Changes

==Overview==

==Overview==

Stormwater filtration is an essential component of urban runoff management. Filtration can improve water quality by removing suspended solids and pollutants which helps meet TSS removal targets and maintain watershed health. Filtration is the process by which stormwater [[Runoff volume control targets|runoff]] is conveyed through a medium to remove solid particles and associated pollutants. Stormwater passes through a filter based on the pressure difference on either side of the filter. In most stormwater treatment applications, the pressure difference is created by gravity (or hydraulic head).

Stormwater filtration is an essential component of urban runoff management. Filtration can improve water quality by removing suspended solids and pollutants which helps meet TSS removal targets and maintain watershed health. Filtration is the process by which stormwater [[Runoff volume control targets|runoff]] is conveyed through a medium to remove solid particles and associated pollutants. Stormwater passes through a filter based on the pressure difference on either side of the filter. In most stormwater treatment applications, the pressure difference is created by gravity (or hydraulic head).

==Applications==

==Applications==

*[[Pretreatment]] options, such as [[Vegetated filter strips|vegetated filter strips]] which function by slowing runoff velocities and filtering out pollutants, can be combined with other stormwater treatment systems in a treatment train approach.

*[[Pretreatment]] options, such as [[Vegetated filter strips|vegetated filter strips]] which function by slowing runoff velocities and filtering out pollutants, can be combined with other stormwater treatment systems in a treatment train approach.

*'''Granular media''' is a multilayer lattice or matrix that traps solids as water flows through the tortuous channels in the media. Examples of granular media include [[sand]] and [[Aggregates|gravel]].

Clogging may occur when solid particles form a film on the filter's surface or accumulate within the media channels to the point where the channels become occluded. Clogging can decrease the effectiveness of a filter. As the filter becomes [[clogging|clogged]], higher pressure is needed to drive stormwater through the filter, until a point is reached at which flow through the treatment system must be redirected to another flow path (usually a [[overflow|bypass]] within or upstream of the system).  

 

*'''[[Geotextiles|Membranes]]''' have very thin separation lattices with openings or pores that remove all particles larger than the nominal pore size of the filter at the surface, thereby acting much like a sieve. Membranes are often pleated to increase the surface area, allowing for more particles to be trapped prior to clogging.

 

Some filters include [[additives]] such as zeolite or iron to enhance the contaminant removal process for target water quality variables by increasing chemical adsorption and/or precipitation.

==Key system design parameters==

===Sizing===

When sizing filtration systems for specific sites using local historical rainfall records, several key system design parameters need to be considered.  These are defined in the sizing section of the [[Filtration MTD]] page.  

When sizing filtration systems for specific sites using local historical rainfall records, several key system design parameters need to be considered.  These are defined in the sizing section of the [[Filtration MTD]] page.  

Non-proprietary [[bioretention]] systems are sized as filters much more conservatively based on design storms, surface ponding depth and [[Flow through media|minimum media infiltration rate]].  The ratio of drainage area imperviousness to the surface area of bioretention facilities (referred to as the impervious-to-pervious ratio) is often many times lower than that for filtration MTDs.  This ensures longer intervals for sediment maintenance and significant reductions in stormwater volumes through infiltration.

Non-proprietary [[bioretention]] systems are sized as filters much more conservatively based on design storms, surface ponding depth and [[Flow through media|minimum media infiltration rate]].  The ratio of drainage area imperviousness to the surface area of bioretention facilities (referred to as the impervious-to-pervious ratio) is often many times lower than that for filtration MTDs.  This ensures longer intervals for sediment maintenance and significant reductions in stormwater volumes through infiltration.

==References==

==References==