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Implementation of new HydroAcoustic technologies in a national hydrometric program : Water Survey of Canada's HydroAcoustic Technical Working Group (HATWG)

Andre Zimmerman has been looking into the development of best practices for salt dilution gauging.
These results were presented at the NASH symposium of the BC Branch CWRA conference Vancouver BC March 2013.



Gabe Sentlinger has been investigating methods for quantification of uncertainty of salt dilution gauging. These results were presented at the NASH symposium of the BC Branch CWRA conference Vancouver BC March 2013.
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C 14 Salt_Dilution_Uncertainty_Metadata_V0.3.ppt

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The BC Branch CWRA conducted a dilution gauging workshop on Mosquito Creek, North Vancouver in March 2013.
Here are my musings on the workshop.

Reflections on NASH Dilution Gauging Workshop – Mosquito Creek 2013-03-08 -by Stu Hamilton

The latent demand for training in dilution gauging methods is much higher than I would have expected. The workshop was capped at 30 students and at least 10 people had to be turned away in spite of very limited promotion of the workshop. The use of dilution gauging methods in BC is also much greater than I realized. Informal discussion amongst participants revealed that several hundreds of dilution gaugings are being done every year in BC.
I think my under-estimate of the use of the method can be blamed on my primary focus being on formal monitoring networks which are generally able to select monitoring locations favorable to area velocity methods. The private sector cannot constrain site selection to the same extent and is more likely to require measurements at locations that would be difficult to impossible to accurately gauge using area-velocity methods.
The primary purpose of the workshop was training and there was no attempt made to conflate that objective with a research objective of quantifying uncertainty. Having said that, consideration of the results of many replicate measurements provoke at least a qualitative assessment of the confidence that a practitioner can have in measurement results.
The program consisted of two area velocity measurements, (ADV and current meter); a constant rate injection measurement replicated with 3 different sensor technologies and processed both as a slug and a constant rate; two Rhodamine dye injections, over two different mixing lengths, measured with redundancy and replication using 2 different sensor technologies; and two salt injections measured over 7 different mixing lengths with redundancy and replication using 7 different technologies. The salt mixing length choices were intended to span the distance from too short (20 m) to too long (154 m) to be able to get an accurate result.
The take-home message that I took from these results is that a ‘best practices’ approach to hydrometric measurement matters. I would start by offering my distinction between standard operating procedures and best practices. Standard procedures describe ‘what’ you do, whereas best practices describe ‘how’ you do it.
An ad hoc group (Andre Zimmerman, Gabe Sentlinger, Robin Pike, Dan Moore and Dave Hutchinson) has been working at developing ‘best practices’ for salt dilution, the results of which were presented in the NASH session of the CWRA Branch Conference. The workshop provided training in these best practices and I think the benefit of the approach is evident in the results. The standard procedures these practices are based on are the Streamline articles published by Dan Moore and Hudson and Pike.
The salt dilution gaugings represented a wide range of hydrographer experience, field technology, mixing lengths and data processing solutions. In spite of all of these factors that influence variability the results were remarkably consistent, in close agreement with the ADV measurement, and probably within the range of predicted uncertainty (as per Gabe Sentlinger’s presentation on quantifying uncertainty in dilution gauging measurements).
The Rhodamine dye injections and constant rate injection have not had the same level of development and training in best practices and all were statistically different (2 SD) from the aggregate mean.
The Rhodamine dye measurements were made with a range of hydrographer experience under the supervision of a very experienced hydrographer. The field technology being used was of very good quality. In spite of these factors the range in results was extremely variable even though some of the replicate measurements were in close agreement with each other. This is almost a worst case scenario – measurements that are inaccurate but which replicate very well - creating a perception of good quality. The variance in results cannot be explained in terms of assumptions about complete mixing because the measurement sites were well within the mixing reach used for the salt dilution gauging.
Rhodamine dye measurements are, apparently, highly sensitive to ‘how’ the measurement is done. To be clear, this workshop was focused on training not on quantification of measurement error, and so these results should not be over-analyzed. However, some things cannot be ‘unseen’ and I, for one, will be skeptical of Rhodamine dye injection measurements until such a time as there is development and adoption of a best practices approach such as was taught for salt dilution at this workshop.
The workshop was sponsored by Hoskin Scientific ( and all of the conference organizers are to be commended for such a successful, well planned and very useful workshop. The presentations from the NASH session of the CWRA BC Branch conference can be found on the NASH wikispace: