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Surface sealing and the water balance

Germany and Belgium

Seminararbeit 2011 23 Seiten

Geowissenschaften / Geographie - Phys. Geogr., Geomorphologie, Umweltforschung



1. Introduction
1.1 Areas of study

2. Methods
2.1 Calculation of the water balance
2.2 Matching of different studies by degree of imperviousness
2.3 Estimation of the relationship of the water balance and degree of imperviousness

3. Results

4. Discussion

5. Conclusion


1. Introduction

Surface sealing or soil surface sealing is the packing or compaction of the earth surface to hinder the infiltration of fluids (EEA, 2011). A measure to compare different types of land use is to set the amount of impervious or totally sealed area in relation to the total area considered. This value is also named the degree of imperviousness. (Leopold, 1968)

In Europe, 1.81 percent of the total area is sealed. This amount seems rather low and does not seem to affect humans or the environment. (EEA, 2010) But in countries such as Malta, Belgium, the Netherlands or Germany it reaches beyond five percent of the total area as shown in the figure 1.

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Figure 1: Degree of imperviousness in European countries (2006) (EEA, 2010)

It is known that the major problems of surface sealing occur in urban areas with higher degrees of imperviousness, which ranges e.g. for European capitals from 20 percent in Stockholm to about 80 percent in Bucharest and this is shown in figure 2. Additionally, the average annual rate of land take was for the period 2000 to 2006 111,788 ha per year and per country or equal to 0.6 percent of the total area of each country (36 European countries) and increased by nine percent compared with the period 1990-2000 (24 European countries) (EEA, 2011). Assuming that that this trend will persist, the degree of imperviousness indicated in figure 2 will increase further.

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Figure 2: Average surface sealing in % of Urban Morphological Zone and per inhabitant (EEA, 2010)

The trade-offs from surface sealing mainly occur in urbanized areas as they have a higher degree of imperviousness as paved roads or buildings are built much more densely. Especially a decrease of the permeability of the soil increases surface runoff and decreases infiltration. Due to the lower infiltration to recharge the groundwater, groundwater aquifers are not sufficiently recharged anymore and the water table declines (Haase & Nuissl, 2007). The filtering capacity of the soil is only used to a much smaller extent as less water moves through the soil. (Emmerling & Udelhoven, 2002) Due to soil surface sealing, the water storage capacity of the soil - a buffer for the variability of precipitation – can be used less due to hindered infiltration. As a consequence the amplitude between peak and base flow increases and the discharge occurs at different times – more at rainstorm events, less in between. The base flow of receiving surface water bodies such as rivers decreases. This means that the water provision in dry periods is weakened as the soil water cannot contribute to the surface runoff the more the soil is sealed. At peak flows the discharge rate and velocity of surface runoff is increased compared to unsealed soils as sealed soils respond faster to rainstorm events. (Pauleit & Duhme, 2000)(Rodhe & Kilingtveit, 1997) A higher share of local precipitation reaches rivers and finally the ocean and is not locally available anymore (Scalenghe & Marsan, 2009).

Also the atmospheric water content in sealed urban areas is lower than in rural areas due to the lack of vegetation, which significantly increases evapotranspiration due to interception. Especially forests with a high-leaf-area index hinder more water to reach the ground so that surface runoff is reduced respectively in urban areas increased. (Hundecha & Bárdossy, 2004) The locally decreased evapotranspiration alters the microclimate in cities and produces a negative feedback. The humidity of the air will decrease. As a consequence, the precipitation in the cities and in areas, where the humidity is transported to, will also decline so that overall amount of water in all components of the water balance will decline (Göbel, Starke, Meßer, & Coldewey, 2011)

These major impacts are also displayed in the generic figure 3.

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Figure 3: Urban water balance for different land use categories and degrees of imperviousness (Ellis, 2008)

Additionally, it has to be considered that urban freshwater – unequal to rural – demand can only be met by additional water supply from their surroundings or by extraction of groundwater (EEA, 2010). So the groundwater resources are threatened from the supply and demand side.

The focus of this report is to find empirical evidence in different studies in urban environments for the above named negative effects of surface sealing on the water balance. Especially the relationship between the components surface runoff, infiltration as well as evapotranspiration and the degree of imperviousness should be investigated at different levels of precipitation. The focus is set on Germany as the total amount of sealed surface in the European countries is highly concentrated, although it is one of the larger countries of Europe. So it can be expected that both more studies on surface sealing and the water balance are available due to the larger size than in Malta or the Netherlands and also most of negative effects of a high degree of surface sealing will be found. An additional case study will be taken from Belgium to test, whether the findings for Germany are also valid for other European countries. In the water balance, the water quantity and not the water quality such as the filtering capacity of the soil is investigated.



ISBN (eBook)
ISBN (Buch)
2.4 MB
Institution / Hochschule
Swedish University of Agricultural Sciences – Department of Aquatic Sciences and Assessment
Surface sealing Water balance Soil sealing impervious runoff precipitation infiltration urban sprawl urbanization



Titel: Surface sealing and the water balance