BMU-Studie "Ökologische Auswirkungen von 380-kV-Erdleitungen und HGÜ-Erdleitungen" (Volume 4.2) (English shop)

Bericht der Arbeitsgruppe Umwelt

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This sub-report presents the environmental effects of extra-high-voltage cables and extra-high-voltage overhead lines, largely as the result of a synopsis of the literature. For the sake of clarity, the presentations are structured – once for underground cables (Chap. 2) and once for overhead lines (Chap. 3) – according to the catalogue of environmental assets of the Environmental Impact Assessment Act (UVPG § 2).

Human health: With regard to human health, the magnetic fields of underground cables and the electric and magnetic fields of overhead lines are the focus of the environmentally oriented analysis. Under the 26th BImSchV 1996 (§ 3 Annex), the immission limit value for magnetic flux density in Germany is 100 μT (50 Hz) and applies to all locations where people may be present on a permanent basis. Although epidemiological studies indicate that effects below this limit value are possible, cause-effect relationships are currently regarded as not demonstrable, so that the Commission on Radiological Protection does not recommend tightening the 26th BImSchV. Against the background of existing knowledge uncertainties, the limit values are provided with high precautionary margins both in some Länder and, in individual cases, abroad. In Switzerland, for example, 100 μT likewise applies as a limit value. In addition, however, a second limit value of 1 μT is defined in Switzerland for continuous exposure at sensitive locations. In Bremen (2004), the Senator for Labour, Women, Health, Youth and Social Affairs even recommends compliance with 0.3 μT for high-voltage lines [The limit values, regulations and recommendations for protecting the population from low-frequency and static electric and magnetic fields, which differ greatly worldwide, were compiled as preparatory work for this study by the ECOLOG-Institut, Hannover (cf. Neitzke and Osterhoff)]. The comparatively low magnetic field immissions and negligible electric field immissions from underground cables – apart from the immediate vicinity – make the use of underground cable technology at the extra-high-voltage level particularly interesting as an alternative to overhead lines from a precautionary point of view. As part of comprehensive precaution, the EnLAG recognises a particular degree of adverse impact from overhead lines within a distance of 400 m from residential buildings within the area of application of a binding land-use plan (B-Plan) or in the unplanned inner area pursuant to § 34 BauGB (if predominantly residential use), and within a distance of 200 m from residential buildings in the outer area pursuant to § 35 BauGB. The State Spatial Planning Programme of Lower Saxony (2008) even establishes the laying of underground cables within these distances on new routes as an objective, although this is justified on the grounds of residential environment considerations rather than considerations of human health.

Animals, plants and biological diversity: Nature conservation law provides traditional protected area systems, the protection of certain biotopes and special species protection – a complex set of rules for avoiding adverse effects on animals and plants worthy of protection and the encroachment on biotopes by the construction and operation of power line routes.

The avifauna is particularly at risk from the construction of overhead line routes for the duration of the operating phase. In the case of underground cables, a particular risk arises for soil-dwelling animal and plant species, above all during the construction phase. Encroachments due to keeping the route clear are lower for underground cables than for overhead lines because of the narrower route width in woody vegetation. For most animal and plant species groups, general indications can be given of possible measures to avoid and reduce adverse effects from the construction and operation of extra-high-voltage lines. Strictly protected areas such as nature conservation areas, national parks, SAC/Natura 2000 sites (FFH sites), biosphere reserves (Zones 1+2), RAMSAR sites and legally protected biotopes pursuant to § 30 BNatSchG should as far as possible not be encroached upon. This applies in principle also to less strictly protected areas such as landscape protection areas, biosphere reserves (Zone 3) and nature parks.

Among the biotopes worthy of protection, wetlands in particular (raised bogs and fens, swamps, active floodplains, water body banks) as well as dry grasslands and specific grassland sites with threat status 1-2 are unsuitable for underground cable laying for various reasons. For overhead line routes, high levels of conflict arise in woody biotopes because of the protection strips ranging from 40 m to more than 70 m in width, particularly in those with threat status 1-2 (above all extensive mixed and deciduous forest biotopes).

Soil: The laying of underground cables in the subsoil can, especially in the construction phase, lead to adverse effects on soil functions through soil compaction, disturbance of the soil structure and of the soil water balance. The installation and operation of extra-high-voltage cables can have adverse effects on the soil, above all with regard to potential warming and desiccation in possibly long phases of stress. Decisive for the risk of situations with strong soil warming occurring is the technical design of the respective extra-high-voltage cable as well as the type of its thermal bedding.

Water: In the course of underground cable laying, possible construction-related effects on groundwater and on surface waters that may be indirectly affected must be taken into account. This applies in particular to wetlands with a high groundwater table or areas with confined aquifers, which require actively induced groundwater lowering for the period of cable laying and could be unintentionally drained. Irreversible damage from underground cable laying can generally be ruled out by construction-related precautionary measures (prudent water management, correct restoration of soil stratification). In the case of overhead lines, small-scale and local construction- and installation-related effects on groundwater may occur at the pylon locations.

Air and climate: During the construction phase, increased exhaust emissions and, in the case of prolonged drought, dust emissions may arise both for underground cables and for overhead lines as a result of the use of vehicles and construction machinery; these, however, have no lasting and negative changes on the climatic conditions.

In the case of overhead lines, audible corona discharges occur in the operating phase under certain weather conditions, and thus an ionisation of air molecules. In some instances, an increased formation of oxidants such as ozone and nitrogen oxides is associated with corona discharges.

Landscape: In the case of underground cables, a swathe 12 m to 25 m wide remains in shrubland and forests after the construction phase. In open country, the route is no longer recognisable from the perspective of the average observer one year after completion. As ancillary structures, joint bays, shaft structures, converter stations and cable transition facilities may have to be taken into account.

Overhead line pylons and the conductor cables connecting them constitute objects visible from afar in the landscape, which are generally perceived visually as intrusive and, in their sequence, as fragmenting the landscape. To assess the effect of overhead lines on the landscape scenery, zones of impairment are usually distinguished. In the study, for comparison with assessment practice for wind turbines, a zoning model is also drawn upon which has gained broad practical relevance in wind farm planning.

Cultural heritage and other material assets: The construction work for underground cables or overhead line routes may endanger cultural monuments, in particular archaeological monuments. The construction of an overhead line can result in visual impairments in the vicinity of cultural monuments, for example churches, which are ruled out as far as possible already at the planning stage.

Synoptic assessment: The environmental facts set out in detail in the text section are summarised in a guidance aid consisting of eight thematic tables, which is intended to facilitate a decision between underground cable on the one hand and overhead line on the other at an upstream planning stage. In these tables, the environmental suitability of underground cables and overhead lines is assessed comparatively on a 5-point scale.

Recommendations: The final section contains our planning recommendations for the further expansion of the extra-high-voltage grid. From an environmental point of view, the following aspects are to the fore:

The planning of extra-high-voltage lines should make full use of the variety of planning, technical and landscape management options for avoiding and reducing environmental impairments. The early involvement of environmental expertise in the planning process is of particular importance.

In selecting the technical expansion option for an extra-high-voltage line (overhead line or underground cable), environmental assets should be given high priority. Close distances to settlements and a high degree of impact on the landscape and townscape frequently suggest an underground cable. If, on the other hand, soils and water bodies worthy of protection are mainly affected, spanning with overhead lines may be advisable. For an initial appraisal at an early planning stage, the synoptic assessment tables presented on the preceding pages are suitable. A sound recommendation, however, cannot be made without ecological on-site investigations.

Existing pre-existing impacts should preferably be used for bundling. However, bundling must not be an absolute criterion, since in various cases extra-high-voltage lines require larger protective distances than the existing linear infrastructure.

Adverse effects from electric or magnetic fields can in principle be minimised by increasing effect distances. Limit values should not be exhausted in this context. Precautionary distances from rooms in which people are permanently present should be set generously.

When laying underground cables at the extra-high-voltage level, all technical options should be exhausted to keep the heat development in the biologically active soil low. Ecological research to determine the carrying-capacity thresholds for heat development in the biologically active soil should be intensified. The state of knowledge concerning the effects of the heat development of an extra-high-voltage cable should be improved within the framework of the pilot projects by means of monitoring investigations on different soils and with different vegetation cover.