episodic river channel form

Episodic river channel form

Derek Booth1,2

Glen Leverich1

Peter Downs1,3

Scott Dusterhoff1

1S T I L L W A T E R S C I E N C E S 2U N I V E R S I T Y O F W A S H I N G T O N3U N I V E R S I T Y O F P L Y M O U T H (U K)

P R E S E N T A T I O N O V E R V I E W

1. What are the elements of “river channel form”?.

2. Why should episodic channels differ from their perennial counterparts?.

3. What is the form of episodic rivers?

Elements of “channel form”:

> Channel planform (the map view)> Channel cross-section> Bed topography (pools, bars, etc.)> Channel-floodplain interrelationships

(“bankfull”, incision, etc.)> Bedload and bed sediment> In-channel and riparian vegetation> Changes in the above over time

All interact in space & time

"As a young man, my fondest dream was to become a geographer. However while working in the customs office I thought deeply about the matter and concluded it was far too difficult a subject. With some reluctance, I then turned to Physics as a substitute."

- Albert Einstein (Unpublished Letters)

Issaquah Creek watershed

ISSAQUAH CREEK PROFILE

≈3000’ relief

18.2 miles

Comparison to Other PNW Studies

0

200

400

600

800

1000

1200

1400

1600

1800

2000

BURP (199

5)This

Stud

y

King C

ounty

(199

5)Mad

ej (19

82)

Slaymak

er (19

93)

Reid (1

981)

Paulso

n low

(199

7)

Paulso

n high

(199

7)

Sedi

men

t Pro

duct

ion

(tonn

es k

m-2

yr-1

)

(270-390)

Forested/Logging

MixedLand Use

Urban

(Nelson & Booth, 2002)

Sediment production from Pacific Northwest watershed studies

~50t/km2/yr

2004

Why are these rivers “different”?

Presenter

Presentation Notes

Upstream of the diversion pre and post

Tectonics:

Uplift rate1 - 2 mm a-1

From Keller and Pinter (2002)

SANTA PAULA CREEK PROFILE

≈5000’ relief

ISSAQUAH CREEK PROFILE

18.2 miles

Santa Paula Creek watershed

Santa Clara River watershed

Sespe Creek watershed

1-22-4 5

1

0.5

0.5

0.3

1-104

2

SOURCES:

Rockwell 1988 Yeats 1988 Çemen, I. 1989 Lajoie et al. 1991 Huftile and Yeats 1995 Orme 1998 Trecker et al. 1998 Blythe et al. 2000

Geologically determined uplift rates

~1 (west) to ~5 (east) mm/yr uplift

U

D

Lower Sespe Creek valley:

Climate:

ISSAQUAH:100-yr 24-hour: 5-9” ppt.

SANTA PAULA:100-yr 24-hour: 9-18” ppt.

(Issaquah = 5-9”)

“The maximum intensity of precipitation…at intervals of 10 to 100 years is greater in portions of the San Gabriel and San Bernardino Mountains in southern California than anywhere else in the continental United States.”

Western Regional Climate Center (http://www.wrcc.dri.edu/)

(59 sq. mi)

Issaquah Creek maximum recorded flow

USGS 11113500 SANTA PAULA CREEK NEAR SANTA PAULA, CA

Annual maximum

discharges

2005

(42 sq. mi)

Presenter

Presentation Notes

Ouch

Presenter

Presentation Notes

Severe incision to bed rock downstream of the diversion and fish ladder

Tributary Total annual load (t a-1)

Annual load (t km-2 a-1)

Landscape lowering rate

(mm a-1)

Sisar Creek 44,000 2,300 0.9

Upper Santa Paula Creek (to Sisar Ck. confluence) 73,000 1,700 0.7

SPC at Harvey Diversion Dam 146,000 2,100 0.8

Mud Creek 24,000 5,800 2.2

Santa Paula Creek at mouth 252,000 2,200 0.8

Predicted hillslope sediment delivery by subwatershed

252,000 0.82200

Santa Paula Creek:

Comparison to Other PNW Studies

0

200

400

600

800

1000

1200

1400

1600

1800

2000

BURP (199

5)This

Stud

y

King C

ounty

(199

5)Mad

ej (19

82)

Slaymak

er (19

93)

Reid (1

981)

Paulso

n low

(199

7)

Paulso

n high

(199

7)

Sedi

men

t Pro

duct

ion

(tonn

es k

m-2

yr-1

)

(270-390)

Forested/Logging

MixedLand Use

Urban

40x

Sediment production from Pacific Northwest watershed studies

~50t/km2/yr

Fine sediment delivery:

Coarse sediment delivery:

Calculated sediment load for Sespe Creek at Fillmore[USGS gage 11113000]

Average yield = 1,109,000 t/yr (1645 t/km2/yr)

Only 8 events have exceeded 2x the “average” sediment load in this 80-year period.

And, ~50% of the total load in just 3 events.

Bullet Points

Day Fire – September 2006

1 per 20 years

1 per 50 years

1 per century

(Wild)fires:

Presenter

Presentation Notes

Frequency of Burn Events: Nearly all of the watershed has burned at least once since 1878. 73% of the watershed has been burned at least twice in that time period (1878-2007).

View of runoff along upper Aliso Canyon in areas recently burned during the 2009 Station Fire.

View of new vegetation growth on hillslopes previously burned during the 2007 Buckweed Fire.

Fire-related hillslope and tributary sediment production and delivery

1986

1934 1971

1959

19171875

1820 1860

1912

1993

1950

Regulation

Levees, Bank Protection, & Aggregate Mining

Irrigated Crops

Ranching

Population

WA

TERS

HED

IIM

PACT

S CH

RON

OLO

GY

Pre-European Colonization Irrigation & Diversions Dams & River

Modifications UrbanizationRanching & Colonization1820 1890 1955 1990

1912: Dry Canyon Reservoir (4.5 mi2)

1934: Bouquet Reservoir (13.6 mi2)

1971-72: Castaic Lake (154 mi2) and Pyramid Lake (293

mi2)

1955 Santa Felicia Dam (Piru) (421 mi2)

1860s drought prompts switch from ranching to

agriculture

16,000 ac irrigated

31,700 ac irrigated

1900s 1949

107,689 ac irrigated

1980

106,480 ac irrigated

132,783

30,7621970 1980

41,73665,563

206,672240,296 291,288

St. F

ranc

is D

am F

ailu

re(5

00,0

00-8

00,0

00 cf

s)

Infrastructure & land use, Lower Santa Clara R.

Human activity:

Recall, the elements of “channel form”:

> Channel planform (the map view)> Channel cross-section> Bed topography (pools, bars, etc.)> Bedload and bed sediment> Channel-floodplain interrelationships

(“bankfull”, incision, etc.)> In-channel and riparian vegetation> Changes in the above over time

Lower Santa Paula Creek (1938)

Lower Santa Clara River

Snoqualmie River nr. Carnation, WA

Los Angeles River

Santa Ynez River through Lompoc, CA

1949

1969

2009

Santa Clara River above Santa Paula, CA

Distributary channels on coalescing alluvial fans:

Sespe Creek through Fillmore, CA

Thalweg Locations in Lower Sespe Creek (1938–2005)

“Active” floodplain

Presenter

Presentation Notes

In GIS, digitized thalweg locations for 6 different years using aerial photos. Important note that the channel has remained relatively confined within the same channel boundaries since 1938 (i.e., no significant lateral migration into floodplain). However, terrace scarps represent former channel boundaries. Background DEM is from 2005 LiDAR data.

The elements of “channel form”:



Newhall Creek

Presenter

Presentation Notes

Photo: Newhall Creek, taken by Bruce Orr

Santa Paula Creek below Harvey Diversion Dam

Upper Santa Clara River

Hasley Canyon, Upper Santa Clara River watershed

San Antonio Creek

Mud Creek

Grade control structure 10’ d/s

Upper San Francisquito Creek

Large flows are the most powerful

Large flows are rare

WHAT IS THE “DOMINANT (or “effective”) DISCHARGE”?

Flow frequency and coarse (>0.0625 mm) sediment load for long-term daily mean flow record for Sespe Creek at Fillmore [USGS gage 11113000].

Large flows are (pretty) rare

Large flows are the most powerful

Large flows, over time, move the most sediment

THE PERSPECTIVE FROM SoCAL:

Flow frequency and coarse (>0.0625 mm) sediment load for long-term daily mean flow record for Sespe Creek at Fillmore [USGS gage 11113000].

THE PERSPECTIVE FROM SoCAL:

Very rare

Horizontal Distance (ft)

19772005

View looking downstream

Elevation (ft)

10x vertical exaggeration

Bank retreatBar growth

Sespe Creek Cross-Section Analysis (1977 & 2005)

550’ (avg. 20’/yr)10’

Presenter

Presentation Notes

Example of lateral migration upstream of channel constriction


Changes in active channel

boundary

Changes in braids

Infrastructure and armoring



boundary

Changes in braids


Wildfire Sediment Production

Watershed-wide predictions:

• BAER (USFS 2006)- 6.1-fold increase(1,663 t km-2 a-1 to 10,188 t km-2 a-1)

• GLU (this study)- 4.7-fold increase(1,760 t km-2 a-1 to 8,200 t km-2 a-1)

• Scott and Williams (1978)- 3-fold increase based on max. possible increase in Fire Factor

G E O M O R P H O L O G Y

Predicted GLU-predicted fine-sediment production for pre-fire and post-fire (Day and Piru fires)

Sediment yield and associated vegetation and litter recovery during the fire-induced ‘window of disturbance’ (based on Shakesby and Doerr 2006).

~101 yr

Post-fire sediment delivery - field evidence

Upper half of the Sespe Gorge (2-5 m deep pools filled with sands in early

2008)

DateGauge Height

Change Aggradation / Incision

m ft

7 May 2003

11 Apr 2005 +1.69 +5.54 Aggradation

3 Mar 2008 -1.67 -5.47 Incision

Presenter

Presentation Notes

Right: aerial view of debris deposit and subsequent scouring of gravelly-sand material directly into Sespe Creek (note: fan into creek)

S U M M A R Y

1. Geology, climate, and watershed disturbance all contribute to “episodic channel form.”

2. Humid-region paradigms are enticingly misleading.

3. Recognition of the differences is widespread; understanding, however, still lags (but is growing).

episodic river channel form

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