1. Hydraulics for Hydrographers Channel Dynamics and Shift Corrections
AQUARIUS Time-Series Software™
Aquatic Informatics Inc.

2. Concepts, terms and definitions Fluvial Processes Hydraulic Geometry
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Concepts, terms and definitions
Fluvial Processes
Hydraulic Geometry
EcoHydraulics
Shift Corrections
Manning’s equation can be used to show that shape of the stage-discharge equation is a function of stream form. In this unit, we learn about the forces that define stream form in natural channels.
Knowledge of how these forces work to change stream form provide a basis for predictions about the stability of the stage-discharge relation at any given station. These predictions can be used to evaluate the period of applicability of stage-discharge relations and to determine ‘realistic’ scenarios for the shifting from one curve to the next.
Hydraulic geometry relations are sensitive to the interaction between stream energy and stream substrate stability. As such, they are very useful indicators of fluvial process dynamics.

3. Mechanics of transport
Fluvial Processes
Mechanics of transport
Solution
Flotation
Suspension
Saltation
Traction
Streams continually wear down the land and transport sediments to the ocean.
The sediment load is a function of topographic relief, lithology of upstream slopes, climate, vegetation, and the nature of active processes.
The transport mechanisms of relevance to hydrographers are the ones that activate higher caliber sediments: suspension, saltation and traction. It is these processes that cause bed and/or bank scour and deposition events that result in changes to a stage-discharge relation.

4. Suspended Load
For a sediment particle to be held in suspension, the settling velocity must be less than or equal to the turbulent velocity
As discharge increases, the suspended load increases at a more rapid rate than the discharge.
The enhanced concentration is due to erosion of the drainage basin, not of scouring of the channel.

5. Revised Universal Soil Loss Equation
Where A = soil loss; R is rainfall erosivity; K is soil erodibility; LS is topography (length of slope and slope); P is a conservative practices factor; and C is a cover factor
Most sediment originates from the landscape
Understanding the landscape upstream of your gauge can help in interpreting Shift Corrections

6. Stoke’s Law for settling velocity of supended particles
Where: Vs is settling velocity; ρp is density of the particle; ρf is density of the fluid; g is gravity; r is radius of particle; and m is viscosity
Density and viscosity of water are nearly constant with respect to the other factors and density of rock particles typically varies between 2.6 to 3.3 the square of the radius of the particle is the most important variable.
It is the larger size particles that will drop out of suspension most quickly when the turbulent velocity decreases after a storm event.

7. Bed Load: Saltation and Traction
Saltation refers to low extended trajectories of sediment particles of particles with less mass than the tractive force.
Traction is the movement of larger particles by rolling or sliding
The concentration and average particle size decrease with distance above the bed. Composition of sediments in the streambed is related to the hydraulic shear stresses required to move particles. Very coarse or bedrock stream beds indicate that suspension is nearly 100 % efficient and that the residence of suspended particles is very limited.
The ‘storm’ of particles moving by saltation comes at the expense of fluid momentum. This cloud of particles acts as a brake on flow.
Active bed transport has an impact on bottom tracking for ADCP measurements that must be compensated by differential GPS positioning. The ‘braking’ effect of these sediments has an impact on the shape of the vertical velocity profile.
Stream reaches with active saltation and tractive transport are hostile environments for deployment of water monitoring sensors.

8. Sixth power law
The radius of the largest particle that can be set in motion by a given velocity is:
Where r is radius; k is a constant that includes gravity and grain density; and v is flow velocity
Therefore a small increase in velocity can have a large increase in the size of particle that can be moved
We can infer from the sixth power law that channel transforming events are going to occur when velocity is high. It is therefore because of the sixth power law that we can use the peak of a flood event to mark the transition from one curve to the next.

9. Hydraulic lift and the critical tractive force
The steep gradient of velocity near the stream bed lowers the pressure on the top of particles resulting in hydraulic lift
The column of water supported by a particle exerts as critical tractive force:
Where Ft is critical tractive force; r is density of water; g is gravity; d is depth of water; and s is the gradient of the stream
The critical tractive force is significant for moving smaller particles whereas the sixth power law is significant in moving larger particles.
Before particles can be set in motion both gravitational and cohesive forces must be overcome. Cohesion becomes more important for smaller particles such as clays and silts. This causes a wide spread between the erosional and the depostional velocities for small particles

10. Erosion, transport and deposition
Fine sands are in the range of 0.063mm to 0.2 mm
Medium sands are in the range of 0.2 mm to 0.63 mm and
Coarse sands are in the range of 0.63 mm to 2.0mm
Gravels are in the range from 2 mm to 64 mm
This relation can be used as a rough guide to determine the range of discharge needed to transport bed material though the control section and either result in scour on the rising limb of the hydrograph or deposition on the falling limb of the hydrograph.

11. Fluvial Landforms
Very large scale features of a stream can be relevant to the stability of a rating curve. This is because the river is a self-organizing system to convey runoff and sediments from the divide to the channel mouth.
The stream form undergoes constant maintenance to ensure equilibrium with the work to be done. The potential energy of a mass of water at the divide is converted to kinetic energy that can move sediments. Sediment transport mostly occurs near the stream bed, at slower velocities that the water in the column above. For this reason a flood wave will pass through a given stream reach much faster than a pulse of sediment will. When a pulse of sediment passes through a stream reach it can be identified as an episode of measurements plotting to the left of the curve as transportation events deposit sediments on the control. If a curve has been established while a pulse of sediment is in the channel there will eventually be an episode where measurements plot to the right of the curve as transportation events remove sediments from the control.

12. Dynamic equilibrium
The hypsometric integral is the ratio of the area above the hypsometric curve to the total area. Hypsometric integrals are considered stable in the range from 0.35 to 0.6.
A low hypsometric integral implies that the basin form is stable with respect to the pattern of stream channels and channel slopes.

13. Hydraulic Geometry

14. Hydraulic Geometry
Channels with resistant bank-forming material such as cohesive silts have large values for ‘f’ and low values for ‘b’
Whereas channels with weak bank forming material such as sand have low values for ‘f’ and high values for ‘b’
The relation between width depth and velocity in natural alluvial channels conform to the Least Action Principle (LAP) as the channel self-adjusts to achieve a state of Maximum Flow Efficiency (MFE). MFE is defined as the maximum sediment transporting capacity per unit of available stream power.
Whereas there are a large number of possible channel sections that can satisfy flow continuity, resistance and sediment transport; only a single channel section will be in stable equilibrium (non-erodible and non-depositional) and also minimize potential energy.

15. Hydraulic geometry
Note the highest measurement on this plot of hydraulic geometry.
The width is higher than predicted and the velocity is lower than predicted.
What might this be telling you about that measurement?
How can this information inform how you draw the rating curve?

16. Hydraulic Geometry
Note the patterns in this plot of residuals of the hydraulic geometry relations against time.
What could these patterns mean with respect to the stability of the hydraulic conditions at this station?
How could you use this information when preparing or evaluating a stage-discharge curve?

17. Beavers Vegetation =leaky weirs Biofilms Submergent Emergent
EcoHydraulics
Beavers
=leaky weirs
Vegetation
Biofilms
Submergent
Emergent
Riparian and LWD

18. Stage data are more indicative of reach storage than of discharge
EcoHydraulics
Stage data are more indicative of reach storage than of discharge
Beavers regulate flow to control water table (e.g. To expand riparian zone) or to regulate water level (e.g. For protection of lodge entrance from predators)

19. Simplistic Hydraulic solutions are invalid
Beaver Dams
Simplistic Hydraulic solutions are invalid
Hydrologic solutions include:
Estimation of flow from representative gauged basins (e.g. using Empirical modeling toolbox)
Interpolation between measurements with adjustments for runoff processes (e.g. using Data Correction Toolbox)
Use of rainfall-runoff modeling (e.g. using custom toolboxes)

20. River ice
The effects of river ice are discussed in the lesson “River Ice Processes and Dynamics”

21. Biofilms
Biofilms are thin layers of algae that form under favourable conditions
They are ‘slippery’ - affecting the coefficient in the rating equation - use a time-based to the right.
If thick enough - the dominant effect may be on PZH, which can be temporarily be handled with a time-based shift to the left.
Note: Rock Snot (Didymosphenia geminata) is transferred from watershed to watershed on waders – clean your waders between measurements if you don’t want to be responsible for its spread

22. Submergent Lotic Vegetation
Vegetation that does not break the water surface affects both the PZH and the Head- Area relation
Note that the effect varies with stage – because high velocities flatten the weeds. At low velocities the weeds have a greater effect on PZH and the Head-Area relation.
Use a time-based knee-bend shift to the left

23. Emergent Lentic Vegetation
In addition to all the effects of submergent vegetation – Emergent vegetation (e.g. lily pads) affect the wetted perimeter -fundamentally altering the Hydraulic Radius upon which the rating curve is based.
Use a time-based, truss shift to the left.
Knowing the timing of emergence is crucial.

24. Riparian vegetation - overhanging
Riparian vegetation competes for sunlight in forests by growing out over the stream channel
Overhanging vegetation may only come in contact with the water during high flows
Overhanging vegetation affects wetted perimeter, and will result in an abrupt stage change at time of contact
Use an upside down knee-bend shift to the left

25. Riparian Vegetation – floating LWD
Sweepers alter the wetted perimeter, PZH, and the Head-Area relation.
Use a time-based shift correction – because they are floating - the effect is more or less uniform with respect to stage.
If the sweeper is nasty – full of green branches etc. –it may not be possible to accurately estimate discharge using simplistic hydraulic assumptions in which case hydrologic methods may be required

26. Riparian Vegetation – spanning LWD
High water – critical flow
Log spanning streambanks
Abstraction and obstruction of flow
Normal rating curve
Stream bed
Use a combination of the base rating curve at low-water, hydrologic (coefficient and exponent are unrelated to base rating curve) estimation from first contact to submergence of the log and a new rating curve at high water

27. Other types of channel dynamics
Variable backwater
Estuaries
Confluences
Anthropogenic effects - Shopping carts, bicycle frames etc.
Evaluate the hydraulic parameters affected and shift according to the type (time-based if the coefficient is affected; stage-based if the exponent is affected; time-based, stage-based if PZH is affected)

28. Even artificial controls are subject to shifts (debris / algae)
Rating Curve Shifts
Natural River Channels are seldom static (Aggradation/Degradation/ Fill / Ice / Weed Growth)
Even artificial controls are subject to shifts (debris / algae)

29. Fluvial dynamics
Aggradation or degradation of the banks generally affects the exponent, which calls for a stage-based correction whereas aggradation or degradation of the bed primarily affects PZH, which usually indicates a time-based, stage-based correction
Fine sands are in the range of 0.063mm to 0.2 mm
Medium sands are in the range of 0.2 mm to 0.63 mm and
Coarse sands are in the range of 0.63 mm to 2.0mm
Gravels are in the range from 2 mm to 64 mm

30. Can be developed in three ways
Shifts in AQUARIUS
Can be developed in three ways
Typing in shift points in the Shift Manager
Adjusting points in the Shift Diagram
On the rating curve zoom plots
Shift dates can be specified in
The Shift Manager
The Time Series Pane (Shift Period Bars)

31. Sometimes Shifts are not static
Shifting by Time
Sometimes Shifts are not static
Weed growth, fill, and scour can take place gradually
AQUARIUS lets you prorate a shift by leaving the ‘end date’ unspecified.
An unspecified ‘end date’ shift will pro-rate into the next shift

32. Preview
In the next lesson: ‘River Ice Processes and Dynamics’ we will look at hydraulic and hydrologic approaches to estimating winter streamflow.

33. Recommended, on-line, self-guided, learning resources
USGS GRSAT training
World Hydrological Cycle Observing System (WHYCOS) training material
University of Idaho
Humboldt College
Comet Training – need to register – no cost

34. Thank you from the AI Team We hope that you enjoy AQUARIUS!