Changes

|''D''||h||Duration of design storm

|''D''||h||Duration of design storm

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|''i''||mm/h||Intensity of design storm

|''i''||m/h||Intensity of design storm

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|''f'''||mm/h||[[Design infiltration rate]] of the underlying native soil, calculated from measured [[Infiltration: Testing| infiltration rate]] and applied [[Infiltration|safety factor]]

|''f'''||m/h||[[Design infiltration rate]] of the underlying native soil, calculated from measured [[Infiltration: Testing| infiltration rate]] and applied [[Infiltration|safety factor]]

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|''n''||-||Porosity of the aggregate or other void-forming fill material(s) in the storage reservoir of the practice.<br> *Note: For systems that have significant storage in open chambers surrounded by clear stone aggregate, an effective porosity value (''n<nowiki>'</nowiki>'') may be estimated for the whole installation and used in the calculations below. Effective porosity will vary according to the geometry of the storage chambers, so advice should be sought from product manufacturers. Permit applications should include the basis for ''n<nowiki>'</nowiki>'' estimates.

|''n''||-||Porosity of the aggregate or other void-forming fill material(s) in the storage reservoir of the practice.<br> *Note: For systems that have significant storage in open chambers surrounded by clear stone aggregate, an effective porosity value (''n<nowiki>'</nowiki>'') may be estimated for the whole installation and used in the calculations below. Effective porosity will vary according to the geometry of the storage chambers, so advice should be sought from product manufacturers. Permit applications should include the basis for ''n<nowiki>'</nowiki>'' estimates.

|''x''||m||Perimeter of the practice

|''x''||m||Perimeter of the practice

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|''K_f''||mm/h||Minimum acceptable saturated hydraulic conductivity of the [[Bioretention: Filter media|filter media]] or [[Topsoil| planting soil]] used in the practice, when compacted to 85% maximum dry density   

|''K_f''||m/h||Minimum acceptable saturated hydraulic conductivity of the [[Bioretention: Filter media|filter media]] or [[Topsoil| planting soil]] used in the practice, when compacted to 85% maximum dry density   

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==To calculate the required storage reservoir footprint area where the depth is fixed or constrained (1D drainage)==

==To calculate the required storage reservoir footprint area where the depth is fixed or constrained (1D drainage)==

To ensure that the water storage capacity of the facility is available at the onset of a storm event, it is recommended to size the storage reservoir despth, d_r, based on the depth of water that will drain via infiltration between storm events. So d_r can be calculated as <br>:

To ensure that the water storage capacity of the facility is available at the onset of a storm event, it is recommended to size the storage reservoir despth, d_r, based on the depth of water that will drain via infiltration between storm events. So d_r can be calculated as:<br>

<math>d_{r} = (\frac{f'}{1000}) \times t </math>

<math>d_{r} = \frac{f'\times t}{n} </math>

Where <br>

Where <br>

''f''' = [[design infiltration rate]] of the native soil (mm/h) <br>

''f''' = [[design infiltration rate]] of the native soil (m/h) <br>

''t'' = [[drainage time]], based on local criteria or long-term average inter-event period for the location.<br>

''t'' = [[drainage time]], based on local criteria or long-term average inter-event period for the location (e.g. 72 hr in southern Ontario).<br>

<br>

<br>

In many locations there may be a limited depth of soil available above the seasonally high water table or top of bedrock elevation into which stormwater may be infiltrated.  In such cases the required storage needs to be distributed more widely across the landscape. <br>

In many locations there may be a limited depth of soil available above the seasonally high water table or top of bedrock elevation into which stormwater may be infiltrated.  In such cases the required storage needs to be distributed more widely across the landscape. <br>

<br>

<br>

To calculate the time (''t'') to fully drain the facility assuming three-dimensional drainage:  

To calculate the time (''t'') to fully drain the facility assuming three-dimensional drainage:  

<math>t=\frac{n\times A_{r}}{f'\times x}ln\left [ \frac{\left (d_{r} + \frac{A_{r}}{x} \right )}{\left(\frac{A_{r}}{x}\right)}\right]</math>

<math>t=\frac{n\times A_{r}}{f'\times x}ln\left [ \frac{\left (d_{r} + \frac{A_{r}}{x} \right)}{\left (\frac{A_{r}}{x}\right) }\right]</math>

Where "ln" means natural logarithm of the term in square brackets <br>

Where "ln" means natural logarithm of the term in square brackets <br>

Adapted from CIRIA, The SUDS Manual C753 (2015).

Adapted from CIRIA, The SUDS Manual C753 (2015).