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Berlin Environmental Atlas

01.12 Soil Functions (Edition 2009)

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01.12.4 Regulatory Function for the Water Balance

Description

The regulatory function for the water balance is determined by the storage or retention capacity of the soils. It has an effect on the groundwater and surface-water runoff. The exchange frequency of the groundwater is used as a criterion for this soil function (cf. Map 01.11.4). A low exchange frequency means that the dwell time of the water is long and the water quantity retained in the soil is high. Thus, a low exchange frequency must be seen as positive for the landscape water balance. Longer dwell times in addition permit a better decomposition of immitted substances, and therefore have a positive effect on the percolation water quality. However, with high storage capacity and low exchange frequency, the new groundwater entry rate is low, since the precipitation water largely remains in the soil, and is taken up by the plants.

Methodology

The regulatory function for the water balance is derived directly from the evaluation of the exchange frequency of the groundwater (cf. Map 01.11.4), which is carried out according to the layers "low", "medium" and "high", where a very low exchange frequency is considered "high", as in Table 1 a low to medium exchange frequency is considered "medium", and a high to very high exchange frequency is considered "low."

Tab. 1: Evaluation of the regulatory function for the water balance, depending on the exchange frequency of the groundwater
Exchange frequency of groundwater per year Regulatory function for the water balance
  Evaluation Designation
< 1 3 high
1-3 2 medium
> 3 1 low
Tab. 1: Evaluation of the regulatory function for the water balance, depending on the exchange frequency of the groundwater (Lahmeyer 2000)

Percolation (without consideration for imperviousness) (cf. Map 02.13.4). was used for the calculation of the exchange frequency of the groundwater. The level of percolation is in turn influenced not only by precipitation and soil conditions, but substantially, too, by the level of evaporation, which is dependent on vegetation, and hence on use. When interpreting the map, it must therefore be taken into account that sections with the same soil associations could be evaluated differently, depending on the vegetation, which affects the percolation.

Diagram for the evaluation of the regulatory function for the water balance
Fig. 1: Diagram for the evaluation of the regulatory function for the water balance

Map Description

Numerous near-natural soil associations receive a high evaluation of regulatory function, with an exchange frequency of groundwater of less than once per year. These include all groundwater-influenced soil associations with bogs and gleys which are supplied with sufficient water in the topmost meter of soil throughout the year. Due to the high evaporation levels of the vegetation, the percolation from precipitation is very low here (cf. Map 02.13.2) - in some cases, groundwater discharge even occurs - so that the exchange frequencies are also very low. The soils of the plateaus of boulder clay/ boulder marl constitute another group. Due to their low permeability, they have great storage space, and a good capacity to retain precipitation water. Like clay soils, dune sites with fine sand as their main soil types also have great storage capacity, and should also be assigned to this class.

Near-natural groundwater-remote sites with a groundwater exchange frequency of once to twice per year achieve a medium evaluation level. These are primarily dystric cambisols on end and push moraines, arenic cambisols on the boulder marl plateaus with sand inlays, and dystric cambisol - eutro-gleyic cambisol associations in the valley-sand sections. In addition, there are soils of aggraded and displaced natural substrate, such as sands and loams, from which regosol - calcaric regosol - hortisol soil associations have developed. Soils with a low evaluation, i.e., an exchange frequency of the groundwater of 3 - 4 times per year, are concentrated in the inner-city area, industrial areas and railway yards (cf. Figure 2). Coarse aggraded material, such as construction rubble and track gravel, provides high soil permeability, so that precipitation water percolates quickly.

Area shares of the regulatory function for the water balance per use class (incl. impervious sections without streets and waters, not all uses, are represented)
Fig. 2: Area shares of the regulatory function for the water balance per use class
(incl. impervious sections without streets and waters, not all uses, are represented)

Excel
[Statistical base of Figure 2 is also available as Excel-File (MS-Excel is required).]

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