Improved function for calculating distributed acceptable load on receiving…

Improved function for calculating distributed acceptable load on receiving waters

Previous method in StormTac Web of producing distributed acceptable load (kg/ha/year), for the watershed to the recipient, has meant that the recipient’s acceptable load (kg/year) has been distributed over the total area (ha) of the watershed area. The new method is based on the fact that the distributed acceptable load is instead based on the recipient’s treatment needs (kg/year), the total load on the recipient (kg/year) and the area of the watershed area (ha).

It is the pollution load via the drainage (such as stormwater and baseflow) that stormwater measures refer to and therefore the new calculation of distributed acceptable load (kg/ha/year) is based on the total load via only stormwater and baseflow from the watershed area, and does not include the part that comes as direct atmospheric deposition on the recipient surface and not as the part of the groundwater that flows directly into the recipient.

The improved function and description in the guide provides the opportunity to distribute the treatment needs to several actors (the Transport Administration, municipalities, operators, etc.). The distribution of the treatment needs is based on the amount of pollutant load the individual operator contributes to in the catchment area.

Improved functions for quantification of uncertainties after scientific review

Improved functions for quantification of uncertainties after scientific review

The revised and improved functions are the result of ongoing work in collaboration with Luleå Technical University with a scientifically reviewed publication on quantification of uncertainties in the StormTac Web application (Wu et al., 2020). The features use a method based on The Law of Propagation of Uncertainties (Taylor, 1994), where absolute uncertainties are calculated from relative uncertainties. This is described in the guide, with reference to the publication (Wu et al., 2020) for more detailed description.

The improvement uses a new function when different values are summed, which reduces uncertainty, while a multiplication gives increased uncertainty, according to a scientifically reviewed paper by Hedbrant and Sörme (2001). This new breakdown using different equations gives changed resulting relative uncertainties for total flow, total load and total concentration before and after treatment, respectively, with consequent changes in calculated absolute uncertainty.

As before, various absolute uncertainties for different substances are obtained, but based so far on assumed relative general uncertainties for concentrations and runoff coefficients from literature values. However, there is a continued collaboration with Luleå Technical University to develop specific uncertainties that take into account the uncertainty in concentrations for each substance and land use from StormTac’s database, as well as for runoff coefficients per land use. That work will be described in a new paper that will also be scientifically reviewed. Implementation of this more advanced uncertainty model is expected to take place within a few months.

18th of March, at the conference VAK2020 Jönköping

18th of March, at the conference VAK2020 Jönköping

Come and meet four of us, on the 18th of March, at the conference VAK2020 (Vatten avlopp kretslopp) in Jönköping, Sweden. There you get the opportunity to ask us questions about StormTac Web and see us show the application live. We will be in Monter 35. Hope to see you there!

/StormTac Team

Updated land-use specific runoff coefficients per land use

Updated land-use specific runoff coefficients per land use

The volume runoff coefficients and the design runoff coefficients have been investigated through supplementary literature studies and compared, after which revisions of the typical template values ​​and interval values ​​have been performed for some land uses. These changed runoff coefficients have also been compiled in the database.

These adjustments refer to typical recommended values, but both of these types of runoff coefficients can still be changed according to site-specific conditions. This e.g. applies to the land use Forest with increased typical runoff coefficients that have been adjusted after extensive empirical studies in Sweden and the US, but which also show large variations between different locations. More about this can be read in a new section in the Guide, under Design Flow.

In the same chapter there is also news from an international study which indicates that there is no significant relationship between the runoff coefficient and the size of the catchment area, which also means that there is no upper value for the catchment area for employing the rational method in the model, so it can be used without a specific upper limit area, provided that site-specific conditions such as longest runoff transport (concentration) time are carefully considered.

Updated typical concentrations for stormwater and baseflow from road…

Updated typical concentrations for stormwater and baseflow from road areas

Updated (reduced) typical concentrations for stormwater for Hg from the following land uses:

– Office area
– Residential area without road ditches, min
– Residential area without road ditches, max
– Multifamily area with street trees in a skeletal soil (macadam-soil mixture) without Local disposal of stormwater in the block
– Multifamily area with street trees in a skeletal soil (macadam-soil mixture) with Local disposal of stormwater in the block
– Multifamily area with biofilter without local disposal in block
– Multifamily area with biofilter with local disposal in block
– Office area with street trees in a skeletal soil (macadam-soil mixture) without Local disposal of stormwater in the block
– Yard area within block
– Artificial turf field

Updated typcical concentrations regarding all substances and the land uses:
– Local street with curbstones
– Local street after reduction in open ditch.

Updated (reduced) baseflow concentrations from road areas for the following substances:
– N, Zn and Cr.

Updated yearly precipitation data (box Precipitation)

Updated yearly precipitation data (box Precipitation)

In the Precipitation box, there are now examples of only selected sites corrected yearly precipitation, however more data on both corrected and uncorrected precipitation incl. references are compiled in the Guide

Scenarios have been implemented to the Recipient model (box…

Scenarios have been implemented to the Recipient model (box Watershed area and box Recipient data)

Different scenarios
Below the box Watershed area, a new Scenario can be added. By adding a new scenario, it is
possible to simulate how the recipient is affected by changes within the watershed area (for
example after an exploitation) or in the recipient (for example, increased volume after dredging).
In Scenario 1, measured concentrations in the recipient can be specified. If
measurements are stated in Scenario 1, a corrected total concentration will be calculated for the
other scenarios. The corrected calculated total content (C,rec,corr) takes into account any over- or
underestimation of the calculated recipient concentration compared with stated measurements in
Scenario 1.

Updated concentration data from recycling center, and data of…

Updated concentration data from recycling center, and data of impregnated and untreated wood

1. Updated concentration data from recycling center

All substances have been updated after extensive flow proportional sampling of stormwater from three Swedish recycling centers. The assignment was carried out by Sweco in 2019 on behalf of Avfall Sverige. The volume-weighted samples have been calculated by StormTac.

2. Data of impregnated and untreated wood

A literature study was conducted whereby 5 case studies were found with data on stormwater runoff from impregnated and untreated wood surfaces, respectively. This data is entered in the database under Other surfaces and can be calculated in StormTac Web by selecting the land use Own and entering the values ​​manually, but data is missing for some substances and only a few data have been found for base flow, so assumptions can be made in the model regarding these. Once more data has been found or estimated, impregnated and untreated wood can be selected for land use in StormTac Web.

Updated concentrations for stormwater and base flow

Updated concentrations for stormwater and base flow

Updated stormwater concentrations for all substances for the following land use:
Block without road with local disposal of stormwater

Updated stormwater concentrations for AAe, FLUO and NAP for the following land use:
Block without road

Updated stormwater concentrations for all land uses for:
4-tert-OP

Updated base flow concentrations for all land uses for:
Alachl
ANT
As
Atraz
Benz
BDE47
BDE99