Austria: The intensification of the agriculture is a main human intervention in the hydrological cycle of Austria especially in the Continental region. The area of land used for agricultural purposes has slightly decreased during the last years but the production has increased. About 800,000 ha of agricultural land has been reformed during the last 100 years. This reforming - land improvement, land consolidation, land drainage, merging of smaller areas, removing of hedgerows - as well as the kind of tillage, kind of crop cultivated, simplification of crop rotation, single-crop farming, etc. has disturbed the water balance of rural areas (decrease of the groundwater renewal rate, decrease of the groundwater table, increase of water discharge, etc.) and increased the risk of erosion.

More than half of the area of the Continental region of Austria is used for agriculture (about 68 % of the total area is used for agricultural purpose, about 47 % is arable land). About 80 % of Austria’s arable land is in the Continental region. In the Alpine region agricultural land mainly consists of meadows, pasture and alpine pasture.

Table B.17 Extent of agricultural and arable land in Austria.

  Agricultural land (km2) Arable land (km2)
Austria (total area 83,860 km2)

1983

35,400 14,220

1992

35,110 14,170

1993

34,820 14,010
Continental Region in Austria (total area 26,310 km2)

1990

17,780 12,270

Source: Federal Ministry of Agriculture and Forestry, Agriculture, Forestry and Water Management in Austria, Edition 1994.

An example of the intensification of agriculture is the cultivation of maize: The main cultivation areas of maize are in the Continental region of Austria (about 83 % of the total maize cultivation area) and about 20 % of the arable land in this region is used for maize cultivation. The cultivation area of maize has increased five times since 1946 and the yield of maize per ha has also increased five times since 1946. 1991 the yield was 8480 kg/ha. Maize cultivation increases the risk of erosion especially if it is cultivated at slopes.

As a main economical benefit, Austria has reached a high degree of self-sufficiency in agriculture.

The effects of the intensification of agriculture for whole Austria include:

  • Intensification of agriculture has increased the risk of erosion. More than 1,000,000 ha are potentially endangered by erosion (erosion caused by precipitation, wind-erosion, mudflow, overflow (inundation), slumping). The maximum loss of soil can be locally up to 80 t/ha.a, this corresponds to a loss of soil of about 5 mm/year. In the eastern part of Austria, mainly the Continental region, beside wind-erosion, erosion caused by precipitation and flooding plays an important role.

  • Reasons for an increase of erosion in Austria mainly are: single-crop farming, increase of maize cultivation, simplification of crop rotation, soil compaction (caused by wheel tracks), deterioration of the soil structure, changes of grassland to arable land and land drainage.

  • Erosion, the removal of soil will reduce the capability of water storage and the filtration capability of the soil; surrounding surface waters may be eutrophic.

  • The soil compaction and deterioration of the soil structure increases the surface runoff and therefore will reduce the groundwater renewal rate of this area.

  • Changes from grassland to arable land will increase the risk of erosion especially in flood plains and affect the groundwater renewal rate.

  • Effects of land drainage see chapter C.1.

  • 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 the increased water demand has to be completed by irrigation. (see also chapter B.2.2).

 

B3.5. Forestry

Information about forestry has been received from Portugal for the Mediterranean region and from Norway.

Norway: Norway saw a dramatic deforestation from around 1600 to the second half of last century. The reason was a growing saw mill industry and timber export, use of timber in the mining industry, local land cultivation and use of fire wood. The last hundred years most of the deforested areas have been forested again, due to changes in mining and forestry industries, and reduced population pressure in the rural areas. There are strong indications that these processes have strongly influenced the runoff regime in Norwegian rivers.

B3.5.1. Deforestation

Portugal: The main reasons for the loss of forestry resources in Portugal are urban development, intensification of agriculture, tourism and fires.

The forest fires have been responsible for the loss of important forestry areas, namely Monchique mountain (Algarve region) and central zone of the country (between littoral zone and Estrela mountain). The last zone corresponds one of the great pine’s tree areas in Europe.

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