Broad-Scale Models Dan Miller + Kelly Burnett, Kelly Christiansen, Sharon Clarke, Lee Benda GOAL Predict Channel Characteristics in Space and Time Assess Potential for Fish Use and Productivity Assess Impacts of Land Use and Natural Disturbance STRATEGY Use 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
A Conceptual Framework for Process Interactions at the Watershed Scale 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 Hierarchical Channel Network History of Events Antecedent Conditions
DEM-Derived Attributes: The Spatial Template Hillslope Gradient Slope Form Contributing Area Hydrologic Response Landslide Susceptibility Debris Flow Routing Landslide / Debris Flow Scour Landslide or Debris Flow Deposition Colluvial Channel Fluvial Channel Channel Drainage Area Gradient Valley Width Tributary Junctions Channel Type / Form Debris Fan, Terrace N km 5
Estimate Habitat Attributes as Functions of Geomorphic Variables Sediment Volume Boulders LWD 70% 60% Harvey East Branch Pools Mean Pool Density (m/m) 50% 40% 30% 20% 10% 0% 0 0.5 1 1.5 2 Mean Sediment Depth (m)
Boulders 30% 25% 20% 15% 10% 5% 0% Upstream Downstream Boulders 0 20 40 60 80 100 Distance from Tributary (m) Spatial Controls on Channel Roughness Boulders and LWD tend to be associated with debris fans at low-order tributary mouths old debris flow deposits LWD Density (#/100m) Sediment Depth (m) 2.0 1.5 1.0 0.5 0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Wood Upstream Downstream 0 20 40 60 80 100 Distance from Tributary (m) Sediment Upstream Downstream 0 20 40 60 80 100 Distance from Tributary (m)
Landslide Volume (cubic meters) Landslide Effects Determined by the Relative Size of the Landslide and Channel 10 8 10 7 Permanent Valley-floor aggradation Landslide dams - lakes 10 6 10 5 Large Effects Transient dams ponds Channel displacement? 10 4 10 3 Increasing Effects LWD, Boulders Jams Few Effects 10 2 0 0.5 1 1.5 2 2.5 3 Transport Potential Channel Size Channel Slope (m/m) * Drainage Area (sq. km)
Channel Characteristics Sediment / LWD Inputs Transport Potential Storage Potential Landslides, Debris Flows Discharge Drainage Area Channel Gradient Valley Width Basin Characteristics Assembly of channel and valley types (size, gradient, width) Size, network location, and spacing of debris-flowprone tributaries
Debris Flows: Addressed in terms of Initiation, Runout, and Deposition Initiation Scour Runout Transport Deposition
Landslide Occurrence What 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 } DEM Empirically calibrate against mapped landslide locations (ODF 1996 storm study, Siuslaw National Forest 1996 landslide inventory)
Landslide Susceptibility as a function of topography and vegetation cover Define a Topographic Index of Landslide Susceptibility Normalized Landslide Density as a Function of the Index 20 %LS %Area 15 10 5 0 1 = A 0.01 1 100 10000 Topographic Index sin( θ ) ( 1 tan( θ )) A -1 = specific contributing area θ = surface gradient Landslide Density (#/sq km) Mean Landslide Density as a Function of Vegetation Cover 5 4 3 2 1 0 Siuslaw Inventory Uncorrected Bias Corrected Bias & Topo Open Mixed Large Conifer Roads Vegetation
Probable Landslide Density (#/km 2 ) based on topography and stand-type Calibrated to February, 1996 Storm; Knowles Creek Basin, OR >0 2-5 5-10 >10
Debris Flow Runout What 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 }DEM Empirically calibrate against mapped debris flow impacts (ODF 1996 storm study)
Probability of Delivery to a Fish-Bearing Channel based on gradient, scour length, tributary junction angles, and stand type Calibrated 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 channel Calibrated to February, 1996 Storm; Knowles Creek Basin, OR <1% 5% 10% >10%
Probability of Direct in-channel Debris Flow Impacts incorporating probability of initiation, transport, and deposition < 5% 10% 15% >15%
Basin-Scale Heterogeneity in Debris Flow Probability < 5% 10% 15% >15% Sweet Creek Knowles Creek
Mean Probability of Debris Flow Impacts 14% 12% 10% 8% 6% 4% 2% Knowles Creek Sweet Creek Greater probability of debris flow impacts at Knowles Creek Low-order channels more prone to impacts than high-order channels 0% 0 1 2 3 4 5 6 7 Stream Order
Vegetation Changes over Time Current 100 years Vegetation affects: Landslide susceptibility Probable debris flow runout distance Open, Roads Mixed Large Conifer
Changes in vegetation cover alter the probability of debris flow impacts These alterations vary as a function of stream order and network structure Proportional Reduction 70% 60% 50% 40% 30% 20% 10% Knowles Creek Sweet Creek 0% 0 1 2 3 4 5 6 7 Stream Order
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 hazard Potential for landslide delivery Probability of debris flow traversal LWD recruitment, road crossings Reach- and basin-scale estimates of channel characteristics Topographic controls on spatial heterogeneity: number, location, and spacing of debris-flow prone tributaries Effects of vegetation change modulated by network structure