SUITMA 2005 Cairo - Thermal and hydrological behaviour of an urban anthropic regosol with strong stagnic properties
SUITMA 2005 Cairo
| This abstract is about one of the papers of the Properties of unconventional soils theme of the SUITMA 2005 symposium. |
| Thomas Latacz,i | Wolfgang Burghardt,ii |
| Wilhelm Kuttler.i |
- i - Department of Applied Climatology and Landscape Ecology, University of Duisburg - Essen, Essen, Germany
- ii - Department of Soil Technology, University of Duisburg - Essen, Essen, Germany.
This presentation deals with the effects of some typical soil modifications found in urban areas and their influence on the thermal and hydrological behaviour of these soils. The object of investigation is an urban anthropic regosol with strong stagnic properties, which frequently occurs in the Ruhr district (North Rhine-Westphalia). The majority of the soil consists of building rubble with different origins. It belongs to the type of today recently increasing build soils with stagno gleyic dynamics.
The aim of this investigation is the determination of the radiation-, energy- and water balance and – taking account of the special properties of the soil – the determination of the thermal and hydrological behaviour of this urban soil. To achieve this it was necessary, beside a precise physical and chemical analysis, to equip the soil down to a depth of 1 m with soil thermometers, TDR-probes and heat flux plates. Additional the short- and long-wave radiation, turbulent fluxes and other meteorological components were determined up to a height of 10 m above the ground.
The examined soil is characterized by a very heterogeneous stratification and shows up to 10 different layers<A[beds|strata]> within the first meter. The deposit of building rubble results in an increased carbonate (> 10 percent by weight) and gravel content (> 70 percent by weight). As a result the pH(CaCl2) is alkaline and lies between 7.5 – 8.
The soil is characterised by a strong compaction in the lower part, so the bulk density increases up to values of approximately 1800 kg m-3. This results in a reduced hydraulic conductivity, so an extreme hydrological behaviour can be expected. This will be proved through the TDR-measurements, where the tendency to reach high water content values (> 45 volumetric percent) in the wet period will be documented.
Both, the compaction, as also the high water content are taking influence on the thermal properties of the soil. Therefore the specific heat, volumetric heat capacity and the thermal conductivity are increased while the thermal diffusivity shows lower values.
This leads to a modified thermal behaviour. In comparison with a less modified soil the urban soil shows lower temperatures in the afternoon and increased values in the night.
The strong dependence of the thermal properties on the water content is shown by the comparison of two days (low/high soil water content). The specific heat increased with the water content by 23 % (1531 J kg-1 K-1) in the upper layer, while lower layers don't show this development (constant water content). The volumetric heat capacity increased comparable (+ 37 %), similar to the thermal conductivity (+ 20 %), while the thermal diffusivity have been reduced by 14 %.
