Classification Chapter6 Stream Process

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Stream Processes

Stream Surveys, Effective Discharge

Rosgen Classification, Streamways, Evolution

Andy Ward, Professor

Food, Agricultural and Biological Engineering

The Ohio State University



Stream Stability

Natural stream channel stability is

achieved by allowing the river to develop a

stable dimension, pattern and profile such

that channel features are maintained andthe stream system neither aggrades nor

degrades

Correctly engineered rigid channels can be

part of a stable stream system.



Indicators Of The Effective Discharge StageIndicators Of The Effective Discharge Stage

A bench that is below the bankfull stage

will usually have signs of coarse

material. An active floodplain will often exhibit

sands, some soil structure, and

vegetation

If there is a good soil structure and high

organic matter content you are probably

above the effective discharge stage.



Effective Discharge Stage IndicatorsEffective Discharge Stage Indicators

Top Of A Point Bar Top Of A Point Bar DepositionalDepositional MaterialsMaterials

Grade Breaks Moss On Boulders

Stain Lines On Boulders



Are Scour Lines

Bankfull Indicators?

Cut BanksCut Banks

Are Poor IndicatorsAre Poor IndicatorsOf BankfullOf Bankfull



Identify land use conditions and changes

Become familiar with conditions at the site

Identify a reference reach

Develop a regional curve

Evaluate existing stream gages

Identify resource needs to conduct the field work

Visit with people who are familiar with the watershed

Purpose

Conducting a Stream and

Watershed Reconnaissance



If a channel relocation is proposed and the currentchannel is stable then only survey the currentchannel.

If the current channel is unstable then a referencereach that represents the stable form of the currentchannel should be surveying in addition to the

current channel.

Reach Survey



Stream Geomorphology SurveyStream Geomorphology Survey Do a survey of one or more representative reaches that

are at least 20 bankfull widths long. Measure the channel profile

Measure the channel cross-section at several locations.

Measure all grade breaks along the profile & cross-section



Radius of curvature

Meander length

Sinuosity

Conduct a Pebble Count

Pools and RifflesPools and Riffles



Riffle Pools Features

(Spaced at 5-7 Bankfull Widths)



One meander length is equal to

10-14 Bankfull Widths





Dimensions

Riffle BlackLick

85

95

105

-40 -20 0 20 40 60 80 100 120

Width from River Left to Right (ft)

E l e v a t i o n ( f t )

Maximum

Bankfull depth

Width at twice max

Bankfull depth

Bankfull width

Mean

Bankfull depth



Using Reach DataUsing Reach Data

Analyze the data to refined estimates of : Effective discharge width, depth, and cross-sectional area

Effective discharge

Mean bankfull flow velocity

Channel bed slope

Shear stress or tractive force at bankfull discharge

1.1 Riffle Typical Cross-Section

88

90

92

94

96

98

100

102

0 5 10 15 20 25 30 35 40

Width from River Left to Right (ft)

E

l e

v

a

t i o

n

( f t )y = -0.0017x + 94.6

R2 = 0.96

y = -0.0016x + 87.6

R2 = 0.99

y = -0.0014x + 89.0

R2 = 0.99

80

85

90

95

100

0 1000 2000 3000 4000 5000 6000

Channel Distance (ft)

E l e v

a t i o

n

( f t )

bed w ater srf Terrace --- BKF --- x-sectio n Linear (B KF)



Profile

86

88

90

92

94

96

98

0 100 200 300 400 500 600 700 800 900

Channel Distance (ft)

E l e v a t i o n

( f t )

bed water srf Terrace --- BKF



Rosgen Classification Of Natural Streams



Rosgen Stream Classification







Stream Type: AW/D < 12 Sinuosity > 1- 1.2 ER < 1.4 S 4 - 10 %





Stream Type: BW/D > 12 Sinuosity > 1.2 ER > 1.4 -2.2 S 2-4%







Stream Type: CW/D > 12 Sinuosity > 1.2 ER > 2.2 S < 2%





Stream Type: DW/D > 40 Sinuosity > 1.2 ER n/a S < 2%







Stream Type: EW/D < 12 Sinuosity > 1.5 ER > 2.2 S < 2%







A Type E Stream In Ohio



Type E Stream In An Urban Park





Stream Type: FW/D > 12 Sinuosity > 1.2 ER < 1.4 S < 2%





Stream Type: GW/D < 12 Sinuosity > 1.2 ER < 1.4 S 2-4%



Typical Problems

Higher downstream flows in the receiving ditch orstream

Higher upstream flows

Outlets restricted

Reduced conveyance due to deposited sediment

Reduced conveyance due to increased roughness

Bank failures

Floodplain modifications

New bridges and/or culverts



Bridges & Culverts

Culverts are often made toowide. This causes depositionupstream and scourdownstream

New culverts often change thedirection of flow and thebedslope. These changes canalso result in downstream

bank instability problems. Use a multi-stage design

for the culvert.



Streamway Concept



Streamway Width

We analyzed 47 published sets of data and toaccount for meander migrations and uncertaintyin the equation we tested a new equation that is a

function of drainage area and provided astreamway that encompassed 41 of the 47 sites:

Streamway width =120*DA 0.43

Where DA is in square miles and the width is in feet.



1989

1951

1966

1980

1997

Drainage Area

30 sq. mi.

Streamway

120 * DA 0.43 = 518 ft

Salt Creek Vinton County, Ohio



Channel Evolution

Pre-Development

Downcutting

Widening

Restored Floodplain



Life at the River!Life at the River!



Thank You!

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Classification Chapter6 Stream Process