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Tab . 17 : Ranges and medians of the calculated total runoff levels of the subbasins
of the Rur catchment .
. . . . . . . . . . . . . . . .
Subbasin Range Median
_ ................. ................. ..............
LowerRur
537 mm/a 202 mm/a
Middle Rur
Upper Rur
Wurrn
Merzbach
Inde
Ellebach
Kali
Urft
Rur catchment
606 rnm/a 112 mm/a
850 mrn/a 90 mm/a
582 rnm/a 161 mm/a
574 mm/a 243 mn9/a
670 mm/a 100 mm/a
657 mm/a
667 mm/a
132 r^m/a
mm/a
942 mm/a 126 r - nfa
The highest medians (243 mm/a and 202 mm/a) are reached in the Merzbach
and the Lower Rur subbasins . In the Wurm and Ellebach subbasins, where
also unconsolidated rocks are predominate, the medians are slightly lower
with values around 150 mm/a . The reason for this finding is the relatively large
occurrence of groundwater- and waterlogging-affected soils in these regions,
which are accompanied with high direct runoff fractions .
The lowest mean groundwater recharge level is reached in the Urft and Kall
subbasins (median : 65 mm/a and 81 mm/a) . In these subbasins impermeable
Devonian solid rocks are predominate . The small pore volume and the associ-
ated low hydraulic conductivity of these rocks lead to relatively high interflow
rates and, therefore only a relatively small fraction of the runoff contributes to
groundwater recharge . Additionally, these subbasins are situated in the lee
site of the high mountains of the Hohes Venn, thus receiving relatively low
annual precipitation rates compared to the south-western part of the catch-
ment .
4.2.4 Direct runoff
Fig . 23 shows the frequency distribution of the direct runoff levels calculated
for Rur catchment . The maximum of the distribution is formed by the class
from 0 to 50 mm/a, in which approx. 28 % of the values are found . About half
of all calculated direct runoff levels are above 200 mm/a . The maximum values
can exceed 800 mm/a (less than 0 .1 %) .
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