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Reservoir Sedimentation and Wildfire in the Sierra Nevada M Reservoir Sedimentation and Wildfire in the Sierra Nevada M

Reservoir Sedimentation and Wildfire in the Sierra Nevada M - PowerPoint Presentation

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Reservoir Sedimentation and Wildfire in the Sierra Nevada M - PPT Presentation

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

sedimentation reservoir model sediment reservoir sedimentation sediment model fire 2009 bulit minear database kondolf watershed reservoirs wrr data time

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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