StormTac model description (including required input data and costs)



StormTac is a storm water and recipient (receiving water) model. It is today, after over 10 years of operation and monthly updates, a fully functioning Excel application, using input data forms and a flowchart. However, it is being developed into a Web application during 2012.

The model is used both for water quantity and quality calculations within watersheds (catchment areas). It integrates processes of runoff, transport, recipient, treatment and flow detention.



This model description covers areas of implementation, unique properties, methods, required input data and license costs.


Water quantity

An increased urbanization and climate effects may cause an increasing number of floods. StormTac can calculate the capacity of the transport system (e.g. sewers and ditches) and required detention volumes for the design rain return time and rain duration, including the implementation of climate factors.



StormTac quantity calculations include:

- Calculation of design flows for different return times, including climate factors. The transport time is calculated so that not the whole watershed area is used for shorter rain durations.

- Design of storm water transport systems, e.g. sewers, ditches and channels.

- Calculation of the flow capacity of designed or existing transport systems.

- Design of storm water flow detention facilities, e.g. dry/wet ponds and detention basins.


Water quality

Metals and nutrients are examples of pollutants in storm water that may cause toxic and eutrophic effects in the receiving waters. StormTac is the tool that can help towards a more sustainable storm water management.

StormTac can be used as a simple-to-use forecast tool (and as such requiring little input data) for water quality and action plans for storm water and surface water, e.g. to be used within the EU water framework directive. It includes a large number (around 100) of substances.



StormTac quality calculations include:

- The quantification of yearly average water flows (yearly runoff volumes of storm water, base flow and groundwater), runoff flows during average rain events etc.



- The quantification of yearly average pollutant concentrations and loads in the discharge points and from different land uses.



- A possibility to compare measured concentration data to calculated values.

- Identification of the largest pollutant sources and discharge locations to a recipient, presenting loads from different land uses and as option even from different materials, such as copper roofs if these specific areas have been set up as input.

- Presentation of data from up to 150 sub watershed areas in each file, to be used in e.g. Action plans for storm water in a whole municipality or for different lake systems.





- Design of storm water treatment facilities (e.g. areas and volumes of wet ponds, filter strips, swales, ditches, constructed wetlands and underground filter basins) regarding used criteria for storm water concentrations in the discharges and/or allowable loads and surface water quality criteria.



- Calculation of treatment reduction efficiencies (% or in- and outlet concentrations and loads) for designed or existing facilities, for different shares of permanent pool area to reduced watershed area (area x runoff coefficient) or for different hares of permanent pool volume to average runoff volume. There are however other parameters that are included for a more site specific and more reliable calculation, such as the effects of inlet and outlet concentrations, the share of water vegetation, flow detention, hydraulic efficiency (length:width ratio etc.) and temperature. The parameters and methods are continuously being updated with more input data.



- Setting up water and mass balances for receiving waters (lakes, sea bays and water courses), including calculation of net internal loading from the sediments (kg/year) or net sedimentation load to the sediments (kg/year).


- Calculation of required treatment load (kg/year) to reach allowable (acceptable) loads (kg/year) to the receiving waters, considering water quality criteria in the receiving waters (ug/l).

- Calculation of the new concentration in the receiving water after reduced load after a designed treatment facility or after changed land use in the watershed area, e.g. after a planned residential area on an existing woodland area. Comparison to water quality criteria, presenting need for more treatment (larger facility, other kind of facility or more facilities in other sub watershed areas) or not.

- Calculation of costs for monitoring and facility (standard calculation and a specific calculation from user input of used materials, linked to the calculated design). Presentation of cost-benefit (facility cost per reduced yearly load)


Unique model properties

The unique properties of the model especially refer to the following:

- It is simple to use and consists of an overall system presentation from a flowchart of the entire watershed system (using clickable boxes and input forms in the flowchart). A changed input from the flowchart results in presented changed outputs within the flowchart (watershed system).

- It requires little input data and no manual (help notes are included in the file), however a short manual that let you begin quickly (“within one hour”) with the calculations is included.

- It integrates watershed and runoff properties with treatment/ detention facilities and impacts on receiving waters. All in one model.

- It includes databases with continuously updated precipitation data, runoff coefficients, concentration data and reduction efficiencies.

- It includes a fine specification of both urban and rural land uses (around 80 land uses, increasing with new updates) and a large set of nutrients and pollutants (around 100 pollutants, increasing with new updates)

See Home of the web page for further information.


Required input data

The model requires very little input data. Watershed area (ha) per land use (e.g. residential area, roads and woodland) is the only obligatory input data. The traffic intensity (vehicles/day) is needed if studying the loads from larger roads within the catchment area. The area and volume of the receiving water are needed for estimating allowable loads. If the sub model “Source model” is used then added input data are road length (m) and material areas (m2). The included databases help to make more accurate analyses by letting you change other input data such as precipitation (mm/month or mm/year), runoff coefficients and water depths or slopes of facilities.

The model parameters can be calibrated to measured data to ensure site specific conditions being considered. In such cases further input data consist of measured flow (l/s or m3/year), precipitation (mm/year), rain intensity (l/s/ha) and sampled concentration (mg/l or ug/l) in storm water, base flow and/or the receiving water.


Methods

The main methodology has been reviewed internationally through scientific papers and a doctoral thesis. The methods are described in more details in these and other model documents and publications, available for downloads from the web page.

The model has been developed to automate the calculations by using land use specific standard values. It is best suited for long-term predictions. Updated rain data are used for Sweden and a number of cities around the Word. Site specific yearly precipitation data and rain intensities can alternatively be a user input.

Runoff water flow is calculated from precipitation data and land use specific runoff coefficients and areas. Pollutant load rate (kg/year) is quantified from calculated flow and from standard concentrations.

The standard concentrations are estimated empirically from a large set of flow proportional field sampling data, which contributes to their general applicability. These are tabled as standard, minimum and maximum values (can be downloaded from the web page).

Base flow and also base flow concentrations and loads are calculated using specific coefficients (infiltration rates and coefficients for leakage/connection into ditches, lakes and storm water sewers) and standard concentrations for base flow (different for different land uses, from measured base flow concentrations). As is the case with standard concentrations and runoff coefficients for runoff the base flow coefficients and concentrations can also be changed by the user. These data have now been published, and can be downloaded.

StormTac includes a large amount of sub models and equations for the design of different storm water facilities. The user can choose between a relatively detailed and a quick, simple design. The resulted dimensions by using different methods and by changing parameter values can easily be reviewed and compared. Examples of included design parameters are runoff coefficients, land use areas, facility permanent water depth, water depth of detention volume, slope, rain depth, outflow, emptying time and reduction efficiency.

The design methods have been employed for a large number of case studies from pre studies to final detailed construction drawings.

Standard concentrations

The data can be downloaded and the corresponding file presents standard, minimum and maximum concentrations for different urban and rural land uses. The standard concentrations should only be used when the storm water from the studied land use is average high, however else values closer to the presented min- or max-values should be used. The background colors indicate the level of uncertainty, based on the number of data values and their uncertainties.

Observe that when using runoff coefficients and standard concentrations for runoff, only the runoff (storm water) part is calculated. In StormTac the base flow part is also calculated, see method description above and a separate table for base flow concentrations in the same data file.

Case studies

StormTac has been used for example in the following case studies, where * indicates that calibration or comparison to measured data has been performed: Nybohov*, Stockholm (residential); Essingeleden*, Stockholm (road); Sätra*, Stockholm (residential); Lake Flaten*, Salem (residential); Flemingsbergsviken*, Huddinge (mixed); Tyresö municipality (mixed); Upplands Väsby municipality* (mixed); Lake Edsviken and Lake Norrviken, Sollentuna (mixed), Lidingö municipality* (mixed); Karlstad municipality (mixed); Fittja, Botkyrka (residential); Reykjavik, Iceland (residential); Kaliningrad, Russia (road) and Lake Titicaca, Peru and Bolivia (mixed).

Calibration to measured data has also been performed for a large number of roads and treatment facilities.


System requirements and user information

- Microsoft Excel 2000 or later is required in recent model, however a web application is being developed and the web application will only require Internet.

- English is the model language of the recent Excel model, however it is possible to get a translation of words from English to Swedish and Norwegian. In the web application the user will also be able to choose Swedish as model language. Other languages can come in the future.

- The number format must be points and decimals in the model must be written in points.


Licence and update fees

The model may be ordered by filling in a request for a Licence agreement in the Contact form. The agreement will then be sent for signing before the model is delivered by a USB memory stick (no extra charge for delivery). This procedure will be changed after the release of the Web application. The contact form can also be used for questions about the model and its costs.

The fees below are reduced in order to finance the on going development of the Web application. They are valid if ordering during Jan.-Feb. 2012, and will after this period probably be increased. The Licence fee is planned to be further increased after the release of the Web application. An order before this release will give access to both the Web application and the Excel application, the later with a large set of extra data bases, sub models and other data.

Licence fee* (for 1-3 users): 40 000 SEK, 4 000 EUR, 6 000 USD.

Additional users (per extra user): 3 000 SEK, 300 EUR, 400 USD.

Yearly update fee** (voluntary): 10 % of the Licence fee.

*) Valid during Jan.-Feb. 2012. After signing a licence agreement you will receive an USB memory stick containing the model and other relevant files (e.g. manual, reports, presentation files and Excel data files). Free delivery. The fee will be reduced by 50% for researchers and students (valid for whole classes, no extra costs for additional users).

**) Yearly updates will include the delivery of the planned Web application and a minimum of 2 updates per year. After the release of the Web application, the model will continuously be updated from the web page, by logging in and as long as the update fee has been paid. When the update fee is paid, updates are valid for a year. Further payments give further yearly updates; if the update fee is not paid, no updates will be available. The model is being updated every month with new data and/or methods.