Stream Ecosystems:
Watersheds to Reaches
•Image: Stream Corridor Restoration: Principles, Processes, and Practices, 10/98, by FISRWG.
Sample Reach
Hydrologic Cycle
Contributing Area: Watershed
A watershed is defined as an area of land that drains water,
sediment, and dissolved materials to a common outlet at some
point along a stream channel (Dunne and Leopold 1978).
Watersheds
Occur at multiple scales
Watersheds range from the
largest river basins, with
watersheds thousands of acres
in size
to
small streams, with
watersheds measuring only a
few acres in size
Delineating Your Watershed
Large Scale Factors to Consider
LATITUDE
ALBEDO
CLIMATE
http://vathena.arc.nasa.gov/curric/weather/storm.html
Watershed Characteristics
Slope
Aspect
Shape
http://www.nrmsc.usgs.gov/research/glacie
r_model.htm
Watershed Characteristics
Land Cover
Surface Roughness
Watershed Characteristics
Soil Characteristics
texture
structure
http://soils.usda.gov/gallery/state_soils/
Permeable
High infiltration
http://www.nre.vic.gov.au/web/root/
Domino/vro/vroimages.nsf/Images/g
loss-ferr/
Impermeable clay
High surface runoff
moisture
http://soils.usda.gov/gallery/state_soils/
Large Macropores
High Infiltration
Cumulative Effects
Land Management Throughout Your
Watershed Can Have Impacts
Downstream
Measuring Physical Characteristics
• What is the function of a stream?
• What data reflect a stream’s ability to function?
• How can the physical data and stream function
be summarized in a useful way?
Stream Function
• To move water
• To move sediment
Each stream balances
erosion, transport,
and deposition in the
context of its climate
and landscape.
A Stream is a Transport Machine
Streams as Transport Machines
Some independent variables, functions of the
watershed influence the stream’s ability to function
as a transport machine:
Elevations, Elevation Change
Sediment load
Discharge (flow)
Bankfull flow (channel forming)
Flood flow (floodplain)
Balancing Water and Sediment
Qs . D50
Qs = sediment load
D50 = sediment size
in balance with
Qw . S
Qw = stream discharge
S = stream slope
Stream Reach Characteristics
Stream Channel - a channel
with flowing water at least part
of the year.
Bankfull – stage of water which
maintains channels (~1.5-2
year recurrence interval)
Floodplain - a highly variable
area on one or both sides of the
stream channel that is
inundated by floodwaters at
some interval, from frequent to
rare.
Terraces – remnants of historic
floodplains
Indicators of Floodplain/Terraces
Collecting Data on Stream Function
When gathering data, choose
parameters that reflect the
stream’s ability to function as a
transport machine:
Bankfull Characteristics
Floodplain Characteristics
Sediment Characteristics
Stream Bank Characteristics
Physical Characteristics
Channel Dimension: map cross-sections
Bankfull width
Mean bankfull depth
Bankfull cross-sectional area
Width: depth ratio
Maximum depth
Channel Pattern: use aerial photos
Sinuosity
Channel Profile: map longitudinal profiles
Bankfull, water surface and channel slopes
Physical Characteristics
Floodplain Characteristics
Floodprone width
Entrenchment ratio
(bankfull width: floodprone width)
Sediment Load Characteristics
D-50
D-84
Bar samples
Stream Bank Characteristics
Field observation
Bankfull Stage
“The bankfull stage corresponds to the
discharge at which channel maintenance is
the most effective, that is, the discharge at
which moving sediment, forming or
removing bars, forming or changing bends
and meanders, and generally doing work
that results in the average morphological
characteristics of the channel.”
Water in Environmental Planning,
T. Dunne and L.B. Leopold,
W.H. Freeman and Co., San Francisco, CA, 1978
Bankfull Flow
~ 1.5-2 year recurrence interval
Bankfull Flow
Baseflow
Big Goose Creek near Sheridan, Wyoming
Indicators of Bankfull Stage
• The height of depositional
features (especially the top of
the pointbar, which defines the
lowest possible level for
bankfull stage)
• A change in vegetation
• Slope or topographic breaks along
the bank
• A change in the particle size of bank material, such as the boundary
between coarse cobble or gravel with fine-grained sand or silt
• Undercuts the bank, which usually reach an interior elevation slightly
below bankfull stage
• Stain lines or the lower extent of lichens on boulders
Cross Section Measurements
Physical Characteristics
Channel Dimension: map cross-sections
Bankfull width
Mean bankfull depth
Bankfull cross-sectional area
Width: depth ratio
Maximum depth
Channel Pattern: use aerial photos
Sinuosity
Channel Profile: map longitudinal profiles
Bankfull, water surface and channel slopes
Width:Depth Ratio
Physical Characteristics
Channel Dimension: map cross-sections
Bankfull width
Mean bankfull depth
Bankfull cross-sectional area
Width: depth ratio
Maximum depth
Channel Pattern: use aerial photos
Sinuosity
Channel Profile: map longitudinal profiles
Bankfull, water surface and channel slopes
Sinuosity
River Distance
Straight Line Distance
Sinuosity
Physical Characteristics
Channel Dimension: map cross-sections
Bankfull width
Mean bankfull depth
Bankfull cross-sectional area
Width: depth ratio
Maximum depth
Channel Pattern: use aerial photos
Sinuosity
Channel Profile: map longitudinal profiles
Bankfull, water surface and channel slopes
Water Surface Slope
Rise/Run
Physical Parameters
Floodplain Characteristics
Floodprone width
Entrenchment ratio
(bankfull width: floodprone width)
Sediment Load Characteristics
D-50
D-84
Bar samples
Stream Bank Characteristics
Field observation
Floodprone Width
Width Where Stage is 2X Bankfull Max Depth
Physical Parameters
Floodplain Characteristics
Floodprone width
Entrenchment ratio
(bankfull width: floodprone width)
Sediment Load Characteristics
D-50
D-84
Bar samples
Stream Bank Characteristics
Field observation
Entrenchment Ratio
Flood Prone Width/Bankfull Width
Entrenchment Ratio
Physical Parameters
Floodplain Characteristics
Floodprone width
Entrenchment ratio
(bankfull width: floodprone width)
Sediment Load Characteristics
D-50
D-84
Bar samples
Stream Bank Characteristics
Field observation
Sediment Characteristics
Boulder
> 256 mm
Cobble
64-256 mm
Pebble
16-64 mm
Gravel
2-16 mm
Sand
0.0625-2 mm
Silt
0.0039-0.0625 mm
Clay
<0.0039 mm
Quantitative Description of Stream
Function
These parameters are the basic delineative
criteria needed to quantitatively describe a
stream’s function and begin assessment if
can organize data in useful system:
Rosgen Channel Classification
Stream Classification
Rosgen Stream Classification
Rosgen classification scheme initially sorts streams into the
major, broad stream types (A-G) at a landscape level
A-headwater
B-intermediate
C and E-meandering
D-braided
F-entrenched
G-gully
Stream types are divided into subtypes based on slope ranges,
and dominant channel material particle sizes.
1-bedrock
2-boulder
3-cobble
4-gravel
5-sand
6-silt/clay
Rosgen Stream Classification
Applied River Morphology, Dave Rosgen, Wildland Hydrology, Fort Collins, Colorado, 1996.
Rosgen Stream Classification
Why Establish Reference Sites?
Establishes a baseline for a broad range of physical, chemical and biological
monitoring.
Monitor trends in fluvial and geomorphic conditions over time
Quantify environmental impacts
Assess stream and watershed response to management
Provide channel and flow facts for water allocation
Support resource inventories (habitat, water quality, vegetation)
Track cumulative effects for entire drainage areas
Contributing to regional, state, national and international databases
Site Selection
Ask the following questions:
What do we want to know about this stream or drainage?
What variations (geology, elevation, land use) exist in the area?
How can we set up the most useful comparisons with the fewest sites?
How can this site contribute to the existing or planned efforts?
How much can be accomplished with present resources?
Site Selection
1. Choose sites with evident natural features-floodplains,
terraces, bars and natural vegetation
2. Reach should include an entire meander length (two
bends) if possible. The length should be at least 20
times bankfull width of the channel.
3. Unless your purpose includes studies of beaver dams,
debris jams, boulder fields, bedrock controls, and
recently adjusted channels (flood, disturbance), select
your site to avoid such features
Natural stream channel stability is….
Stable dimension, pattern, and profile
such that, over time, the channel
features are maintained and the stream
system neither aggrades nor degrades”
for a given climate.
Applied River Morphology, Dave Rosgen,
Wildland Hydrology, Pagosa Springs, Colorado, 1996.
Major Sub-Basins of Wyoming