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2019 Breaking up with Lane - Rethinking equilibrium and stability in stream restoration



We explored the concepts of equilibrium and stability and their role in stream assessment and restoration. The Natural Equilibrium Paradigm—the idea that streams naturally strive towards an optimally stable form that balances flow and sediment transport—is the underlying premise of stream stability definitions that presume static channel morphology with no aggradation or degradation. It is also the foundational assumption of popular hierarchical stream assessment frameworks and natural channel design methods. After researching the history of Lane's Balance and the basis of equilibrium theory in fluvial geomorphology and then reviewing 70 years of scientific research that has come forth since since equilibrium theory was popularized in the 1940s, our conclusion is that this paradigm is contrary to prevailing scientific views of how most stream systems behave. The predominance and importance of stochasticity, disturbance, discontinuity, disequilibrium, dynamics, and resilience is increasingly emphasized in modern stream science. Restoration practitioners must follow suit. The continued insistence that streams naturally seek equilibrium, that aggradation and degradation are unnatural, and that stream stability and stream function depends on a static equilibrium channel form is an outdated paradigm. This talk explains the fall of the Natural Equilibrium Paradigm using an allegory about relationships.
This talk is a personal story about our relationship with Lane’s Balance. We think it sheds some
light on what we believe as a community, why there’s been so much turmoil in our field, and
maybe a little about what the future holds. I hope you like allegories.
We also want to have a little fun with you guys. Sometimes we get so busy and take ourselves
so seriously we forget we’re all just humans trying to do little something nice for the rivers we
This talk has more questions than answers, and we’ll consider it a success if we can simply get
you to stop for a few minutes to think about how the concepts of equilibrium and stability
shape your view of stream restoration.
We all know Lane’s balance. It’s the most iconic symbol in our field.
If you have a stream that’s in balance, and you change sediment or streamflow, or if you tweak
sediment size or slope, the balance shifts to predict how it will either aggrade or degrade.
It’s super intuitive, right?
Or is it?
It’s actually not at all that simple.
Emory Wilson Lane (1955)
Henry Joseph
Mackin (1948)
(1697) Grove Karl
(a.k.a. Captain
William Morris
Davis (1894)
Lots of French
(1700s 1800s)
 
Lane’s balance is named after Emory Lane, but his famous 1955 paper is pretty is really just a
plea to engineers telling them to pay attention to what these other guys had been saying.
* The idea of equilibrium in natural steams is most eloquently presented in Henry Mackin’s
1948 paper “Concept of the Graded Riverbut it traces back through William Davis, Grove
Gilbert (a.k.a. Captain Bold), and a bunch of French guys to an Italian from the 17th century
named Domenico Guglielmini.
Did you know that the graphic representation of Lane’s Balance doesn’t appear in anything
these guys wrote? It appeared mysteriously some time later.
One thing you get from reading the history of equilibrium is a feel for the theory’s limitations in
both time and space. Turns out that when they spoke of equilibrium, they were talking about a
pretty small set of the world’s rivers and a pretty narrow range of time scales.
Lane’s Balance applies only to graded streams. And by graded streams I mean
those that are not obviously DEgrading at the top of watersheds
And those that are not obviously Aggrading at the bottom
The zone in the middle (the zone of transport) is where you MIGHT find graded streams in
Million years
Billion years
 
Process domain
And the time scale is even more important.
Geomorphic equilibrium does not apply over the longest time scales like millions of years. In
those time spans erosion and deposition are overwhelmed by massive planet-scale processes
like climate change and uplifting.
And it doesn’t apply to human time scales like decades either, because these are too
sensitive to the natural fluctuation of state variables. Also, most changes are threshold-type
responses at this level.
The best way to think of this is that all the factors in Lane’s Equation are actually
highly variable functions. The relationship is only valid if you are analyzing it at a time
scale long enough to get an average over the full range of natural variability.
Like for stream discharge, you need to be looking at a time scale long enough to
include the full range of floods, droughts, and everything in between.
The equilibrium concept explains general trends over hundreds or thousands of years.
Million years
Billion years
Process domain
So, this is the zone where equilibrium might apply.
But even within this zone, it only applies to streams that flow through valleys of deformable
material, and where sediment discharge is continuous.
If geomorphologists have discovered anything in the 70 years since Mackin’s paper, it is that
there is a lot of discontinuity out there.
These realities further limit the range where equilibrium concepts can even begin to apply.
The main point is this: We almost always use Lane’s Balance to infer some sort of inherent
dynamic equilibrium in stream systems. But Lane’s Balance does not imply that at all! It
refers to a general morphological pattern exhibited by a narrow range of stream types over a
very limited time scale.
Stay in your lane, Lane!
I didn’t really know all that when Lane and I first met.
It was love at first site. I was infatuated.
She has that effect on everyone.
Lane’s Balance is intellectually seductive.
It suggests order. It suggests equilibrium. To many it implies stability, and to some, justice.
In other words, the symbol implies so much more than the limited theory it represents.
Natural Equilibrium Paradigm
Natural Equilibrium
Lane’s Balance exemplifies the Natural Equilibrium Paradigm — the idea that natural streams
are in equilibrium, and that equilibrium is what imparts natural form and function.
It implies that equilibrium and stability are inherent qualities of natural functioning stream
It implies that stream impairment is a disruption of balance and loss of stability.
And that when streams are knocked out of balance, they strive to re-establish it.
And it implies that when we impair a stream, we can fix it by helping it re-establish balance.
A convenient relationship
Powerful heuristic
Assessing function
Doing restoration
Understanding stability
Natural Equilibrium Paradigm
The idea of Natural Equilibrium is a comfortable and convenient way of thinking about rivers
and streams.
Let’s face it. Stream ecosystems are wickedly complex. It’s nice to have someone by your side
to help you make sense of it all.
The Natural Balance is a powerful heuristic. It is a convenient conceptual model.
But is it a good model or a bad model?
True models help us focus on what’s important. False models lead us astray.
Bad models, like bad relationships, can make us do things we later regret.
Let’s think about how the paradigm guides us through:
Understanding stability
Assessing function, and
Doing restoration
1. Thou shalt transport the streamflows and sediment of thy watershed.
2. Thou shalt maintain thy dimension, pattern, and profile.
3. Thou shalt not aggrade nor degrade.
(per Rosgen 1996)
Natural Equilibrium Paradigm
Stability. For us, it is not so much about how much, but what kind.
The definition I learned, and the one most frequently cited, states that in order for a stream to
be stable it must in the present climate—now, for the sake of argument, let’s ignore the fact
that the present climate is changing…
…In order to be stable, it (1) must transport the streamflows and sediment of its watershed
while (2) maintaining its dimension, pattern, and profile without (3) either aggrading or
This definition is founded explicitly on the premise that natural streams strive for equilibrium,
but we know that isn’t always true. In fact, at the time scales that matter, it is usually false.
When streams experience a change in conditions, like a flood or burst of sediment, they simply
respond. They don’t know that there is some statistically optimal form to strive towards.
In order to meet this definition, you would have to hold the needle on Lane’s Balance straight
down and fix both the sliders (since you aren’t allowed to aggrade, degrade, or change form).
So where does that leave us? There are zero degrees of freedom in this model. No room for
adaptation or resilience.
1. Thou shalt transport the streamflows and sediment of thy watershed.
2. Thou shalt maintain thy dimension, pattern, and profile.
3. Thou shalt not aggrade nor degrade.
Natural Equilibrium Paradigm
Pollock et al (2014)
Here’s a natural stream near my house.
I suppose it has to transport the water and sediment of its watershed, but it also retains a
healthy portion of each, so I don’t know about #1.
It regularly changes shape, so #2 is out.
And while I haven’t gone out and measured it, there is plenty of science that shows systems
like this are slowly aggrading. So much for #3.
And yet there is also good scientific evidence showing that streams like this persist for
thousands of years.
Would you call this system unstable simply because it retains water and sediment?
Or because it changes shape?
Or because it slowly aggrades?
Do you think this stream needs any help from us performing its natural functions?
These are the kinds of questions you start asking when you look outside the lens of the Natural
Equilibrium Paradigm and apply some good old-fashioned common sense.
1. Thou shalt transport the streamflows and sediment of thy watershed.
2. Thou shalt maintain thy dimension, pattern, and profile.
3. Thou shalt not aggrade nor degrade.
Natural Equilibrium Paradigm
Resistance Balance Resilience
Sigh. It’s been rough between me and Lane lately.
We’ve been wrestling over this stability definition a long time.
The concept of stability is important, but I really don’t think this definition captures it.
I think we may just be growing apart, me and Lane.
In the old days, we thought about stability mostly as a factor of resistance to erosion. (Are
the stream bed and banks strong enough to resist erosion?)
The first big paradigm shift got us thinking a lot more about equilibrium. (Is the stream in
balance with its incoming flow and sediment?)
And now we are realizing the importance of adaptability and resilience. (How does it deal
with disturbance and stress?)
Notice that the trend is increasing appreciation of stochasticity, dynamics, and disturbance—all
things we know are common and important in the natural world.
Natural Equilibrium Paradigm
“Higher” functions
Reference =
stable equilibrium channel Natural Equilibrium
Now let’s look at stream assessment.
If we assume that natural functioning streams ought to be in stable equilibrium,
then evaluating function is largely a matter of assessing channel stability.
This is the rationale underlying hierarchical frameworks like the stream functions pyramid.
The foundation of the pyramid is an assessment of channel stability using hydrological and
geomorphological parameters.
Models like this assume that “higherfunctions (like biogeochemical processes and all the
plant and animal communities in stream ecosystems) are a product of stability and can
mostly be inferred.
Natural Equilibrium Paradigm
Reference =
Natural stream
“Higher” functions
Natural Equilibrium
But the real issue is one of reference.
I have to think that if we are evaluating natural function, the proper reference is a natural
unimpaired stream, not a hypothetically stable one.
Natural Equilibrium Paradigm
Pollock et al (2014)
Natural Equilibrium
Tension has been building between Lane and me.
Here are two mountain meadow reaches that I study. I am sure that the one on the left is more
natural and less impaired. I think it is a better reference even though it is surely less in balance
than the E-channel on the right.
* But that’s because I’m looking at it outside the lens of the Natural Equilibrium Paradigm
implied by Lane’s Balance.
In fact, the better function in the natural stream on the left is a direct result of its disequilibrium
and dynamic form!
Disequilibrium is what drives the formation and maintenance of physical and biological diversity
The riparian and stream biota have evolved with, and are dependent upon, the complexity
and disturbance inherent to a naturally dynamic system.
The stream on the left is also more stable by virtue of its resilience and dynamic (not static)
Now, we could force that stream on the left into equilibrium and get it to behave more like the
one on the right, so that it conveys its flow and sediment in a properly efficient manner.
And the Natural Equilibrium Paradigm pretty much tells us we should!
But if we build that, they would leave! They being all the functions and the complexity and the
biota, that is.
And aren’t those the things we said we care about most?
Natural Equilibrium Paradigm
Natural Channel Design
The application of fluvial geomorphology to
create stable channels that do not aggrade or
degrade and that maximize stream functions
given site constraints (Harman and Starr 2011)
Natural Equilibrium
1. Thou shalt transport the streamflows and sediment of thy watershed.
2. Thou shalt maintain thy dimension, pattern, and profile.
3. Thou shalt not aggrade nor degrade.
Natural Channel Design is the application of fluvial geomorphology to create stable channels
that do not aggrade or degrade.
Again, the assumption is that streams are naturally stable by virtue of equilibrium. And that
functionality is a product of that stability. Therefore, to restore functions, we must attain
balance and stability.
In 1953, Leopold and Maddock said that all channel design is based on the premise that
natural channels tend toward equilibrium.
Well, there you have it.
66 years and still going strong.
Continuity equations,
roughness equations,
hydraulic models,
sediment functions…
Reference reach
Natural Equilibrium Paradigm
Goal =
stable equilibrium channel
  
The goal of natural channel design is a stable equilibrium channel, but there are two ways to get
In the analytical method, people derive design parameters using equations and models to
solve for equilibrium.
In the analog method, you get those parameters from a reference reach that you presume to
be stable.
Nobody ever does exclusively one method or the other, but there are definitely two different
And they really don’t get along with each other.
I wonder if all the turmoil and fighting isn’t more a sign of deeper insecurity about the whole
approach, rather than simple disagreement over methods.
Natural Equilibrium Paradigm
How it usually goes…
1. Thou shalt transport the streamflows and sediment of thy watershed.
2. Thou shalt maintain thy dimension, pattern, and profile.
3. Thou shalt not aggrade nor degrade.
Reality check.
Are we ever really confident we can nail sediment balance to build a stable static channel in
perfect equilibrium?
It sure doesn’t seem like it.
In almost all cases where I’ve seen Natural Channel Design applied, you also get a healthy dose
of bank hardening, grade control, and artificial structure.
I don’t blame people for doing this. If I was being graded by the three stability commandments,
I’d probably add some safety factors too!
Natural Equilibrium Paradigm
Standards for ecologically
successful river restoration
(Palmer et al 2005)
1. Guiding image of dynamic state
2. Ecosystems are improved
3. Resilience is increased
4. No lasting harm
5. Ecological assessment
NCD Goal = stable equilibrium channel
Ecological Goal = dynamic natural system →
How it usually goes…
I hate to be too hard on natural channel design and sediment balance, because I truly believe
these were the process-based restoration concepts of their day. But that day has come and
gone. Science has come a long way since the 1950s, and we need to get with the times.
For us, it is not about who’s name is on the approach or what you call it, it comes down to
whether the approach helps us succeed in ecological river restoration.
Does the goal of creating a static equilibrium channel go with the guiding image of a
dynamic state?
Does it improve ecosystems?
Does it increase resilience?
I’m afraid that stabilizing channels often does quite the opposite.
But, of course, I am peeking over the top of my Natural Equilibrium Paradigm glasses again.
Natural Equilibrium Paradigm
Standards for ecologically
successful river restoration
(Palmer et al 2005)
1. Guiding image of dynamic state
2. Ecosystems are improved
3. Resilience is increased
4. No lasting harm
5. Ecological assessment
Ecological Goal = dynamic natural system →
Goal: Natural
Goal: Specific function
or habitat type
Goal: Stabilization
(Gillilan et al 2005)
When Palmer et al published their ecological standards, practitioners responded by defining
these three categories: Restoration, Enhancement, and Control
The Natural Equilibrium Paradigm would have us view them as something of a sequence.
First order of business is to establish balance by stabilizing the system.
Then we can start enhancing it with habitat or other attractive features, incrementally
gaining more and more restoration as we go.
I guess it’s no wonder people became so comfortable using the term “restorationfor pretty
much any activity that manipulates a river.
But we see it differently. We see these as three different and often competing goals.
The road to ecological restoration does not necessarily pass through control and stabilization.
Oftentimes it goes in entirely the opposite direction.
We might gain benefits from controlling and enhancing rivers, but we shouldn’t expect a whole
lot of ecological success until we’re ready to embrace the guiding image of a dynamic natural
That time is now.
Natural Equilibrium Paradigm
Static channel form
and equilibrium are
not universal criteria
for stability
Stream functions are
not just the product
of stable equilibrium
Restoration is not just
creating stable
equilibrium channels
It’s time to let go of the Natural Equilibrium Paradigm.
It was nice and convenient thinking of streams as simple ordered systems that are either in or
out of balance. But when I really think about it, I know it isn’t true.
Static channel form and sediment balance are not universal criteria for stability
Stream functions are not simply a product of stable equilibrium
And restoration is not just creating stable channels.
It’s going to be lonely without Lane, but it’s time to move on.
We’re breaking up.
Natural Equilibrium Paradigm
To be continued…
Breaking up is never easy. But the sadness won’t last forever. We’ll be better off in the long
run. But more importantly, so will our streams.
And just in case you are wondering, Lane and I are still friends. We have nothing against Lane’s
Balance. We just have to stop pretending it means more than it does.
Disequilibrium is not unnatural.
It’s OK to be out of balance.
Embrace your dynamic self.
Beechie, TJ, D Sear, JD Olden, GR Pess, JM Buffington, H Moir, P Roni, MM Pollock. 2010. Process-
based principles for restoring river ecosystems. BioScience 60: 209222.
Burchsted, D, M Daniels, E Wohl. 2013. Introduction to the special issue on discontinuity of fluvial
systems. Geomorphology. 205: 1-4.
Buffington, JM, DR Montgomery. 2013. Geomorphic Classification of Rivers. In: Shroder, J, E Wohl (ed.)
Treatise on Geomorphology. Academic Press, San Diego CA, vol. 9. Fluvial Geomorphology: 730-767.
Cluer, B and C Thorne. 2013. A Stream Evolution Model Integrating Habitat and Ecosystem Benefits.
River Research and Applications. 30: 135154.
Dust, D, E Wohl, 2012. Expanded Lane’s Balance. Geomorphology 139-140: 109-121
Gilbert, GK. 1887. Report on the geology of the Henry Mountains. U.S. Geographical and Geological
Survey of the Rocky Mountain Region. U.S. Government Printing Office, Washington, D.C.
Gillilan, S. K. Boyd, T Hoitsma, M Kauffman. 2005. Challenges in developing and implementing ecological
standards for geomorphic river restoration projects: a practitioner’s response to Palmer et al.
(2005). Journal of Applied Ecology, 42, 223 227.
Harman, W, R Starr, M Carter, K Tweedy, M Clemmons, K Suggs, C Miller. 2012. A Function-Based
Framework for Stream Assessment and Restoration Projects. US Environmental Protection Agency,
Office of Wetlands, Oceans, and Watersheds. Washington DC. EPA 843-K-12-006.
Harman, W, R Starr. 2011. Natural Channel Design Review Checklist. US Fish and Wildlife Service,
Chesapeake Bay Field Office, Annapolis, MD and US Environmental Protection Agency, Office of
Wetlands, Oceans, and Watersheds, Wetlands Division. Washington, D.C. EPA 843-B-12-005
Leopold, LB, T Maddock. 1953. The Hydraulic Geometry of Stream Channels and Some Physiographic
Implications. U.S. Geological Survey Professional Paper No. 252.
Lane, EW, 1955. The importance of fluvial morphology in hydraulic engineering. American Society of Civil
Engineers Proceedings Separate 81 (745), 117.
Leopold LB, MG Wolman, JP Miller. 1964. Fluvial Processes in Geomorphology. WH Freeman and
Company, San Francisco, CA.
Mackin JH. 1948. Concept of the graded river. Bulletin of the Geological Society of America 59, 463512.
Palmer, MA, ES Bernhardt, JD Allan, PS Lake, G Alexander, S Brooks, J Carr, J, S Clayton, CN Dahn, J
Follstad Shah, DL Galat, S Gloss, P Goodwin, DD Hart, B Hassett, R Jenkinson, GM Kondolf, R Lave, JL
Meyer, TK O’Donnell, L Pagano, E Sudduth, E. 2005. Standards for ecologically successful river
restoration. Journal of Applied Ecology, 42, 208 217.
Pollock MM, TJ Beechie, JM Wheaton, CE Jordan, N Bouwes, N Weber, C Volk. 2014. Using beaver dams
to restore incised stream ecosystems. BioScience 64: 279290.
Polvi LE, Wohl E. 2012. The beaver meadow complex revisitedthe role of beavers in post-glacial
floodplain development. Earth Surface Processes and Landforms 37: 332346.
Polvi LE, Wohl E. 2013. Biotic drivers of stream planform: implications for understanding the past and
restoring the future. BioScience 63: 439452.
Rosgen, D. 1996. Applied River Morphology. Wildland Hydrology Books. Pagosa Springs, CO
Rosgen, D. 2006. Watershed Assessment of River Stability and Sediment Supply (WARSSS). Wildland
Hydrology Books. Fort Collins, CO
Skidmore, PB, FD Shields, MW Doyle, and DE Miller. 2001. Categorization of Approaches to Natural
Channel Design. In: Proceedings of the ASCE Wetlands Engineering and River Restoration
Conference, Reno, NV.
Wohl, E. 2014. Rivers in the Landscape. Wiley & Sons Ltd. West Sussex, UK.
Wohl, E., ND Beckman. 2013. Leaky rivers: Implications of the loss of longitudinal fluvial disconnectivity
in headwater streams. Geomorphology 205: 2735
Wohl, E, SN Lane, and AC Wilcox. 2015.The science and practice of river restoration, Water Resources
Research, 51.
Wohl E, PL Angermeier, B Bledsoe, GM Kondolf, L MacDonnell, DM Merritt, MA Palmer, NL Poff, D
Tarboton. 2005. River restoration. Water Resources Research 41: W10301.
ResearchGate has not been able to resolve any citations for this publication.
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provides insight into both the longer-term range of riv-erine forms and processes under a similar hydroclimatic regime and the underlying landscape template for resto-ration. Along the continuum of restoration from purely process-based modeling to restoring to a reference condi-tion, analysis of the historical range of variability of channel planform bridges these extremes by to reconstruct the past without requiring all biotic and physical processes and their interactions to be fully understood, a requirement that can be very difficult to meet in many systems. Biotic influences on stream planform Stream planform is typically characterized as a single-thread channel or as a multithread channel, with secondary channels that branch and rejoin downstream. Single-thread channels are further distinguished as straight or meandering on the basis of sinuosity, which is the ratio of a channel's length to its straight-line distance; a meandering channel has a sinuosity greater than 1.5. Multithread channels can be dif-ferentiated as braided channels, in which flow is separated by bars within a defined channel, or as anabranching channels, in which individual channels are separated by vegetated or otherwise stable bars and islands that are broad and long relative to the width of the channels and that divide flows at P rocess-based restoration of fluvial systems is intended
River restoration is one of the most prominent areas of applied water-resources science. From an initial focus on enhancing fish habitat or river appearance, primarily through structural modification of channel form, restoration has expanded to incorporate a wide variety of management activities designed to enhance river process and form. Restoration is conducted on headwater streams, large lowland rivers, and entire river networks in urban, agricultural, and less intensively human-altered environments. We critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration as a social process. We also examine challenges for scientific understanding in river restoration. These include: how physical complexity supports biogeochemical function, stream metabolism, and stream ecosystem productivity; characterizing response curves of different river components; understanding sediment dynamics; and increasing appreciation of the importance of incorporating climate change considerations and resiliency into restoration planning. Finally, we examine changes in river restoration within the past decade, such as increasing use of stream mitigation banking; development of new tools and technologies; different types of process-based restoration; growing recognition of the importance of biological-physical feedbacks in rivers; increasing expectations of water quality improvements from restoration; and more effective communication between practitioners and river scientists. This article is protected by copyright. All rights reserved.
Fluvial systems include natural and human-created barriers that modify local base level; as such, these discontinuities alter the longitudinal flux of water and sediment by storing, releasing, or changing the flow path of those materials. Even in the absence of distinct barriers, fluvial systems are typically discontinuous and patchy. The size of fluvial discontinuities ranges across scales from 100 m, such as riffles, to 104 m, such as lava dams or major landslides. The frequency of occurrence appears to be inversely related to size, with creation and failure of the small features, such as beaver dams, occurring on a time scale of 100 to 101 years and a frequency of occurrence at scales as low as 101 m. In contrast, larger scale discontinuities, such as lava dams, can last for time scales up to 105 years and have a frequency of occurrence of approximately 104 m. The heterogeneity generated by features is an essential part of river networks and should be considered as part of river management. Therefore, we suggest that “natural” dams are a useful analog for human dams when evaluating options for river restoration. This collection of papers on the studies of natural dams includes bedrock barriers, log jams and beaver dams. The collection also addresses the discontinuity generated by a floodplain — in the absence of an obvious barrier in the channel — and tools for evaluation of riverbed heterogeneity. It is completed with a study of impact of human dams on floodplain sedimentation. These papers will help geomorphologists and river managers understand the factors that control river heterogeneity across scales and around the world.
In 1955, Lane introduced the qualitative expression QwS α QsDs to relate water discharge (Qw), channel slope (S), sediment discharge or load (Qs), and a representative bed sediment size (Ds) for a river reach under dynamic equilibrium conditions. For over 50years, Lane's relation has provided a unique conceptual model useful to engineers, geomorphologists, and educators for visualizing and describing the concept of dynamic equilibrium in rivers. However, the ability of Lane's relation to describe river adjustments is inherently limited because the expression cannot account for the changes in cross-sectional, planform and bedform geometry that are typically associated with complex channel adjustments.By demonstrating that Qs is inversely proportional to the width-to-depth ratio (W/d), we expand Lane's relation to include the width-to-depth ratio as a cross-sectional geometry term: QwS α QsDs (W/d). We further demonstrate that the slope term (S) is proportional to the total change in elevation along a channel (∆z) and inversely proportional to sinuosity (P) and bedform amplitude (H¯a): S α ∆z/(PH¯a). The introduction of the width-to-depth ratio and expressing channel slope in terms of channel geometry expands the original Lane's relation to explicitly include measures of cross-sectional, planform and bedform geometry as additional degrees of freedom. This significantly broadens the usefulness of Lane's original relation as a conceptual model and allows the visualization of complex river responses that commonly involve adjustments to cross-sectional, planform, and/or bedform geometry.