©2015 Aquatic Informatics Inc. 1 Shifting the Paradigm by Blending Best Practices Or: what to do when the shift hits the fan…

©2015 Aquatic Informatics Inc. 1

Shifting the Paradigm by Blending Best Practices

Or: what to do when the shift hits the fan…


Shift Happens…


Streamflow (discharge) is a highly influential environmental variable Our knowledge and understanding of discharge is made possible by the use of stage-discharge rating curves

Our knowledge and understanding of water in the environment is limited by rating curve ephemerality!

What to do when the shift hits the fan…


“Best Practice”

Shift

Blends

Effective Stage


Divergence in Standards of Practice

“Since 1941 United States abandoned standards established by the International Association of Scientific Hydrology and published two volumes; the work was sponsored by 11 Federal agencies and done by the American Geophysical Union under leadership of R.K. Linsley”

Kolupaila (1961)

Canada was not a participant in IASH


Water Supply Paper 888 (1943)

WSP 888 was adopted by Canada but not by the rest of the international community

Only rectilinear plots of ratings are shown – no mention of log-log plottingLots of discussion of cause of shift but little in the way of specific guidance in what to do


Water Supply Paper 2175 (1982)

WSP 2175 (1982) fully describes the current USGS methodology.

Shifts and log-log plotting fully described


In Theory…

Manning’s equation, where Area = f(H-e).

A generic rating equation where all relevant variables except for stage, collapse into either the coefficient or exponent and are assumed to be remain constant.

𝑄=1𝑛𝑆0.5( 𝑓 (𝐻−𝑒 )

𝑃𝑤)0.67

𝑓 (𝐻−𝑒)

𝑄=𝑐𝑜𝑒𝑓 𝑓 (𝐻−𝑒) 𝑒𝑥𝑝


In Practice…

e


Time Scales

• Abrupt (step)• E.g. Debris on control• Instantaneous effect on

channel conveyance

• Episodic (transient event) • E.g. Scour/fill• Stability event instability

‘new normal’

• Trending• E.g. Weed growth• Incremental growth/decay

Specific Discharge Curves

time


Problem Statement

How can I generate a continuous record of discharge when the control conditions are unstable?

A posteriori Use-case: the pre and post conditions are well constrained by gaugings (i.e. I can use inductive reasoning)A priori Use-case: there are too few gaugings to definitively identify the transition (i.e. I need to use abductive reasoning)


European Approach

Apply time-series corrections to the stage data to create an ‘effective stage’ input to the rating curve until such a time that a new, stable, regime is established.

True Stage

Effective Stage

Discharge (true stage)

Discharge (effective stage)

Field visits


Australasian approach

Maintain a history of curves and choose a curve that most closely represents the current conditions. Smoothly transition from one curve to the next.

• Family of curves • Curves of same shape that differ in stage offset

• Type curves• Curves of differing shape• May, or may not, converge at top end


Family of Curves

Log-log scale

Rectilinear scale


Type Curves

Rectilinear scale

Log-log scale


Blending (a.k.a. smoothing, phasing)

Start A

Curve A Curve B

Start B Effective B

0%

100%

In effect


Curve transition

stage

discharge


North American Approach

Shift the rating curve with up to 3 stages of departure and allow for either smooth or abrupt transitions between shifts.

Rectilinear scale

Log-log scale

Shift diagram


Single point shift


2-point (a.k.a. knee-bend) shift


3-point (a.k.a. truss) shift


Curve transition


The best of both worlds

New gauging ‘hints’ at the shape of a new curve


Shift then blend…


Shift then blend…

pathology Effective stage Blend Shift

Change in offset Drift correction Family of curves Single-point

Tail-wagging 2-point drift Type curves Knee-bend

Bulge 3-point drift Type curves Truss

Complete blow out blend blend blend

Questions & Answers

©2015 Aquatic Informatics Inc. 1 Shifting the Paradigm by Blending Best Practices Or: what to do when the shift hits the fan…

Documents

discharge rating curves

fan2015 aquatic informatics

use of rating curves

discharge implication

international collaboration

dynamic rating curves

use of stage

slope stage discharge