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At least 649 records · Page 36Linked to original sources
USGS1982

Soil conservation and the reduction of erosion and sedimentation in the Coon Creek basin, Wisconsin

The Coon Creek basin, in the Driftless Area of Wisconsin, has been strikingly transformed by soil conservation measures since the 1930's. Comparison of sheet and rill erosion by use of the Universal Soil Loss Equation, shows 1975 erosion rates on upland fields to be about one-fourth those of 1934. Average annual sedimentation accumulation in small reservoirs declined from about 5,000 megagrams per square kilometer in 1936-45 to about 50 megagrams per square kilometer in 1962-75. Analysis of deposition in tributary valleys suggests that annual rates declined from about 3,700 megagrams per square kilometer in the 1930 's to about 35-70 megagrams per square kilometer in recent years. These reductions in erosion and sedimentation are due principally to improvements in land management and, to a lesser degree, to changes in land use. (USGS)

Professional Paper↗
USGS1982

Erosion and sedimentation in the Kenai River, Alaska

The Kenai River is the most important freshwater fishery in Alaska. The flow regime is characterized by high summer flow of glacial meltwater and periodic flooding caused by sudden releases of glacier-dammed lakes in the headwaters. Every part of the stream is a known or potential salmon-spawning site. The stream channel is underfit, attributed to regional glacial recession and drainage changes, and locally is entrenched in response to geologically recent changes in base level. Throughout the central section of the river the channel is armored, a condition with implications for the ability of this section of channel to support the spawning and rearing of salmon. The entrenched section of the channel has been stable since 1951. Bank erosion is active both upstream and downstream from the entrenched channel, however. Although erosion rates have been generally constant since 1951, evidence suggests a possible recent decrease in bank stability that may be related to changes in river use. As population and recreation use increases, development can pose a hazard to the productivity of the stream through increased suspended-sediment concentration resulting directly from construction and, with greater potential for long-term impact, indirectly from bank erosion. A short-term hazard to both stream and developments is the cutoff of meander loops, the risk of which is increased by canals and boat slips cut in the surface layer of cohesive, erosion-resistant sediment on the flood plain within nonentrenched meander loops. A long-term hazard is an increase in bank erosion rates resulting from loss of vegetation on the high (up to 70 feet) cutbacks of entrenched and partially entrenched section. (USGS)

Professional Paper↗
USGS1982

Perennial-streamflow characteristics related to channel geometry and sediment in Missouri River basin

Geometry, channel-sediment, and discharge data were collected and compiled from 252 streamflow-gaging stations in the Missouri River basin. The sites represent the complete ranges of hydrologic and geologic conditions found in the basin. The data were analyzed by computer to yield equations relating various discharge characteristics to variables of channel geometry and bed and bank material. The equations provide discharge as the dependent variable for the purpose of making estimates of discharge characteristics at ungaged sites. Results show that channel width is best related to variables of discharge, but that reduction of standard errors can be achieved by considering channel-sediment properties, channel gradient, and discharge variability. The channel-material variables do not exert uniform effects on width-discharge relations and, therefore, are considered as sediment-data groups, or stream types, rather than as terms in multiple power-function equations. Relative to streamflow, narrowest channels occur when streams of steady discharge transport sufficient silt and clay to form stable, cohesive banks but have a small tractive load of sand and coarser sizes. Stable channels also are associated with high channel gradients, which cause high channel roughness and bed and bank armouring by coarse particle sizes. The widest, most unstable channels are found with streams that apparently transport of large tractive load of sand sizes. The downstream rates of change of width with discharge reflect these trends, suggesting that a given bed-material load necessitates a minimum width over which the tractive material can be moved.

Missouri River basin↗