Stage-Discharge Time Series - Calvert Island - Archived Version 1.0

Streamflow calculation; a component of the Kwakshua Watersheds Program

In natural streams it is not possible to continuously measure stream discharge, thus an indirect approach was used, where river height (stage) was continuously measured at a gauging station using a pressure transducer, with periodic manual measurements of discharge along the range of potential stages to develop a stage-discharge rating curve. Low flows were manually measured using the velocity-area method, with either a Swoffer Current Velocimeter or a Sontek Acoustic Doppler Velocimeter. Moderate to high flows (generally greater than 1cms) were measured using the salt dilution method, either manually (dry salt) and/or remotely (starting in the fall of 2015), using a fully automated system to release pre-defined volumes of salt solution at pre-defined water stages at an upstream location, with permanently installed electrical conductivity sensors located down-stream, one on either side of the stream to measure the salt wave passing through. Data are available in near real-time using the Hakai Telemetry Network (Floyd and Brunsting, 2015). A calibration factor, required for the salt dilution method, was manually calculated at a minimum twice per barrel refill of salt solution, once at the initial fill and the other with the remaining solution before re-fill.

All discharge measurements were assigned a relative uncertainty, based on fluctuations in the flow velocity profile (for area-velocity method), or based on the uncertainty in the volume of salt solution, the EC sensor resolution and the EC sensor calibration factor (for salt dilution method). Measurements with uncertainties higher than 20%, with noise or malfunctioning conductivity sensors, or with high uncertainties in stage monitoring were excluded from further analysis. The remaining discharge-stage measurements were plotted as a power-law equation (Q = Ce*(H-h0)^A) in excel, to analyze if there were clear outliers, to determine the approximate value of h0 and to determine if the data could be fitted on one curve, or if they would fit better on a low flow and high flow curve, separated by an 'inflection point'. After this, the rating curve equation was optimized using a non-linear least-squares fitting Python model (LMFit, 2015). A detailed description of these methods have been documented in the MSc thesis of Maartje Korver (2015). Finally, this discharge time-series was created using 5 minute average stage measurements. Extra caution must be taken when using calculated discharges greater than the highest measured discharge (noted in this file as 'Max measured discharge' ), because the extrapolation of a rating curve beyond a set of measurements is usually highly uncertain and can greatly over or under estimate discharge. THESE DATA are provided AS IS and will continuously improve as additional discharge measurements are taken. Users should re-check for periodic updates to the rating curves and subsequent discharge files. If errors are found please contact Bill.Floyd@viu.ca.

REFERENCES Floyd W, Brunsting R. 2015. Hydrology and Climate. Establishing a hydrological and meteorological observation network on an outer coast island of the coastal temperate rainforest. http://www.hakai.org/research/kwakshua-watershed-program/hydrology-and-climate
LMFit Development Team. 2015. Lmfit, Least-squares Minimization with Bounds and Constraints. http://lmfit.github.io/lmfit-py/, version 0.8.3. Korver MC. 2018. Uncertainty analysis of stage-discharge rating curves for seven rivers at Calvert Island, British Columbia, Canada.

The following paragraphs summarize the content of the different tabs of the stage-discharge time series calculation sheets.

METADATA Version number, version date and list of edits done to the spreadsheet. Contact info, location information, site description, general field methods, general data QC and analysis and watershed specific comments.

INSERT RATING CURVE EQUATION A rating curve is a power law equation relating water level (stage) to streamflow (discharge). The rating curve coefficients displayed in this tab were calculated in a separate file (not included here). If interested to view this file or to know more about rating curve calculation methods, please contact Bill Floyd (Bill.Floyd@viu.ca).

PLOT RATING CURVE A display of the rating curve and the discharge measurements used to create the rating curve.

DISCHARGE TIME SERIES 5 minute average stage measurements and discharge calculations for a full water year (Oct to Sep). Date and time - Start: date and start time of the 5 minute time span over which stage data, recorded every second, are averaged. Displayed in Pacific Standard Time. Date and time - End: date and end time of the 5 minute time span over which stage data, recorded every second, are averaged. Displayed in Pacific Standard Time. Stage SSNxxx 5 min Avg: 5 minute average stage in cm for watershed xxx. SSNxxx refers to the Hakai ID of the pressure transducer used for stage measurements. Stage SSNxxx QC label: Quality control label of the stage measurement. QC labels can be IP= Missing data, so stage was linearly interpolated, or C = erroneous data, corrected. Stage data was considered erroneous when accuracy limit: the volume of water in m3 that was discharged at a flow rate higher than the highest measured discharge. % of total discharge > accuracy limit: the percentage of total discharge that was discharged at a flow rate higher than the highest measured discharge. This shows the fraction of the calculated discharges that should be used with caution. % of time > accuracy limit: the percentage of time in which discharge was higher than the highest measured discharge. This shows the fraction of time in which the discharge calculations have a high uncertainty.

Access and Use

Licence: Appropriate credit must be given to Hakai Institute and the authors of the dataset.

Data and Resources

Dates

Metadata Created October 26, 2018, 22:48 (UTC)
Metadata Updated October 26, 2018, 22:48 (UTC)
Reference Date(s) 2015-11-29 (Creation)
2016-02-19 (Publication)
Frequency of Update
Metadata Date October 17, 2018, 22:30 (UTC)

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Additional Info

Field Value
Contact Email data@hakai.org
encoding utf8
metadata-language eng
progress completed
resource-type dataset
Responsible Party Hakai Institute (Point of Contact, Processor)