Trends in Sediment Delivery Trends in Sediment Delivery from Bay Area Watersheds from Bay Area Watersheds

determined from determined from sediment budget analysissediment budget analysis

Peter W. DownsPeter W. Downs

Stillwater Sciences, Berkeley, CAStillwater Sciences, Berkeley, CA

Lagunitas Creek Lagunitas Creek – sediment budget since 1983– sediment budget since 1983

Periods

1850-1918: European arrival &

resource development

1919-1945: regulation and grazing

1946-1982: intensive damming

1983-present: raising of Peters

Dam, planning, mitigation

= 93.3 km2

= 64.3 km2

= 55.7 km2

= 49.0 km2

= 19.1 km2

Total area = 281.4 km2

Data sources

Establishing rates

• existing quantitative sediment source

inventories

• analysis of sequential aerial photographs

• hillslope and in-channel reconnaissance

• digital terrain modeling of GLUs for

extrapolation

• soil production / diffusion model application

• road sediment model application

Corroborating rates

• literature review of nearby process rates

estimates

• analysis of gauging records for sediment yields

• bathymetric surveys of Nicasio Reservoir

Management scenarios

• sediment transport modeling

ApproachApproach

Finite set of probably relevant Finite set of probably relevant processesprocesses

Process categoryProcess category ProcessesProcesses MethodMethod

Hillslope mass Hillslope mass wastingwasting

Creep / biogenic transportCreep / biogenic transport

Shallow and deep Shallow and deep landslidinglandsliding

Numerical modeling (UCB)Numerical modeling (UCB)

Field surveys / air photosField surveys / air photos

Overland FlowOverland Flow Sheetwash and Rill erosionSheetwash and Rill erosion Field surveysField surveys

Channel productionChannel productionHead advance / knickpointHead advance / knickpoint

Gullying and incisionGullying and incision

Bank erosionBank erosion

Field surveys / air photosField surveys / air photos

Structure / vegetation agesStructure / vegetation ages

Field surveysField surveys

Road-relatedRoad-related

Cut & fill failuresCut & fill failures

Surface and crossing Surface and crossing erosionerosion

Gully formationGully formation

Numerical modeling Numerical modeling (SEDMODL2), field surveys(SEDMODL2), field surveys

AgricultureAgricultureSurface wash, accelerated Surface wash, accelerated runoff, shallow landsliding, runoff, shallow landsliding,

bank destabilizationbank destabilizationField surveys / air photosField surveys / air photos

UrbanUrban Fine sediment release, Fine sediment release, accelerated runoffaccelerated runoff Field surveys / air photosField surveys / air photos

Channel ManagementChannel Management

Destabilization: Destabilization: straightening, riparian veg straightening, riparian veg

removalremoval

Forced storageForced storage

Field surveys / air photosField surveys / air photos

Routing and StorageRouting and StorageSediment transportSediment transport

Channel & overbank Channel & overbank storagestorage

Numerical modeling (TUGS)Numerical modeling (TUGS)

Field / x-section dataField / x-section data

Discrete hillslope sources Discrete hillslope sources

From air photo analysis

From field surveys

Extrapolation via Geomorphic Landscape Extrapolation via Geomorphic Landscape UnitsUnits

Road-related Road-related erosion – erosion –

SEDMODL2SEDMODL2

Channel-related Channel-related erosionerosion

Bank erosion

Channel incision

0.1

1

10

100

1000

10000

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000

Instantaneous discharge (cfs)

Su

sp

en

de

d s

ed

ime

nt

dis

ch

arg

e (

ton

s/d

ay

)

field measurements (WY 2005-2008)

LOWESS fitted curve

0.01

0.1

1

10

100

1000

10000

100000

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000

Daily mean discharge (cfs)

Su

sp

en

de

d s

ed

ime

nt

dis

ch

arg

e (

ton

s/d

ay

)

field measurements (WY 2004-2006)

LOWESS fitted curve

0.01

0.1

1

10

100

1000

10000

100000

0 2,000 4,000 6,000 8,000 10,000 12,000

Instantaneous discharge (cfs)

Su

sp

en

de

d s

ed

ime

nt

dis

ch

arg

e (

ton

s/d

ay

)

field measurements (WY 1990-2006)

LOWESS fitted curve

Corroboration 1:Corroboration 1:Gauged sediment Gauged sediment

yieldsyields

San Geronimo

Lagunitas @ SPT

Lagunitas @ PRS

Gauge Location

Average annual

bedload(t a-1)

Average annual

suspended

sediment load(t a-1)

Average annual total

sediment load(t a-1)

Average annual

unit total sediment

load(t km-2 a-

1)

San Geronimo Creek at

Lagunitas Rd. bridge (MMWD

gauge)

1,670 3,668 5,337 231

Lagunitas Creek at Samuel P.

Taylor State Park (USGS gauge 11460400)

641 3,631 4,272 131

Lagunitas Creek at Pt. Reyes

Station(USGS gauge 11460600)

2,584 14,640 17,224 276

140

145

150

155

160

165

170

0 20 40 60 80 100 120 140 160 180

Horizontal Distance (ft)

Ele

vati

on

(ft

NG

VD

29)

pre-1961

1976

1987

1990

2008 Long Profile

100

110

120

130

140

150

160

170

180

190

0 100 200 300 400 500 600 700 800 900 1,000

Horizontal Distance (ft)

Ele

vati

on

(ft

NG

VD

29)

pre-1961

1976

2008

Section 12B-12A

Section 6A-6B

Corroboration 2:Corroboration 2:Bathymetric yieldsBathymetric yields

Study area

Contributing drainage

area(km2)

Sediment yield into reservoir study area(t a-1)

MMWD estimate for the period of 1961-1970/6

Stillwater Sciences

bathymetry survey

estimate for the period of 1961-2008

Stillwater Sciences GLU estimate for the period

of 1982-2008

Nicasio/Halleck Creek arm 54.9 15,100 25,479 17,533

Entire Nicasio Reservoir

(u/s of Seeger Dam)

93.2 32,640 N/A 26,595

Bathymetric Bathymetric yieldsyields versus versus

GLU GLU

Watershed

Area

Sediment yield derived from

sediment rating data

Unit rate

Bathymetry survey

estimate

Unit rate

Sediment delivery

estimated from extrapolated field survey

Unit rate

km2 WY 1983–2008t a-1 t km-2 a-1

WY 1961–2008a

WY 1961–1976b

t km-2 a-1 WY 1983–2008t a-1 t km-2 a-1

San Geronimo

Creek23.1 5,340 231 n/a 8,850 383

Lagunitas Creek at

Samuel P. Taylor

32.7 4,270 131 n/a 12,330 377

Lagunitas Creek at Pt.

Reyes Station 62.4 17,220 276 n/a 19,700 316

Nicasio/Halleck Creek

arm54.9 n/a 25,500 a 464 17,550 320

Whole Nicasio Reservoir

93.2 n/a 32,640 b 350 26,600 285

Comparison of sediment delivery / yield Comparison of sediment delivery / yield resultsresults

SedimentSedimentBudget – Budget –

sub-sub-watershewatershe

dd

Sediment Yields t a-1

M = mainstemT = tributary & hillslope

SedimentSedimentBudget – Budget –

processesprocesses

Sediment Yields t a-1

42%

26%

20%

Unit

Hillslope &

tribs

Main-stem

Total Yield

t km-2 a-1 t km-2 a-1 t km-2 a-

1

SanGeron 316 69 385

LagCr: SGC to

DG206 142 348

Devils Gulch 227 42 269

LagCr: DG to

Nicasio214 -82 133

Regulated Nicasio

Cr129 374 503

LagCr:NC to PRS

227 157 384

Implications for the SF Bay…or “So Implications for the SF Bay…or “So What?”What?”

Lagunitas CreekLagunitas Creek (62.4 km (62.4 km22) ) • 1983-2008 ~ 1983-2008 ~ 330330 t km t km-2-2 a a-1-1

– (Gauges = 131 – 276; bathymetry = 350 – 464; GLUs = 285 – 383)(Gauges = 131 – 276; bathymetry = 350 – 464; GLUs = 285 – 383)

Southern Tomales bay sedimentationSouthern Tomales bay sedimentation (226-132 km (226-132 km22): Rooney & ): Rooney & Smith (1999)Smith (1999)

• 1861-1931: 325 t km1861-1931: 325 t km-2-2 a a-1-1 (prograded primarily 1862-1918) (prograded primarily 1862-1918)

• 1931-1957: 290 t km1931-1957: 290 t km-2-2 a a-1-1

• 1957-1994: 190 t km1957-1994: 190 t km-2-2 a a-1 -1 (dry period; not efficient trapping) (dry period; not efficient trapping)

Redwood Creek (22.7 kmRedwood Creek (22.7 km22))• Pre 1840: 34 t kmPre 1840: 34 t km-2-2 a a-1 -1

• 1841-1920: 304 t km1841-1920: 304 t km-2-2 a a-1 -1 – Euro Arrival and Resource Development:– Euro Arrival and Resource Development:

• 1921-1980: 324 t km1921-1980: 324 t km-2-2 a a-1 -1 – Engineering as Management: – Engineering as Management:

• 1981-2002: 1981-2002: 198198 t km t km-2-2 a a-1-1 – Recovery & Restoration – reduces with incision – Recovery & Restoration – reduces with incision

• Future: 154 t kmFuture: 154 t km-2-2 a a-1-1 – because of legacy destabilization of tributaries – because of legacy destabilization of tributaries

-150

-100

-50

0

50

100

150

200

250

300

350

Se

dim

en

t Y

ield

(t

km

-2 a

-1)

Yield from mainstem storage

Tributary watershed production

Total sediment production

Tributary watershed production including

Green Gulch

Total watershed yield including Green Gulch

Pre-1840

1841

-19

20

1921

-19

8019

81-2

002

Period

-150

-100

-50

0

50

100

150

200

250

300

350

Se

dim

en

t Y

ield

(t

km

-2 a

-1)

Yield from mainstem storage

Tributary watershed production

Total sediment production

Tributary watershed production including

Green Gulch

Total watershed yield including Green Gulch

Pre-1840

1841

-19

20

1921

-19

8019

81-2

002

Period

Redwood Creek ‘Wolman Curve’Redwood Creek ‘Wolman Curve’

Pre- 1840

1841 - 1920

1921 - 1980

1981 - 2002

Redwood Redwood CreekCreek

Estuarine Estuarine Deposits Deposits

Jon Warrick’s Jon Warrick’s slidesslides

Infilling: you bet! – Redwood Creek Big Infilling: you bet! – Redwood Creek Big LagoonLagoon

Time periodTime period

MeasureMeasure Unit Unit raterate

Pre-Pre-18401840

1841-1841-19201920

1921-1921-19801980

1981-1981-20022002

Total Yield to Total Yield to Big LagoonBig Lagoon

mm33aa-1-1 454454 40574057 43244324 23762376

Sedimentation Sedimentation rate (ave = rate (ave = 14%BL+50% 14%BL+50% susp susp intercepted)intercepted)

mmamma-1-1 2.6 2.6

0.6-4.50.6-4.523.3 23.3

5.7-40.65.7-40.624.7 24.7

6.1-43.26.1-43.232.3 32.3

3.3-56.63.3-56.6

Morphological Morphological rate rate

mmamma-1-1 0.8-1.20.8-1.2 11.211.2 11.211.2 5.6-86.85.6-86.8

Sea-level riseSea-level rise mmamma-1-1 1.05-1.05-1.51.5

1.11.1 2.12.1 2.12.1

Thoughts…Sac/SJR vs. SF Bay Area Thoughts…Sac/SJR vs. SF Bay Area Tribs?Tribs?

• Pre-European – less “well-connected”: effective area smaller, overbank Pre-European – less “well-connected”: effective area smaller, overbank storage;storage;• ~30 t km~30 t km-2-2 a a-1 -1 ??

• Post-arrival, “resource development”, channel management, first flush:Post-arrival, “resource development”, channel management, first flush:• > 350 t km> 350 t km-2-2 a a-1-1; 500 t km; 500 t km-2-2 a a-1-1 over decades? over decades?

• Now, “normal” developed use = > 300 t kmNow, “normal” developed use = > 300 t km -2-2 a a-1-1

• Much from channelsMuch from channels

• Under “protective custody” = < 200 t kmUnder “protective custody” = < 200 t km -2-2 a a-1 -1 in high relief watershedin high relief watershed

• Incision (loss of alluvial storage) is a very effective delivery mechanismIncision (loss of alluvial storage) is a very effective delivery mechanism• 100% delivery; very little overbank storage100% delivery; very little overbank storage

• Not just volumes: changing sediment sources, and sediment caliberNot just volumes: changing sediment sources, and sediment caliber

Conceptual Model Conceptual Model Yields proportional to:Yields proportional to:• ReliefRelief

• Relative erodibility (geology)Relative erodibility (geology)

• Frequency of large floods / high intensity precipitation events – ENSOFrequency of large floods / high intensity precipitation events – ENSO

• Fire / earthquakes triggering landslidesFire / earthquakes triggering landslides

• Effective contributing area – tributary disconnectionEffective contributing area – tributary disconnection

• (Availability of marsh / lagoon / estuary habitat )(Availability of marsh / lagoon / estuary habitat )

• Land use history: agriculture vs. conservation managementLand use history: agriculture vs. conservation management

• Road and railRoad and rail

• Channel management impacts on disconnecting floodplains: straightening Channel management impacts on disconnecting floodplains: straightening (drainage or flood control)(drainage or flood control)

• Dams: existing and former – supply reduction them increaseDams: existing and former – supply reduction them increase

• Urban development – supply increase then reduction then increase…Urban development – supply increase then reduction then increase…

• Aggregated mining – interception possibly, more likely narrowing and Aggregated mining – interception possibly, more likely narrowing and baseline related incisionbaseline related incision

• 1 / Area1 / Area