Calculation of regression constant för calculation of rain intensities…

Calculation of regression constant för calculation of rain intensities for the whole World

Calculation of a regression constant for calculating rainfall intensities I (l/s/ha) for the entire World has been implemented in the box Design flow in StormTac Web. The function is derived from the equation developed by Dahlström (2010) and uses a target search (goal seek) function to iterate a regression constant, alpha, which controls the rain intensities over input data in the form of selected return time (year), specified rain durations (min) and rain intensities (l/s/ha). The generated regression constant alpha can be used for rain intensities for optional rainfall durations and replaces the default values in the model. The result will be different local/regional rainfall intensities used to calculate design flows and the required flow detention volume. If you want the model to always start with a calculated regression constant, you can manually enter it under the sheet (tab) Settings, but this should not be done if the license is used by offices in different locations.

Alternatively, you can, as before, manually enter each rain intensity for specified durations in the boxes (tables) at the boxes Design flow and Flow detention. The latter provides more accurate values, but the alpha value can be used for all return times.

Release v19.4.1

Implemented recipient criteria concentrations for sea and sea bays

Implemented recipient criteria concentrations for sea and sea bays

Recipient limit (criteria) concentration values for sea and sea bays (EU Water Directive) have been implemented. Choices between lake, watercourse or sea/sea bay are first made in the Recipient data box, after which the current limit values are automatically filled in the Water quality criteria box. These criteria values can then be changed if recipient-specific limit values apply to one or more substances.

Implementation of results from StormTac Web to GIS for…

Implementation of results from StormTac Web to GIS for presentation in maps in GIS

Implementation of results from StormTac Web to GIS for presentation in maps in GIS. Pollution maps per sub-watershed are presented with choices between the following results (one at a time) at the bottom of the MR-report, creating a CSV file that can be imported into the GIS application:
– Total concentration (stormwater + baseflow) as a mean for the area’s discharge to the recipient (ug/l).
– The total load (stormwater + baseflow) from the area’s discharge to the recipient (kg/year).
– The total load (stormwater + baseflow) per area from the area’s discharge to the recipient (kg/ha/year).
– The acceptable load of the areas (kg/year) to meet specified limit values in the recipient.
– The treatment needs of the areas (kg/year) to meet specified limit values in the recipient.
In the GIS application you can then create a join layer where you can use the column Area as target field / join field to match the areas you have in the GIS project and present the results by substance and area.

Calculation and reporting of sub-flows from facilities via stormwater…

Calculation and reporting of sub-flows from facilities via stormwater and groundwater, respectively

For the facilities in the biofilter box, the sub-flows are now calculated from these via stormwater and groundwater, respectively, so that in result report 4.2, not only the values of the total amount of outgoing pollution are obtained, but also specifically the part of this amount that is transported via stormwater and the part of this that is transported down to the groundwater.
The basis for this division of flows is the specified hydraulic conductivity for substructure / subsoil / terrace, with default value of 8.0 mm/h. The calculation takes into account that this velocity is not constant but consider the flow the conductivity gives through the facility’s ground and side surfaces. This flow’s share of total annual flow is calculated as the basis for the proportion of stormwater that flows down to the groundwater. This also requires the user to provide information on the length and side slope of the facility.

Applying the Parameter “Irreducible Concentration” in Modelling of Stormwater…

Applying the Parameter “Irreducible Concentration” in Modelling of Stormwater Treatment Facilities

Thomas Larm and Anna Wahlsten from StormTac corporation have written a scientific paper that has been published  in “Journal of Civil Engineering and Architecture”, 2019. The paper “Applying the Parameter “Irreducible Concentration” in Modelling of Stormwater Treatment Facilities” compiles minimum outflow concentrations from stormwater databases of different types of stormwater treatment facilities (e.g. swales, wet ponds, wetlands, biofilters and underground retention basins with filters). These data are used for the suggested values of specific “irreducible concentrations” (Cirr). The minimum outflow concentrations or “irreducible concentrations” (Cirr) refer to a stormwater treatment facility’s inability to reduce pollutant concentrations below a certain level. Cirr has significant impact regarding the choice of facility type and its calculated dimensions. This design parameter and the calculated outflow concentrations can be used to investigate the need for combined serial facilities or complemented design elements with more planted vegetation or installed filters. Such elements can be required to decrease Cirr and thereby reach project specific limit outflow concentrations and loads.

We recommend the use of a model that should include the calculation of runoff quality, to be based on a detailed land use specification, include site-specific design parameters, calculated outflow concentrations and loads of specified pollutants of relevance to design stormwater treatment facilities (STFs) for the receiving water.

The paper is available from “Downloads/Publications”.

Added reference data on runoff coefficients from green roofs

Added reference data on runoff coefficients from green roofs

Reference data on runoff coefficients from green roofs have been added to the guide, based on different roof slopes and substrate thickness.

Updated standard concentrations for Recycling Center, and concentrations for…

Updated standard concentrations for Recycling Center, and concentrations for overflow water (CSO) and measurement data from watercourses in the database

Updated standard concentrations
-Standard concentrations for Recycling Center have been updated with data from flow proportional samples. These have also been compiled in the database.

New sheet in the database
-Compilation of concentrations for Overflow Water in a new sheet “Overflow water (CSO)”, Combined Sewer Overflow.
-In the same sheet there is also a compilation of concentrations for outgoing wastewater.

Measurement data from watercourses
The “Surface water” sheet has been updated with measurement data from a number of watercourses with data from Järfälla and Gothenburg.

Quantification of uncertainties

Quantification of uncertainties

Quantification of uncertainties have been implemented regarding stormwater flows and required flow detention volume and pollution transport (concentration and quantity) of various pollutants from existing and planned areas before and after different types of treatment and detention measures.

There is a large demand to get further knowledge about the uncertainties in different parameters of indata and of the modelled results. This quantification of uncertainty would provide an improvement and extension of the tool and be of benefit to the action work in accordance with the Water Directive.

Each part where there are inputs and outputs of uncertainties is based on data from literature studies and selected methods are generally scientifically accepted.
The uncertainties are specified as input fields in the form of relative percent uncertainties (recommended default and interval values that can be changed by the user).

Results are presented in the results report R as absolute uncertainties (+/-) for the following parameters:
– stormwater flow (l/s)
– base flow (l/s)
– groundwater and base flow concentration (µg/l)
– total content before and after treatment (µg/l)
– total load before and after treatment (kg/year)
– design flow (l/s)
– required detention volume (m3)

There will be continuous further development around this quantification of uncertainty in the form of scientific papers in collaboration with Luleå University of Technology.

Updated calculation of Hydrauic efficiency and of the reduction…

Updated calculation of Hydrauic efficiency and of the reduction efficiency for drain inlet filters

The treatment effect of wet ponds, wetlands, sedimentation basins and underground sedimentation basins is affected, among other things, by the parameter Hydraulic efficiency. The parameter is now calculated from Thackston’s equation (Thackston et al., 1987; Stockholms stad, 2017). It is reported as before in the result report.

The effect of the treatment effect on the hydraulic efficiency has also been changed by a revised calculated factor that depends on the length:width ratio. As before, it is based on data from Vikström et al. (2011) but is now calculated on the basis of the updated calculated hydraulic efficiency and from more detailed functions between hydraulic efficiency and treatment effect.

The treatment effect of inlet drain filters is also updated as a result of obtained supplementary measurement data, presented in the database.