How to estimate flows

Once you've defined or uploaded a catchment, click on the catchment outlet. Save the catchment if you haven't already.

From here you can estimate flows, and download the catchment boundary shapefile, edit the name or delete the catchment.

Advanced settings

As the use of data from all relevant local data gauges is recommended, local data is incorporated within every flow estimate as default. See Local Data Algorithm for further details. You can unselect 'include local data' under the advanced setting.

Use of lake adjustment is available in Scotland and is incorporated within every flow estimate as default. See Lake Adjustment for further details. You can unselect 'use lake adjustment' under the advanced setting.

We recommended you use the full available period of record for flow estimation. Some regulators have selected alternative periods of record to be made available to all Qube users for flow estimation in their country of jurisdiction. These can be selected under the advanced settings.

Flow Results

Once you've selected 'Estimate flows', Qube models the catchment and displays the flow results window, containing catchment summary statistics, flow duration curves, gauges, ROI stations and Time Series.

Read these notes if you are using a user-defined catchment.

Catchment summary statistics

Catchment summary statistics are displayed at the top of the tab. Runoff, used to derive annual mean flow, is for the full period of record or the specific alternative period of record if selected for the flow estimate.

Flow duration curves

The Flow duration curves (FDC) tab presents the FDCs chart, and a bar chart of the annual and monthly mean flows. Note that local data gauges are based upon the regulators selection for flow estimation in their country of jurisdiction.

FDC

The FDC chart can be saved as an image . Flow statistics and catchment descriptors can be exported as a csv or xml.

You can change the FDC chart y-axis (linear, log) and flow units (m³/s, % mean flow) via the settings .

Click on the relevant annual or month in bar chart below to display the associated FDC.

Up to two seasonal series can be added.

Annual and Monthly Mean Flow

Click on the relevant bar in bar chart to display the associated FDC above.

Gauges

The Gauges tab presents the local data gauges used within the estimate and any other nearby gauging stations or spot gauges. Selecting in the table, will highlight the gauged catchment on the map. You can also select to plot the gauged FDC on your catchment estimated FDC.

For the other gauges, this is filtered to gauged catchments within 10% of the estimated natural mean flow. You can increase this filter to up to 50%, which would present gauged catchments with a mean flow of between half and double your catchments mean flow.

Note - the gauges tab is not available if you select not to use local data.

ROI Stations

Presents the Region Of Influence gauging stations used within the flow estimate, their weight in the pool and the Q95 as % mean flow for reference.

Time Series

You can generate a Time Series for your catchment based upon the natural FDC. Click on the generate time series button.

A natural daily mean flow time series is generated and plotted. The time series can be exported to csv . Hoovering over the chart presents the date and corresponding daily mean flow.

Click, drag and release on the chart to zoom to a selected period. Double click on the chart to return to the full period.

Considerations for a user-defined catchment

Catchment boundaries are used within the flow estimation relative to impoundment catchments and local data gauge catchments. Therefore a warning to check your catchment boundary is displayed if you model a user-defined catchment using the Local Data Algorithm.

If the user-defined boundary is significantly different to a local data gauge catchment boundary, you should consider unselecting 'use local data' under the advanced settings for this catchment.