The document discusses methods for assessing channel shape and function, including measuring channel dimensions, sediment balance, width to depth ratios, meander patterns, floodplains, headcuts, and alluvial fans. Specific metrics are described such as expected meander belt width and considerations for evaluating meander bends. Signs of channel instability and impairment are provided for incised channels, over-widened channels, and where roads intersect channels and floodplains. Alluvial fans are described as dynamic landforms where sediment is deposited.

1. Indicator 3: Aquatic Habitat
3.3. Channel Shape and Function
Watershed Condition Framework Application Workshop
Polyana, Ukraine
July 23-27, 2018
Sheela Johnson
Natural Resource Specialist, USDA Forest Service

2. Channel Shape and Function
• Review of channel measurements and sediment
balance
• Identifying impaired function from aerial and field
observation
• Width to depth ratio
• Meanders
• Floodplains
• Headcuts
• Alluvial fans
• Methods

3. www.fs.fed.us
Channel Evaluation
floodplain
bankfull
Valley type
Bed and bank
material

4. Sediment Balance
Sediment Load Stream Discharge
Source:Rosgen 1996

5. Sediment Balance
Sediment Decrease or
Water Flow Increase
Sediment Increase or
Water Flow Decrease
Source: Rosgen 1996
EROSION DEPOSITION

6. Change in Width to Depth Ratio
Incised channel
Sources: Cuyahogaswcd.org,
https://www.como.gov/utilities/stormwater-engineering/319-grant/step-pool/
Stages of change in an
incised channel

7. Change in Width to Depth Ratio
Over-widened channel
Sources: NRCS,
Cuyahogaswcd.org,
https://www.dcswcd.org/Dave%20Post%20Project%20Frame.htm
Stages of change in a
widened channel

8. Channel Instability: Headcuts
Source: New York Department of Environmental Conservation
Headcuts migrate upstream due to
erosion at the drop off point.
Eroded sediment deposits downstream

9. Meander Belt Width
Expected
meander
belt width

10. Roads constricting meander
bends

11. Roads constricting meander
bends

12. Considerations for meander
bends
• Is meander geometry
appropriate for the
stream type?
• Are sediment or wood
deposits likely to cause
channel movement?
• Can bank materials
withstand erosion on
the outer bend?
• Has the channel been
altered in the past?

13. Floodplain Disconnection

14. Floodplain crossings
1. Find an alternate crossing location when possible
2. Span or provide floodplain relief where floodplain
crossings are unavoidable

15. Roads in floodplains
Warning signs:
• Stream bed elevation similar to
road elevation
• Sharp meander bend near road
• Valley changes from narrow to
wider
• Steep tributaries deposit a lot of
material in the main channel
• Gravel bars and side channels
change after large storms
This road is now a stream

16. Alluvial fans
Slope change

17. Topography of an alluvial fan
Alluvial fan

18. Alluvial fans are dynamic locations
Where will the water go next?
Photo: NPS, Death Valley National Park Unnamed tributary to Tunnel Brook, WMNF
Gently sloping, cone- to fan-shaped landforms created by deposition of
eroded sediment at the base of mountain ranges