Showing papers on "Stream power published in 2004"

Lithofacies and Transport of Clastic Sediments in Karstic Aquifers

Abstract: Karst aquifers demand continuous transport of clastic sediments if the conduit system is to remain open. Sediments are injected into the aquifer by sinking surface streams and through sinkholes, vertical shafts, open fractures, and other pathways from the land surface of sufficient aperture to permit gravity- and inwash-driven transport. Much transport of clastic sediments tends to be episodic with sediment loads held in storage until moved by infrequent flood events. Although the overall mix of clastic material depends on material available in the source area, distinctly different facies are recognizable depending on the flow dynamics within the conduit system. The facies are most clearly recognized when the source areas provide a wide variety of particle sizes from clays to boulders. In order of decreasing stream power, one can distinguish (i) diamicton facies: masses of unsorted, unstratified clays through boulders carried as a slurry during high energy flood events, (ii) thalweg facies: coarse gravel to cobble size material, well winnowed, forming armoring on underground streams that moves only during flood flow, (iii) channel facies: usually well sorted and often well stratified silt though gravel carried as bedload at intermediate stream powers, (iv) slackwater facies: mostly clay and silt carried as suspended load and deposited from floodwaters backfilled into the conduit system, (v) backswamp facies: mostly clay derived from the insoluble residue of the limestone, deposited under phreatic conditions with little lateral transport.

Limits of downstream hydraulic geometry

Abstract: Adjustments to flow width, depth, and velocity in response to changes in discharge are commonly characterized by using downstream hydraulic geometry relationships. The spatial limits of these relationships within a drainage basin have not been systematically quantified. Where the erosional resistance of the channel substrate is sufficiently large, hydraulic driving forces presumably will be unable to adjust channel form. Data sets from 10 mountain rivers in the United States, Panama, Nepal, and New Zealand are used in this study to explore the limits of downstream hydraulic geometry relationships. Where the ratio of stream power to sediment size (Ω/ D 84) exceeds 10,000 kg/s3, downstream hydraulic geometry is well developed; where the ratio falls below 10,000 kg/s3, downstream hydraulic geometry relationships are poorly developed. These limitations on downstream hydraulic geometry have important implications for channel engineering and simulations of landscape change.

Anabranching and maximum flow efficiency in Magela Creek, northern Australia

Abstract: [1] Anabranching is the prevailing river pattern found along alluvial tracts of the world's largest rivers. Hydraulic geometry and bed material discharge are compared between single channel and anabranching reaches up to 4 times bank-full discharge in Magela Creek, northern Australia. The anabranching channels exhibit greater sediment transporting capacity per unit available stream power, i.e., maximum flow efficiency (MFE). Simple flume experiments corroborate our field results showing the flow efficiency gains associated with anabranching, and highlight the prospect of a dominant anabranch, which is found in many anabranching rivers. These results demonstrate that anabranching can constitute a stable river pattern in dynamic equilibrium under circumstances in which a continuous single channel would be unable to maintain sediment conveyance. We propose the existence of a flow efficiency continuum that embraces dynamic equilibrium and disequilibrium (vertically accreting) anabranching rivers.

A graded stream response relation for bed load–dominated streams

Abstract: [1] The relation between equilibrium stream channel morphology and three independent governing variables, discharge, sediment supply, and valley slope, is investigated using a stream table. The experiments are based on a generic physical model of a laterally active gravel bed stream and directed by a recently published rational regime model. While a variety of channel adjustments are possible, the primary adjustment observed was in the channel slope. Other adjustments, such as surface armor composition and cross-sectional shape, were minor in comparison. The equilibrium slope is well predicted by a linear function of sediment concentration which is bounded by two thresholds: one associated with the minimum stream power necessary to deform the bed and the other associated with the maximum sediment feed that can be transported by the available flow. The results suggest that the system tends to move toward the minimum slope capable of transporting the sediment supply, in the process increasing the flow resistance for the system. Whether or not a minimum slope or a maximum system-scale flow resistance is reached cannot be determined given the available data, but there appears to be a unique slope (or, at least, a limited range of slopes) for which a stable alluvial channel morphology can be established for a given sediment concentration. The implications of this behavior are evaluated for the theoretical basis of the extremal hypothesis used to close the formulation of a rational regime model.

Long-term growth of a valley-bottom gully, western Iowa

Abstract: Growth of a permanent, valley-bottom gully from 1964 to 2000 was determined annually from survey and sediment-discharge data and compared with runoff and baseflow discharges. Data were analysed to test the hypothesis that rates of gully growth decay exponentially with time in response to shrinking catchment area caused by gully enlargement. Also, monthly values of growth rates and runoff, averaged over the 36-year record, were analysed with mass-wasting data to determine the extent to which colluvium availability affected growth rates seasonally. From 1964 to 2000, the gully volume increased by 9200 m3, accounting for 34 per cent of sediment yield from the watershed. There were tight power-law relationships between annual growth rates and annual runoff, with runoff exponents of 1·57 and 1·30 for headward and volumetric growth, respectively. Increases in gully length, area, and volume were fitted successfully assuming an exponential decay in growth rate with time. Rather than being due to a decrease in catchment area, however, the decline in growth rate was caused by a 77 per cent decrease in the ratio of runoff to baseflow, which also widened the gully and reduced the mean slope of its banks. Order-of-magnitude seasonal changes in erosion efficiency, defined as the fraction of stream power used to evacuate sediment from the gully, were roughly correlated with colluvium availability, as indicated by seasonal changes in the number of bank mass-wasting events. No more than 2·2 per cent of stream power was used to evacuate sediment during any month. This study demonstrates the danger of attributing declining rates of gully growth to a shrinking catchment area if corroborative runoff and baseflow data are not available. Moreover, it illustrates that stream power alone provides only a rough and physically indirect measure of erosion potential. Copyright © 2004 John Wiley & Sons, Ltd.

Comparison of hydraulic geometry between sand- and gravel-bed rivers in relation to channel pattern discrimination

Abstract: A comparison has been made between the hydraulic geometry of sand- and gravel-bed rivers, based on data from alluvial rivers around the world. The results indicate a significant difference in hydraulic geometry among sand- and gravel-bed rivers with different channel patterns. On this basis, some diagrams for discrimination of meandering and braided channel patterns have been established. The relationships between channel width and water discharge, between channel depth and water discharge, between width-depth ratio and water discharge and between channel slope and water discharge can all be used for channel pattern discrimination. The relationship between channel width and channel depth can also be used for channel pattern discrimination. However, the accuracy of these relationships for channel pattern discrimination varies, and the depth-discharge relationship is a better discriminator of pattern type than the classic slope-discharge function. The cause for this difference has been explained qualitatively. To predict the development of channel patterns under different natural conditions, the pattern discriminator should be searched on the basis of independent or at least semi-independent variables. The relationship between stream power and bed material grain size can be used to discriminate channel patterns, which shows a better result than the discriminator using the slope-discharge relationship. Copyright (C) 2004 John Wiley Sons, Ltd.

A conceptual model of the role of excess energy in the maintenance of a riffle¿pool sequence

Abstract: There is much debate over the role of hydraulic ‘reversal’ in the maintenance of riffle–pool sequences in gravel-bed channels. It is, however, generally acknowledged that the pool has the greatest maximum energy during flood flows allowing scour and pool maintenance. Little emphasis has been placed on the reversal period in many previous studies despite its potential importance being noted in the seminal study of Keller [Geol. Soc. Am. Bull. 82 (1971) 753]. This is potentially significant, as reversal may only occur for short periods at the peak of flood hydrographs; hence, the hydraulic argument behind riffle–pool maintenance is based around what is often a marginal energy excess in the pool for a very short period of time. This study uses the magnitude frequency concept of Wolman and Miller [J. Geol. 68 (1960) 54] and applies it to an investigation of the temporal dominance in morphologic unit stream power between a series of four pools and three riffles derived from measured flow and calculated energy slopes on the upland gravel-bed River Rede, Northumberland. The geomorphologically effective flow regime is used to define temporal balances between riffle and pool energy levels. The geomorphic work carried out by riffles and pools, as described by the excess stream power ( Ω − Ω c ) capable of transporting the bed sediments, displayed a broad balance for the upstream four units before reducing significantly at pool 3 and rising again for the subsequent two units which appear particularly energetic. These findings contrast with hydraulic theories of riffle–pool maintenance, e.g., Keller [Geol. Soc. Am. Bull. 82 (1971) 753]. For sediments to be transferred through a riffle–pool sequence whilst maintaining a quasi-equilibrium form, the pools should carry out the same amount of work as the riffle upstream in order for it not to fill with sediment. Although stream power reversal did occur for some riffle–pool units, the magnitude and longevity of the reversal did not balance the energy exerted at riffle locations. Armouring and shallow gravel depth at riffle 3 appear to indicate scouring in response to high excess stream power found in this area. However, there was no evidence of sub-dominant pools 3 and 4 filling in response to low stream power.

Oscillations in arid alluvial-channel geometry

Abstract: Arid alluvial channels on piedmonts and valley floors often exhibit an oscillating pattern of narrow, deeply incised reaches and wide, shallow reaches with a characteristic wavelength. How do these oscillations develop and what controls their wavelengths? To address these questions we developed a two-dimensional numerical model that couples erosion and deposition in a channel bed with cross-sectional widening and narrowing. This model is inherently unstable over a range of spatial scales dependent on the channel width, depth, and slope. In the initial phase of model evolution, wider-than-average channel reaches become zones of distributary flow that aggrade, lose stream power, and further widen in a positive feedback. Simultaneously, narrower-than-average reaches incise, gain stream power, and further narrow. In the second stage of model evolution, this instability is balanced by the diffusive nature of longitudinal profile evolution, and solitary topographic waves propagate in the upstream direction with a characteristic wavelength and amplitude. The model predicts a specific quantitative relationship between the oscillation wavelength and channel width, depth, and slope that is verified by a database of channel geometries in southern Arizona.

River of Change: a Model for the Development of Terraces Along the Bow River, Alberta

Abstract: Researchers working in the Bow River valley have identified a minimum of four alluvial terraces, the upper two of which have been designated as paired terraces. Over the past 35 years, they have attempted to correlate these alluvial landforms and to generate models for the development of the terraces along the section of the Bow River between Calgary and the Rocky Mountains. In this study, Mazama ash and an early Holocene paleosol are used to correlate the terrace suites examined by previous researchers and to generate a model which accounts for the development of the upper two sets of paired terraces. These paired terraces reflect major episodes of aggradation and degradation that result from changes in independent variables such as climate and uplift. The initial episode of aggradation, dating from the late Pleistocene, is the result of paraglacial processes in a sparsely vegetated, yet saturated environment. Following a brief episode of degradation at the end of the Younger Dryas, the second episode of aggradation, dating from 9000 to 5000 BP, is caused by increased sediment load and lowered stream power during the Hypsithermal.

The Mekong River: Morphology, Evolution and Palaeoenvironment

Abstract: The Mekong, the largest river in Southeast Asia, shows striking variations in channel form and behaviour along its course. It appears to link several different types of channel rather than continuing in an orderly progression. Eight different river units have been identified along the lower 2000+ km of the river from the Chinese border to the sea across Southeast Asia. The exercise was carried out using satellite images, field visits, topographical maps, and various publications of the Mekong River Commission including large-scale river maps. The boundaries between such units are sharp and not gradual. They are different from each other depending on their morphological characteristics, their behaviour and whether the channel is bedrock-controlled. The Mekong flows for nearly 4000 km before being a freelymoving river with overbank flooding and course changes across the wide plain of Cambodia. Prior to that the channel is essentially structure-guided. It is a seasonal river with high flows during the southwestern monsoon and periodic floods late in the wet season. This linkage of several identifiable river units and the location of the present course of the river have not been properly explained. The estimated stream power of the Mekong in large floods seems to be very low when compared to what is required to erode a large channel in rock even along geological lineations. The opening of the South China Sea and the lowlands of Southeast Asia are associated with extrusion tectonics resulting from the Indian Plate colliding with the Eurasian Plate and building of the Himalaya Mountains from Eocene onwards. The present course of the river is likely to have been determined at least primarily from this event, and possibly also associated with stronger monsoon systems in the Early Holocene as recognised for South Asia. Morphology comparable to that of the Mekong seems to exist in several other major rivers of Southeast Asia and there could be a regional pattern, but investigation on this topic has hardly started.

Sediment transport predictor in the Ganges river

Abstract: In this study, the unit stream power formula and modified unit stream power formula have been applied for the estimation of sediment transport in the Ganges river. The modified unit stream power function is applicable to high concentration of fine sediment. The annual variation in the percent of fine suspended discharge shows that the Ganges river at Hardinge bridge contains a substantial amount of wash load. Based on observed data, sediment transport has been computed using Yang’s stream power formula and modified Yang’s formula. Comparison between computed and observed sediment discharge shows that Yang’s formula over-predicts the sediment transport. The discrepancy ratio and standard deviation indicate the accuracy of the sediment transport predictors. Modified Yang’s formula performs better for Ganges river. The modified Yang’s sediment transport formula can be used in modeling sediment load in the Ganges river. The Yang’s formula can also be used after adjusting the computed sediment load by an appropriate multiplying factor. © 2005 Institution of Engineers, Bangladesh. All rights reserved.

Stream power generation

Abstract: PROBLEM TO BE SOLVED: To provide a power-generating device in which power can be easily generated using flows such as natural wind/water, etc., anywhere. SOLUTION: Power is generated with rotary force of a shaft by placing a large number of windmills/water-wheels arranged in parallel on the shaft in the nature such as water or air. COPYRIGHT: (C)2005,JPO&NCIPI

Sediment Load in Runoff Under Laboratory and Field Simulated Rainfall

Abstract: Soil erosion is one of the most important problems in the Loess Plateau of China affectingsustainable agriculture. Near Luoyang (Henan Province, China), field plots were constructed tomeasure soil erosion rates under conventional tillage practices using field-simulated rainfall.Field rainfall experiments were carried out to compare previous results from laboratoryrainfall simulations on the same soil for interrill conditions. Although in the laboratoryexperiments, a strong correlation was found between the stream power of the runoff water andthe unit sediment load, this sediment transport equation overestimated the field rainfallsimulation results. Another sediment transport equation derived by Nearing et al. for rillerosion was in better agreement with the results of the field experiments, although it alsooverestimated these values. The measured sediment load values during the field rainfallsimulations were also lower than those found during field experiments on the same soil but witha loosened surface layer. This difference indicates the importance of soil physical conditionof surfce like soil structure and aggregate size, which may contribute to the discrepancybetween the field and laboratory experiment results.

Sediment Load in Runoff Under Laboratory and Field Simulated Rainfall

Abstract: Soil erosion is one of the most important problems in the Loess Plateau of China affecting sustainable agriculture. Near Luoyang (Henan Province, China), field plots were constructed to measure soil erosion rates under conventional tillage practices using field-simulated rainfall. Field rainfall experiments were carried out to compare previous results from laboratory rainfall simulations on the same soil for interrill conditions. Although in the laboratory experiments, a strong correlation was found between the stream power of the runoff water and the unit sediment load, this sediment transport equation overestimated the field rainfall simulation results. Another sediment transport equation derived by Nearing et al. for rill erosion was in better agreement with the results of the field experiments, although it also overestimated these values. The measured sediment load values during the field rainfall simulations were also lower than those found during field experiments on the same soil but with a loosened surface layer. This difference indicates the importance of soil physical condition of surfce like soil structure and aggregate size, which may contribute to the discrepancy between the field and laboratory experiment results.

Application of Remotely Sensed Data to Sediment Load Estimation by A Distributed Rainfall-Sediment-Runoff Catchment Model

Abstract: This paper describes a physically-based distributed rainfall-sediment-runoff model for floods and sediment movement in a catchment scale. A grid-cell based kinematic wave runoff (KWR) model simulates surface and subsurface flows on each grid-cell, while soil transportation capacities of sheet erosion are calculated based on the unit stream power theory to model sheet erosion and deposit processes. Constructed model is applied to the Lesti River basin, which is located in the upper Brantas River basin, East Java, Indonesia. Land cover condition in the basin is studied with three different kinds of remotely sensed data including ADEOS/AVNIR, LANDSAT7/ETM+, and TERRA/MODIS. The verification indicated that the model well reproduces the sedimentation record during a rainy season from November 1995 to April 1996, which suggests the potential ability of the model. The integrated sediment management (ISM) in river basins, from upper streams to estuaries, has become increasingly important. The sediment problems have been dealt with independently in the areas, such as mountains, alluvial areas, plains, and estuaries. Local managements independently conducted affect sediment environment in other areas. In addition, human activities, such as land use change and dam construction, also affect the sediment movement in large scales over long terms. Therefore, the concept of integrated management dealing with sediment movement in whole basins has become recognized more important and realistic. For ISM, it is necessary to establish methods to predict sediment movement both in basins and in streams. The advanced research on sediment transportation in a river stream has been conducted from a viewpoint of sediment hydraulics. In a catchment scale, however, there are still uncertainties in the prediction of sediment movement. The distributed runoff model, which has been studied in hydrology, makes water movement in basins clear by using spatially distributed information. This paper constructs a rainfall-sediment-runoff model by combining sediment yield, deposit, and transportation processes with the grid-cell based Kinematic Wave Runoff (KWR) model 1) . Geographical Information System (GIS) and Remote sensing (RS) are useful tools in the modeling. The constructed model is applied to the upper Brantas river basin, East Java, Indonesia. Covered with large amounts of volcanic ash, this area yields much sediment from cultivated lands, forests, and even urban regions. Surface flow in the areas covered by volcanic ash is the main cause that yields the sediment in the areas. The transportation capacity of the surface flow on each grid-cell must be considered to model the sediment yield and deposit processes. The transportation capacity is calculated based on the Unit Stream Power (USP) theory 2) . The

Soil properties important to stream development on mined lands

Abstract: Fluvial processes and channel development on landscapes have recently received more attention as designers attempt to establish or replace natural streams on disturbed or degraded sites. Several approaches using similar parameters have been developed to evaluate stream development and erosion processes on natural soils and landscapes. Such approaches include the Manning's and stream power equations for stream development, and the Universal Soil Loss Equation (USLE) and the Bank Erosion Hazard Index (BEHI) for erosion. Soil properties used in these methods to evaluate erosion potential include texture (clay, silt and sand contents), bulk density, aggregate stability, rock fragments, soil horizons, rooting density and vegetation cover. Soil scientists have developed a well-known descriptive system for identifying and classifying disturbed soils and this information should be used to more fully evaluate the process of channel development on new landscapes. Therefore, the soil properties used in classification can be evaluated in designing channels and streams on disturbed lands, and refinements on interpreting these physical properties in the context of stream design need to be made.