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
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
IEO IEOAWRA – AnchorageMay 4, 2009
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
IEO IEOAWRA – AnchorageMay 4, 2009
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)
IEO IEOAWRA – AnchorageMay 4, 2009
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
IEO IEOAWRA – AnchorageMay 4, 2009
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
IEO IEOAWRA – AnchorageMay 4, 2009
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
IEO IEOAWRA – AnchorageMay 4, 2009
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. 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
IEO IEOAWRA – AnchorageMay 4, 2009
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
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
IEO IEOAWRA – AnchorageMay 4, 2009