For the basin calculation it necessary to insert the size of the area that was made impermeable, the thickness of the gravel above the chambers (15 cm recommended) and the thickness of the gravel under the chambers (10 cm recommended). See the table below for other parameters.
* Approximate data for the basin calculation * Rainfall indicators can be found at the basin nearest weather station * NaN = Non Available Number: decimal numbers have to be inserted with a dot, not with a comma.
INTENSITY
RAINFALL IN 30
LOW
30 mm
AVERAGE
45 mm
HIGH
60 mm
TYPE OF GROUND
SPEED OF INFILTRATION(m/s)
Clay
0.000000001
(1e-9)
Marl
0.00000001 :: 0.0000001
(1e-8 :: 1e-7)
Silt
0.000001
(1e-6)
Fine sand
0.00001
(1e-5)
Coarse sand
0.0001
(1e-4)
Crushed stones
0.001
(1e-3)
TYPE OF SURFACE
φ
Roofs covered with plates or shingles
0,9 ÷ 1,0
Levelled roofs covered with CLS
0,7 ÷ 0,8
Levelled green roofs
0,3 ÷ 0,4
Paved surfaces
0,7 ÷ 0,9
Earth roads
0,4 ÷ 0,6
Grassy surfaces
0,1 ÷ 0,4
Residential areas
0,3 ÷ 0,7
Woods
0,1 ÷ 0,3
Farmlands
0,2 ÷ 0,6
For the calculation of rainwater’s volume to accumulate it is necessary to know the surface that was made impermeable by the urbanization. This surface is the result of the sum of the covering areas such as: roads, squares, sidewalks, ecc…that were adjusted with the relative flow coeffiecient which depends on the construction materials (see the table below and in italic the global coefficents)
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