1. Sediment Transport & Geomorphology
Objectives
Learn basic concepts of sediment transport and fluvial geomorphology
Understand sediment budgets (sources, sinks, pathways for sediment)
Discuss infrastructure and ecosystem response

2. Sediment Transport and Geomorphology in Planning Steps
Characterize Physical Attributes of
Existing conditions
Reference conditions
Future w/o project conditions
Alternatives
70% of ecosystem restoration efforts are linked to sediment and geomorphology
1. Geomorphic analysis doesn’t give you a precise answer, but it is a fact that much of the work we do these days is linked to the effects of sediment transport and geomorphology.

3. Sediment Transport & Geomorphology
mechanics of sediment erosion, transport, and deposition by water
Geomorphology
geologic science of landscape formation
H&H is the big driver affecting sediment transport and geomorphology

4. Too Much/Too Little Sediment
Problems with too much sediment
Raised flood profiles
Reduced underwater light
Decreased capacity of hydraulic structures
Problems with too little sediment
Incision (channel lowering)
Delta loss
Scour at hydraulic structures
Human’s and other biota have adapted to a river’s historical condition, and a change in that condition (more or less sediment) invariably creates problems.

5. Sediment Size Clay < 0.004 mm Silt 0.004 - 0.0625 mm
Sand mm
Gravel > 2mm
The larger the sediment particle, the less readily it is picked up by flow at a given speed, and if picked up, the shorter the distance it is likely to travel before re-settling
Clay and silt are considered fine sediments
Sand and gravel are considered coarse sediment
Note: Protocols for cobble bed mountain streams may differ, where fines may be considered anything less than 5.6 mm.
Sediment can be described by size

6. Descriptions of Sediment Load
Ability to Measure
Mode of Transport
Location in River
Measured Load-Sediment that
can be measured with a sampler
Suspended Load-Sediment that
can be found at any depth. Includes
fine and coarse sediment
Wash Load – sediment that
passes over bed without deposition.
exchanges with banks/floodplain
Sediment can be described using load descriptions, and keeping the terminology straight is important.
Bed Load is difficult to measure in sand bed streams and is often assumed to equal 5 to 15% of the total sediment load, though much higher values have been measured. On the Chippewa River in west central Wisconsin, USGS measurement indicate that bed load is 50% of the total sediment load.
Un-Measured Load-Sediment in the
lowest portion of the water column
that cannot be measured with most
samplers
Bed Load-Sediment that
creeps or hops along bed
(coarse material)
Bed Material Load – sediment that
exchanges with and is found in
measureable quantities in bed

7. Suspended Load Curves (based on measured SS)
Suspended sediment
can be measured using
samplers
A plot of suspended
sediment load versus
water discharge. Note
order of magnitude
variation.
1. Suspended sediment load data on the Missouri River.
2. Note logarithmic scales. At a flow of about 50,000 cfs, the measured sediment load varies from 10,000 to 100,000 tons/day
3. Research in small “natural” basins has shown that sediment concentration doesn’t increase with water discharge, suggesting that the sediment rating curves that we are used to looking at are a result of anthropogenic effects (John Gray, USGS)
Suspended Sediment Load (tons/day) = Sediment Concentration (mg/L) * Water Discharge (cfs) * .0027

8. Bed Load Bed load moves in waves at a certain
Sketch & Bathymetry from Dvd Abraham
and Thad Pratt, ERDC
Bed load moves in waves at a certain
speed (or celerity). The celerity (c) is given
by dividing the distance ∆x by time ∆t.
Problem is that measuring c is difficult and
expensive, and calculating it is uncertain even
with good models and data.
Often we just assume that bed load is 5% to
15% of the total sediment load.
1. Helley Smith samplers are placed on the bottom of rivers and streams to measure bed load. They work OK in gravel bed streams usually hand-held. They don’t work very well in sand bed rivers and streams.

9. Calculating Sediment Transport
There are dozens of sediment transport functions that predict sediment transport based on:
sediment size, weight, and fall velocity
water velocity and depth
channel width
channel slope and roughness
water temperature
Many assumptions are made
Choose functions appropriate for your conditions
250 KHz Geoswath echo sounder. The boat is RTK GPS positioned and compensated for pitch,
heave and roll. Horizontal accuracy is stated as +/- 2 cm and vertical resolution of bathymetric
elevations is approximately 3 cm in 50 meter of water.

10. Lane’s Balance says that sediment discharge and sediment
Sediment discharge and sediment grain size tend to balance against water discharge and slope
At a watershed scale, sediment balance doesn’t exist for entire watersheds.
At a river reach scale, sediment balance can occur.
Lane’s Balance says that sediment discharge and sediment
grain size tend to balance against water discharge and slope

11. Sources, Sinks, Pathways
Rio Puerco, NM
Sources
Bed
Banks (Bluffs)
Ravines & Gullys
Watershed
Watershed Sources depend on:
geology and topography of the watershed
magnitude, intensity, duration, and distribution of rainfall
vegetative cover; and the extent of cultivation and grazing.
Regression methods are used to develop soil loss relationships
Source
Sink
Erosion on the outside of a bend is a source of sediment
Deposition on the inside of this bend is sink for sediment

12. Sources, Sinks, Pathways
Floodplains
Valley side slopes
Deltas
Off - channel areas
USACE Dredges
Most rivers cannot transport all of the sediment that is eroded within its channels and watersheds, so every river system has sinks for sediment.
This city park became a sink for sediment.

13. Sources, Sinks, Pathways
The capacity of a stream to transport sediment depends on
hydraulic properties of the stream channel and sediment properties
Sediment Transport = F (hydraulic properties & sediment properties)
slope
velocity grain size distribution
channel geometry cohesiveness
roughness
Note that the hydraulic properties are the same as those that we discussed in hydraulics.
Temperature can have an effect on sediment transport
If the grain size is large (cobbles) or if the material has cohesive properties, sediment transport may be limited
pathway
sink

14. Sediment Budgets, Watershed Scale
Whitewater River Sediment Budget,
NRCS, 1965 to 1994
Sources of sediment estimated by AGNPs model
Sinks determined by historic survey comparison
Sources (1000’s tons/year)
Sheet & Rill
Erosion
555
Ephemeral & Classic
Gully Erosion 72
Streambank
Erosion 86
Headwaters
Sediment Load
To Mississippi River 24
Colluvium
553
Sandbars &
Streambank
Deposits 17
Tributary
Valley
Deposits 36
Main
Valley
Deposits 63
Whitewater Delta
Deposits 20
Every river is different, some because they have been altered or because of natural geological events, may pick up more sediment near the mouth.
The point here is that sources and sinks are rarely in balance and the transport capacity of the “pathway” (the river channel) varies significantly from reach to reach.
Sinks (1000’s tons/year)
Only 24,000 tons/year of the total 713,000 tons/year from
sheet and rill erosion, ephemeral & classic gully erosion, and
streambank erosion is transported to the mouth of the river.

15. Sediment Effects on Water Quality
The majority of sediment transport in a given year occurs during seasonal high water events
Sediment transport during other times can have a significant effect on underwater light, nutrient loads, substrate.

16. Suspended Sediment Concentration (SSC) is Different than Total Suspended Solids (TSS)
SSC sampling: Iso-kinetic sampling where the velocity and concentration in the
sampler intake is equal to the velocity and concentration in the surrounding water is required to
ensure sediment samples that represent the true sediment load.
See USGS protocols by Edwards and Glyssen (1999)
and Davis (2005)
TSS sampling (e.g. automatic water samplers (or pump samples)
Often are not iso-kinetic, however this is not a problem for fine
sediments.
The SSC analytical method uses the entire water-sediment
mixture in the analysis. (ASTM D-3977)
A TSS analysis entails withdrawal of an aliquot (or part) of the original sample for subsequent
analysis. (SM D). It is OK to use if the sediments are fine sediments, but don’t use if coarse
sediments are in the sample.
For more information see
TSS sampling is cheaper than SSC, and is used if coarse sediments are not a concern (e.g. for water quality sampling).
Need to be aware of sampling protocols.

17. SSC median bias = -1.8%; 25th percentile = -4.4%; 75th percentile = 0.0%
TSS median bias = -16%; 25th percentile = -32%; 75th percentile = 8%
Same lab, TSS results of 3 QA test sets (35 samples); SSC results of 2 QA test sets (18 SSC)
Data from USGS

18. Geomorphology Geologic science of landscape formation
High Energy
Channel
Geologic science of landscape formation
Fluvial Geomorphology
landscape formation by streams
1. The sediment depositing in this delta was eroded from some upstream site, transported down the river to this site, and deposited where the channel enters the backwater because of the low energy environment in the backwater.
Low Energy
Backwater

19. Watershed and Channel Alteration will change H&H Causing Geomorphic Responses Including:
Channel incision
Channel plugging
Land loss along channels
Gullying
Floodplain deposition
In other words, many of the USACE missions are affected by sediment transport

20. Geomorphic Responses may Affect:
Infrastructure: Bridges, FRM
Human uses: Drinking water, recreation, agriculture
Aquatic Habitat
Commercial Navigation
Water Quality: Underwater light, nutrients, contaminants
In other words, many of the USACE missions are affected by sediment transport

21. Spatial Scales Changes in: Channel geometry Slope Roughness
Cause changes in
Sediment transport
Geomorphic processes
Channel Capacity
1. Remember Lane’s relationship: Sediment load and sediment size are proportional to water discharge and slope.
2. The water discharge at Hendrum (river mile 5) is about 2,880 cfs, while the water discharge at Twin Valley (river mile 60 is about 1480.
3. The lower reaches of the Wild Rice River don’t have the capacity to transport all of the sediment from upstream sources.

22. Time-Scales
Annual geomorphic changes like sand bar migration, bank erosion, point bar building occur due to seasonal high flows
Long-Term geomorphic change like incision or delta building or loss might be natural or anthropogenic.
Climate variation, watershed development, channelization, dams, urbanization affect geomorphic change at both scales.
Fluvial Geomorphic Analysis must account for time scales. For instance is a shift in conditions due to land use change over the last few decades or longer term change driven by past geologic events or climate variration.

23. Use Multiple Tools for Sediment Transport and Geomorphological Analysis
Field Investigations
Existing conditions substrate, bankfull conditions, vegetation, discussion with local experts
Surveys:
Cross sections, profiles, sediment cores
Analytical Techniques
Numerical Models:
Watershed models
River models
Aerial photo comparisons
Change from Historic conditions
Sediment Budgets
Specific Stage Discharge Analysis
A combination of techniques usually is needed to establish multiple lines of evidence.

24. Erosion of a River Bend Sink Source Sink
Geotechnical Failure From Bend
Migration And Toe Erosion
Low Flow Cross Section
High Flow Cross Section

25. Flood of Record Washed Out Railroad, Undermined Houses
This flood of record probably caused direct erosion of the bank
Note RR tracks hanging

26. River Meandering and Effects of 0.2 % Chance Flood
Significant migration occurred in the 37-year period between these two photographs.
The flood of record in 2002, caused significant floodplain erosion in this highly altered river reach.

27. Geomorphic Response to Watershed Development
Floodplain Deposition, Channel Incision

28. Whitewater River Avulsion August 2007
Highway 61 Bridge
Canadian Pacific RR Bridge
Whitewater River Avulsion
August 2007
New Mouth of
Whitewater River
Avulsion is a sudden change in channel position, with abandonment of old channel.
Whitewater River shortened
By about 6,000’
Old Mouth of
Whitewater River

29. Culvert Outlet Failure

30. Channelization Sediment Deposition, Loss of Capacity
Many channelized reaches of rivers were oversized resulting in lower velocities and sediment deposition. They essentially became sinks for upstream sediment sources.
This agricultural levee break resulted in deposition of sand on the farmers field.
Agricultural Levee Break

31. Island Loss And Erosion Increased Connectivity Sediment Deposition
Geomorphic Response to Raised Water Levels
In Lower Pool 8
Island Loss And Erosion
Increased Connectivity
Sediment Deposition
1938
1954
1991
Extensive land loss has occurred in the lower ends of navigation pools on the Upper Mississippi River

32. Bridges
Usually footings are deep enough to handle a certain amount of scour.
Changed hydrological conditions (climate variation, land use change) or changed hydraulic conditions (dam removal, debris) can create greater scour levels
A scour signature may not last. See the next six images. Note that the bottom elevation is about at the start of this event.

35. Summary of Rising Flood

38. Summary of Falling Flood

39. Bridge TH 212 over Minnesota River Overflow Abutment Fill and Approach Panel Lost Q500 = 7,300 cfs Q1997 = 10,000 cfs
Excerpts from Inspectors Notes:
4/4 108” below NW, channel has shifted to east
4/5 69” from SE wingwall, deck vibrating, riprap eroded, looking down through water.
4/6 2:00 PM Panel undermined, water flowing under it.
4/6 5:00 PM Panel fell in.
TH 212 Minnesota River Overflow just west of Granite Falls, MN.
In 1997 a roadway failed upstream redirecting main channel flow into the overflow channel. Approximate Q1997 = 10,000cfs, V1997 = 10 fps.
(Q500 = 7300 cfs)
District Bridge Inspector observed scour making measurements with a sonar device, visible signs of structural distress (deck vibrating and riprap eroded) noted prior to failure.
Road was closed to traffic prior to panel falling in.
Bridge superstructure and substructure in good condition.

40. Bridge 54002 Bridge is still structurally stable, but from the travelers perspective it failed.
Bridge upstream which used to catch debris washed out.
Repairs $200,000 replace fill, panels, road, guard rail, riprap.

41. Long Lake Water Control Structure after 2001 Flood

42. ~ The End ~