An illustration of an hydrometric savant.

Complex Rating Curves & the Hydrometric Savant

Imagine, for a minute, your stereotype of a person of learning; especially one with detailed knowledge in some specialized field of science. I expect the person filling your mind’s eye is not a ruddy-faced bloke with a substantial belly and a thick Queenslander accent wearing shorts and R.M.Williams boots.

Appearances are deceiving.

I first met Ray ‘Rainman’ Maynard in Nelson, New Zealand. At first, I could only understand every third word he said. That was only because every third word was ‘bloody’, his favorite adjective, adverb and expletive. I was able to, very gradually, tune my ear to his thick accent and discovered that what he talked about mostly was extreme rainfall and discharge events and the unique problems these events cause for the measurement and monitoring of water resources.

The next day we drove down the west coast to Greymouth and then across the Island to Christchurch. Ray’s remarks on the varying climates, hydrology, geology, and ecosystems that we were passing proved that he has both a keen eye and a deep understanding of the role that water plays in forming the landscape and the role that the landscape plays in the distribution of water.

During the following 2 days at the Ratings Workshop in Christchurch I learned a lot.

I take pride in being able to learn something new about hydrometry from every stream hydrographer I talk to but I am not accustomed to getting a schooling like I did from Ray.

His first presentation was on Australian Rating curves. Starting from the very first slide I noted that in Australia it looks like they use houses as control features. In Ray’s home town, Bundaberg, they get storms that dump a lot of water in a short period of time into channels that lack sufficient gradient to move water along efficiently. Bull sharks and salt water crocodiles are some of the objective hazards of flood gauging in Queensland. His extensive experience with extreme gauging combined with a very sharp mind has resulted in great insight into how ratings can and should be developed and managed.

His second presentation on Complex Rating Curves is based on more experience with managing ratings in unsteady flow conditions than anyone I have ever met before. I believe this presentation is just a scratch on the surface of Ray’s depth of knowledge of the subject but even at that it is a lot to absorb.

We really need to have a full workshop focused on this topic alone.

The steady flow assumption is never strictly true, all of the time, in any stream. For many streams the effect of unsteady flow is less than gauging uncertainty and/or invisible because of insufficient gaugings during unsteady flow conditions. Absence of evidence is not evidence of absence. The burden of proof is to demonstrate, by targeted stream gauging, that the effect of unsteady flow is insubstantial.

The world is a better place because of improved accuracy of extreme flow records made possible by Ray’s ability to combine a strong science foundation with solid practical experience and hard work. This is something that every stream hydrographer can, and should, aspire to.


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  • Tefaruk Haktanir
    Posted at 12:24 pm, April 27, 2016

    Unfortunately, I do not have time to read, or to browse through at least, those, apparently very helpful presentations or papers in those workshops. Personally, I always wondered about the rising or falling stage during the travel of the trolley suspension cart of the gaugers from one end of the stream to the other which may realistically happen at a serious flooding, and the resultant ambiguity of the final measurement of stage versus discharge, by the old conventional method, I mean. Otherwise, during a quiet day, which may have steady flow conditions, the stage and discharge are probabşy those of too low a discharge, and the extrapolation of the rating curve to rare flooding stage will not obviously reflect truth. I am a faculty member, busy with teaching three under-graduate and two post-graduate courses, all being different subjects indeed. Plus I have a couple of M.S. theses projects presently fulfilled. These cannot be true alibis, pretexts, but still, I do not have neither sufficent time nor desire for learning these new and valuable methods of stream-flow gauging. I wish I were more idealistic.

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