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
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