StreamStream ClassificationClassification
ChristianChristian LenhartLenhart ,, Ph.D.,Ph.D., Assistant Professor, MSU - Biology and U of M Bioproducts & Biosystems Engineering Why classify streams?
To eliminate variability by stratification (grouping) To understand fluvial processes To facilitate communication amongst managers To develop appropriate restoration and management actions Channels behave differently Form vs. function
Darwin’s finches Form/function link in streams
Stream dimensions are adjusted to flow and sediment load (Lane’s equation) Sediment transport capacity strongly linked to hydraulic radius τ = γ * S * R Shear force = specific weight of water* slope*hydraulic radius (units of lbs/ft 2 or kg/m 2) Wide shallow channels have low sediment transport efficiency
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Pipe – optimal E and G channel types – high efficiency; efficiency low width: depth ratio
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Schumm (later modified by Simon) Montgomery and Buffington: geology of mountain streams Rosgen – empirically derived classess Simon and Schumm Channel Evolution Model
Most southern Minnesota streams are in stages 3-5, especially 4 and 5 Widening more dominant in main channels Slight incision (1-2 ft) can be important Small streams - III Montgomery and Buffington
Alternative to Rosgen system for mountain west streams Sediment supply/transport balance Rosgen classification scheme Classification key for natural rivers Entrenchment ratio
Incision of a stream within its valley Flood-prone width/bankfull width Critical to sediment transport processes as well as bank erosion and water Range : Very entrenched <1.4 - 2.2 (not) Low number = more entrenched Types A, G, F are entrenched Types E, C not entrenched (much) Width-Depth ratio
Key to sediment transport processes Wide streams are less efficient at carrying sed load; reduced depth decreases shear force – this is why ditches aggrade >40 W:D ratio is a braided stream (Type D), cannot carry sediment load Narrowest W:D ratio is Type A, E, G (<12), most efficient at transporting sediment Sinuosity
Range From 1.0 to > 1.5 (about 2) In Midwest, E Type most sinuous Often first to be altered by changed hydrology ( can change from E to C Type) Widespread channelization (ag and roads) Loss of sinuosity increases slope, sediment transport efficiency; ↓ habitat variability Bed materials
Modifier of Rosgen Types 1. Bedrock – uncommon in midwest, does occur 2. Boulder – uncommon in Minnesota (except North Shore of Lake Superior) 3. Cobble - Uncommon (North Shore and lower portions of rivers dropping into MN River valley) 4. Gravel – common in undegraded and higher gradient Midwest streams 5. Sand – many Midwest streams 6. Silt clay – many Midwest streams Type B – high gradient, cobble bed
(Rosgen photo) Type C – typical Midwestern stream; not entrenched; Elm Creek near Trimont Slightly entrenched Ratio > 2.2 Type E – headwaters stream (E5-6) Type G – gully (Rosgen photo) Type D – braided channel- Platte River, NE
Platte River Initiation of multiple channels Elm Creek, MN Type F4 (Rosgen photo) Lily Creek by Fairmont What are Ditches ? Often C or E in MN – Stage II in Siomon CEM Rosgen G6 – Gullies Simon CEM: Stage III Dominant process: downcutting Channel Evolution Channel adjustment in Minnesota Elm Creek example
Widening in lower reaches Entrenched headwaters Ditches – aggrading, still entrenched “C creep” – channel widening moving E5 C5 upstream
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0 33 29 25 21 17 13 9 5 1 Channel Widening: Simon CEM – IV Rosgen E to C (or F) Lower Elm Creek adjustment Channel evolution in Driftless area
Pre-Euro settlement, channels less entrenched Farming hillslopes eroded sediment; deposit in valley (3-8 feet at Rush Creek site) Channel then downcut over time, and evolved to a stable E type entrenched within a larger valley 2007 Flood blew out E stream, widening 2 x Rush Creek example
Trout stream, type E, narrow (50 ft), deep 2007 flood widened to 100 feet (now type C , F Linkage between stream form and function
Simon CEM
Stages III-V all have high sediment load
Stage III has highest bedload
Stage IV-V high suspended load
Stage I and VI are stable
Has been tested in Minnesota CEM stage and sediment load in MRB
58% of channels unstable in Western Corn Belt Ecoregion: Stages III, IV and V (Simon et al. 2008) Stage III-V channels have average sediment yield of 243 Tons/y/km 2 Stage I and VI (stable types) had 20.3 tons/y/km 2 on average Ravines
Abundant along Minnesota, Blue Earth and bigger rivers
Often C type channels with G at headcuts and below Rosgen link between stream type and fluvial processes
Types A-B, high transport capacity, little aggradation possible Type D – often at alluvial fans at base of steep slopes, streams have high bedload, unable to transport it all Type G – downcutting, unstable stream type Rosgen form-function
Type E – narrow width-depth ratio (<12) increases sediment transport efficiency; slight entrenchment (<1.4) allowing frequent floodplain overflow Type C – slightly entrenched, higher width – depth ratio (12-40) Entrenchment
Critical to turbidity issue
Reduced floodplain deposition of sediment
Increases sediment transport efficiency More precise measure: Bank height to bankfull height (used in BEHI) range 1 – 3 or 4 Incision disconnects floodplain
Elm Creek near Huntley
8 7 Active channel 6 5 4 3 2 1 Historic channel 0 -1 0 50 100 150 200 Issues with classification
Static in time Doesn’t quantify processes (hydrology, sediment transport) How do you know where stream has been and where is it going? What are “natural” background rates of channel erosion Identifying bankfull elevation
Difficult without experience; often higher than first thought Need to look at multiple point bars Look for flat recent floodplain deposits Verify with regional curve and/or stream gage data Quantifying processes
Measuring change over time
Monitoring (bank pins, resurvey)
Aerial photo analysis (long-term rates) Modeling:
Bank erosion – BSTEM (USDA - Simon et al.) BEHI, BANCS (Rosgen’s WARSSS)
Sediment transport – bed load, suspended load
RiverMorph (Rosgen - like)
CONCEPTS (USDA – Simon et al.) Channel Management issues in MN
In Minnesota River Basin – Channel widening is main issue ( “C creep” and/or conversion to F) Loss of sinuosity has occurred under the radar In Ravines/gullies- downcutting (bed erosion) is dominant process In ditches; overwidening is issue – aggradation occurs; counteract via 2-stage ditch (an E type within ditch walls) Loss of headwaters streams Watershed-scale management strategies for stream erosion
Most techniques are labor intensive & expensive (vanes, rip rap, bioengineering) Are there less expensive ways
Ag practices using perennial plants in riparian zone
Diversion of stream from major bluffs
Watershed management for hydrology Demonstration site design: Phase I
Key Perennial crops
New cattle fencing
Oxbow reconnection
Cattle crossing
Cross vane
Willow buffer
Existing fence