Calculation Points

Overview

Calculation points (also known as Flood Estimation Points - FEPs) are locations where hydrological analyses, particularly flood estimation, can be conducted. These points can be created wherever you have access to FEH (Flood Estimation Handbook) catchment descriptor data. These descriptors may originate from loaded FEH catchment descriptors or NRFA (National River Flow Archive) gauge stations that come with associated catchment descriptors.

Calculation Points allow a full flood estimation workflow to be followed, including data review, ReFH2 and WINFAP analysis, hydrograph reconciliation, climate change analysis and export to simulations as a hydrograph library. 

What is a Calculation Point?

Also known as Flood Estimation Points (FEP) are central to Hydrology+. Each Calculation Point is a location on a river where hydrological analysis is to be undertaken, typically these points coincide with either a river gauging station or catchment descriptors purchased via FEH Online. Each Hydrology+ project can support many Calculation Points, allowing complex schematisation of catchments. Calculation Point data includes; FEH Catchment Descriptors, River Gauge Data, ReFH2 analysis, WINFAP analysis, climate change uplifts, hydrograph libraries.

If you have not used Calculation points previously, you may be interested in our Quick Start guide and Tutorial, which are ideal for first-time users. 

Using Calculation points

Before creating calculation points, you need to create a Hydrology+ project.  Each project can contain multiple Calculation Points, allowing detailed catchment schematisation.  Instructions on setting up projects are here.

Calculation points can be added to Hydrology+ projects for performing your hydrological analyses.  The hydrological estimation workflow consists the following steps:

1. Create a Calculation point from FEH catchment descriptors or NRFA gauge stations with associated catchment descriptors. 

2. The Catchment descriptor tab will be auto-populated. Edits can be made and comments added.  Alterations are tracked using version control.

3. The ReFH2 tab provides the option to perform a new analysis to estimate flood hydrographs - for this you will need ReFH2 installation on your machine, and access to a licence. You can also review analysis performed previously, even without an ReFH2 licence. 

4. The WINFAP tab provides the option to perform a new analysis to estimate peak flood flows - for this you will need WINFAP installation on your machine, and access to a licence. You can also review analysis performed previously, even without a WINFAP licence. 

5. The Hydrograph library tab allows you to create, reconcile and store hydrographs. Additional scaling can be applied, to account for climate change, for instance. These reconciled hydrographs can then be exported to use in 1D river and 2D simulations as a Hydrograph Library.

Creating Calculation points

A Calculation point can be created from an FEH catchment descriptor by selecting Create calculation point from the right-click menu. This option is available from both the Map view and FEH Tabular View.

A Calculation point can also be created from a NRFA Peak Flow gauge station that has FEH catchment descriptors associated with it. To do this, select Create calculation point from the gauge label or from the right-click menu.

A window will appear to provide a name, description and comments for the Calculation point. These can be edited later. Click OK and the Calculation point will be added to the Map view.   

NOTE: Basin Location is automatically set based on the hydrological basin in which the catchment lies, rather than the location of the calculation point alone. The basin location is used to specify climate change uplifts under the Hydrograph Library tab, where it can also be changed from default.

Viewing Calculation points

Calculation points can be displayed on the Map and listed in a table. Both views are available from the Hydrology+ tab. Click View calculation points to view the icons in the Map view and click Calculation point Tabular View to list the calculation points in a table.

To view the properties of a Calculation point: 

• From the map view, right-click on the Calculation point and select Calculation point properties.

• From the tabular view, right-click on the Calculation point and select View calculation point info. 

• From the tabular view, double-click on the Calculation point in the table.

Deleting Calculation points

To delete a Calculation point from a Hydrology+ project, on the Hydrology+ tab, ensure View calculation points is on. Right-click on the Calculation point in the Map view, and select Delete calculation point.

More information on Calculation Points can be found in the technical reference article.