Monitoring Headwater Streams for Landscape Response to ?· Monitoring Headwater Streams for Landscape…

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Monitoring Headwater Streams gfor Landscape Response to

Climate ChangeClimate Change

Matthew OConnor, PhDOConnor Environmental, Inc.

www oe i comwww.oe-i.comHealdsburg, California

IEO IEOAWRA AnchorageMay 4, 2009

OverviewOverview

Headwater stream geomorphology Headwater stream geomorphology Response to hydrologic change Monitoring to detect change

Effects of land management Effects of climate change

IEO IEOAWRA AnchorageMay 4, 2009

Headwater Streams as Indicators of Change

Dietrich and Dunne, 1993 The Channel Head, IN Channel Network Hydrology (Eds., Bevin and Kirkby).

Instability at channel heads can generate destructive debris flows orInstability at channel heads can generate destructive debris flows or gullying, and heavy sediment loading downstream. Because the channel-head location at any time is controlled by the relative magnitudes of sediment supply and the erosion potential due to runoff fluctuations in climate or land use which alter runoff ratesrunoff, fluctuations in climate or land use, which alter runoff rates, surface erodibility and sediment supply, cause shifts in channel head location. Therefore, the channel head may be the element of the coupled hillslope-channel system that is most sensitive to changes in external factors Erosion and deposition cycles whichchanges in external factors. Erosion and deposition cycles which sweep through drainage basins may be largely influenced by shifts in the balance controlling channel-head locations

IEO IEOAWRA AnchorageMay 4, 2009

Headwater Stream GeomorphologyHeadwater Stream Geomorphology

Swale/zero orderSwale/zero order basin

No surface channel Topographic

convergenceg Subsurface flow

accumulation Colluvial soil

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The Channel HeadThe Channel Head Slopes < 45 degreesp g Defined banks Soil mantle 1 to 5 ft

thick Subsurface flow

d i idrives erosion Often discontinuous

with vegetated stepswith vegetated steps Springs in wetter

regions

IEO IEOAWRA AnchorageMay 4, 2009

g

Headwater Stream GeomorphologyHeadwater Stream Geomorphology

Discontinuous or intermittent surface channelS il i Soil or organic substrate

Minimal channel Minimal channel erosion

Topographic opog ap cconvergence with lateral soil creep

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Headwater Stream GeomorphologyHeadwater Stream Geomorphology

First order channelFirst order channel Substantial fluvial

erosion Resistant channel

substrate Gravel Bedrock Woody debris

Bank erosion

IEO IEOAWRA AnchorageMay 4, 2009

Headwater Stream GeomorphologyHeadwater Stream Geomorphology

Debris flow originatingDebris flow originating in colluvium-filled bedrock hollow Steep slope gradient Colluvial soil

l ti taccumulation to some critical depth

Triggered byTriggered by hydrologic forcing (typically an extreme storm or flood)

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storm or flood)

Headwater Stream ResponseHeadwater Stream Response Changes in flow

P k ff Peak runoff Annual runoff Seasonal flow Seasonal flow Increase or decrease in flow

Erosion processesErosion processes Surface flow surface erosion or mass

failure of undermined steps at plunge pools Subsurface flow seepage erosion Landsliding

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Headwater Stream ResponseHeadwater Stream Response

Response to land managementResponse to land management Urban development

Forest canopy removal Forest canopy removal Timber harvest Conversion to agricultureConversion to agriculture

Increases in peak flow

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Headwater Stream ResponseHeadwater Stream Response

Forest canopy removalForest canopy removal 20 to 30% increase in peak flow in coastal

redwoods in northern California Increase in annual runoff Expect variation among ecosystems

Anticipated channel response Headward erosion at channel head Accelerated channel and bank erosion Rates uncertain

IEO IEOAWRA AnchorageMay 4, 2009

Monitoring Headwater Streams-T hi STopographic Survey

Channel response may be subtle in short termChannel response may be subtle in short term Natural variability Change expressed over time-years or decades?g p y Response to hydrologic events

Approaches to detection and measurement of change Detailed topographic surveys Extensive channel surveys

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Monitoring Topographic ChangeMonitoring Topographic Change

Cross-section surveysCross section surveys Swale

Channel head zone Channel head zone Channel

L it di l fil Longitudinal profile survey Oriented to detecting vertical change in

channel bed as well as channel extension

IEO IEOAWRA AnchorageMay 4, 2009

IEO IEOAWRA AnchorageMay 4, 2009

IEO IEOAWRA AnchorageMay 4, 2009

Extensive Channel SurveysExtensive Channel Surveys

Combine with detailed topographicCombine with detailed topographic surveys in a 2-stage sampling design

Map channel heads Map channel heads Watershed scale

R i l l Regional scale Describe location of channel heads and

process changes that may occur

IEO IEOAWRA AnchorageMay 4, 2009

IEO IEOAWRA AnchorageMay 4, 2009

Extensive Channel SurveysExtensive Channel Surveys

ResourcesResources GPS survey equipment LiDAR topographic mappingp g p pp g Robust statistical methods (e.g. GLMs capable of

evaluating potential covariates) Locate, describe and identify channel heads Monitor to observe horizontal change in channel

itiposition Other hydrologic and ecosystem parameters

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Analytical ApproachesAnalytical Approaches

Extensive regional ChanneledExtensive regional data sets

Reveal differences in

Dra

inag

e A

rea

Unchanneled

Channeled

Existing conditions Response to change

00

Slope

Landslide

Example Slope drainage area

Landslide

1.0

10.0

Acre

s

Colluvium

Landslide

relationship0.0

0.1

0.1 1.0 10.0 100.0

Sl %

Area

LandslideResidual Soils

IEO IEOAWRA AnchorageMay 4, 2009

Slope %

Application to Climate and H d l i Ch i Al kHydrologic Change in Alaska

Direct measurement of physical changep y g Sensitive to change Complements other data sets and models

Regional differences Regional differences Boreal forest (drier?) v. coastal forests (wetter?)

Channel response in permafrostp p Network extension, soil drainage

Vegetation responseWetter v drier Wetter v. drier

Accelerated growth Fire

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