Heavy mineral compositions of sands from Oregon beaches, rivers and sea cliffs have been determined in order to examine the causes of marked along-coast variations in the beach-sand mineralogy. The study area extends southward from the Columbia River to the Coquille River in southern Oregon. The heavy-mineral compositions were determined by standard microscopic identification with additional verification by X-ray diffraction analyses. Initially the beach-sand samples were collected as single grab samples from the mid-beachface, but significant selective sorting of the important heavy minerals prevented reasonable interpretations of the results. Factor analysis of multiple samples from the same beach yielded distinct factors which correspond with known mineral sorting patterns. The effects of local sorting were reduced by the subsequent use of large composite samples, permitting interpretations of along-coast variations in sand compositions. Four principal beach-sand sources are identified by factor analysis: the Columbia River on the north, a Coastal Range volcanic source, sands from the Umpqua River on the south-Oregon coast, and a metamorphic source from the Klamath Mountains of southern Oregon and northern California. The end members identified by factor analysis of the beach sands correspond closely to river-source compositions, the proportions in a specific beach-sand sample depending on its north to south location with respect to those sources. During lowered sea levels of the Late Pleistocene, the Columbia River supplied sand which was dispersed both to the north and south, its content decreasing southward as it mixed with sands from other sources. The distributions of minerals originating in the Klamath Mountains indicate that the net littoral drift was to the north during lowered sea levels. With a rise in sea level the longshore movement of sand was interrupted by headlands such that the Columbia River presently supplies beach sand southward only to the first headland, Tillamook Head. At that headland there is a marked change in mineralogy and in grain rounding with angular, recently-supplied sands to the north and rounded sands to the south. The results of this study indicate that the present-day central Oregon coast Consists of a series of beaches separated by headlands, the beach-sand compositions in part being relict, reflecting the along-coast mixing at lower sea levels and subsequent isolation by onshore migration of the beaches under the Holocene sea-level transgression. This pattern of relict compositions has been modified during the past several thousand years by some addition of sand to the beaches by sea-cliff erosion and contributions from the rivers draining the nearby Coastal Range. / Graduation date: 1987

Bull Run Watershed was set aside in late the 1800s as the water supply source for the City of Portland. Other than two dams being constructed, Reservoir #1 (1929) and Reservoir #2 (1962), development of the land had been minimal as public access was restricted. In the early 1960s, land management changed with increased road building and timber removal raising concerns about increased sediment discharge into the reservoirs. The objective of this study is to evaluate how much and how fast the sediment has accumulated in Reservoir #1, and to determine if the rate of sediment accumulation has changed over time. Three methods are utilized: 1) differencing map comparing pre- and postimpoundment sediment conditions, 2) analysis of tree-stumps on reservoir floor, and 3) gravity coring of reservoir sediment. Combining these methods, sediment volume is estimated between 254,000-422,000 cubic meters (332,000-552,000 cubic yards) and the rate of accumulation between 11.5-19.1 tonnes/km2/yr, reflecting a relatively low sediment yield rate. Two anomalous event-layers were identified in gravity cores collected. These are interpreted to be the 1964 flood and the 1972 North Fork Slide. Using these two events, sediment yield rate was divided into different historical segments: 15.33 (1930-1965); 43.62 (1965-1972); and 17.00 tonnes/km2/yr (1972-1993). The increase from 1965-1972 is attributed to either residual affects from the 1964 flood and/or changes in land management activities during this time. The source of the reservoir sediment is primarily from upper tributaries, with 20 percent being attributed to the anomalous events. Smaller amounts of sediment come from the reservoir side walls as lake levels raise and lower. Suspension and turbidity conditions in the reservoir are affected by the dynamics of the drainage system including seasonal fluctuations. Turbidity remains high at the upper reaches of the reservoir before settling out closer to the dam. Some sediment possibly leaves the reservoir over the spill-way or when water is removed for power production.

Pre-flood (1995), and post-flood (1996) channel stability surveys were conducted on 22 reaches along Oak Creek, Benton County, Oregon in an effort to note if the flood of February 1996 altered the channel and if the channel stability survey that was being used accurately predicted the channels resistance to change resulting from a flood. The channel stability survey that was used was the method described in the 'Channel Stability Evaluation and Stream Reach Inventory' designed by the USDA Forest Service, Northern Region, in Colorado (Pfankuch, 1978). This was a non-parametric study, based on an opportunity to reoccupy survey locations from a previous study. A model was proposed to describe the 1995 ratings as predictions for change should a flood event occur. This predicted change was compared to the actual change that occurred as a result of the 1996 flood in order to test the surveys ability to accurately predict change. Changes in the survey totals, the 15 channel stability indicator items that compose the survey, and the sediment distribution were evaluated within and between years at the reach, station and stream scale. An increase in the percentage of fine gravel occurred at all scales when post-flood and pre-flood sediment distribution was compared. Except for an increase in fine gravel, the stream remained similar to its pre-flood state. In 1995, the stream's channel stability was rated as 'fair', indicating that a moderate amount of change should take place if a flood occurred. The 1995 predictions for change did not match the actual change observed after the February 1996 flood at the three scales when defined by the survey totals. When independently evaluating the fifteen individual channel stability indicator items, a considerable amount of change was detected at the reach level. Although change occurred in the indicator items at each reach, the stream average for each of the independent indicator items was similar between the two years. This may indicate that, although change occurred at the reach level, the stream maintained its physical diversity after the flood. The survey method was unable to accurately predict changes to Oak Creek incurred by the February 1996 flood when viewed at the entire stream level, yet it may be more applicable at the reach level when viewing specific changes to channel stability indicator items. In general, the Stream Reach Inventory and Channel Stability Evaluation is designed for observational efficiency but does not have sufficient scientific basis or measurement precision to accurately predict the extent or type of channel change. / Graduation date: 1998