Rainfall data for the design of sewer detention basins

40
Table 3.6
Volwnes of the detention basins obtained with the
traditional method expressed by Eq. (2.18) M~imum
water depth 3.5 m. The volumes are given in m /ha
re
a·
Return
period
years
Catchment Maximum permi outflow (1/s ha d) re
5.0 10 0 20.0 30 0
Bergsjon 131 51
Linkoping 1 1 86 48 30
Linkoping 2 130 96 47
Bergsjon 171 124 90 74
Linkoping 1 161 112 72
Linkoping 2 169 123 87 71
Bergsjon 208 155 116 100
Linkoping 1 197 142 98 78
Linkoping 2 206 154 113 97
Bergsjon 274 203 156 140
Linkoping 1 262 188 138 118
Linkoping 2 272 201 1 137
The basin volumes were underestimated by, on average, 10-12%. The
underestimations are larger for the larger Linkoping 1 catchment
than for the smaller catchments probably because the routing of
the hydrographs are more important in a large catchment than in a
small one. The underestimations are also larger for the small
outflows of 5 1/s·hared and 10 l/s·hared than for the other outflows
Sjoberg and Martensson (1982) obtained underestimations of approximately
15-40% when comparing design of percolation basins by
h i s tori c a 1 storms w i t h des i g n by the t r ad i t i on a 1 method . I t i s
clear that the traditional method gives underestimations that are
larger for small outflows than for larger outflows. A summary of
the results obtained in the present study and the results obtained
by Martensson and Sjoberg are shown in g 3.2