GOALPredict Channel Characteristics in Space and Time

• Assess Potential for Fish Use and Productivity

• Assess Impacts of Land Use and Natural Disturbance

STRATEGYUse Understanding of Watershed Processes

as a Guide for Empirical Models

• Identify Controls on Habitat Formation

• Determine Appropriate Data Structure – put available information to the best use

Broad-Scale ModelsDan Miller + Kelly Burnett, Kelly Christiansen, Sharon Clarke, Lee Benda

A Spatial Template –Sediment Production, Delivery, Storage

Dynamic Drivers –Storms and Floods trigger erosional

events and drive sediment movement;Changes in vegetation alter erosional

susceptibility and transport potential

A Branched and HierarchicalChannel Network

History of Events –Antecedent Conditions

A Conceptual Framework for Process Interactionsat the Watershed Scale

HillslopeGradientSlope FormContributing Area

Hydrologic ResponseLandslide SusceptibilityDebris Flow Routing

ChannelDrainage AreaGradientValley WidthTributary Junctions

Channel Type / FormDebris Fan, Terrace

N

Landslide / Debris Flow ScourLandslide or Debris Flow DepositionColluvial ChannelFluvial Channel

km

5

DEM-Derived Attributes: The Spatial Template

SedimentVolume

BouldersLWD

Pools

Harvey East Branch

0%

10%

20%

30%

40%

50%

60%

70%

0 0.5 1 1.5 2

Mean Sediment Depth (m)

Mea

n P

oo

l Den

sity

(m

/m)

Estimate Habitat Attributes as Functions ofGeomorphic Variables

0%

5%

10%

15%

20%

25%

30%

0 20 40 60 80 100Distance from Tributary (m)

Bo

uld

ers

Upstream

Downstream

0

0.5

1.0

1.5

2.0

0 20 40 60 80 100

Distance from Tributary (m)

LWD

Den

sity

(#

/10

0m

)

UpstreamDownstream

Boulders Wood

Spatial Controls on Channel Roughness

Boulders and LWD tend to be associated with debris fans at low-order tributary mouths – old debris flow deposits

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 20 40 60 80 100Distance from Tributary (m)

Sed

imen

t D

epth

(m

) Upstream

Downstream

Sediment

102

103

0 0.5 1 1.5 2 2.5 3

Transport Potential – Channel SizeChannel Slope (m/m) * Drainage Area (sq. km)

Lan

dsl

ide

Vo

lum

e (c

ub

ic m

eter

s)

?

Large EffectsTransient dams – pondsChannel displacement

Increasing EffectsLWD, BouldersJams

Few Effects

PermanentValley-floor aggradationLandslide dams - lakes

104

105

106

107

108

Landslide Effects Determined by the Relative Size of the Landslide and Channel

Channel Characteristics

• Sediment / LWD Inputs

• Transport Potential

• Storage Potential

Landslides, Debris Flows

Discharge ∝ Drainage AreaChannel Gradient

Valley Width

Basin Characteristics

• Assembly of channel and valley types (size, gradient, width)

• Size, network location, and spacing of debris-flow-prone tributaries

Debris Flows: Addressed in terms of Initiation, Runout, and Deposition

Initiation

Scour

Transport

Deposition

Runout

Landslide OccurrenceWhat factors affect landslide susceptibility?

• Balance of Forces

• Pore-Pressure Gradients

• Effective Soil Strength

Estimate probability of soil failure as a function of:

• Surface Gradient

• Specific Contributing Area

• Stand Type

• Forest Roads

Empirically calibrate against mapped landslide locations (ODF 1996 storm study, Siuslaw National Forest 1996 landslide inventory)

} DEM

( ))tan(1)sin(1 θθ −= −AA-1= specific contributing area

θ = surface gradient

Define a Topographic Indexof Landslide Susceptibility

0

5

10

15

20

0.01 1 100 10000

Topographic Index

%LS

%Area

Normalized Landslide Densityas a Function of the Index

Siuslaw Inventory

0

1

2

3

4

5

Open Mixed LargeConifer

Roads

Vegetation

Lan

dsl

ide

Den

sity

(#/s

q k

m)

UncorrectedBias CorrectedBias & Topo

Mean Landslide Densityas a Function of Vegetation Cover

Landslide Susceptibility as a function of topography and vegetation cover

>0

2- 5

5-10

>10

Probable Landslide Density (#/km2) based on topography and stand-typeCalibrated to February, 1996 Storm; Knowles Creek Basin, OR

Debris Flow RunoutWhat factors affect runout distance?

• Gravitational acceleration

• Changes in mass

• Frictional deceleration and deposition

Estimate probability of runout to any point as a function of:

• Channel gradient

• Tributary junction angles

• Probable volume –using cumulative scour length as a proxy

• Riparian stand type

Empirically calibrate against mapped debris flow impacts (ODF 1996 storm study)

} DEM

Probability of Delivery to a Fish-Bearing Channel based on gradient, scour length, tributary junction angles, and stand typeCalibrated to February, 1996 Storm; Knowles Creek Basin, OR

<30%

60%

90%

>90%

Probability of LWD Recruitment based on probability of upslope landsliding and delivery to a fish-bearing channelCalibrated to February, 1996 Storm; Knowles Creek Basin, OR

<1%

5%

10%

>10%

Probability of Direct in-channel Debris Flow Impactsincorporating probability of initiation, transport, and deposition

< 5%10%15%>15%

KnowlesCreek

SweetCreek

< 5%10%15%>15%

Basin-Scale Heterogeneity in Debris Flow Probability

Greater probability of debris flow impacts at Knowles Creek

Low-order channels more prone to impacts than high-order channels

0%

2%

4%

6%

8%

10%

12%

14%

0 1 2 3 4 5 6 7

Stream Order

Knowles Creek

Sweet Creek

Mean Probability ofDebris Flow Impacts

Current 100 years

Open, RoadsMixedLarge Conifer

Vegetation Changes over Time

Vegetation affects:• Landslide susceptibility• Probable debris flow runout distance

0%

10%

20%

30%

40%

50%

60%

70%

0 1 2 3 4 5 6 7

Stream Order

Knowles CreekSweet Creek

Changes in vegetation cover alter the probability of debris flow impacts

Proportional ReductionThese alterations vary as a function of stream order and network structure

Goal: Topographic, vegetation cover, and landslide/debris flow mapping at coarse scales to infer channel/habitat characteristics at finer scales

Accomplishments:Landslide susceptibility and debris-flow-runout probability as functions of topography and vegetation cover

Landslide initiation hazardPotential for landslide deliveryProbability of debris flow traversal – LWD recruitment, road crossings

Reach- and basin-scale estimates of channel characteristicsTopographic controls on spatial heterogeneity:

number, location, and spacing of debris-flow prone tributariesEffects of vegetation change modulated by network structure