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.

Updated standard concentrations for the sum of PAH16 and…

Updated standard concentrations for the sum of PAH16 and individual PAHs, especially for rural areas

Updated values for standard concentrations for stormwater and base flow for PAH16 and respective individual PAHs for all rural types of land use such as woodland and meadows etc. and also for allotment area. Many values were previously stated as 0 in concentration for the individual PAHs, which have now been updated with estimated concentration data, which is lower than for other land uses, but this will give slightly higher estimated total concentrations and loads than before if these land uses are used.

The updated concentration data are marked in the database and implemented for new projects that are started as from 2019-05-27.

Calculation of acceptable concentration from development areas

Calculation of acceptable concentration from development areas

Based on calculated acceptable load (kg/year) and calculated flow, an acceptable concentration (µg/l) from the area is also calculated, which can also be used as a limit value. It is possible to check an outlet concentration after measures and compare with this limit value, which can give answers to whether the acceptable load is achieved for the area or if additional measures are needed.

This calculated acceptable concentration requires a recipient calculation, with input of area/land use in the recipient watershed area, and also inputs of area and volume of the receiving water, with advantage also measured concentration data from the receiving water body (see the guide).

Revised function for runoff from the land use surface…

Revised function for runoff from the land use surface water within the summed (sub)watershed areas

The revision effects the following calculated values:

– total concentration from summed (sub)watershed areas presented in the MR-report, where surface water is included as land use in one or more of the (sub)watershed areas, which before resulted in wrong values but now this is corrected.

– the runoff coefficient and the runoff (l/s) in areas that include the land use surface water.

The revision does not effect calculated concentrations and loads from each separately calculated area, even if surface water is included! The revision does not effect the results in the recipient model!

Automatical calculation of sewer inner diameter based on Qdim,…

Automatical calculation of sewer inner diameter based on Qdim, slope and material selection

Previously, in the box “Sewer” you needed to test different inner diameters to cope with the design flow.
A new function has been created which automatically calculates the inner diameter and gives a recommendation on pipe dimension.
This calculation can now be done in the box Sewer where a new section has been added.
Supplements have been made in report 2. Transport and flow detention.

New equation for designing required detention volume at heavily…

New equation for designing required detention volume at heavily throttled outlets

The rain intensity I was previously calculated with Dahlström’s equation (Dahlström, 2010) for all durations, but at extremely throttled outflows, it may be the question of durations that are 24 hours or longer before the required maximum detention volume is obtained.

For such long durations, from one to four days, the intensity is now calculated according to Dahlström (1979). This procedure is in accordance with P110 (Svenskt Vatten, 2016).

This results in lower intensity at design durations ≥ 24 hours than previous method gave, but the same as before in most cases (<24 hours). Before, the maximum required level of flow detention could not be achieved up to 4 days, but the new values for rain intensity (l/s/ha) mean that maximum volume can be achieved at lower outflows. This results in a lower detention volume being required than before at extremely throttled outlets where the design rain duration is ≥ 24 hours.

Automatical calculation of studied flow (l/s) from input share…

Automatical calculation of studied flow (l/s) from input share of the yearly runoff volume.

Before, different values of the studied flow were tested in the box Design flow until it resulted in a certain share of the yearly runoff volume. A new function has now been created which automatically calculates the flow for a given share. This is done by clicking on a symbol to the right of the Design flow box. In the form that is then opened, you fill in the share by which the flow is automatically calculated and will be entered in the model’s box Design flow.

Normally, the studied flow is set to include 90% (80-90%) of the yearly runoff volume.

New standard concentrations and revised min and max reduction…

New standard concentrations and revised min and max reduction efficiencies

– Reduced standard concentrations for phosphorus from Meadows and Woodland and meadows after comparing with other land uses.

– Revised min and max treatment effects of various types of treatment facilities for certain substances after an investigation of all values. The revisions are reported in the database.

These changes apply to new projects created from 2019-03-21. The changed values are also displayed in the updated database. You can enter the values for the standard phosphorus levels manually in existing projects.