News in the Recipient-model

– Updated method for calculating pollutant load (Lin) on the recipient for substances without specified measurement data.
The method now includes calculated retention (Lret) with the same equation as for the calibrated method based on measurement data. This means that for substances for which measurement data is not available or has not been filled in the Recipient data box, calculated concentrations are used and then the updated method for calculating total load is used, taking into account Lret.
Although this method provides improved calculation of the pollutant load on the recipient, the use of the calibrated method based on measured concentrations in the recipient is recommended in view of the uncertainty in calculating recipient concentrations since there are complicated processes in the recipients.

– Updated method for calculating acceptable load on the recipient for substances with dissolved or bioavailable limit values.
The method now always uses calculated or measured concentrations in the same fraction as the limit values refer to, by automatically calculating missed inputs In the recipient data box to the same fraction. Bio-met can still be used for calculating bioavailable fractions, else the fractions are calculated from data from case studies (compiled in the Recipient data box). The user can alternatively employ own fractions by filling in the missing input data in the box.
The updated method calculates acceptable pollutant loads (Lacc) as total fractions even for substances with limit values specified in dissolved or bioavailable fractions. The results are therefore directly comparable with, e.g., total pollutant load (Lin), required pollutant load (ΔL) and (sub)watershed pollutant loads before and after treatment.
The update does not affect substances with limit values in the total fraction, such as for phosphorus (P).

Calculation of reduced available volumes for flow detention in ditches and swales, taking into account the longitudinal slope

The calculation is done automatically by specifying a longitudinal slope for the ditch or swale in the Biofilter box. This takes into account that the volume available for detaining peak flows decreases more the greater the longitudinal slope.

It is also possible to use the functions with series connection of ditches or export of the ditch to an area downstream, the latter if stormwater outlets are added along the length of the ditch. This makes it possible to simulate the effect of dividing the ditch with weirs to increase the flow detention effect by obtaining a larger total available volume for flow detention.

In general, the flow detention effect of ditches and swales decreases with increasing size of the catchment area. The calculation of both the required and available detention volume of ditches and swales also takes into account, as before, the thickness and pore content of the underlying plant bed and the hydraulic conductivity of the surrounding soil, the area of ​​the ditch for direct precipitation on the surface, side slope and ditch length. It is also possible to see the effect of any specified raised well in the ditch/swale on the flow detention, and now also taking into account the longitudinal slope.

This is described in more detail and visualized in the following article:

Larm T., Wahlsten A. Nordgren M. and Kjellin J. (2024). Optimized design of biofilters and swales/ditches for flow detention and treatment. Tidskriften Vatten (In Swedish).

Dimensioning and calculation of flood volumes and increased flows at a longer (secondary) return time

For areas with a risk of flooding and risk of damage to the infrastructure in cases of impounded flows on the ground and in basements, etc., the flow detention volume is calculated for a rain with a longer return time (e.g. 10, 20. 30, 50 or 100 years) than the return time for which the detention facility is dimensioned (e.g. 2, 5 or 10 years). This volume minus the detention volume at a shorter design return time gives the flood volume at a longer return time. This is done in StormTac Web by entering a so-called secondary (longer) return time in the Design flow box, whereby the results are presented in the report.

Calculation of the flood volume and the increased extra flow that occurs at most during the flood (in addition to the flows for which the facility is dimensioned) is done in StormTac Web, both for an individual flow detention facility via the Flow detention box and in the facility boxes wet pond and biofilter, including for series-connected facilities.

Updated method for calculating acceptable pollutant load to the recipient

To meet the environmental quality standards (EQS), i.e., the goals of good status in surface waters, urban stormwater management must be designed with considerations given to the required pollutant treatment removals needed to protect the receiving waters according to the Water Framework Directive. The recipient model in StormTac Web calculates the annual pollutant load (kg/year) that can be transported to the recipient without exceeding the set criteria concentrations, i.e., the acceptable load (kg/year). The acceptable load (L_acc) of the watershed area (kg/year) represents which pollutant load (kg/year) can be allowed to come from the catchment area without exceeding EQS.

We have now updated the method for calculating L_acc with a higher accuracy even when there is no measured concentration in the surface water.

When there is measurement data, the same result is obtained as before when the model calculated L_acc from criteria pollutant concentrations and measured concentrations in the recipient’s water mass, together with calibrated pollutant load on the recipient. By now instead directly calculating L_acc from the criteria concentration (C_cr) and calculated outflow (Q_out) from the recipient, the same result is obtained as before when using measurement data. However, a different result is obtained when there is no measurement data from the recipient. The same equation is now used for both cases.

It can be said that L_acc does not vary directly (but indirectly) with changed pollutant load on the recipient (L_in), but it varies with changed outflow (Q_out) and thus inflow. Increased exploitation, which normally results in increased impermeable areas in the catchment area and increased annual flows, thus results in increased L_acc. In other words, it is not directly measured recipient concentration and calculated pollutant load per se that affect L_acc. The fact that increased flows result in increased L_acc is explained by the fact that the recipient’s retention time is decreased, which provides a greater opportunity to receive an increased pollutant load.

May 6, Requirements for Stormwater effluent concentration criteria with regard to EQS – webinar

VA-guiden is arranging a webinar in collaboration with StormTac AB and Länsstyrelsen Stockholm on the importance of a recipient perspective in action planning for stormwater treatment. The webinar will highlight why the recipient needs to be considered in detailed planning to enable compliance with the EQS, what requirements can be set in a detailed planning process, and the importance of the right action in the right place.

The webinar will highlight Länsstyrelsen Stockholm role in the planning process, including their assessments of the impact of a detailed plan and its compatibility with current environmental quality standards (EQS). Anna Wahlsten and Maria Nordgren from StormTac AB will present a methodology for designing requirements with the recipient in focus and how a strategic action plan within the catchment area can be developed.

⏳ The last day to register is May 2, 2025.

More information: https://lnkd.in/dvdUq-dV

Export with consideration of upstream flow detention – new automation with improved functions

The developed export function now facilitates the export of upstream sub-catchments, including flow detention to downstream areas. This capability supports designs that consider upstream flow detention and enables the simulation of sequential sub-catchment detention facilities.

This development allows for the evaluation of interactions between detention volumes across various rainfall durations and the optimization of design outflows for both upstream and downstream facilities. In some cases, this can significantly impact the efficiency of these facilities.

Transport time, calculated for the flow path between the upstream and the downstream facility, is a new parameter implemented to refine accuracy in calculation of downstream flow detention volume when considering upstream flow detention. The transport time determines how the upstream flow impacts the downstream facility for different rainfall durations. It is also used to calculate the longest flow path within the composite catchment area, relevant for longer durations where flow detention does not occur upstream.
The results will indicate when upstream detention effectively influences downstream areas and when it does not. This optimization considers varying runoff times within sub-watersheds, transport times between upstream and downstream facilities, and outflows, in line with the methodologies of Giudice et al. (2014) and Ngo et al. (2016).

Treatment Guidelines for stormwater with regard to EQS

Guidelines for stormwater treatment is a complex subject. A lot of time is spent responding to statements and revising documents due to projects’ impact on the recipient and Environmental Quality Standards (EQS) not having been successfully evaluated. To avoid this and to provide supervisory authorities with the necessary tools, which are not facilitated by general benchmarks for stormwater discharge, it is crucial to use a method based on the recipient to assess compliance with EQS.

StormTac has lengthy involvement in developing a requirement framework for compliance with EQS from a recipient perspective that is reasonable and straightforward to use for municipalities, consultants, and regulatory authorities. The foundation of this work is recipient modeling, which can be used both for setting requirements in detailed planning and for strategic action planning in a catchment area. This work has been carried out in collaboration with county administrative boards and Havs- och Vattenmyndigheten, where the developed methodology is anchored and agreed to provide the essential information and tools for regulatory work.
So far, we have initiated the process of developing guidelines for stormwater treatment with an EQS- and recipient perspective together with Järfälla Municipality, VA SYD, Roslagsvatten, and Kungsbacka Municipality amongst others.

Contact us for a meeting via info@stormtac.com, and we can discuss how we can help your municipality move forward.

Looking forward to hearing from you!

New facility type in the basin box: underground permeable macadam basin

The basin box has been completed with a choice of specifying hydraulic conductivity k6, where k6=0 is the default and indicates the previous macadam basin with a tight bottom. The equation for calculating the exfiltration flow rate is given in the guide. The result for the new permeable bottom facility type is less required flow detention volume with increased permeability (k6 value).

New Publication! Optimized design of biofilters and swales/ditches for flow detention and treatment

New Publication! In the latest issue of “Tidskriften VATTEN”, Thomas Larm, Anna Wahlsten and Maria Nordgren from StormTac have together with Johan Kjellin from Tyréns written the publication: “Optimized design of biofilters and swales/ditches for flow detention and treatment” (In Swedish).
 
Current climate changes and urbanization increase the pollutant transport to the recipients as well as the risk of floodings. New stormwater solutions or optimized designs for existing measures are needed to achieve both effective treatment and flow detention. 
 
Studies of biofilters often focus on treatment, but their flow detention ability is rarely studied. This study presents an optimized design of biofilters and swales, which provides both good treatment and flow detention during heavy flows. The height of the drain inlet is adapted to required flow detention and/or treatment, and the drain inlet connects both to the drain sewer and the outlet.
The results showed that the new biofilter design can have similar or even higher capacity for flow detention compared to dry and wet ponds for the same stormwater facility area. The facility-specific parameters with the greatest impact on the required detention volume for biofilter were (in desending order): 1) Height of the well (drain inlet) above the plant bed; 2) Subsoil hydraulic conductivity and 3) Height of the flow detention volume.

Read more in the latest publication of “Tidskriften Vatten nr 1 2024”
Link: Tidskriften Vatten nr 1 2024

New publication on the impact of the runoff coefficient on rain duration and intensity

New publication on the impact of the runoff coefficient on rain duration and intensity

In the latest issue of “Tidskriften VATTEN”, Thomas Larm and Anna Wahlsten from StormTac have together with Tyréns and Luleå tehnical University written the publication: “Effects of green areas and design rains on runoff coefficients for design of stormwater facilities”.

The publication contains information and recommendations regarding how to calculate adapted runoff coefficients for calculated design flows and required detention volume, which are not static according to tables in P110 but are adapted according to the following factors:

– Design rain duration, which affects the degree of soil saturation and the infiltration, and thus the runoff coefficient to be used in the calculations.
– Design rain intensity for design rain duration, where higher intensity gives a higher runoff coefficient.

Proposed functions and reported diagrams can be used to obtain a more adapted runoff coefficient for your calculations, which can be manually entered as new input data in the model until further notice, but which we will implement in the model as an option.

The publication also shows how various factors, such as climate factors and the effect of green areas, affect the dsign flow and the required detention volume. This can provide increased understanding of how sensitive different factors are in the calculations so you know which are the most important to investigate more closely and how much they can affect the results.

Read more in the latest publication of “Tidskriften Vatten nr 4 2023” Link: https://lnkd.in/d5wt8zFv

New function for import – From SCALGO Live to StormTac Web

New function for import – From SCALGO Live to StormTac Web

StormTac and Scalgo have started a collaboration with the aim of simplifying for our joint users.

It is now possible to import data regarding area per land use within a catchment area created in SCALGO Live to StormTac Web.

Improved calculation of sediment growth and maintenance frequency in wet ponds and underground basins

Improved calculation of sediment growth and maintenance frequency in wet ponds and underground basins

The calculations in StormTac Web now take into account facilities in series so that for each facility of the pond/wetland type, underground basin with filter cassette and underground sedimentation basin in the results report, you can see the sediment growth rate (mm/year) and number of years until sediment removal. The calculations also take into account other types of facilities in the series that are placed upstream and which increase the time for maintenance because they separate part of the sediments before they enter the facility downstream.

It is recommended that in each project with design of wet ponds, wetlands and underground basins with or without filter cassettes, see the maintenance frequency calculated for the current design of the facility and especially its bottom surface, which may result in increased size of the facility. It is not only the required treatment and flow detention that affect the dimensioning, but also the calculated maintenance frequency.