Stage-Discharge Time Series - Calvert Island - Archived Version 2.0
Stage-Discharge Time Series - Calvert Island - Archived Version 2.0
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). A 95% confidence interval was plotted around the rating curve following the methods described by Herschy, RW (1994). 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. Herschy RW. 1994. The analysis of uncertainties in the stage-discharge relation. Flow Meas. Instrum., Vol. 5 No. 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 <0 or when physically impossible jumps in stage data were recorded. Discharge calculated: calculated discharge, based on rating curve equation, in m3/s. Discharge measured: discharge as measured in the field in m3/s. Max discharge measured: The highest discharge measured up-to-date in m3/s. This is a rough indication for the accuracy level of the calculated discharge; if higher than the maximum discharge measured, the uncertainty of the calculation is high and should be used with caution. Discharge CI (95%) max: maximum possible calculated discharge value based on the 95% confidence interval around the rating curve. Discharge CI (95%) min: minimum possible calculated discharge value based on the 95% confidence interval around the rating curve. PLOT TIME SERIES Display of calculated discharge in m3/s over time, as well as the maximum measured discharge value (to visually show which calculated discharges plot above this line and should be used with caution) and the discharge measurements taken in this specific time period. STATISTICS Total discharge: the total volume of water in m3 discharged through the outlet of the watershed and time period specified in the spreadsheet. Total discharge > max measured Q: the volume of water in m3 that was discharged at a flow rate higher than the highest measured discharge. % of total discharge > max measured Q: 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 > max measured Q: 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. ACKNOWLEDGEMENTS We wish to thank everyone involved in the design, installation and maintenance of the automated salt dilution system. Without the discharge data obtained from this method, the rating curves would have had very high uncertainty at moderate to high flows, resulting in a poor quality discharge data set. Finalizing the data set required the help of many people and organizations. Hakai Energy Solutions (HES) provided innovative solutions to our power, infrastructure and programming needs for the automated salt dilution system and telemetry network. HES staff who assisted with installations and design include Jason Jackson, Parker Christensen, Darren Cashato, Michel Stigter, Andrew Sharroak and Dave Snow. Stewart Butler from Vancouver Island University (VIU) helped with field maintenance, installations and data processing; Shawn Hateley and Will McInnes from the Hakai Institute helped with IT support, installations and field maintenance. And finally there were many Hakai Institute field assistants that helped take manual discharge measurements, install infrastructure and weigh and carry salt into the watersheds, including Nelson Roberts, Grant Callagari, Lawren McNab, David Norwell, Midoli Bresch, Ben Millard-Martin, Carolyn Knapper, Ondine Pontier, Christian Standring, Libby Harmsworth, Chris Coxson and Kaia Bryce. And a final thanks to John Fraser and Robert Hudson who provided much fruitful discussion in developing automated discharge gauging systems over the past 10 years. Finally, we are grateful for the excellent care of the facility staff at Calvert Island.
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salt dilution method
Kwakshua Watersheds Program
Stage-discharge time series
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