Effects on evaporation rates from different water-permeable pavement designs.
ABSTRACT The urban water balance can be attenuated to the natural by water-permeable pavements (WPPs). Furthermore, WPPs have a 16% higher evaporation rate than impermeable pavements, which can lead to a better urban climate. Evaporation rates from pavements are influenced by the pavement surface and by the deeper layers. By a compared evaporation measurement between different WPP designs, the grain size distribution of the sub-base shows no influence on the evaporation rates in a significant way. On the contrary, a sub-base made of a twin-layer decreases the evaporation by 16% compared to a homogeneous sub-base. By a change in the colour of the paving stone, 19% higher evaporation rates could be achieved. A further comparison shows that the transpiration-effect of the grass in grass pavers increases the evaporation rates more than threefold to pervious concrete pavements. These high evapotranspiration rates can not be achieved with a pervious concrete paving stone. In spite of this, the broad field of application of the pervious concrete paving stone increases the importance in regard to the urban climate.
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ABSTRACT: A new laboratory evaporation measurement device (LEMD) was developed to estimate the evaporation rates of urban surface materials. Here, evaporation is induced by means of a constant heat input and airflow. The evaporation can be measured using two different methods concurrently. Method 1 is based on a balance, which measures the mass loss over time. In method 2 the water vapour transport in the air is measured by humidity sensors thus enabling the calculation of the evaporation rate. Test measurements show a sensitivity of method 2 against influences from the environment, therefore, method 1 was used for subsequent measurements. With the assistance of the LEMD, an estimation of the evaporation rates for different materials was determined within a short period of time and with low costs.First measurements were carried out at 29 different urban surface materials. The main focus was placed on pervious concrete materials. In general, a more evenly distributed evaporation from pervious concrete was observed. It was possible to select pervious materials with anticipated higher evaporation rates for a subsequent field test. Especially two-layered pervious materials with a fine grained top layer and a coarse grained bottom layer show the highest laboratory evaporation rates. Furthermore, very low evaporation rates (even lower as from impervious materials) were observed for pervious materials with coarse grained aggregates. If these results can be verified in the field, it will be possible in future to regulate the urban water balance through the targeted deployment of different types of water-permeable pavements.Fuel and Energy Abstracts 12/2011;
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ABSTRACT: Storm water control in urban areas helps to conserve the natural water balance and to protect soil and groundwater from hazardous substances. This paper introduces the concept for a near-natural storm water control system, including an associated decision-making chart. In this concept, the quantitative aspects of storm water infiltration are checked first. All important factors and their parameters, which enable a judgement on the tolerance of rising groundwater levels, are identified and evaluated. If the predicted rise in groundwater level is considered tolerable, the qualitative aspects of storm water infiltration are then checked. Again, all important factors and their parameters, which enable a judgement on the hazards to the soil and groundwater, are identified and evaluated. The presented concept also includes recommendations and demonstrates alternative control systems. Urban planners and public authorities are regarded as potential users of this concept.Environmental earth sciences 11/2013; · 1.57 Impact Factor