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Global Variables
Model the units as cellular storage controlled by a Hydro-Brake® Flow Control:
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Rainfall and Network Details
Enter the return period and other rainfall details as normal
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Time/Area Diagram
Enter the time Area details as normal. In this instance the catchment area is relatively small with evenly shaped characteristics. We have therefore assumed that the time/area diagram is linear in form.
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Cellular Storage Details
Enter the dimensions of the Stormcell® here.
For this instance the Stormcell® Storage System we are
looking at is 31.2 m (13 blocks) long, 8.4 m (7
blocks) wide and 1.04 (2 blocks) deep. We therefore input
the data as a surface area, in this case 31.2 m x 8.4 m
gives a surface area of 262.08 m². The downstream
invert should be input as the invert level of the bottom
of the blocks. The cover level is the cover level above
the storage system. For this example we have used relative
levels of 8 for the invert level of the blocks and 10,
as the cover level as shown on the sketch at the end of
these notes.
Within the table you can make allowances for
the infiltration coefficient of the ground if the Stormcell® is
to be used as an Infiltration structure as well as storage.
If it is used as a Infiltration structure a factor of safety
will have to be incorporated into the design. The porosity
of the Stormcell® , 95%, can also be inputted into the
table.
For this example we have assumed that there is no
infiltration, so the factor of safety will be ignored.
If the sides of the tank are to be battered (ie. for an installation
deeper than 3 m to the base of the blocks)
then the area of the tank should be varied accordingly. The
diagram at the top right of this window shows the profile
of the tank.
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Hydro-Brake® Outflow Control
The invert of the control chamber
needs to be input here. This will usually be the same
as the invert level of the distribution pipe(s) at
the downstream end of the Stormcell® Storage
System. From the sketch at the end of these notes it can
be seen that the invert level for this example will be 7.5.
The design head then needs to be given. This is usually
the top water level (top of the Stormcell® ) minus the
invert level of the outlet pipe:
9.04 - 7.5 = 1.54 m
The desired flow restriction is also given. By clicking on the
calculator icon a range of Hydro-Brake® Flow Controls
are given. In this particular instance the 119 mm Type 'MD
6' gives the best head/discharge curve, which will result
in a lower storage requirement. The simulation can now commence
by clicking the
icon.
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Summary of Results
Small amendments may need to be applied to the model to tweak
the Hydro-Brake® Flow Control size if you find
you are not discharging the maximum allowable pass forward
flow. This will usually involve reducing the design head
by small increments.
The amount of storage provided by the
Stormcell® in the attached sketch is as follows:
31.2m x 8.4m x 1.04m x 0.95 (void ratio) = 258.93m³
The summary below indicates a storage volume of 257.8 m
3 for the critical, winter storm of 180 minute. The overall
amount of storage provided by the system illustrated (storage
in Stormcell® , pipes below Stormcell® and single sized stone above perforated pipes) will in fact give a volume in excess of the required 257.8m³.
The proposed Stormcell® Storage System will therefore be sufficient for this site.
Micro Drainage and Win Des are registered trademarks of Micro Drainage Ltd. The software and screen displays are copyright Micro Drainage and all rights are reserved.
