Micro Drainage: Surface Water
Guidance Note
September 2012
v1.0
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Micro Drainage: Surface Water
Guidance Note
September 2012 v1.0
Table of Contents
1
The Modified Rational Method ................................................................ 3
2
Greenfield Runoff Calculator .................................................................. 9
3
Storage Design .................................................................................. 16
4
Storage Tank/Pond ............................................................................. 22
5
Lined Soakways ................................................................................. 33
6
House Soakaways............................................................................... 38
7
Infiltration Basin ................................................................................. 43
8
Cellular Storage ................................................................................. 48
9
Permeable Paving/ Porous Paving ......................................................... 54
10 Hydro-Brake ...................................................................................... 60
11 Orifice ............................................................................................... 63
12 Saving Storage Structure Results as a .pdf ............................................ 65
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Guidance Note
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1 THE MODIFIED RATIONAL METHOD
1. Open the Modified Rational Method Spreadsheet
2. The following message will appear. It doesn’t matter whether you click
“yes” or “no”
3. Once you have selected an option the following spreadsheet will open
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4. Fill in the parts of the spreadsheet highlighted in pink in the screenshot
below
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Assumed Discharge Rate
for large and small sites

The assumed discharge rate for large and small sites is calculated
automatically from the site areas by the spreadsheet. The size of
the site will determine which Assumed Discharge Rate value is filled
in.

For Time of Entry, use 4 minutes for steep sites or sites with
buildings and peaked roofs. For flat sites use a Time of Entry of 1
minute.

Values for the WRAP class, SAAR, M5:60 and ratio of M5:60 to
M5:2 rainfall days should be taken from the Wallingford Maps. Once
these values have been input, the spreadsheet will calculate the
Soil Index, Ratio (r) and the UCWI automatically

The value for the routing coefficient should always be 1.3

Select an appropriate value for climate change. 30% residential,
20% anything else.
5. When the parameters for the “Input Parameters” tab have been filled in,
go to the “i calculation” tab of the spreadsheet.
6. The spreadsheet should look as follows
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Micro Drainage: Surface Water
Guidance Note
September 2012 v1.0
7. Fill in the box below highlighted in pink
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Micro Drainage: Surface Water
Guidance Note
September 2012 v1.0
8. The Time of Flow is the distance it takes for water to travel from the
highest point of the site to either the sites lowest point or its drainage
network.
For example, there is a 0.81 ha site that falls from south west to north
east. The distance from the south western corner to the north eastern
corner is 132.8 m. Assuming the velocity for droplet of water is 1 m/s, it
would take 132.8 seconds for water to travel 132.8 m, which would mean
the Time of Flow would be 132.8 seconds
After the Time of Flow is filled in, the spreadsheet will automatically
calculate the time of concentration, the rainfall intensities and fill in all
remaining blank cells, like so:
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9. Cv and the flow from impermeable areas will automatically be calculated
by the spreadsheet.
The values for Cv can be found in the “Cv Calculation” tab of the
spreadsheet and the calculated flow rates can be found in the “Q
Calculation” tab of the spreadsheet.
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2 GREENFIELD RUNOFF CALCULATOR
1. Open Micro Drainage Source Control, the following screen will appear
2. Double
click on Rural Runoff (QBAR/ADAS)
The following screen should appear:
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3. The default screen will always be set to the IH 124 Input method. You
must ensure that you select the ICP SuDS Method. Click on the second
option on the bottom left hand side menu.
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4. Fill in the boxes with site specific data for Return Period, Area, SAAR, Soil
and Region.

The return period typically used is 100

It is recommended that the ICP SuDS method is only used for sites
below 50 ha of area and that the IH 124 method be used for sites
greater than 50 ha.
However, for larger sites it is better to calculate the runoff for 1 ha
of area and then multiply the results for each return period by the
sites total permeable area. This will give a better representation of
the sites greenfield runoff rate.
Additionally, although it is possible for the ICP SuDS method to be
used for sites up to 50 ha, I tend to just use it for areas up to 10
ha. If the impermeable area is greater than 10 ha then I will
calculate the greenfield runoff rate for 1 ha of area and multiply it
by the overall impermeable area to get the sites runoff rate.
 The SAAR is taken from the Annual Average Rainfall map of the
Wallingford Maps.
 The value for the Soil parameter is the Soil Index Value. In order to
work out the Soil Index it is necessary to know what WRAP class
the site falls under. The WRAP class can be found on the Winter
Rain Acceptance Potential Maps of the Wallingford Maps. The
corresponding Soil Indexes are as follows:
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WRAP Class
1
2
3
4
5
Soil Index
0.15
0.30
0.40
0.45
0.50
 The Region value can either be selected from the drop down menu
Or by clicking the button (
) next to the drop down menu and
selecting the correct region from a map as follows:
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A region will show up red when you hover your mouse over it. To select a
region just click on it.
5. Once all the above parameters have been input, click the calculate button
(
) located beneath the Region select button
6. The Return Period Flood table will be populated with the results like so:
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7. In order to save the results, click the print button (
top left hand corner of the window.
) located in the
This will produce the following screen:
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Click the print button (
file to a .pdf
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) once again in the new window and print the
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3 STORAGE DESIGN
1. Open Micro Drainage Source Control. The following screen will appear.
2. Select the “Start a New Job” option
3. The following window will appear, allowing you to define the Global
Variables
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4. Leave the “Inflow” and “Additional Inflow” data as it is.
5. Select a suitable “Storage Structure” from the drop down menu
The most commonly used storage structures are:
 Tank or Pond
 Lined Soakaway
 House Soakaway
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 Infiltration Basin
 Porous Car Park Structure
 Cellular Storage
6. If infiltration is not possible at the site, then select a suitable “Outflow
Control” from the drop down menu
The most common used outflow controls are:
 Orifice
 Hydro-Brake
7. Select “None” for the “Overflow Control”
8. Set Climate Change to 30% for residential and 20% for everything else.
9. Click the “OK” button and the following window will appear where Rainfall
and Network Details can be defined
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10.The return period used is generally 100
11.The M5:60 is taken from the Rainfall Depths (M5 – 60 minutes) map of
the Wallingford maps
12.To get the Ratio R first find the sites Ratio of M5 – 60 minutes to M5 two
day rainfalls map from the Wallingford maps. Then divide the value by
100 to get R.
For example, if the value of the M5 60 to M5 2 is 30, R would be 0.3.
13.Once these parameters have been filled in, click the “OK” button.
14.The following window will open
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15. Input the value of the post developed sites impermeable areas into the
area box for the first timestep.
If the total impermeable area is under 1.75 ha then it is possible to use
only one timestep. This would mean you would input the value for the
total impermeable areas into timestep 1 (0-4 minutes).
If the total impermeable area is 1.75 ha or more, it would be better to use
a number of timesteps, splitting the amount of impermeable area between
each one.
For example, if a site had 6.357 ha of impermeable area, the time area
diagram would look as such:
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16.Once the Time Area Diagram window has been filled in click the “OK”
button.
17.The next window that opens will allow you to define the parameters of the
storage structure. This will depend on what storage structure was initially
selected in the Global Variables window.
18.If infiltration is possible, the storage design will be complete.
19.If infiltration is not possible, a new window will open allowing you to
define the parameters for the outflow control device you selected in the
global variable stage. You will then be able to specify a discharge rate and
define what level the water will have to reach before the outflow control is
required. This will enable you to reduce the rate of runoff before surface
water is discharged to a watercourse, drain or sewerage network.
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4 STORAGE TANK/POND
Project Number 2141 Catterick Road Colburn has been used as an example for
the purpose of this exercise.
1. Open Micro Drainage Source Control
2. Select “Start a New Job”
3. In Global Variables select the following then click “OK”.
Please note that the climate change percentage is dependent on the type
of development. For this particular example, the proposed development is
residential.
4. In the following window fill in the site specific Rainfall and Network details
then click “OK”.
E.g.
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5. Fill in the amount of impermeable area from the post developed site then
click “OK”.
6. The next window that opens will allow you to design your Tank or Pond
Structure.

Set the Cover Level to 1.500 m. This is true for most tanks/ponds.

Make sure the invert level is set at 0.000 m.

Estimate the Area of a pond. Considering the size of the
impermeable area, a Tank with an area of around 95 m2 to 115 m2
would probably be required. Do not worry if the area you specify is
incorrect, as this can be changed later.
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
Once the parameters of the Tank or Pond Structure have been
defined, click “OK”.
7. A new window will open allowing you to define the parameters of the
Hydro-Brake Outflow Control.

Set the invert level to 0.000 m

Set the Design Head to 1.000 m. This is a generalised value and is
the level water would have to reach before the Hydro-Brake started
working.

The design flow is the maximum allowable discharge rate. The
Hydro-Brake will ensure that the Design Flow is not exceeded. It is
usually the flow rate of the 1 in 2 year existing impermeable runoff
rate. In some cases a water company or the LPA will impose a
maximum discharge rate.

Choose an appropriate Hydro-Brake Type from the drop down menu
and then click “OK”. The parameters used with this example are as
follows
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8. The following screen will appear. Click “Go” to analyse the results.
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“Go” analysis
button
9. The following window will appear with a summary of results. A box will
also appear asking you whether you want to save.
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10. Click “Save As” and save the file in your
nnnn_project>Technical>Drainage>MicroDrainage
When saving, give the file name the below format
nnnn yymmdd <Type of Storage Structure> 100yCC <flow rate>lsec
E.g. 2141 120619 Tank 100yCC 92.3 lsec
11. When the project is saved you will see the following
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12. The event highlighted in red is the critical storm event. For this event, it
is important to look at and consider the:





Maximum
Maximum
Maximum
Maximum
Status
Water Level (m);
Depth (m);
Control flow (l/s);
Volume (m3); and
A good measure of determining whether a Storage Structure is suitable or
not is by evaluating these things.
The Status should be “OK” if it says flood then it will be necessary to
increase the size of the storage tank.
Additionally, for a typical storage tank you want the results to be equal to
or be as close as possible to the following values.

The Maximum Water Level and Maximum Water Depth should be
equal to the “Design Head” defined in the Hydro-Brake Outflow
Control window. In this case, the Design Head is 1.00 m, so the
values should be as follows
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
Maximum Water Level = 1.00 m
Maximum Water Depth = 1.00 m
The Maximum Control flow should be the same as “Design Flow”
value defined in the Hydro-Brake Outflow Control window. In this
case it should be
-
Maximum Control = 92.3 l/s
13.The Maximum Water Level, Maximum Water Depth and Maximum Control
can be changed by either increasing or decreasing the size of the storage
tank. In this case, the values are below those required, so it will be
necessary to reduce the size of the storage tank.
This is an iterative method and the new storage tank size should be set at
the value for the Maximum Volume of the Critical Event.
In this case that value is 102.8 m3.
14.The size of the Storage Tank can be changed by going to Edit>Tank or
Pond Structure
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15.Change the value of the Area in the Area Depth table to that of the
Maximum Volume for the Critical Event and then click “OK”.
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The results will automatically update themselves.
16.Repeat this process until the values for the Maximum Water Level,
Maximum Water Depth and Maximum Outflow values are satisfactory.
17.The final results for this example should be as follows
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5 LINED SOAKWAYS
Project Number 2064 Old Bawtry Road, Finningley has been used as an example
for the purpose of this exercise.
Please note that for this particular example the lined soakaway has been
designed to accommodate runoff from only one property. This means that for 16
of the residential units of housing, a total of 16 lined soakaways were required to
accommodate them.
1. Open Micro Drainage Source Control
2. Select “Start a New Job”
3. In Global Variables select the following then click “OK”.
Please note that the climate change percentage is dependent on the type
of development. For the purpose of this particular example, the
development is residential.
4. In the following window fill in the site specific Rainfall and Network details
then click “OK”.
E.g.
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5. Fill in the amount of impermeable area of one roof from a single post
developed house then click “OK”.
6. The next window that opens will allow you to design your Lined Soakaway
Structure.

Set the Cover Level to 2.000 m. The average soakaway is set to a
depth of 2.00 m.

If Infiltration Tests have been done, input the infiltration rate into
the Infiltration Coefficient Base (m/hr) and Infiltration Coefficient
Sides (m/hr)
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
If infiltration tests have not been done, then assume an infiltration
rate between 0.1 m/hr and 0.2 m/hr for both the Infiltration
Coefficient Base and Infiltration Coefficient Sides.
If infiltration at the site is possible then it is likely that the actual
infiltration rate is a lot higher than this. The reason why an
assumed infiltration rate in this range is used, is because it is a
conservative value.

Set the Number Required to 1
7. Click “OK” once the parameters have been set like so
8. Click the “Go” button to analyse the results. The following screen should
appear.
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9. As you can see, with this particular example the storage structure isn’t
quite right, causing a Flood Risk and a Flood to occur with certain rainfall
events.
Additionally, it would be ideal if the Maximum Water Level (m) and
Maximum Depth (m) did not exceed 1.500 m. This is to allow a freeboard
of 0.500 m.
It will be necessary to edit the Lined Soakaway Structure until it is large
enough to accommodate the runoff.
10.Go to edit>Lined Soakaway Structure
11.Change the value of the Ring Diameter and then click “OK”. Please note
that the most common sizes for precast concrete ring soakaways are:
0.900 m, 1.050 m, 1.200 m, 1.350 m, 1.500 m, 1.800 m, 2.100 m and
2.400 m.
12.Repeat this process until the Status is “OK” and the Maximum Water Level
and Maximum Depth are as close to 1.500 m as possible.
13.The final results for this example are below.
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6 HOUSE SOAKAWAYS
Project Number 2037 Kilnwick Road, Pocklington has been used as an example
for the purpose of this exercise.
Please note that for this particular example the house soakaway has been
designed to accommodate runoff from only one property. Each residential
property requires its own individual house soakaway.
1. Open Micro Drainage Source Control
2. Select “Start a New Job”
3. In Global Variables select the following then click “OK”.
Please note that the climate change percentage is dependent on the type
of development. For the purpose of this particular example, the
development is residential.
4. In the following window fill in the site specific Rainfall and Network details
then click “OK”.
E.g.
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5. Fill in the amount of impermeable area of one roof from a single post
developed house then click “OK”.
6. The next window that opens will allow you to design your House
Soakaway Structure.

Set the Cover Level to 2.000 m. The average soakaway is set to a
depth of 2.00 m.

If Infiltration Tests have been done, input the infiltration rate into
the Infiltration Coefficient Base (m/hr) and Infiltration Coefficient
Sides (m/hr)

If infiltration tests have not been done, then assume an infiltration
rate between 0.1 m/hr and 0.2 m/hr for both the Infiltration
Coefficient Base and Infiltration Coefficient Sides.
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If infiltration at the site is possible then it is likely that the actual
infiltration rate is a lot higher than this. The reason why an
assumed infiltration rate of this range is used, is because it is a
conservative value.

Select a suitable pit width. Considering the size of the impermeable
area, 1.5 m would be a good starting point.
If this is not big enough, the pit width can always be edited later on
to accommodate the property.

Set the Number Required to 1
7. Click “OK” once the parameters have been set like so
8. Click the “Go” button to analyse the results. The following screen should
appear.
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9. As you can see, with this particular example the storage structure isn’t
quite right, causing a Flood Risk and flood to occur with certain events.
Additionally, it would be ideal if the Maximum Water Level (m) and
Maximum Depth (m) did not exceed 1.500 m. This is to allow a freeboard
of 0.500 m.
It will be necessary to edit the House Soakaway Structure until it is large
enough to accommodate the runoff.
10.Go to edit>House Soakaway Structure
11.Change the value of the Pit Width and then click “OK”.
12.Repeat this process until the Status is “OK” and the Maximum Water Level
and Maximum Depth are as close to 1.500 m as possible.
13.The final results for this example are below.
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7 INFILTRATION BASIN
Project Number 2076 Former Acre Mill, Stacksteads, Bacup has been used as an
example for the purpose of this exercise.
1. Open Micro Drainage Source Control
2. Select “Start a New Job”
3. In Global Variables select the following then click “OK”.
Please note that the climate change percentage is dependent on the type
of development. For the purpose of this particular example, the
development is residential.
4. In the following window fill in the site specific Rainfall and Network details
then click “OK”.
E.g.
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5. Fill in the amount of impermeable area of one roof from a single post
developed house then click “OK”.
6. The next window that opens will allow you to design your Infiltration Basin
Structure.

Set the Cover Level to 1.500 m. This is a standard cover level for
an infiltration basin.
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
If Infiltration Tests have been done, input the infiltration rate into
the Infiltration Coefficient Base (m/hr) and Infiltration Coefficient
Sides (m/hr)

If infiltration tests have not been done, then assume an infiltration
rate between 0.1 m/hr and 0.2 m/hr for both the Infiltration
Coefficient Base and Infiltration Coefficient Sides.
If infiltration at the site is possible then it is likely that the actual
infiltration rate is a lot higher than this. The reason why an
assumed infiltration rate of this range is used, is because it is a
conservative value.

Select a suitable area.
If this is not the right size, then alterations can be made iteratively
later on. For now, assume an area
7. Click “OK” once the parameters have been set like so
8. Click the “Go” button to analyse the results. The following screen should
appear.
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9. As you can see, with this particular example the storage structure is a lot
bigger than required.
Additionally, it would be ideal if the Maximum Water Level (m) and
Maximum Depth (m) were set at 1.000 m. This is to allow a freeboard of
0.500 m.
It will be necessary to edit the Infiltration Basin Structure until it is large
enough to accommodate the runoff.
10.Go to edit>Infiltration Basin Structure
11.Change the value of the Area and then click “OK”.
12.Repeat this process until the Status is “OK” and the Maximum Water Level
and Maximum Depth are as close to 1.000 m as possible.
13.The final results for this example are below.
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8 CELLULAR STORAGE
Project Number 2107 194-196 High Road, Harrow Weald has been used as an
example for the purpose of this exercise.
Please note that it is possible to design cellular storage with or without
infiltration. Infiltration was not suitable with this example, so it was necessary to
use a Hydro-Brake to regulate flow rate.
1. Open Micro Drainage Source Control
2. Select “Start a New Job”
3. In Global Variables select the following then click “OK”.
Please note that the climate change percentage is dependent on the type
of development. For the purpose of this particular example, the
development is residential.
4. In the following window fill in the site specific Rainfall and Network details
then click “OK”.
E.g.
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5. Fill in the amount of impermeable area of one roof from a single post
developed house then click “OK”.
6. The next window that opens will allow you to design your Cellular Storage
Structure. Please note that the sizing for cellular storage is highly
variable, it is important to know what depth cell you are designing for,
before setting the parameters.

Set the Cover Level to 1.500 m.
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
For this example infiltration is not possible so leave the infiltration
rates at 0.0 m/hr.
If infiltration was, however, possible, input the infiltration rate into
the Infiltration Coefficient Base (m/hr) and Infiltration Coefficient
Sides (m/hr) and specify an infiltration area.

This is an example for a Cellular Storage Unit with a depth of 120
mm. The cellular storage will be set at a depth below tarmac, a sub
base and gravel.

It is necessary to specify an invert level for cellular storage, for this
example there will be an invert level of 1080 mm. Please see below
diagram for the purpose of this example.

Please note that the invert level will depend on the depth of the
cellular unit. 1080 mm is a suitable invert level for a cellular unit of
120 mm, but this will not be suitable for cellular units of higher
depths.
Select a suitable area or specify an area. For this example there is
216 m2 of car parking. This area is where the cellular storage is
proposed to be located.
Since the cellular storage unit you selected has a depth of 120 mm,
it will be necessary to specify the area for depths up to 120 mm.
7. Click “OK” once the parameters have been set like so
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8. A new window will open allowing you to define the parameters of the
Hydro-Brake Outflow Control.

Set the invert level to 0.000 m

Set the Design Head to 1.170 m. This is the level water would have
to reach before the Hydro-Brake started working.

The design flow is the maximum allowable discharge rate. The
Hydro-Brake will ensure that the Design Flow is not exceeded. It is
usually the flow rate of the 1 in 2 year existing impermeable runoff
rate. In some cases a water company or the LPA will impose a
maximum discharge rate.

Choose an appropriate Hydro-Brake Type from the drop down menu
and then click “OK”. The parameters used with this example are as
follows
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9. Click the “Go” button to analyse the results. The following screen should
appear.
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10.As you can see, with this particular example the storage structure is
suitable for the post development site.
The sizing for the cellular storage has been designed exactly. In order to
do this, it is necessary to know the exact specifications of the cellular
storage unit that will be used.
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9 PERMEABLE PAVING/ POROUS PAVING
Project Number 2056 1-3 Chiltern Hill, Chalfont St Peter has been used as an
example for the purpose of this exercise.
Please note that for this specific example infiltration is suitable, but if an outflow
control device is used, it is possible to use permeable paving on sites where
infiltration is not possible.
1. Open Micro Drainage Source Control
2. Select “Start a New Job”
3. In Global Variables select the following then click “OK”.
Please note that the climate change percentage is dependent on the type
of development. For the purpose of this particular example, the
development is commercial.
4. In the following window fill in the site specific Rainfall and Network details
then click “OK”.
E.g.
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5. Fill in the amount of impermeable area post development.
6. The next window that opens will allow you to design your Porous Car Park
Structure. For this particular example a sub base of 400 mm.

Set the Cover Level to 1.500 m. This is a general value for
permeable paving design with a sub base of 400 mm. If a different
depth of sub base is selected, then it will be necessary to use a
cover level appropriate to that specific sub base. The structure of
the porous paving, for this example, will look like so
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
If Infiltration Tests have been done, input the infiltration rate into
the Infiltration Coefficient Base (m/hr) and Infiltration Coefficient
Sides (m/hr).

If infiltration tests have not been done, then assume an infiltration
rate between 0.1 m/hr and 0.2 m/hr for both the Infiltration
Coefficient Base and Infiltration Coefficient Sides.
If infiltration at the site is possible then it is likely that the actual
infiltration rate is a lot higher than this. The reason why an
assumed infiltration rate of this range is used, is because it is a
conservative value.

Select a suitable Invert Level. This will once again depend on the
depth of the sub base.

The permeable paving will be placed in the car park. The car park
has an area of approximately 718 m2. Input an appropriate Length
and Width that will reflect the area of the car park.

Enter a value for the Slope. If this is unknown press the Display
Slope Calculator button
window will open
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next to the Slope box. The following
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Fill in the values for the DSIL, Length and Fall and click “OK”. The
DSIL is the value of the Invert Level. The Fall can be calculated with
the topographic survey by taking an approximation of the average
difference between the higher range levels and lower range values.
The Slope Calculator will automatically calculate the Slope of the
site.
7. Click “OK” once the parameters have been set like so
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8. Click the “Go” button to analyse the results. The following screen should
appear.
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9. As you can see, with this particular example the storage structure is
suitable for the post development site.
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10 HYDRO-BRAKE
1. You will have already selected Hydro-Brake for the Outflow Control in the
Global Variables.
2. When you have defined the parameters for the Global Variables, Rainfall
Data, Time Area Diagram and storage structure, the Hydro-Brake Outflow
Control window will open.
This will allow you to define the parameters of the Hydro-Brake.
3. Once you have input a suitable Design Head and Design Flow, it will be
necessary to choose a Hydro-Brake. This can be done by selecting an
option from the drop down menu like so:
4. The suitability of a Hydro-Brake can be assessed by looking at the
Headloss Flow table and the graph next to it.
You would expect a good Hydro-Brake to reach high flow rates at lower
Headloss values. The graph of a good Hydro-Brake should look as follows:
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
The turquoise line represents the maximum flow rate.

The red line represents where the Hydro-Brake starts working. It is
where a vortex occurs.

The squiggle in the dark blue line represents a vortex. Water enters
the Hydro-Brake before being spun around to cause an acceleration
in the flow rate and a vortex to appear. This regulates the flow rate
and ensures that water is discharged from the Hydro-Brake at the
specified Design Flow.

A good Hydro-Brake is one that has the vortex occurring at the
maximum flow rate ie. The redline, turquoise line and dark blue
squiggle are all in line.
5. It is not always possible to achieve results, with the Hydro-Brake, as
those above. Just try to achieve as good a fit as possible when selecting a
Hydro-Brake.
6. The only time a Hydro-Brake would be unsuitable is if the following error
message appeared in red.
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The error message means that the Hydro-Brake selected is not suitable
and flow rates will exceed those specified in the design flow. For this
reason it would be necessary to select a different Hydro-Brake.
7. Additionally, the Hydro-Brake would also be considered unsuitable if it
produced the following graph:
By looking at the graph you can see that there is no vortex or indication
that the Hydro-Brake has started to work. This is because the HydroBrake selected is too large, meaning water would be able to flow through
it without being attenuated and thus negating the need for a Hydro-Brake.
Since there is no attenuation, there is no limitation placed on the runoff
rate.
So a Hydro-Brake that produces the above graph would not be a suitable
choice.
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11 ORIFICE
1. You will have already selected Orifice for the Outflow Control in the Global
Variables.
2. When you have defined the parameters for the Global Variables, Rainfall
Data, Time Area Diagram and storage structure, the Orifice Outflow
Control window will open.
This will allow you to define the parameters of the Orifice.
3. If you do not know what diameter to use, one can be selected by clicking
on the “Calculate Diameter” button
appear
. The following window will then
4. Input the values for Design Depth and Design Flow and then click “OK”.
The Orifice Outflow Control window should update itself automatically like
so
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5. Click “OK” and then press the “Go” button
to check the results. If
the Orifice is not suitable you can change the size by going to
edit>Orifice Outflow Control
When changing the diameter of the orifice, increase or decrease the
Diameter by small increments. Orifices are very sensitive to change so the
diameter may only need to be changed by a couple of milimeters.
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12 SAVING STORAGE STRUCTURE RESULTS AS A .PDF
1. Once you have completed the design of your storage structure it will be
necessary to .pdf the results.
2. Click the print button (
).
Print Button
3. The following window will open. On the bottom left hand side menu, tick
check the boxes for:



Summary of Results;
Inflow Details; and
Model Details
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4. Click the “Update Preview” button. The window should update itself like
so:
5. Click the print button (
) and then print to .pdf, ensuring that the
.pdf is saved with the same name as the Micro Drainage Source Control
file.
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