Rates Of Sediment Removal Research Articles

Temporal and spatial variations in the solute content of an alpine stream, Colorado Front Range

Seven years of discharge and water quality records define temporal and spatial patterns of solute movement in a Colorado alpine stream system. Dissolved solids concentrations are low, generally less than 30 mg 1 −1 and occasionally less than 3 mg 1 −1 at the highest elevations. Calcium is the dominant cation and bicarbonate and sulfate are the main anions. Temporal changes in solute concentrations are dominated by an annual cycle with high values in late winter and spring that decrease rapidly during early summer and then return more slowly through fall. This pattern corresponds to the seasonal streamflow regime and reflects differential elution of the snowpack by meltwater and changing proportions of surface and subsurface water in the streamflow. The amplitude of the annual cycle of solute concentration is reduced with increasing catchment area and where the groundwater contribution to flow is relatively high. In general, solute concentrations increase down valley but this trend is reversed in the case of biologically important solutes, such as nitrate and potassium. Rates of geochemical denudation are dominated by the volume of water discharge and thus are highest in the parts of the basin that accumulate the greatest depths of winter snow. They vary between 5 and 26 g m −2 yr −1 for different parts of the catchment and average less than 9 g m −2 yr −1. These rates are low compared to those from high-elevation catchments elsewhere but are an order of magnitude higher than rates of sediment removal from the basin.

THE NATURE AND RATE OF ALLUVIAL FAN AGGRADATION IN A HUMID TEMPERATE ENVIRONMENT, NORTHWEST WASHINGTON

Comparatively little is known about net aggradation on alluvial fans, despite fan construction wherever sediment-delivery rates from uplands exceed sediment-removal rates from receiving basins. In January 1983, 20 alluvial fans in the forested Cascade foothills, northwest Washington, experienced net aggradation in response to debris torrents and stream floods triggered by intense warm rains falling on antecedent snow. Five trenches were excavated to 5 m depth on the Mills Creek fan to place the 1983 event in temporal perspective. The deposits reflect normal streamflow, hyperconcentrated streamflow and debris torrent (flow) conditions. One trench revealed residues of 7 events since 1720 BP. Net rates of Holocene aggradation, based on sediments overlying late Pleistocene fluvioglacial deposits, average 0.42 m ka-1. Net rates for later Holocene time range from 2.17 m ka-1 since 1720 BP to 2.36 m ka-1 since 430 BP. These recent rates exceed the local value for the entire Holocene and rates for humid temperate...

Variations in solids loadings to roadside gully pots

The contribution and composition of road surface particulate loadings as received by roadside gully pots is assessed together with the influences of rainfall and highway surface runoff characteristics. Sediments are well sorted with almost 90% of sediment grading curves lying within a narrow distributional band. Organic grading curves show a distinct diminution in grain sizes, with 10% organic material and 25% bitumen content associated with particulates less than 60 microns. Sediment removal rates showed a seasonal variation which was strongly influenced by both rainfall and surface flow characteristics. The antecedent dry period length appears to have only a minor affect upon the availability of road surface sediments.