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| Installation & Copyright | About the GREAT-ER model | Running GREAT-ER | Creating new catchments | Results & Interpretation | Miscellaneous | |
Running GREAT-ER
Start using GREAT-ER
Q: How can I start the GREAT-ER software?
Q: How can I start a GREAT-ER simulation?
Q: What are the essential steps to run and analyse a simulation with GREAT-ER?
Q: How can I shift between Expert and Easy-To-Use Mode? What are the differences between them?
Scenario
Q: What is a GREAT-ER Scenario?
Q: How can I create a new GREAT-ER scenario?
Q: How can I load an existing GREAT-ER scenario?
Substances
Q: How can I add a substance or modify a substance database?
Q: What is the meaning of the 7 cards of the Substance dialog?
Q: What information do I need on a substance to perform a simulation with GREAT-ER?
Q: How can I introduce input parameters as a distribution?
Q: To which classes of chemicals has GREAT-ER been applied?
Q: For which chemicals and applications is GREAT-ER not recommended?
Catchments
Q: What is a catchment?
Q: How can I edit and/or modify a catchment?
Q: How can I select a subset of a catchment?
Q: How can I unselect a sub-catchment?
Q: Why is it interesting to make some sub-catchments?
Q: What kind of analysis can I perform on a sub-catchment?
Q: How can I add files with monitoring data?
Q: How can I add shapefiles with monitoring points?
Q: How can I find a particular stretch of a catchment on the map on the basis of its ID?
Models
Q: How can I select a model? What is the best model for my simulation?
Q: What data are necessary for the chosen model? Where do I have to introduce these data?
Q: What is the meaning of the 4 cards of the model parameters dialog?
Q: How can I introduce input parameters as a distribution?
Q: How many simulations are necessary to obtain relevant results?
Q: What is duration of a simulation?
Simulations
Q: How can I run a simulation?
Q: How can I abort a simulation progress?
Analysis
Q: What kind of Analysis can I perform with GREAT-ER?
Q: How can I calculate percentiles of concentration?
Q: What are PECinitial and PECcatchment?
Q: How can I calculate PECinitial and PECcatchment?
Trouble shooting
Q: Where can I get information on GREAT-ER messages?
Q:Why PECcatchment weighted by flow increment is not calculated for some basins?
Q: How can I start the GREAT-ER software?
A: If you have created a shortcut during the installation procedure, start GREAT-ER using this icon. Another solution is to start ArcView, select the item Open Project from the menu File, browse through the directory tree to the directory of your GREAT-ER installation and open the great-er.apr.
Q: How can I start a GREAT-ER simulation?
A: The essential steps to run a simulation of GREAT-ER are presented as a tutorial (pages 2-38) in the GREAT-ER User Manual (1557 Kb). This guided tour through the main features of GREAT-ER takes about 30 minutes.
Q: What are the essential steps to run and analyse a simulation with GREAT-ER?
A: You have to create a new scenario, specifying a scenario name and a related directory, selecting a substance and a catchment and specifying number of Monte-Carlo Shots. The model complexity mode by default is mode 1. You can then run a simulation and display the results as spatial distribution or concentration profile. The model results can be analysed to calculate PECinitial and PECcatchment. More information is available as a tutorial (pages 2-38) in the GREAT-ER User Manual (1557 Kb).
Q: How can I shift between Expert and Easy-To-Use Mode? What are the differences between them?
A: GREAT-ER offers two modes for the user interface. You can shift from one to another selecting Expert Mode or Easy-To-Use Mode in the GREAT-ER menu. GREAT-ER starts by default in the easy-to-use mode. The expert mode gives access to ArcView/GIS operations and commands. We suggest to use the Easy-to-Use mode if you are not familiar with ArcView/GIS. This mode is sufficient for undertaking model simulations and viewing the basic results. This way, it is impossible to harm the system and/or underlying GREAT-ER data sets. Click here for further information on ArcView/GIS.
Q: What is a GREAT-ER Scenario?
A: A Scenario is the collection of data needed to perform a simulation with GREAT-ER. It consists of the following data: a title; the identity of a catchment (the catchment data themselves are not part of a scenario), the substance dataset; the attributes of the discharges sites; and, the model parameters. Scenarios can be saved for later use. More information is available in the Basic Concepts part (pages 6-20) of the GREAT-ER User Manual (1557 Kb).
Q: How can I create a new GREAT-ER scenario?
A: To create a new scenario, select New Scenario item from the GREAT-ER menu and follow the instructions. More information is available as a tutorial (pages 2-38) in the GREAT-ER User Manual (1557 Kb).
Q: How can I load an existing GREAT-ER scenario?
A: If at least one scenario is contained in the scenario database, you can open it using the Open Scenario item in the GREAT-ER menu. Moreover, you can also open a scenario using the Import item if a scenario was previously saved as an export file (.zip file).
Q: How can I add a substance or modify a substance database?
A: It is easy to add a substance or edit substance data. The substance database contains all the substance-specific information for any substances that have to be included: identification parameters (CAS No, etc.), physico-chemical properties, partitioning, degradation, sewage treatment removal, in-stream removal and market data, depending on what information are available. To add or edit a substance, select New Substance or Edit Substance items respectively in the Substance menu. A substance dialog is then open where you can introduce or modify substance-specific information. It is split in seven cards corresponding to the different categories of substance information.
Q: What is the meaning of the 7 cards of the Substance dialog?
A: The substance dialog is split in 7 categories presented as 7 different cards: (i) Identification: The identification card is the first one presented to the user upon entering the substance data. It is compulsory to give the substance a name and parameters that may ease identification. (ii) Sewage treatment removal: These data determine how much removal will occur during sewage treatment. (iii) In-stream removal: This card enables you to control the elimination processes within the river. (iv) Market data: these cards enable you to specify a general consumption value for the substance. (v) Physico-chemical and (vi) degradation properties. (vii) Partitioning: It presents the solid/water partition coefficient (Kd) of the substance. If entered here, will override any estimated values calculated from physico-chemical properties. The cards (v) to (vii) are used only in model complexity 2 and 3.
Q: What information do I need on a substance to perform a simulation with GREAT-ER?
A: Depending on the selected models, different parameters will be used to run a simulation. For simplest model (1), GREAT-ER requires fixed removal efficiency for the sewer and the sewage treatment (expressed as the fraction removed) and an aggregated first-order elimination rate of in-stream removal is required. For higher modes, more detailed information on physico-chemical properties, degradation, partitioning, sewage treatment removal, in-stream removal and market data is required.
Q: How can I introduce input parameters as a distribution?
A: All input parameters of the models can be introduced as a fixed value or as a distribution. You can click on the Distribution button on the left of the model parameter dialog and choose one of the following distributions: normal, lognormal or uniform. However, for technical reasons, market data cannot be introduced as a distribution.
Q: To which classes of chemicals has GREAT-ER been applied?
A: Various chemicals emitted from point sources can be simulated with GREAT-ER. For example, detergent ingredients, pharmaceuticals, phosphates, pesticides, dyes, caffeine, plasticizers, etc.; many other applications are still possible.
Q: For which chemicals and applications is GREAT-ER not recommended?
A: This should be evaluated on a case-by-case basis and on scientific judgement. The model is not specifically designed for compound such as inorganic nitrogen forms (ammonia, nitrite/nitrate) or metals.
Q: What is a catchment?
A: The catchment data mainly consist of spatial data sets. They contain different kind of information: digital river network, digital background maps, hydrological information for the river map, WWTP, sewer connection and discharge data.
Q: How can I edit and/or modify a catchment?
A: Catchment data are mostly not editable within the easy-to-use mode. You can only select a new catchment for the currently active scenario by selecting Select Catchment item in the Catchment menu. Nevertheless, several site-specific parameters can be changed using Edit Market Data and Edit Discharge-Site Data items from the Catchment menu. The mouse pointer style changes to identify a new mode and you have to click on the catchment map to choose the object to be edited. You can then add additional input into the treatment plant, customize the elimination-rate, the treated fraction of incoming sewage, etc. For more information, please read pages 19-20 of the GREAT-ER User Manual (1557 Kb).
Q: How can I select a subset of a catchment?
A: It is possible to focus on an area of interest by selecting a subset of the current catchment. The item Select Subcatchment of the Catchment menu enables the selection of a sub-catchment for a simulation. After selection, the mouse pointer will change its shape and you can then select the appropriate river stretches by clicking on it. The end of the selected river is then indicated on the map by a big red dot and the new simulation will then only work on all upstream stretches.
Q: How can I unselect a sub-catchment?
A: You can select the Unselect Subcatchment item in the Catchment menu to undo a former sub-catchment setting.
Q: Why is it interesting to make some sub-catchments?
A: This feature reduces the simulation time if only a smaller sub-catchment is of interest. It should be noted however, that not all the analysis functions will work on sub-catchment data.
Q: What kind of analysis can I perform on a sub-catchment?
A: It is possible to calculate percentiles of concentrations (Csim) and river profiles but PEC calculations are not available if a sub-catchment is selected.
Q: How can I add files with monitoring data?
To be completed
Q: How can I add shapefiles with monitoring points?
To be completed
Q: How can I find a particular stretch of a catchment on the map on the basis of its ID?
A: When you have selected a catchment, shift to expert mode (select the Expert mode item in the GREAT-ER menu). Select Query item in the Theme menu. You have then to double click on the field [Rivernet-id], click on =, double-click on the river ID and select New Set. The selected river is then colored in red on the map.
Q: How can I select a model? What is the best model for my simulation?
A: By default, all sub-models are set to the lowest complexity mode. You can open the selected model dialog by the selection of Select Model item in the Model menu. The current version of GREAT-ER comes with a model system covering three sub-models (sewer, treatment and river) presented as different cards of the dialog. There are three complexity modes for each of these sub-models:
- Complexity mode 1 allows GREAT-ER simulations with minimum chemical and environmental input parameters. No in-sewer removal is assumed to occur. Chemical elimination in WWTP is described by a lumped first order removal efficiency, which depends on the type of treatment. Chemical elimination in rivers is described by first-order in-stream removal, assuming a lumped first order rate coefficient.
- For the complexity mode 2, GREAT-ER simulations need more detailed WWTPs data, as well as more detailed chemical parameters. In-sewer removal is assumed to be a lumped first order percentage, and is taken directly from the chemical parameter set.
- Complexity mode 3 is similar to mode 2; only the river changes in complexity.
You need to select Impose default complexity mode to confirm the choice of your model mode.
Click here for more information on these models and parameters.
Q: What data are necessary for the chosen model? Where do I have to introduce these data?
A: The Select Model dialog in the Model menu allows selecting the complexity mode for the different models. Then, you have to check that all the input parameters are available for the simulation. For input parameters on substances, use Edit Substance in the Substance menu; for input parameters on environment and specific properties of sewer, waste water treatment and river models, use Edit Model Parameters in the Model menu. GREAT-ER aids users with a colour coding with the dialogs. Parameters colour-coded green are definitely not used by the current model selection, nevertheless it is possible to edit these parameters. Black colour-coded parameters might be used within the current model selection and if so these need to be specified. For higher complexity modes, the Default button can be used to assign pre-selected values to different parameters. If parameters are missing when you try to run the simulation, a dialog box will present them. For more information, try the tutorial.
Q: What is the meaning of the 4 cards of the model parameters dialog?
A: These are input parameters describing the conditions of the natural or engineered environment to be modelled.
Q: How can I introduce input parameters as a distribution?
A: Input parameters of a model can be introduced as a fixed value or as a distribution. You can click on the Distribution button on the left of the model parameter dialog and choose one of the following distributions: normal, lognormal or uniform. If no input parameters are entered as distribution, the GREAT-ER output will reflect the hydrological flow distribution only.
Q: How many simulations are necessary to obtain relevant results?
A: GREAT-ER is based on Monte Carlo routine to provide a stochastic approach. The number of Monte Carlo shots performed during a simulation has to be entered in the Model Selection dialog. The minimum number of shots recommended to obtain a stable simulation result is shown in the table below. You have to note that even with a high number of simulations, the results end will always vary slightly.
| Small catchement/simple | Large catchement/complex | |
| Csim mean | 500 | 2500 |
| Csim 90% | 2500 | 5000 |
Q: What is duration of a simulation?
A: This depends on size and complexity of the catchment but also of the performance of your PC (processor speed, memory, etc.). During simulation, a new window appears, displaying the progress of the simulation, and the total estimated duration.
Q: How can I run a simulation?
A: When you have created a scenario, selected substance, catchment data and the required model, you can start the simulation by selecting Start Simulation item in the Simulation menu.
Q: How can I abort a simulation progress?
A: If you just click on the simulation progress window, a dialog appears asking you if the simulation should be continued. The simulation will be aborted if you select No.
Q: What kind of Analysis can I perform with GREAT-ER?
A: After a model run has been completed, the Analysis menu provides various facilities for analyzing the results. Since the results are stored as lognormal frequency distribution, it is possible to calculate percentiles of concentrations for different river stretches or PEC (Predicted Environmental Concentration) values.
Q: How can I calculate percentiles of concentration?
A: GREAT-ER calculates a distribution of concentration for each stretch. The Calculate River Csim item of the Analysis menu enables users to calculate any percentile from this distribution. After specifying a percentile (between 0 and 100 percent) the values will be derived per stretch and a new field will be added to the result table. A new theme is displayed in the scenarios view with the same colouring as the used for mean values. For more details, read pages 49-50 of the GREAT-ER User Manual (1557 Kb).
Q: What are PECinitial and PECcatchment?
To be completed
Q: How can I calculate PECinitial and PECcatchment?
A: After a model run has been completed, select PECinitial or PECcatchment items in the Analysis menu to calculate PECinitial or PECcatchment respectively. The calculation of PEC values can be based on any of the previously derived percentile of the model results.
Q: Where can I get information on GREAT-ER messages?
A: The typographic conventions and the meaning of main messages (hints, warnings and errors) are summarized in the GREAT-ER User Manual (1557 Kb) at pages 55-65. If you have recurring technical problems or if you want to report bugs, please contact ECETOC.
Q: Why PECcatchment weighted by flow increment is not calculated for some basins?
A: This appears to be caused by memory limitations..