Christian Christian LenhartLenhart, Ph.D., , Ph.D., Assistant Professor, MSU Assistant Professor, MSU -- BiologyBiologyand Uand U of M of M BioproductsBioproducts & & BiosystemsBiosystems EngineeringEngineering

Stream ClassificationStream Classification

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/ft2 or kg/m2)

-2

0

2

4

6

8

10

12

14

0 5 10 15 20

E and G channel types – high efficiency;

low width: depth ratio

-2

0

2

4

6

8

10

0 5 10 15 20 25 30 35

Pipe – optimal efficiency

Wide shallow channels have low sediment transport efficiency

Classification systems

� Schumm (later modified by Simon)� Montgomery and Buffington: geology of

mountain streams� Rosgen – empirically derived classess

Simon and SchummChannel 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 Rosgensystem 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 Types1. Bedrock – uncommon in midwest, does occur2. 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 streams5. Sand – many Midwest streams6. Silt clay – many Midwest streams

Type B – high gradient, cobble bed

(Rosgen photo)

Type C – typical Midwestern stream; not entrenched;

� Slightly entrenched

Ratio > 2.2

Elm Creek near Trimont

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)

What are Ditches ?

Often C or E in

MN – Stage II in Siomon CEM

Lily Creek by Fairmont

Rosgen G6 – Gullies Simon CEM: Stage IIIDominant 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 upstream

0

10

20

30

40

50

60

70

159131721252933

1854

2007

E5 C5

Channel

Widening: Simon CEM – IVRosgen 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/km2

� Stage I and VI (stable types) had 20.3 tons/y/km2 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

-1

0

1

2

3

4

5

6

7

8

0 50 100 150 200

Historic channel

Active channel

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

KeyPerennial crops

New cattle fencing

Oxbow reconnection

Cattle crossing

Cross vane

Willow buffer

Existing fence

Demonstration site design: Phase I