Forest Hydrology Issue: Interaction of forests, fish, and climate One of the dominant pathways by which land cover change affects freshwater fish habitat is via sediment loading associated with forest disturbance Vegetation management, forest fires, and forest roads affect both the amount of sediment available for transport and the amount of surface water available to transport it. The interaction of climate with these processes has not previously been explored but is likely to have implications for integrated management and conservation efforts, especially recovery of PNW salmon (for which expenditures in the region are several hundred $million annually). An enhanced ability to project the likely effects of climatic change, fire, and vegetation management on sediment transport would improve our understanding of forest-aquatic interactions and the scientific basis for forest management.

Research questions What are the relative contributions of sediment generation from landslides, road and road cut erosion, and surface erosion over the general landscape, and how do these relative contributions vary over the climate regimes represented by forested areas of the PNW? How do the amounts and proportions of sediment generated from the above sources compare to sediment generated by extreme storms, droughts, and fire regimes, and to sedimentation amounts under forest different management scenarios? How will sediment generation from PNW watersheds respond to the interaction of land cover change with climatic variability and change at decadal to century time scales?

Approach Modify existing Distributed Hydrology-Soil- Vegetation Model (DHSVM) to include the capability to represent sediment generation by slope failures, and hillslope and road erosion, as well as sediment routing through channel systems (partially completed, see Doten et al, 2004, in review, WRR) For both “generic” watersheds and specific demonstration applications, conduct evaluations of impacts of alternative forest policy and management scenarios with respect to harvest, thinning, prescribed burning, and road construction or obliteration, and evaluate (via “shuffled deck” experiments), climate risk (and effects of changing climate) associated with these scenarios.

Distributed hydrology-soil- vegetation model (DHSVM) Physically based hydrologic model that represents the effects of –Topography –Soil –Vegetation Solves the energy and water balance at each grid cell at each timestep

Erosion and Sediment Transport Module HILLSLOPE EROSION Soil Moisture Content CHANNEL ROUTING Precipitation Leaf Drip Infiltration and Saturation Excess Runoff DHSVM Q Q sed Sediment MASS WASTING Erosion Deposition ROAD EROSION Sediment Channel Flow

Failure Prediction Mass wasting algorithm performed at a finer resolution TOPMODEL topographic wetness index used to redistribute soil saturation (Beven and Kirkby, 1979; Burton and Bathurst, 1998) Run for critical times

Overroad Flow Routing Routing takes into account crown road crown road- side ditch hillslope fillslope

Erosion Sediment becomes available for transport by: –three mechanisms (hillslopes) –two mechanisms (roads) shearing by overland flow leaf drip impact raindrop impact Mechanisms of Soil Particle Detachment

Sediment Routing Road surface sediment: Routed according to the crown type. Added to the road-side ditch is routed through the network to a culvert. Delivery from culvert to stream based on proximity and particle size: Particle Size, mm Percent Delivered ≤ Hillslope: If a pixel contains a channel (including road- side ditches), all sediment enters the channel. Hillslope Sediment Routing