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Berlin Environmental Atlas

01.11 Criteria for the Evaluation of the Soil Functions (Edition 2009)

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01.11.4 Exchange Frequency of the Soil Water

Description

The exchange frequency of the soil water indicates how quickly the water in the animate soil zone is replaced by incoming precipitation water. The lower the exchange frequency, the longer the dwell time of the water in the soil. Longer dwell times have a compensating effect on the groundwater flow rate, and permit a better reduction of certain immitted substances.

Methodology

The exchange frequency of the soil water has been calculated as a relationship (quotient) between the percolation (in mm per annum, long-time mean values) and the utilizable capillary capacity of the effective root space (mm).

The percolation was calculated with the help of the ABIMO runoff formation model of the Federal Institute of Hydrology, as the difference between precipitation and evaporation. This model incorporates surface-section-specific data on precipitation, land use, vegetation structure, capillary capacities (from the soil types), and depth to water table (i.e., from the surface) (Glugla et al 1999) (cf. Map 02.13.4)

For the determination of the percolation in connection with the evaluation of soil functions, the effect of sealing has not been considered here, i.e. the calculation was carried out under the assumption of completely unsealed conditions. In the proximity of sealed soils, exchange frequencies increase considerably again, due to runoff precipitation water.

The utilizable capillary capacity of the effective root space was derived from the Soil Association Map, and the land uses by means of the schematic soil profiles of soil associations in Grenzius (1987).

Since the exchange frequency of the soil water is ascertained only seldom, there are no general evaluation standard. The values ascertained in Berlin were therefore evaluated in such a way that each level covers a similarly large share of the city's area.

Table 1: Levels of the exchange frequency of the soil water
per annum Level Designation
< 1 1 very low
1 - < 2 2 low
2 - < 3 3 medium
3 - < 4 4 high
≥ 4 5 very high
Table 1: Levels of the exchange frequency of the soil water

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