Showing papers on "Stream power published in 1990"

Flood hydrology and geomorphic effectiveness in the central Appalachians

Abstract: This paper compares hydrologic records and geomorphic effects of several historic floods in the central Appalachian region of the eastern United States. The most recent of these, occurring in November 1985, was the largest ever recorded in West Virginia, with peak discharges exceeding the estimated 500-year discharge at eight of eleven stations in the South Branch Potomac River and Cheat River basins. Geomorphic effects on valley floors included some of the most severe and widespread floodplain erosion ever documented and exceeded anything seen in previous floods, even though comparable or greater rainfall and unit discharge have been observed several times in the region over the past 50 years. Comparison of discharge-drainage area plots suggests that the intensity and spatial scale of the November 1985 flood were optimal for erosion of valley floors along the three forks of the South Branch Potomac River. However, when a larger geographic area is considered, rainfall totals and discharge-drainage area relationships are insufficient predictors of geomorphic effectiveness for valley floors at drainage areas of 250 to 2500 km2. Unit stream power was calculated for the largest recorded flood discharge at 46 stations in the central Appalachians. Maximum values of unit stream power are developed in bedrock canyons, where the boundaries are resistant to erosion and the flow cross-section cannot adjust its width to accommodate extreme discharges. The largest value was 2570 W m−2; record discharge at most stations was associated with unit stream power values less than 300 W m−2, but more stations exceeded this value in the November 1985 flood than in the other floods that were analysed. Unit stream power at indirect discharge measurement sites near areas experiencing severe erosion in this and other central Appalachian floods generally exceeded 300 W m−2; reach-average values of 200-500 W m−2 were calculated for valleys where erosion damage was most widespread. Despite these general trends, unit stream power is not a reliable predictor of geomorphic change for individual sites. Improved understanding of flood impacts will require more detailed investigation of interactions between local site characteristics and patterns of flood flow over the valley floor.

Theoretical model of optimal drainage networks

Abstract: A simulation model of drainage network optimization is presented in which channels shift to minimize total stream power pgQS within the network. The simulation model starts from an arbitrary initial stream network developed on a square matrix, such as produced by random headward growth. Discrete stream capture then is simulated within the network, occurring wherever a new stream linkage would produce a steeper course than the original. Such capture produces a network with minimum power optimization but flow directions constrained to eight directions. Individual segment end points are then allowed to migrate by iterative relaxation with a direction and rapidity of motion governed by the gradient of stream power at the node. This valley migration is subject to the constraint that the sources and outlet remain fixed. The resulting networks are visually and morphometrically more similar to natural stream networks than the original networks produced by the random headward growth model.

Channel avulsion and river metamorphosis: The case of the Thomson River, Victoria, Australia

Abstract: Channel avulsion occurred on the Thomson River in Victoria, Australia, in 1952 along a 12 km length of the valley. A comparison of the old and new channels reveals considerable differences in channel characteristics. The old channel was perched above the floodplain on an alluvial ridge such that when bankfull capacity was exceeded, floodwaters concentrated on the lowest part of the floodplain some distance away. This is where the new channel formed. It is an incised channel with larger capacity and longer meander wavelength than the old channel and is also shorter and steeper. The new channel is subject to larger floodflows and a more variable flood regime than the old course because of the differences in the channel/floodplain relationship and channel capacity. The resulting concentration of stream power along the new course is responsible for the contrast in channel characteristics and for the more rapid meander migration. This example shows that river metamorphosis can occur without major environmental changes. Measures of channel geometry such as gradient, sinuosity, and meander wavelength therefore cannot be used in palaeohydrological work to infer climatic or other environmental changes without independent supporting evidence. Differences in channel geometry can arise simply from changes in the relationship between the channel and its loodplain.

Fluvial Dynamics of Thorium‐230 in the Church Rock Event, Puerco River, New Mexico

Abstract: The largest accidental surface release of radioactive materials in the United States occurred 16 July 1979, when a uranium tailings pond collapsed near Church Rock, New Mexico, releasing 378,500 m3 of liquids and 1000 mg of solids into the Puerco River. The resulting flood wave distributed radioactive thorium-230 through an 80-km reach of the river. A detailed analysis of 48 km of the entrenched channel shows that radionuclide concentrations in stream-bed sediments fluctuated irregularly with increasing distance from the source of contamination instead of declining exponentially as might be expected from hydraulic and geographic theory. Hydraulic calculations at 154 cross-sections in the 48-km reach show that concentrations of radionuclides in channel sediments were inversely related to unit stream power generated during the peak of the flood wave. Concentrations were also inversely related to the length of time that shear stress exceeded critical values during the passage of the flood wave. Regi...

Flood dynamics of a concrete‐lined, urban stream in Kansas City, Missouri

Abstract: Brush Creek drains a 76·1 km2 watershed within urban Kansas City, Missouri and eastern Kansas. A concrete-lined reach trending 6·1 km through the Plaza District of Kansas City, Missouri has been the focus for several major floods over the past ten years. Channel geometry, slope, and floodwater elevations were determined in the field for segments of the concrete-lined section of Brush Creek for a flood event that occurred on September 18, 1986. Discharge was computed by indirect methods and compared to a value determined from a rating curve established by the Water Resources Division of the U.S.G.S. Boundary shear stress, unit stream power, and average velocity were also computed in order to establish a quantitative relationship between sediment distribution, volume, and size fractions; and flow dynamics operating throughout the channel during this event. Boundary shear stress ranged from 91-96 Nm−2, stream power was 528-557 Wm−2, while average velocity was 5-8 ms−1. These values were sufficient to displace concrete slabs as large as 5 m long by 4·6 m wide by 0·23 m thick weighing an estimated 12 245 kg. As the channel was sediment free and unsecured prior to the flood, the distribution of deposits and subsequent channel scour provide valuable evidence for potentially hazardous sections of this urban stream.

Effects of fluctuating levels of lake superior on morphological adjustments in the neebing‐mcintyre floodway, thunder bay, Ontario Canada

Abstract: The Neebing-McIntyre Floodway, a relatively straight, trapezidal flood-control channel, was constructed in 1983 to dispose of the combined flows of the Neebing and the McIntyre rivers into Lake Superior. Because of its location in a transitional fluvial/lacustrine environment, related processes had direct and indirect impacts on its morphological readjustments. During the post-construction period (1983-88) the combined peak flows of the Neebing and the McIntyre rivers never exceeded the two-year design floods for the floodway, resulting in relatively low stream power and sediment transport rates. The average rate of sedimentation in the new channel (1100 m3 y−1) was thus much lower than the designers' estimated volume (11 800 m3 y−1). These low-flow events coincided with high water levels in Lake Superior in 1985-86, reinforcing the normal backwater effect in the floodway and further dampening its stream power. During this event the floodway behaved hydraulically almost like a reservoir, with fluctuating water levels and wind-generated waves as the principal geomorphological agents of bank erosion. Estimates based on volumetric surveys indicate annual rates of bank erosion ranging from 0.03 to 0.16 m3 m−1 of bank length, with an average annual rate of 0.1 m3 m−1. The bank materials are composed of highly erodible sandy loam and loamy sand, which have a tendency to disperse and liquefy relatively easily. There are no significant spatial variations in erosion rates along a given bank but contrasts in the magnitude of erosion between the north and the south banks can be related to the relative exposure of a bank to average wind velocities, total duration of winds and the effective wind-wave fetches.

River side track traffic system utilizing stream power

Abstract: PURPOSE:To eliminate public hazard and save energy by mounting a water wheel on a vessel, rotating it by flowing river water to get driving power, and running a running device on a track. CONSTITUTION:When a water wheel 2 is rotated by river water stream, a rotating power is transmitted through a power transmitter 3 to driving wheels 12 of a support/guide/running device 18 and runs a vessel 1 alongside a track 8. A magnet 14 then increases the adhesiveness between the support/guide/ running device 18 and rail 8, and a propelling force is given firmly to the running device 18 in propelling energy by water stream generated by the water wheel 2. Thus public hazard is eliminated and energy can be saved.