Please left click to advance through the show
• Infiltration and Attenuation Calculator
• BRE 365 and CIRIA 156 infiltration
• Map Based FSR Rainfall
• Ability to manually enter FEH data
• Fixed flow / Orifice / Vortex Controller
• Output to MS Word
• Vista / Win 7 Compatible
CRM Stormflow main screen.
To start in FSR mode click the rainfall icon
Select the area from the UK map, then click on the town
closest to the project
Enter the optional Catchment Name, the area of buildings and dense surfacing. Run off
coefficients default to 95% and 90% but can be changed.
Enter the storage details as length, width and depth. Assume a size to start with, which can
be refined in light of results.
Next, the outflow details are selected, the options being soakaway, fixed outflow, orifice
plate or vortex controller. In this case we are aiming for a max discharge of 11 l/s.
The orifice plate has been selected, a size of 75mm entered, which gives a peak outflow of
21.9 l/s, and shows the storage fails, due to inadequate size
Next, the storage size is adjusted to bring the water level within the storage depth, and the
reduced height brings the outflow to approximately the desired flow. If an exact correlation
were required, the orifice size could be modified, and the storage rechecked.
For Vortex controllers the user can enter water depth and flow rate data, then call a defined
controller from a pull down list. The insert shows the vortex controller data entry page.
The final attenuation option is the fixed outflow. This option assumes a constant discharge
regardless of head, such as would be generated by a pumped outfall, where the change in
static head was a small component of total pump head losses.
CRM Stormflow will also size a soakaway using either the BRE method or the CIRIA 3D
method of calculation. The infiltration rate is input in m/hour. For the CIRIA 3D case a Safety
Factor is also selected – in this case ‘minor inconvenience’.
A combination of a infiltration and attenuation can also be assessed but only with
attenuation by the fixed outflow method.
As a new feature in CRM Stormflow version 6 if a project contains more than one
attenuation tank or soakaway then these can be added to a single data file, accessed in turn
using the tab system, deleted if necessary, and all output as one Microsoft Word file.
Project details can be input by opening the Project Window, these will be sent to Microsoft
Word when the design is output. The project can also be saved to a file and re-opened using
buttons on the tool bar or by using the pull down menues.
Client: ABC Construction
Project: New Office Development
Catchment: Car Park and Building 1
Catchment Details: Storage Details:
Buildings 2000 m2 x 95 % Length 12.5 m
Dense surfacing 1250 m2 x 90 % Width 10 m
Effective Area 3025 m2 Depth 1.2 m
Porosity 95 %
Safety Factor against flooding = 5 Area Increase 0 %
Rainfall Details: Outflow Details:
Return Period 100 years Infiltration rate 0.36 m/hr
Climate Change Factor 0 % Attenuation Control
r value 0.3 Control Diameter - mm
M5-60 19 mm Discharge rate 0 l/s
Duration Intensity Required
mm mm/h storage (m3)
5 min 11.0 131.9 34.163
10 min 16.9 101.5 52.152
15 min 21.1 84.3 64.554
30 min 29.1 58.2 87.342
45 min 34.4 45.9 101.377 Results:
60 min 38.4 38.4 111.317 Outcome: Pass
2 hours 48.9 24.4 132.975 Critical Storm Duration 4.85 hrs
6 hours 66.9 11.2 144.151 Hmax 1.162 m
24 hours 96.1 4.0 57.725 Time to half empty 5.8 hrs
Typical Output to Microsoft Word
For more details contact CRM on: