Changes

This article is specific to [[bioretention]], vegetated systems that infiltrate water to the native soil. <br>

If you are designing a planted system which does not infiltrate water, see advice on [[Planters: Sizing]].

 

This article is specific to [[bioretention]], vegetated systems that infiltrate water to the native soil.

{{TOClimit|2}}

If you are designing a planted system which does not infiltrate water, see advice on [[Planters: Sizing]].<br>

 

{{TOClimit|3}}<br>

Many of the dimensions in a bioretention system can be predetermined according to the function of the component. There is greatest flexibility in the ponding depth, filter media depth and the depth of the internal water storage reservoir beneath the optional underdrain pipe. The table below describes some recommended values to use to begin the design process.   

Many of the dimensions in a bioretention system can be predetermined according to the function of the component. There is greatest flexibility in the ponding depth, filter media depth and the depth of the internal water storage reservoir beneath the optional underdrain pipe. The table below describes some recommended values to use to begin the design process.   

 

{| class="wikitable"

{| class="wikitable"

|-

|-

| colspan="2" |75 ± 25 mm

| colspan="2" |75 ± 25 mm

|  

|  

* 0.7 for wood based

* 0.7 for shredded wood

* 0.4 for [[stone]]

* 0.4 for [[stone]]

|-

|-

| 200 mm diameter pipe

| 200 mm diameter pipe

| Not applicable

| Not applicable

| 0.4

| 0.4 for clear stone aggregate in which the pipe is embedded

|-

|-

| Storage reservoir (''d_r'')

| [[Bioretention: Internal water storage|Internal water storage reservoir]] (''d_r'')

| See below

| See below

| See below

| See below

| 0.4

| 0.4 for clear stone aggregate below the perforated pipe; Higher effective porosity can be achieved by including void-forming structures

|}

|}

Before you begin you will need to know the following;<br>

Before you begin you will need to know the following;<br>

This spreadsheet tool has been set up to perform all of the bioretention sizing calculations shown below and allows side-by-side comparison of equation outputs for each potential design approach or constraint scenario.<br>

This spreadsheet tool has been set up to perform all of the bioretention sizing calculations shown below and allows side-by-side comparison of equation outputs for each potential design approach or constraint scenario.<br>

{{Clickable button|[[Media:Infiltration Sizing 20200525 locked.xlsx|Download the infiltration practice sizing tool]]}}

{{Clickable button|[[Media:Infiltration Sizing 20220617 locked (1).xlsx|Download the infiltration practice sizing tool]]}}

==Decide if an underdrain will be included==

==Decide if an underdrain will be included==

* Step 4: Calculate the infiltration water storage depth of the practice, d_i which is the depth of water stored by the practice that can drain by infiltration alone.<br>

* Step 4: Calculate the infiltration water storage depth of the practice, d_i which is the depth of water stored by the practice that can drain by infiltration alone.<br>

For practices without an underdrain, components contributing to infiltration water storage include the surface ponding, mulch and filter media depths (i.e. total depth of the practice).  The infiltration water storage depth of the practice can be calculated as:

For practices without an underdrain, components contributing to infiltration water storage include the surface ponding, mulch and filter media depths (i.e. total depth of the practice).  The infiltration water storage depth of the practice can be calculated as:

<math>d_{i}=d_{p}'+ (d_{m}\times n_{m}) + (d_{f}\times n_{f})</math>

<math>d_{i}=d_{p}'- (d_{m}\times (1-n_{m})) + (d_{f}\times n_{f})</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*d_p' = Design surface ponding depth (m)

*d_p' = Design surface ponding depth (m)

*n_f = Porosity of filter media}}<br>

*n_f = Porosity of filter media}}<br>

For practices with an underdrain where the perforated pipe is elevated off the bottom, infiltration water storage is provided by the depth of the storage reservoir below the invert of the underdrain perforated pipe, d_r, and only the portion that can reliably drain by infiltration within the specified inter-event drainage time, t.  So the infiltration water storage depth of the practice can be calculated as:

For practices with an underdrain where the perforated pipe is elevated off the bottom, infiltration water storage is provided by the depth of the storage reservoir below the invert of the underdrain perforated pipe, d_r, and only the portion that can reliably drain by infiltration within the specified inter-event drainage time, t.  So the infiltration water storage depth of the practice can be calculated as:

<math>d_{i}= f' t </math>

<math>d_{i}= f'\times t</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*f' = [[Design infiltration rate]] of underlying native soil (m/h)

*f' = [[Design infiltration rate]] of underlying native soil (m/h)

*t = [[Drainage time]] (h), time required to fully drain the active storage components of the practice (i.e. surface ponding and infiltration water storage depths), based on local criteria or long term average inter-event period for the location}}<br>

*t = [[Drainage time]] (h), time required to fully drain the internal water storage reservoir of the practice, based on local criteria or long term average inter-event period for the location}}<br>

For practices with an underdrain where the perforated pipe is installed on the bottom and connected to a riser (e.g., standpipe and two 90 degree couplings), infiltration water storage is provided by the storage reservoir depth between the inverts of the riser outlet (i.e invert elevation of the top 90 degree coupling) and reservoir bottom, and is calculated the same way as above.<br>

For practices with an underdrain where the perforated pipe is installed on the bottom and connected to a riser (e.g., standpipe and two 90 degree couplings), infiltration water storage is provided by the storage reservoir depth between the inverts of the riser outlet (i.e invert elevation of the top 90 degree coupling) and reservoir bottom, and is calculated the same way as above. See [[Bioretention: Internal water storage]] page for further design guidance and information on water quality treatment benefits of internal water storage reservoirs or zones in partial infiltration bioretention designs.<br>

 

See [[Bioretention: Internal water storage]] page for further guidance on water quality treatment benefits of internal water storage reservoirs or zones in bioretention.

To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events (i.e. includes inactive water storage), which increases hydraulic head and thereby, infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.

To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events (i.e. includes inactive water storage), which increases hydraulic head and thereby, infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.

*K_f = minimum acceptable saturated hydraulic conductivity of the filter media (m/h), see [[Bioretention: Filter media|Filter media]] for guidance}}<br>

*K_f = minimum acceptable saturated hydraulic conductivity of the filter media (m/h), see [[Bioretention: Filter media|Filter media]] for guidance}}<br>

<br>

<br>

For practices where flow is delivered directly to the storage reservoir:

For practices where flow is delivered directly to a subsurface (underground) water storage reservoir:

<math>A_{p}=i\times D\times A_{i}/[d_{i} + (f' \times D)]</math>

<math>A_{p}=i\times D\times A_{i}/[d_{i} + (f' \times D)]</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*d_i = Infiltration water storage depth (m), see above for equations for with and without underdrain designs

*d_i = Infiltration water storage depth (m), see above for equations for with and without underdrain designs

*f' = design infiltration rate of the underlying native soil (m/h)

*f' = Design infiltration rate of the underlying native soil (m/h)

*D = Design storm duration (h)}}<br>

*D = Design storm duration (h)}}<br>

* Step 6: Compare required surface area of the practice to available space.<br>

* Step 6: Compare required surface area of the practice to available space.<br>

You can use the infiltration practice sizing tool noted above to adjust d_p, d_i, A_p or A_i to find practice dimensions that provide the required storage volume and will drain within the specified drainage time, while keeping R between 5 and 20.

You can use the infiltration practice sizing tool noted above to adjust d_p, d_i, A_p or A_i to find practice dimensions that provide the required storage volume and will drain within the specified drainage time, while keeping R between 5 and 20.

==Determine the required surface area of the storage reservoir==

==Determine the required surface area of the internal water storage reservoir==

* Step 8: Calculate the surface area of the storage reservoir, A_r (m²) needed to capture the infiltration volume target for the design storm event: <math>A_{r}=V_{i}/[d_{i}+(f'\times D)]</math>

* Step 8: Calculate the surface area of the storage reservoir, A_r (m²) needed to capture the infiltration volume target for the design storm event: <math>A_{r}=V_{i}/[d_{i}+(f'\times D)]</math>

{{Plainlist|1= Where:

{{Plainlist|1= Where:

<br>

<br>

*Step 9: Calculate the required storage reservoir depth, d_r (m):

*Step 9: Calculate the required storage reservoir depth, d_r (m):

<math>d_{r}=d_{i}'\times 1/n_{r}'</math>

<math>d_{r}=d_{i}'/n_{r}'</math>

{{Plainlist|1= Where:

{{Plainlist|1= Where:

*d_i' = Design infiltration water storage depth (m)

*d_i' = Design infiltration water storage depth (m)