Continuous Simulator

The Vflo™ Continuous Simulator extension provides a method for long-term runoff simulation and continuous water budget accounting of the hydrologic cycle. Continuous Simulator supports solution of rainfall input for long time periods, extending from days to years. Soil moisture accounting is tracked continuously in a single-layer soil subject to evapotranspiration, infiltration, and rainfall with wetting front redistribution. Potential evapotranspiration is input, then modified according to available rainfall and soil moisture in each model grid. Output includes instantaneous flow rate, average flow rate over time step, average depth of flow over drainage area upstream of watch point, and total cumulative depth upstream.

Up to four file types may be required: 1) a BOP file (*.bopx, *.bop) that contains representative Green and Ampt infiltration properties, soil depth, and watch points, 2) an evapotranspiration timeseries, either in the form of climatological values for an annual cycle, or a timeseries of values for a specific period, 3) precipitation input maps in ESRI ASCII grid, CSV, UF, or Level II and 4) a filter file (BAG file, *.bag), if precipitation input maps are not in the BOP file resolution. Note that abstraction values are not applied during Continuous simulations as they are considered specific to the event for which they are set.

Continuous Simulator is different from Desktop Vflo™ because the effects of soil moisture are tracked by the model, rather than input as degree of saturation before any particular event. Continuous Simulator establishes the soil model so that it is continuously updated based upon distributed rainfall and evapotranspiration rates, making the model response properly initialized for any event. Soil moisture is redistributed throughout the soil profile at the beginning of each day of rainfall data. The soil model, i.e., depth and porosity, affects the performance of the model and the timeseries of soil moisture.

This extension is especially useful for preparing and evaluating a model for real-time operational use, or for modeling complex dynamic systems involving aquifer recharge, spring flow, and distributed runoff. Continuous Simulator results may be evaluated to arrive at a set of model parameters that reproduces the effects of both infiltration rate excess and saturation excess runoff. Infiltration rate excess results when infiltration rate controls the runoff response. Saturation excess results when the soil layer becomes saturated and the runoff response depends mainly on accumulation of infiltrated rainfall. For each day of rainfall data, Continuous Simulator outputs a timeseries of the degree of saturation for each watch point. The timeseries may be evaluated to determine whether the model becomes saturated or dries out at appropriate times during the simulation period.

A Continuous Simulator license must be present in the Vflo™ directory in addition to a Desktop Vflo™ license in order to access Continuous Simulator functions within Vflo™. To order Continuous Simulator, contact Vieux & Associates, Inc.

Preparing to use Continuous Simulator

The most important step for using Vflo™ Continuous Simulator is to assemble a BOP file that contains representative Green and Ampt infiltration properties, soil depth, and potential evapotranspiration rates. For information on assembling a BOP file, see Overview: Building a Vflo™ model.

For information on developing infiltration parameter maps in GIS, see Tutorial: Formatting parameter maps in GIS.

For information on loading evapotranspiration, see Evapotranspiration, with special attention to the section Using Continuous Simulator to continuously track soil moisture.

For information on establishing watch points, see Watch points.

For information on file format requirements for precipitation files, see the New rainfall files section.

Running Continuous Simulator

1. First, check that a Continuous Simulator license is located in the Vflo™ directory.

If no license is present, Continuous functions will be inaccessible in the Vflo™ interface. If a license is present, then the Analysis | Continuous Vflo menu option will be accessible, as shown at right.

2. Open the previously prepared BOP file.

In Vflo™, select File | Open and open the desired BOP file (*.bop, *.bopx). Before running Continuous Simulator, make sure that representative infiltration and evapotranspiration parameters have been established for the model. In addition, check that watch points have been established for all locations for which data output is desired.

3. Open Continuous Simulator.

Within Vflo™, select Analysis │ Continuous Vflo as shown above. The Vflo Continuous wizard dialog window will appear.

4. Load rainfall to use with the continuous simulation by following the steps outlined in the load new rainfall files section of the Precipitation Overview page.

5. Select output options.

Select Allow Simultaneous Rainfall and Evapotranspiration, if desired.

Select the Output File location using the Browse button. In the Choose Output File window, browse to the desired directory, then enter the desired file name in the File name field. Click Open. In the Vflo Continuous window, enter the desired Output and Input Intervals in minutes.

If desired, select Output Distributed Flow in Directory and Browse to the directory location. In the Choose Output Directory window, browse to the desired directory. No file name should be entered in the File name field; rather, the File name field should show the directory address.

Operate the Input interval (min) and Output interval (min) spinners to control the resolution of the simulation and its output, specified in minutes.

Once an output directory and all other desired output options are selected, click Finish. A Progress window will indicate when output has been processed.

Viewing Continuous Simulator output

Continuous Simulator output will be in the form of two tab delimited text files (*.txt). The primary output file will be a timeseries with a header line, named and located as specified by the user (for detailed info on selecting the name and location of Continuous Simulator output files, see Step 7 above). Output will resemble the data below. This data is provided only to demonstrate the format of Continuous Simulator output; actual output will contain data specific to the BOP and rainfall files loaded. In this sample Continuous Simulator solution, two watch points were established, named Watch Point 1 and Watch Point 2. In the output text file, a header line describes the sequence of information for subsequent lines. The sequence is as follows:

1. Time

(in format: YYYY/MM/DD HH:MM:SS)

2. Instantaneous flow rate for the first watch point

(Watch Point 1-Inst Flow Rate)

3. Average flow rate over the selected timestep for the first watch point

(Watch Point 1- Avg Flow(cfs))

4. Average depth of flow over the drainage area upstream of the first watch point

(Watch Point 1-Depth(in.)(Area=322.492 mi^2))

5. Total cumulative depth over the drainage area upstream of the first watch point

(Watch Point 1-Total Depth(in)(Area=322.492 mi^2))

6. Instantaneous flow rate for the second watch point

(Watch Point 2-Inst Flow Rate)

7. Average flow rate over the selected timestep for the second watch point

(Watch Point 2- Avg Flow(cfs))

8. Average depth of flow over the drainage area upstream of the second watch point

(Watch Point 2-Depth(in.)(Area=123.673 mi^2))

9. Total cumulative depth over the drainage area upstream of the second watch point

(Watch Point 2-Total Depth(in)(Area=123.673 mi^2))

In addition, a saturation timeseries with percent saturation for each watch point will be output to the designated output directory. The saturation timeseries file name will be that of the primary output text file, with "_saturation" added to the end of the name. For example, if the output file name is "Continuous_output.txt", the saturation timeseries file name will be "Continuous_output_saturation.txt". The header of the saturation timeseries will resemble that of the example shown below, for a BOP file with two watch points established: Watch Point 1 and Watch Point 2.