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Berlin Environmental Atlas

01.11 Criteria for the Evaluation of the Soil Functions (Edition 2006)

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01.11.9 Filtration Capacities

Description

The filtration capacity of a soil indicates its capacity to bind dissolved and suspended substances in the soil and not let them reach the groundwater. The decisive factor is the type of soil and the resulting speed with which precipitation water moves through it by the force of gravity. Therefore the filtration capacity of gravelly and sandy soils with high water permeability is low, since the water moves more than two meters per day in water-saturated soil, while for soils consisting of boulder clay, the speed of movement amounts to only 0.1 to 0.2 meters per day.
However, how much water - if any - actually moves toward the groundwater (depending on evaporation/ vegetation) has not been taken into account in the evaluation of Filtration Capacity. This has been partly taken into account under the criterion Exchange Frequency of the Soil Water (cf. Map 01.11.4).

Methodology

The filtration capacity of the soils is ascertained on the basis of the water permeability (kf value) (cf. Map 01.06.10). The thickness of the filtration path up to the groundwater is not considered under this method.
The evaluation is carried out in three categories, based on Table 1. Soils with high water permeability, with kf levels 4-6, are assigned a low filtration capacity, and less permeable soils, with kf levels 1-2, are assigned a high capacity.

Table 1: Evaluation of Filtration Capacity, Based on the Levels of Water Permeability
Water permeability [cm/d] Water permeability Level Filtration capacity
< 1 1 very low 3 high
1 - < 10 2 low 3 high
10 - < 40 3 medium 2 medium
40 - < 100 4 high 1 low
100 - < 300 5 very high 1 low
≥ 300 6 extremely high 1 low
Table 1: Evaluation of Filtration Capacity, Based on the Levels of Water Permeability (Lahmeyer 2000)

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