J Toby Minear and Scott Wright California Water Science Center United States Geological Survey Outline Introduction What is reservoir sedimentation How does fire affect sedimentation 3W model for reservoir sedimentation in California ID: 397988
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Slide1
Reservoir Sedimentation and Wildfire in the Sierra Nevada Mountains, CA
J. Toby Minear and Scott WrightCalifornia Water Science CenterUnited States Geological SurveySlide2
Outline
IntroductionWhat is reservoir sedimentation?How does fire affect sedimentation? ‘3W’ model for reservoir sedimentation in CaliforniaSedimentation study with Sierra Nevada Conservancy
How we could use your help…Slide3
Reservoir blocks downstream transport of sediment
Sediment accumulates in the reservoir = reservoir sedimentation
Reduced sediment supply to downstream areas
“
Hungry water” = downstream erosion of bed and banks
Reservoir
sedimentation
Erosion of bed and
banks from “Hungry water”
Reservoir Sedimentation
Sediment
Sediment
Dam
WaterSlide4
Effects of Fire on Sediment Dynamics
Fires in S. CA and Coast Ranges:Fires can increase sediment loads 5-120+ times the pre-fire levelIn particular, the ‘fire-flood’ scenario
leads to highest sediment ratesTypically 5+ years before rates return to pre-fire levels
Effects are not as well
known for the Sierras
CalFire
fire history databaseSlide5
Modeling Reservoir Sedimentation in the Sierras
Mutiple dams in the same watershed and changes to trap efficiency with time are major issuesMinear and Kondolf (2009) came up with a method to address this issue: ‘3W’ model
Estimates long-term sediment yields from reservoir sedimentation records; applies these yields to unmeasured reservoirsAccounts for multiple dams in the same watershed and changes in trap efficiencyUser-chosen time-step (yearly time-step for 2009 paper) and number of sub-regions (geomorphic regions for 2009 paper)Slide6
Reservoir Sedimentation in
California: ‘3W’ Model- 12 geomorphic
regions- 1,391
dams
- 70 dams
with measured
sedimentation rates
3W model: statistical approach; based on geomorphic regionto estimate median
sediment yield
Minear and Kondolf, 2009, WRR
Black dots = measured reservoirsWhite dots = unmeasured reservoirsSlide7
3W Model Results
Sediment yield rates by geomorphic region:
Minear
and
Kondolf
, 2009, WRRSlide8
3W Model Results
Estimated reservoir capacity remaining in 2008 (as percent of original)
Minear
and
Kondolf
, 2009, WRRSlide9
3W Model Results
Estimated reservoir sedimentation in acre-feet
Minear
and
Kondolf
, 2009, WRRSlide10
Limitations of the 3W model
Reservoir B,Bulit 1957
Reservoir C,
Bulit
1933
Reservoir A,
Bulit 1949
Reservoir F,Bulit 1947
Reservoir E,Bulit 1964Reservoir D,
Bulit 1984
1. Not GIS friendly
2
. Difficult to include GIS attributes / modeling
- e.g watershed parameters, fires, soils, climate, climate change, etc.
time
hydrology
3. No hydrologySlide11
Objectives of this study
1. Determine better reservoir sedimentation rates in the Sierra, particularly related to fire2. Compile existing reservoir sedimentation records into a single, publicly accessible database
**We could use help from local partners to help obtain the sedimentation and capacity dataSlide12
Improved R
eservoir Sedimentation Model
Dam data
(size, date constructed,
s
edimentation, operation)
Gage data
(hydrology + sediment)
++
GIS data: watershed factors(fire history, slope, aspect, watershed size, mainstem length, etc.)
Addressing sediment concerns and long-term reservoir storage in the Sierras (both in the reservoir and downstream)Slide13
Publicly Accessible D
atabase
Interagency project to update nation-wide reservoir sedimentation database: http://ida.water.usgs.gov/ressed/
T
he RESSED database:Slide14
Future Steps
Next Phase: Field studies of individual reservoirsDetermine sedimentation rates related to fireAdditional bathymetric mapping, coring, sediment mappingWill depend on finding interested partnersSlide15
Questions?
jminear@usgs.gov