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Berlin Environmental Atlas

02.13 Surface Runoff, Seepage, Total Runoff and Evaporation from Precipitation (Edition 2005)

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Surface Runoff

After the mean total runoff has been calculated as a difference between precipitation and real evaporation, surface runoff is determined in a second work step. Surface runoff corresponds to the total runoff on roof areas which drains into the sewage system. Areas not connected to the sewage system thus produce no surface runoff. Non-built-up sealed areas infiltrate a part of their drainage into the sub-surface, depending on the type of surface (surface-cover types). This Infiltration factor is dependent on the width, age and type of the seams. The non-seeping runoff is passed to the sewage system as surface runoff - depending on the degree of connection to the sewage system - or, if the sewage system does not receive it, seeps away at the edge of the sealed areas. Those portions of the precipitation onto roof areas not connected to the sewage system also seep away (cf. Tab. 1). The difference between total runoff and surface runoff thus corresponds to seepage as a basic quantity for new groundwater formation.

For the application of the method for urban areas, the parameters n and the infiltration factors had to be determined for the various sealing materials. Both lysimeter tests were evaluated with different sealing materials and calculations for wetting loss (cf. Wessolek/Facklam 1997). The quanta selected for the stated parameters are listed in Tab. 2. The change of these parameters due to compression and silting of the joints associated with the ageing process has been taken into account. However, due to still insufficient scientific bases, this information still involves certain uncertainties. Moreover, a different grouping of surface-cover types into surface-cover classes would be desirable from a hydrological point of view.

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Tab. 2: Effectivity Parameter n und Infiltration Factor Fi for Various Surface Sealing Classes

Excel
[Table is also available as Excel-File (MS-Excel is required).]

In order to provide an impression as to how the various area uses, sealing parameters and conditions of the sewage system would affect the water balance, the ABIMO model was used for approx. 35 model surfaces with different input quantities; the results are shown in Table 3. The relationship between surface runoff, sealing and evaporation is decisively dependent of the extent of sealing and the passage of rainwater to the sewage system.

Tabelle 3 - Dummy
[Approx. 51 KB size.]

Tab. 3 : Relationship between Surface Runoff, Seepage and Evaporation for Sample Surfaces of different Uses, Sealing Types (cf. Köppel/Deiwick 2004)

Excel
[Table is also available as Excel-File (MS-Excel is required).]

As a result of these calculations, updated long-term mean values for total runoff, surface runoff and seepage are available for each of the 25,000 separate areas. These values have been shown classified in mm/year in these maps; the totals in cu.m./year have also been calculated and averaged. It must be taken into account that the values shown are mean values covering the blocks represented as uniform areas; in fact, however, they have non-homogeneous structures. The runoffs of sealed and unsealed areas have been standardized to average values per block. In addition, the runoff of roadways has been attributed to the adjacent blocks. The maps do not show, for instance, how great the seepage capacity of a square meter of unsealed ground is. For this purpose, another full-coverage and block-referenced calculation has therefore been carried out with changed marginal parameters, i.e., assuming completely unsealed conditions. The results of this calculation are shown in Map 02.13.4.

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