Validation of rating curve
In the section about the fitting of rating curves the following fitting procedures of stage-discharge data is dealt with:
- single and compound channel rating curve
- rating curve with unsteady flow correction
- rating curve with backwater corrections using:
- constant fall, and
- normal fall.
The option <Validation of rating curve> covers the situation where a rating curve was developed previously and additional measurements become available. With hymosthe validity of the existing rating curve for the new measurements can be evaluated. A comparison of multiple rating curves is also possible in this function.
Analysis
The analysis starts with the selection of the stage-discharge measurements and the rating curve. In addition the number of data used for the fitting of the original rating curve and the standard error of the fit have to be entered for each water-level interval, in which the rating curve has been splitted, to allow statistical tests.
Validation can be done in various ways:
- examination of the goodness of fit from the stage-discharge plot
- examination of tabulated results:
- difference between observed and computed discharge
- time sequence of difference
- relative difference
- statistical test on fit.
hymoscarries out a Student t-test on differences between the rating curve and the new measurements.
Let the number of data used to determine the rating curve be N and the number of new data N~1~ and the percentage difference in both cases be denoted by respectively DQ and DQ~1~ then the test statistic t becomes:
with:
Application
Select the function <Validation of Rating Curve> from the Flow Measurements functions map. To execute the function, the following selections must be made.
Station Codes
Select a station by clicking the checkbox in the stations list. HYMOSwill extract all Stage-Discharge data for this station within the specified period from the database and place them in the spreadsheet on the form.
Graph
From the data in the spreadsheet a graph can be made by pressing the <Graph> button on the <Validation of Rating Curve> form. All water levels and discharges on dates with a 'flag' not equal to zero will be presented in the graph. In the graph window menu the user can select to view the data on a normal or logarithmic scale. To exit this graph window select <Close> from the <File> menu.
Rating Curve option
Select a Rating curve function by selecting the function in the list box. HYMOSwill now present all rating curves from the selected type for the selected station in the relations list box on the form.
Relations
Select an existing rating curve from the list box by clicking it with your mouse. The coefficients and characteristics of the rating curve will be presented in the relations spreadsheet.
When the option "Multiple rating curves" is selected, more than 1 rating curve can be selected.
After you made your selections press <Execute> and analyse the results as a graph, table and report. To show the graph on screen select <Graph> from the functions tab. To analyse the report press <Report> from the functions tab.
