Shift adjustment
Background
When the river bottom near the control section varies in time, shift adjustments on the water level series may be considered in the conversion of stages into discharges. For this the following procedure can be used:
1. Computation of shifts
2. Completion of shift series
3. Adjustment of original water level series with shift.
This Shift Adjustment function only calculates the shifts from the measured stage discharge data and the calculated and stored rating equation. The results of the function will be shifts on dates where stage discharge data are in the HYMOS database for the selected processing period. This time series with shift values can be stored in the database. The second step of the procedure must be performed with the Interpolation function , using the linear interpolation option. The third step of the procedure must be done with the Series Transformation function where the interpolated shift values are added to the original water level series.
Computation of shifts
The water level shift is computed from the power type rating curve as follows:
03 - Stage discharge^image002.gif!
Dh = hr - hm
where:
Qm = measured discharge
hm = measured water level
hr = rated water level for Qm
a,b,c = rating curve parameters
Dh = shift.
The shifts (in cm) can be stored as an equidistant series. To evaluate the significance of the shift a time series plot of the shift series is advised. The report of the shift function contains the results of the computations with the calculated shifts and the % difference of the measured and computed discharge.
Completion of shift series
Since the shift values from the stage-discharge measurements will contain many missing data when presented as an equidistant series, this series have first to be completed, e.g. by linear-interpolation between the shift values. The result of this Shift Adjustment function must first be saved to the database before it can be used in the interpolation function.
Adjustment of original water level series with shift
To create the water level series for the stage-discharge conversion the shift series is, after being converted to the right unit, replaced by the original water level series adjusted for shift:
hr (t) = hm (t) + Dh(t)
where:
hr (t) = rated water level series
hm (t) = original water level series
Dh(t) = interpolated shift series.
Adding two series can be done with the Series Transformation function.
Application
Select the function <Shift Adjustment> from the flow measurements function map. To execute the function the following selections must be made.
03 - Stage discharge^image003.gif!
Series Codes
Select a series by clicking the checkbox in the <Series codes> list, this series is the series with shift values. HYMOSwill extract all Stage-Discharge data for the station from this series together with the single rating curves within the specified period from the database. The rating curves are shown in the relations list box as information.
After this series selections press <Execute>. HYmoswill calculate the shifts and present 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. The computed shift values can be saved to the database by selecting the <Save> function.
The underneath text is an example of the report of the Shift Adjustment function.
SHIFT ADJUSTMENT COMPUTATION
BHIMA AT PARGAON
WATER YEAR 1996
RATED RATED FULL
NO. DATE GH Q GH Q SHIFT DIFF. REMARK
(M) (M3/SEC) (M) (M3/SEC.) (CM) %Q
1 16/ 6/96 508.35 53. 508.34 54. -1. -1.87
2 17/ 6/96 508.35 56. 508.36 54. 1. 4.01
4 18/ 6/96 508.30 48. 508.32 44. 2. 8.43
6 19/ 6/96 508.30 48. 508.32 44. 2. 8.61
8 21/ 6/96 509.05 252. 509.21 210. 16. 19.92
Notes:
- With the Shift Adjustment function only daily shift values can be computed.
- The function can only be used for single rating curves.
- When multiple stage discharge data are present for 1 day, only the first data value of that day is used in the function.
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