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Debris Flows and Landscape Interactions:

Simulations with a landscape model incorporating forest-geomorphic interactions in the Oregon Coast Range indicate that the removal of wood from mountain watersheds would likely result in at least doubling the average runout length of debris flows and increasing the maximum runout length by 400%. These results, part of the Coastal Landscape Analysis and Modeling Study (CLAMS), a collaboration including researchers from OSU's College of Forestry and the USDA Forest Service Pacific Northwest Research Station, suggest that timber harvest could have large consequences for both hazards and aquatic habitat by promoting extension of debris flow impacts into valleys and streams previously unaffected by such catastrophic processes.

The above work spawned studies of debris dams and their effects over geologic time and of where and of sediment storage in headwater valleys.

Questions for ongoing and future research include the following: (1) Can riparian buffers mitigate the effects of forest harvest on aquatic habitat? (2) Given the important role of wood in this system, what might the effects of climate change be? (3) What are the roles of debris flows and wood in the evolution of valley morphology over geologic time? (4) How do sediments deposited by debris flows fit into the sediment budgets of larger basins, e.g., what is the evacuation time distribution of sediments in valleys at the transition between mass-movement and fluvial processes?

Current Projects:

Application of the CHILD model to determine the probability of wood and sediment delivery to a critical reach: This study, funded by the National Council for Air and Stream Improvement (NCASI), will follow up on the above modeling study and examine the effects of forest practices on debris flows and sediment transport, particularly in fish-bearing streams.

Sediment Storage at the Transition Between Debris-Flow and Fluvial Processes: This study, funded by the National Science Foundation (Geomorphology and Land-use Dynamics, EAR-0545768), will use airborne laser-swath mapping (ALSM, aka LiDAR) to measure sediment volumes and radiocarbon dating to estimate evacuation time distributions for sediment stored in mountain stream valleys in the Oregon Coast Range. The first paper from this study indicates that, while most sediment is evacuated within a few hundred years, some remains for millennia.

Recently, detailed study of sediment deposits at the mouths of two different tributaries with similar-sized mainstem streams in the Oregon Coast Range revealed different dynamics of sediment delivery and storage, as well as different effects on sediment routing through the adjacent mainstems. The smaller (0.14 km²), steeper (10%) tributary has a much larger deposit, a fan composed predominantly of bouldery debris flow deposits, whereas a tributary that is 10X larger (1.5 km²) and half as steep (5%) has a deposit only one-tenth the size and composed predominantly of fluvial silt, sand, and gravel. The sediment residence times, calculated from extensive radiocarbon dating, in the two tributary deposits are actually similar, at 1400 and 1700 years, respectively, and in both cases a significant amount of sediment remains for several millennia before being evacuated. The key difference between the tributaries is that sediment delivery from the smaller one is dominated by debris flows with a recurrence interval of about 100 years, whereas debris flows usually stop upstream of the mouth of the larger. The smaller tributary's fan-shaped, bouldery deposit traps 60% or more of the sediment eroded from the contributing watershed, but less than 1% of the larger tributary's deposits are trapped at its mouth. The delivery, or not, of debris flows to the mainstems has a substantial, and somewhat counter-intuitive, effect on sediment storage in the adjacent mainstem valleys. Bouldery deposits delivered by the smaller tributary help the adjacent mainstem valley store about 7X the amount of sediment stored in the mainstem adjacent to the larger tributary, but the residence time of sediment in the latter valley reach is almost 10X greater (4000 years vs. 400 years): debris flows entering the former stream force its channel to move and therefore erode deposits more frequently than in the latter, where boulders from infrequent debris flows trap some sediments for much longer times, some exceeding 10,000 years. This study implies that small, steep, debris flow-delivering tributaries have disproportionately large effects on the delivery, storage, and transport of gravels crucial for the spawning of threatened and endangered salmonids.

River Meandering and Landscape Interactions:

An analysis of historical bank erosion rates of the Willamette River, Oregon, with a model of river meandering recently provided the first quantitative measurement of the erodibilities of different geologic units forming the river's banks. Specifically, we found that modern floodplain deposits are only 2-4 times more erodible than partially cemented sediments likely deposited during the last ice age. While artificial revetments were found to be ten times more resistant than the banks formed of ancient deposits, the lack of revetments on these naturally resistant banks suggests that landowners are actually comfortable with moderate rates of bank erosion such as might be accomplished by replacing revetments with natural vegetation. This research was conducted in collaboration with a project funded by the National Science Foundation's Biocomplexity Intitiative and including researchers in OSU's Departments of Bioengineering and Fisheries and Wildlife and UO's Department of Landscape Architecture.

My interest in channel migration and recent initiatives aimed at restoring the river by removing revetments led me to investigate the gravel migration leaves behind and specifically its effect on stream temperature.

Questions for ongoing and future research include the following: (1) What kinds and amounts of geomorphic change would likely result from removal of revetments? (2) Given that bar formation will likely accompany migration, what are the important hydrologic functions of those bars, especially with respect to the magnitude of hyporheic flow through them and associated cooling effects? (3) What are the mechanisms responsible for these functions? (4) How much and what kind of restoration might achieve cooling that would significantly improve water quality for salmonids?

Current Projects:

Heat Budget in the Hyporheic Zone of a Large, Gravel-Bed River: This pilot study, funded by the National Science Foundation (Hydrological Sciences, EAR-0538075) will use hydrologic and geophysical field techniques and hydrologic modeling to quantify the heat budget of a single gravel bar on the Willamette River, Oregon.

Modeling Meandering in the Landscape: An ongoing study seeks to find the sensitivities of valley morphology to bank and bed material properties with CHILD.

Predicting a Migration Corridor for the Missouri National Recreational River: This study is a collaboration with Robb Jacobson (USGS) and funded by the National Park Service. We will develop a model for predicting the migration of this relatively free-flowing, braided reach of the Missouri River in order to delineate a 100-year migration corridor. The first step will involve use of a calibrated meandering model. Subsequent steps (contingent on funding) will involve incorporation of braiding processes (e.g., bifurcation).