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Berlin Environmental Atlas

01.11 Criteria for the Evaluation of the Soil Functions (Edition 2018)

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01.11.4 Exchange Frequency of Soil Water

Description

The exchange frequency of 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 more powerful reduction of certain inputs.

Methodology

The exchange frequency of soil water has been calculated as a ratio (quotient) between the percolation (in mm per annum, long-time mean values) and the usable field capacity of the effective root zone (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 area-specific data on precipitation, land use, vegetation structure, field capacities (from the soil textures), and depth to groundwater (i.e., from the surface) (Glugla et al. 1999) (cf. Map 02.13.4)

In the determination of the percolation as part of the evaluation of soil functions, the effect of impervious coverage was not considered, i.e. the calculation was carried out under the assumption that the surfaces were completely pervious. In the proximity of impervious soils, exchange frequencies increase considerably again, due to runoff precipitation water.

The usable field capacity of the effective root zone was derived from land use data and the Map of Soil Associations while incorporating the soil profile models devised by Grenzius (1987) associated with the individual soil associations. Since the exchange frequency of soil water is not commonly determined, there are no generally applicable evaluation standards. The values determined for Berlin were thus categorized so that each level covers a similar proportion of the municipal area.

Tab. 1: Exchange frequency levels of 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
Tab. 1: Exchange frequency levels of soil water

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