From H2Know-how Manual

Trending data with the the H2knOw-how chart page is one of the most commonly used and most powerful features in our tool set. Any timeseries or collection of timeseries data can be viewed through the chart page.

Using the Chart Page

Several of the main features of H2knOw-how charts are described below: GraphPage1.pdf

  1. Use drop down box to switch between all available locations within the active project
  2. Switch to Average Recurrence Interval (ARI) Analysis page
  3. Zoom controls for the graph (left to right):
    • (Default) Click-and-drag window zooming
    • Zoom out to larger x-axis range
    • Revert to previous zoom level
    • Pan across chart by click-and-drag
    • Zoom out to available data range
  4. Toggle the graph legend on and off
  5. Select dates for the beginning and end of the time range
  6. View all Inflow and Infiltration (I/I) events for sub-catchment if applicable (in separate window)
  7. Add a new I/I event for the selected gauge based on the dates in the current data range
  8. View all events in which an active threshold was breached if applicable (in separate window)
  9. Add an additional trend from another location within the active project to the existing graph
  10. Switch to scatter plot. This allows any two variables to be plotted and correlated against each other for further insight into the conditions at the monitoring location (e.g. depth vs velocity)
  11. Access raw data in tabular format (in separate window).
  12. Export data to a .pdf file
  13. Export data data to another location or applicable software
  14. Control which trends are visible at any given time on the graph. Valuable statistics for each selected trend are also given

Specialised Trending Tools

Scatter Plot

The scatter plot function can be accessed using the icon in any chart. Scatter plots are used to compare and correlate two variables against each other, such as in the example below for pipe depth vs flow velocity:


The scatter plot area is blank upon entry, and only creates a plot after available variables are chosen for the X and Y axes. This can be done simply using the drop-down boxes under the "Axis" column in the "Chart Summary" below the graph (As can be seen in the figure).

The legend of the plot, shown in the top left of the chart above, is used to indicate relative concentrations of data. Yellow circles represent a single data point while orange represents between 4-6 data points and black represents more than 10 points. This helps to visualise what data most affects the trend between the two variables.

ARI Analysis Tool

The Average Recurrence Interval (ARI) analysis and estimation tool can be found by selecting the "ARI Analysis" tab next to Time Series in the tab bar.


The ARI, for a selected rainfall event, is the average time period between which events of that magnitude or greater are expected.

For example, as in the first row of the image above, the event in which a 20-minute long rain event was measured would be expected to occur once every 6.89 years according to NIWA High Intensity Rainfall Design System (HIRDS) statistics. This would be known as a 6.89 year rain event. A different statistical method, TP108, finds this 20-minute rain event to be a 7.7 year event.

Calling a rain event a 2 year event, for example, does not imply that the chosen amount of rain in its specified time interval will occur just once every two years. It instead is statistically likely to occur just once on current data, but in any given 2 year period may occur more than once, or perhaps not at all.

The two rows in the "Summary" windows above represent two methods used for ARI Analysis:

This page can be expanded by clicking the icon in the "Details" column. This gives the results below.


The Depth-Duration-Frequency curve shown above is an example of rainfall depth for each time interval calculated for the selected event period, this can then be compared to the selected statistical model (HIRDS or TP108) for each ARI (2 yr, 5 yr through 100yr). All points on the graphs are available in tabulated format below the chart. The user can interact with the chart by using the scroll wheel on the mouse.

These tables can be interpreted easily. For example, the second row has an interval of 0.33, which is measured in hours and corresponds to 20 minutes. In a 20 minute period, the current event saw an average of 20.04mm. This compares to 18.05mm for a 5 year event or 21.24mm for a 10 year event. This is why the ARI value in this row shows a 7.7 year event, which falls in between the average rainfall in 5 year and 10 year events as expected.