Project name:
Name of station: Choose the rainfall station tat is closest to the project site

Catchment area and runoff configuration

Impervious catchment area: m² Specify the impervious catchment area that is connected to the treatment system. It is usually not economical to treat runoff from pervious surfaces, as runoff only occurs during long rainfall events after the soil has become saturated. This only accounts for a very small part of the annual rainfall, with the majority of runoff ocurring in small, frequent rainfall events.
Runoff is modelled using inception losses and loss through evaporation
Click here to show/hide additional input for runoff calculations
Inception losses (cracks, uneven surface etc.): mm For impervious surfaces, enter the initial loss. The first depth of rainfall equal to this value is retained in the surface before any runoff occurs, and this water is then lost as evaporation. Evaporation varies depending on time of year and is based on evapotranspiration data.
A value for initial loss of 0.5-1.0mm is appropriate for roof areas, and 1.0-2.0mm for surfaces such as roads and parking areas.
Inception losses evaporates according to season, but in maximum: hours Specify the maximum time it takes for the initial loss to evaporate. Since evaporation is modelled based on evapotranspiration, this will be less in colder months. Since evaporation still occurs even when there is little evapotranspiration a value of between 24 to 48 hours for each mm of initial loss should be entered.

Cross-section and configuration of raingarden

Width of the filter surface (Wf): m Enter the width of the filter surface that effectivly filters / infiltrates stormwater.
Length of the filter (Lf): m Enter the length of the filter surface that effectivly filters / infiltrates stormwater.
Maximum depth of detention storage over filter surface (Md): mm Enter the maximum depth of ponding water over the filter surface before bypass
Width of detention storage, maximum water level (Wd1): m Enter the width of the extended detention area over the filter surface at the maximum water depth before the system bypasses.
Width of detention storage, at filter surface (Wd2): m Enter the width of the extended detention area at the filter surface.
Click here to show/hide more details of the raingarden
Capacity of diversion to raingarden (inlet, pit grate etc.): l/s Enter the diversion capacity from the catchment to the raingarden (stormwater pits, roof gutters, pipes, openings in gutter etc.).
Saturated hydraulic conductivity of filter media (Ksat): mm/tim Specify the rate of which water filters through the raingarden, the hydraulic conductivity (in mm / hour).
It is important that the value used is realistic and allows for some clogging of the filter surface over time. Suitable values varies depending on the soil media used, suggested values are shown below.

Clean sand 360 mm/hr (use a maximum of 180mm/hr)
Sandy soil / sandy loam 100-200 mm/hr (use a maximum of 50-100mm/hr)
Silty soil 36 mm/hr (use a maximum of 18mm/hr)
Depth of filter media layer (Fd): mm Enter the depth of the filter media
Void ration of filter media (Vf): % Specify the porevolume of the filter media that can fill with water for temporary detention. This volume only matters if the system can only drain through infiltration to surrounding soil.
Internal side batter of filterlayer, 1V: H Enter the internal side slope of the filter media, entered as horizontal distance per 1 unit of vertical distance.
Depth of drainage and transition layer (if applicable) (Dd): mm Enter the total depth of drainage layer (gravel) and any transition layer (sand) if such is used to separate filtermedia and drainage.
Void ration in drainage layer: % Specify the porevolume of the drainage layer that can fill with water for temporary detention. This volume only matters if the system can only drain through infiltration to surrounding soil.
Internal side batter of drainage layer, 1V: H Enter the internal side slope of the driainage layer, entered as horizontal distance per 1 unit of vertical distance.
Water infiltrates to surrounding soil: (Unchecked=No, Checked=Yes)
Infiltration capacity (hydraulic conductivity) of surrounding soil: mm/hr Tick the box if the system does not have a impervious base and water can infiltrate to the surrounding soil.
If water do infiltrate to the surrounding soil, specify the infiltration capacity of the surrounding soil (in mm/hr). This can vary a lot depending of the site soil, and if possible local measurements should be taken.
Approximate infiltration rates for different soil types are presented below. it is recommendet that these values are divided in two to allow for some surface clogging over time.

Coarse sand 3600 mm/hr
Fine sand 360 mm/hr
Silt 36 mm/hr
Clay / sand 3.6 mm/hr
Clay / silt 0.36 mm/hr
Dense clay 0.00 mm/hr
The raingarden drains through subsoil drainage: (Unchecked=No, Checked=Yes)
Distance from the bottom of the raingarden to invert of subsoil drainage: mm Tick the box if the treatment system drains through a subsoil drainage system. The subsoil drainage system is not assumed to be limiting for the system performance, and is assumed to be sized to collect the maxuímum flow that can pass through the system.
If the drainage is l´not located at the base of the system, enter the distance from the base of the raingarden to the invert of the drainage pipe. If the system can infiltrate water to the surrounding soil this means that a volume of water is detained at the base of the system that can only be lost through infiltration to the surrounding soil and to the groundwater.


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