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

Monitoring Headwater Streams gfor Landscape Response to

Climate ChangeClimate Change

Matthew O’Connor, PhDO’Connor 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


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


Headwater Stream GeomorphologyHeadwater Stream Geomorphology

• Swale/zero orderSwale/zero order basin

• No surface channel• Topographic

convergenceg• Subsurface flow

accumulation• Colluvial soil


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


g


• Discontinuous or intermittent surface channelS il i• Soil or organic substrate

• Minimal channel• Minimal channel erosion

• Topographic opog ap cconvergence with lateral soil creep



• First order channelFirst order channel• Substantial fluvial

erosion• Resistant channel

substrate– Gravel Bedrock– Woody debris

• Bank erosion



• 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)


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


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


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


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


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


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


Extensive Channel SurveysExtensive Channel Surveys

• ResourcesResources– GPS survey equipment– LiDAR topographic mappingp g p pp g– Robust statistical methods (e.g. GLM’s capable of

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

itiposition• Other hydrologic and ecosystem parameters


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

Landslide

Residual Soils


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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