©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…

©2015 Aquatic Informatics Inc. 2

Shift Happens…

©2015 Aquatic Informatics Inc. 3

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…

©2015 Aquatic Informatics Inc. 4

“Best Practice”

Shift

Blends

Effective Stage

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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

©2015 Aquatic Informatics Inc. 6

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

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Water Supply Paper 2175 (1982)

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

Shifts and log-log plotting fully described

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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

©2015 Aquatic Informatics Inc. 9

In Practice…

e

©2015 Aquatic Informatics Inc. 10

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

©2015 Aquatic Informatics Inc. 11

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)

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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

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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

©2015 Aquatic Informatics Inc. 14

Family of Curves

Log-log scale

Rectilinear scale

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Type Curves

Rectilinear scale

Log-log scale

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

Start A

Curve A Curve B

Start B Effective B

0%

100%

In effect

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Curve transition

stage

discharge

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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

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Single point shift

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

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

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Curve transition

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The best of both worlds

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

©2015 Aquatic Informatics Inc. 24

Shift then blend…

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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