Changes

==Design Assumptions==

==Design Assumptions==

[[Rainwater harvesting|Rainwater harvesting (RWH)]] is ideal for sites that cannot infiltrate water (e.g. contaminated soils, WHPAs, IPZs, etc.), zero-lot-line developments, extensive gardens and landscapes. Components include: catchment area (e.g. rooftop), filter to remove coarse debris, cistern storage, and a connecting pipe network. Additional components include pumps to lift water to higher elevations, additional water filtration and treatment. <br>

[[Vegetated Filter Strip]]s are gently sloping, densely vegetated areas designed to treat runoff as sheet flow from adjacent impervious areas. Filter strips function by slowing runoff velocities and filtering out sediment and other pollutants. Filter strips may be comprised of a variety of [[trees]], [[shrubs]], and [[vegetation]] to add aesthetic value as well as water quality benefits. <br>

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

* Native soil infiltration rates for Full, Partial and No Infiltration Design scenarios were assumed to be 20 mm/h, 10 mm/h and 2 mm/h, respectively, and a safety factor of 2.5 was applied to calculate the design infiltration rate.  

* Native soil infiltration rates for Full, Partial and No Infiltration Design scenarios were assumed to be 20 mm/h, 10 mm/h and 2 mm/h, respectively, and a safety factor of 2.5 was applied to calculate the design infiltration rate.  

* Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, removal of sediment from pretreatment structures annually, and removal of weeds twice a year (where applicable). Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ surface infiltration rate testing (where applicable)

* Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, removal of sediment from pretreatment structures annually, and removal of weeds twice a year (where applicable). Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ surface infiltration rate testing (where applicable)

* Can be used throughout the year if they are located underground or indoors to prevent problems associated with freezing.

* Maximum contributing flow path length across adjacent impervious surfaces should not exceed 25 metres.   

* Separate plumbing, pumps, pressure tanks, and backflow preventers are necessary for indoor use of harvested water.   

* Impervious surfaces draining to a filter strip should not have slopes greater than 3%.

* Back-up water supply system arrangements, that can be drawn upon when the cistern runs dry , are also necessary for indoor uses.

* The flow path length across the vegetated filter strip should exceed the maximum flow path length across the impervious surface draining to it.  

* Storage tanks in low elevated areas will increase volume of rainwater stored, but will increase the amount of pumping needed to distribute water. 

* Have a flow path length of at least 5 metres.

* Cisterns should be placed on or in native, rather than fill, soils.  

* Underground tanks and piping to and from cisterns should either be located below the local frost penetration depth or insulated to prevent freezing.

* An [[underdrain]] (minimum 200 mm perforated pipe) is only needed when native soil infiltration is less than 15 mm/hr or infiltration is precluded.

* [[Overflow]] devices should be designed to avoid causing ponding or soil saturation within 3 metres of building foundations. 

* [[Pretreatment]] is needed to remove debris, dust, leaves, and other debris that accumulates on roofs and can cause clogging within the RWH system.

===Notes===

===Notes===

* The tool calculates costs for new (greenfield) development contexts and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal.  

* The tool calculates costs for new (greenfield) development contexts and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal.  

** Land value and equipment mobilization and demobilization costs are not included, assuming BMP construction is part of overall development site construction.

** Land value and equipment mobilization and demobilization costs are not included, assuming BMP construction is part of overall development site construction.