Showing papers on "Stream power published in 2005"

Knickpoint recession rate and catchment area: the case of uplifted rivers in Eastern Scotland

Abstract: Knickpoint behaviour is a key to understanding both the landscape responses to a base-level fall and the corresponding sediment fluxes from rejuvenated catchments, and must be accommodated in numerical models of large-scale landscape evolution. Knickpoint recession in streams draining to glacio-isostatically uplifted shorelines in eastern Scotland is used to assess whether knickpoint recession is a function of discharge (here represented by its surrogate, catchment area). Knickpoints are identified using DS plots (log slope versus log downstream distance). A statistically significant power relationship is found between distance of headward recession and catchment area. Such knickpoint recession data may be used to determine the values of m and n in the stream power law, E = KAmSn. The data have too many uncertainties, however, to judge definitively whether they are consistent with m = n = 1 (bedrock erosion is proportional to stream power and KPs should be maintained and propagate headwards) or m = 0·3, n = 0·7 (bedrock incision is proportional to shear stress and KPs do not propagate but degrade in place by rotation or replacement). Nonetheless, the E Scotland m and n values point to the dominance of catchment area (discharge) in determining knickpoint retreat rates and are therefore more consistent with the stream power law formulation in which bedrock erosion is proportional to stream power. Copyright © 2005 John Wiley & Sons, Ltd.

Wood storage in a wide mountain river: case study of the Czarny Dunajec, Polish Carpathians

Abstract: Storage of large woody debris in the wide, mountain, Czarny Dunajec River, southern Poland, was investigated following two floods of June and July 2001 with a seven-year frequency. Within a reach, to which wood was delivered only by bank erosion and transport from upstream, wood quantities were estimated for eighty-nine, 100 m long, channel segments grouped into nine sections of similar morphology. Results from regression analysis indicated the quantity of stored wood to be directly related to the length of eroded, wooded banks and river width, and inversely related to unit stream power at the flood peak. The largest quantities of wood (up to 33 t ha−1) were stored in wide, multi-thread river sections. Here, the relatively low transporting ability of the river facilitated deposition of transported wood while a considerable length of eroded channel and island banks resulted in a large number of trees delivered from the local riparian forest. In these sections, a few morphological and ecological situations led to the accumulation of especially large quantities of wood within a small river area. Very low amounts of wood were stored in narrow, single-thread sections of regulated or bedrock channel. High stream power facilitated transport of wood through these sections while the high strength of the banks and low channel sinuosity prevented bank retreat and delivery of trees to the channel. Considerable differences in the character of deposited wood existed between wide, multi-thread channel sections located at different distances below a narrow, 7 km long, channellized reach of the river. Wood deposited close to the downstream end of the channellized reach was highly disintegrated and structured into jams, whereas further downstream well preserved shrubs and trees prevailed. This apparently reflects differences in the distance of wood transport and shows that in a mountain river wider than the height of trees growing on its banks, wood can be transported long distances along relatively narrow, single-thread reaches but is preferentially deposited in wide, multi-thread reaches. Copyright © 2005 John Wiley & Sons, Ltd.

Using airborne multispectral imagery to evaluate geomorphic work across floodplains of gravel-bed rivers

Abstract: Fluvial processes of cut and fill alluviation and channel abandonment or avulsion are essential for maintaining the ecological health of floodplain ecosystems char- acteristic of gravel-bed rivers. These dynamic processes shape the floodplain landscape, resulting in a shifting mosaic of habitats, both above and below ground. We present a new and innovative methodology to quantitatively assess the geomorphic work potential nec- essary to maintain a shifting habitat mosaic for gravel-bed river floodplains. This approach can be used to delineate critical habitats for preservation through land acquisition and conservation easements, often critical elements of river restoration plans worldwide. Spa- tially explicit modeling of water depth, flow velocity, shear stress, and stream power derived from surface hydraulic measurements was combined with airborne multispectral remote sensing for detailed modeling of floodplain water surfaces over tens to hundreds of square kilometers. The model results were then combined within a GIS framework to determine potential nodes of channel avulsion that delineate spatially explicit zones across the flood- plain where the potential for geomorphic work is the greatest. Results of this study dem- onstrate the utility of integrating existing multispectral remote sensing data coupled with time-lagged ground-based measures of flow hydraulics to model fluvial processes at rela- tively fine spatial resolutions but over broad regional extents.

The form and function of headwater streams based on field and modeling investigations in the southern Appalachian Mountains

Abstract: Headwater streams drain the majority of most landscapes, yet less is known about their morphology and sediment transport processes than for lowland rivers. We have studied headwater channel form, discharge and erosive power in the humid, moderate-relief Valley and Ridge and Blue Ridge provinces of the Appalachian Mountains. Field observations from nine headwater (< < < < 2k m 2 drainage area), mixed bedrock‐alluvial channels in a variety of boundary conditions demonstrate variation with respect to slope-area channel initiation, basic morphology, slope distribution, hydraulic geometry, substrate grain size and role of woody debris. These channels display only some of the typical downstream trends expected of larger, lowland rivers. Variations are controlled mainly by differences in bedrock resistance, from the formation level down to short-wavelength, outcrop-scale variations. Hydrologic modeling on these ungauged channels estimates the recurrence of channel-filling discharge and its ability to erode the channel bed. Two-year recurrence discharge is generally larger and closer to bankfull height in the Valley and Ridge, due to low soil infiltration capacity. Discharge that fills the channel to its surveyed bankfull form is variable, generally exceeding two-year flows at small drainage areas (< < < <0·5 km 2 ) and being exceeded by them at greater drainage areas. This suggests bankfull is not controlled by the same recurrence storm throughout a channel or physiographic region. Stream power and relative competence are also variable. These heterogeneities contrast relations observed in larger streams and illustrate the sensitivity of headwater channels to local knickpoints of resistant bedrock and armoring of channels by influx of coarse debris from hillslopes. The general lack of predictable trends or functional relationships among hydraulic variables and the close coupling of channel form and function with local boundary conditions indicate that headwater streams pose a significant challenge to landscape evolution modeling. Copyright © 2005 John Wiley & Sons, Ltd.

River dredging, channel dynamics and bedload transport in an incised meandering river (the River Semois, Belgium)

Abstract: Dredging in the rivers of the Ardenne is generally carried out on a smaller scale to that described in the literature and is not conducted for commercial purposes. Extractions within the river channel are made in order to prevent flooding; hence the quantity of gravel extracted is limited. This study aims to evaluate the impact of dredging and the resilience of the riverbed in the Semois. This river is found in the south of the Ardenne region and is characterized by large incised meanders, a narrow floodplain, few pebble bars, numerous bedrock outcrops and a limited stock of sediment. The bed is particularly flat and shallow and the bankfull discharge (130 m3 s−1) is frequently attained (0.9 yr). Pebble tracers allowed the critical parameters (discharge, Shields criterion, and stream power), the diameter of mobilized sediment and the distance of sediment transport to be determined. A major dredging campaign resulted in the formation of a channel nearly 1 km long and 2 m deep which functioned as a sediment trap. Topographical cross-sections made before and after the dredging campaign and again 4 yr later allowed bedload discharge to be estimated (1.1 t km−1 yr−1). In order to examine the efficiency of the sediment trap, the sediment transport equations of Meyer-Peter and Muller, Schoklitsch, Bagnold and Martin were applied. With the exception of Bagnold's equation (1980), the observed transport values and those calculated theoretically are relatively close. Between October 1997 and June 2001, 5010 t were caught in the sediment trap. For the same period the equations calculate values between 6147 and 10 571 t. The overestimation from the theoretical calculations may result from a lack of sediment supply due to the characteristics of the basin and the frequency and magnitude of flood events during the study period. From the magnitude of the sediment transport rate, a return to the initial state of the riverbed (before dredging) may be expected after approximately 10 yr. Despite the scale of the dredging campaign for a river of this size, its results are limited in terms of flood prevention. Copyright © 2005 John Wiley & Sons, Ltd.

Estimate of sediment yield in a basin without sediment data

Abstract: In this study, three mathematical models for the estimate of sediment yield, due to soil and stream erosion, at the outlet of a basin are presented. Each model consists of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The rainfall-runoff and the stream sediment transport submodels are identical in the three mathematical models. The rainfall-runoff submodel that is used for the computation of the runoff in a sub-basin is a simplified water balance model for the soil root zone. For the estimate of soil erosion in a sub-basin, three different submodels are used alternatively, owing to the fact that erosion or sediment yield data are not available. The soil erosion submodels are (a) a modified form of the classical Universal Soil Loss Equation (USLE, [Foster, G.R., Meyer, L.D., Onstad, C.A., 1977. A runoff erosivity factor and variable slope length exponents for soil loss estimates. Transactions of the ASAE, 20 (4), 683–687]) taking into account both the rainfall erosion and the runoff erosion, (b) the relationships of Poesen [Poesen, J., 1985. An improved splash transport model. Zeitschrift fur Geomorphologie, 29, 193–211] quantifying the splash detachment, as well as the upslope and downslope splash transport, (c) the relationships of Schmidt [Schmidt, J., 1992. Predicting the sediment yield from agricultural land using a new soil erosion model. Proceedings of the 5th International Symposium on River Sedimentation. Karlsruhe, Germany, pp. 1045–1051] including the momentum flux exerted by the droplets and the momentum flux exerted by the runoff. The sediment transport submodel for streams aims to estimate the sediment yield at the outlet of a sub-basin. This quantity results by comparing the available sediment amount in the main stream of a sub-basin with the sediment transport capacity by stream flow, which is computed by the relationships of Yang and Stall [Yang, C.T., Stall, J.B., 1976. Applicability of unit stream power equation. Journal of the Hydraulics Division, ASCE, 102, 559–568]. The mathematical models were applied to the basin of Kompsatos River, in northeastern Greece, with an area of about 565 km2. The whole basin was divided into 18 natural sub-basins for more precise calculations. Monthly rainfall data were available for 27 years (1966–1992); therefore, the calculations were performed on a monthly basis. The deviation between the three mean annual values of sediment yield at the basin outlet, for 27 years, resulting from the three mathematical models is relatively small.

Testing Bedload Transport Formulae Using Morphologic Transport Estimates and Field Data: Lower Fraser River, British Columbia

Abstract: Morphologic transport estimates available for a 65-km stretch of Fraser River over the period 1952–1999 provide a unique opportunity to evaluate the performance of bedload transport formulae for a large river over decadal time scales. Formulae tested in this paper include the original and rational versions of the Bagnold formula, the Meyer-Peter and Muller formula and a stream power correlation. The generalized approach adopted herein does not account for spatial variability in flow, bed structure and channel morphology. However, river managers and engineers, as well as those studying rivers within the context of long-term landscape change, may find this approach satisfactory as it has minimal data requirements and provides a level of process specification that may be commensurable with longer time scales. Hydraulic geometry equations for width and depth are defined using morphologic maps based on aerial photography and bathymetric survey data. Comparison of transport predictions with bedload transport measurements completed at Mission indicates that the original Bagnold formula most closely approximates the main trends in the field data. Sensitivity analyses are conducted to evaluate the impact of inaccuracies in input variables width, depth, slope and grain size on transport predictions. The formulae differ in their sensitivity to input variables and between reaches. Average annual bedload transport predictions for the four formulae show that they vary between each other as well as from the morphologic transport estimates. The original Bagnold and Meyer-Peter and Muller formulae provide the best transport predictions, although the former underestimates while the latter overestimates transport rates. Based on our findings, an error margin of up to an order of magnitude can be expected when adopting generalized approaches for the prediction of bedload transport. Copyright © 2005 John Wiley & Sons, Ltd.

Wash load and bed-material load transport in the Yellow River

Abstract: It has been the conventional assumption that wash load is supply limited and is only indirectly related to the hydraulics of a river. Hydraulic engineers also assumed that bed-material load concentration is independent of wash load concentration. This paper provides a detailed analysis of the Yellow River sediment transport data to determine whether the above assumptions are true and whether wash load concentration can be computed from the original unit stream power formula and the modified unit stream power formula for sediment-laden flows. A systematic and thorough analysis of 1,160 sets of data collected from 9 gauging stations along the Middle and Lower Yellow River confirmed that the method suggested by the conjunctive use of the two formulas can be used to compute wash load, bed-material load, and total load in the Yellow River with accuracy.

Two Dimensional Mapping of River Bathymetry and Power Using Aerial Photography and GIS on the Brazos River, Texas

Abstract: Effective management of river environments requires efficient means of gathering data on the rivers, including stream power and other hydraulic attributes. Traditional methods of data collection are spatially limited and can be restrictively expensive. This study utilizes hydraulically‐calibrated aerial photography and GIS to calculate cross‐sectional and mean stream power on a stretch of the Brazos River in central Texas. Field measured water depths are regressed against image brightness values to establish a highly accurate depth to reflectance curve. GIS‐derived water surface slopes are then combined with estimated water depths to map fully two‐dimensional hydraulic processes. This type of image‐based river monitoring provides both an advance in measurement accuracy and in temporal monitoring.

Catchments and the Physical Template

Abstract: This chapter describes the various geomorphic and hydrologic processes such as catchments that influence riparian system development and maintenance. Catchments are areas of the land surface in which all the runoff drains to a single point on a stream or river channel, and are bounded by drainage divides; catchments have been known to range from hundreds of square meters in size to millions of square kilometers. Catchment drainage networks may have dendritic, palmate dendritic, or trellised forms, depending on the nature of underlying geology. These networks vary in drainage density and gradient, which affect riparia by impacting flood intensity and stream power, respectively. The most basic geomorphic processes in catchments are erosion, transport, and deposition. These processes operate across all time and space scales but vary in relative importance along drainage networks. Erosive processes dominate headwater regions, whereas deposition processes dominate the bottom of catchments draining to the ocean or into enclosed basins. Transport dominates in the mid-reaches of river systems. Erosion scours and eliminates riparian habitats and occurs when the shear stress imposed by flowing water exceeds the shear strength of the material over which it flows. The dominant forms of erosion include down-cutting and lateral movement of channels and scouring of channels and floodplains. Hydrologic processes strongly influence riparian habitats as the transport medium for sediments, but the presence or absence of water by itself is also an important control on riparian form and function. Flooding is a key process that distributes surface water to riparian environments and sets up gradients that drive surface water-groundwater exchanges. Four characteristics of floods, which are especially important to riparian and floodplain ecosystems are magnitude, frequency, timing, and duration.

Prediction of total bed material discharge

Abstract: A new and user-friendly formula for the computation of total bed material load in alluvial channels under equilibrium transport conditions has been developed based on the stream power concept and diffusion theory. The advantages of this formula include: high accuracy in prediction, the ease of computation and the wide range of application. The total sediment concentration is computed directly using the variables of flow depth, mean flow velocity, energy slope, median sediment size and sand density, and water temperature. The verification for the new equation uses over 3500 published total-load data from flume studies, and the over-all results show that 84% of the data are predicted within 0.5 and 2 times the measured values. This is an encouraging score considering the large database and the range of variables covered.

High-resolution total stream power estimates for the cotter river, namadgi national park, australian capital territory.

Abstract: INTRODUCTION Fluvial form and behaviour vary as a function of position among the numerous variables within a landscape. Channel gradient, degree of channel confinement, catchment hydrology and flood history, sediment character and supply, vegetation and human impacts to some degree all control stream form and behaviour. Bagnold (1966) adopted stream power as a theoretical basis for evaluating bedload transport. Since, it has been widely used to better understand such form and behavioural characteristics, in particular channel patterns and meander dynamics (Ferguson 1981) and changes induced as a result of human intervention (Brookes 1988). Stream power has also been used as a factor to delineate riverbed processes, notably when braiding has taken place (Van den Berg 1995).

Power controlling method in base station

Abstract: The method includes following steps: 1) with the evaluation result for down stream reception quality, user terminal creates TPC instruction that is sent to base station; 2) the base station demodulates the down stream TPC instruction, and gets the regulation for the down stream transmitting power. The user terminal creates up stream TPC instruction and up stream reception quality index according to evaluating result for up stream reception quality, and generates a down stream power regulation according to up stream reception quality index, and adjusts the down stream transmitting power of base station by using down stream transmitting power regulation and the down stream TPC instruction; 3) the base station transmits the TPC instruction to user terminal that adjusts up stream transmitting power according to the up stream TPC instruction.

Introduction: Description and classification of alluvial estuaries

Abstract: This chapter presents a classification of estuaries and related types of salt intrusion. Subsequently, it focuses on the characteristics, peculiarities, and the resulting behavior of alluvial estuaries. The shape of an alluvial estuary is similar all over the world. The width reduces in upstream direction as an exponential function. In coastal plain estuaries, there is no significant bottom slope, but in estuaries with strong relief, the depth may decrease exponentially. As a result in both types of alluvial estuaries, the cross-sectional area varies exponentially, and so does the flood volume, also called “tidal prism” (the volume of water that enters the estuary on the tide). Morphological equilibrium and minimum stream power lie at the cause of this typical shape. There is a similarity between the exponential reduction of the width of an estuary (in upstream direction) and the exponential increase of the drainage area of a catchment (in downstream direction). The topography is key to estuary processes. The fact that water flows as it does is strongly influenced by the medium through which it flows. In principle, the nonlinear hydraulic equations can demonstrate irregular and unpredictable behavior, but in alluvial estuaries, it is seldom observed. The interaction of estuary processes with topography is a key feature of this chapter.

Geomorphologic units and sediment transport in a very low relief basin : Rio Quequén Grande, Argentina

Abstract: The aim of this work was to identify the geomorphological units within the drainage network of the Rio Quequen Grande low relief basin, situated in the southeast section of the province of Buenos Aires, and to quantify the present sediment transport rate. For this purpose field surveys and satellite images were analysed. The former included measurement of bed material grain size and channel hydraulic geometry, in order to set up a bed and a suspended load measurement programme. Six main geomorphic units were identified: Ranges, Perirange Aeolian Hillocks, Hillocks with Lagoons, Relic Hills, a Poor Drainage Alluvial Plain and an Alluvial Plain. Bed load discharge and suspended sediment concentration measured during a bankfull flood are very low, given the relatively high stream power of 287 W m -1 . The measured bed load discharge was three to five orders of magnitude lower than six applied bed load equations, presumably due to low sediment availability.

Improving sediment discharge prediction for overbank flows

Abstract: The Ackers and White (Journal of Hydraulic Division, ASCE, 1973, 99, No. NY11, 2041–2060) and the Yang (Journal of Hydrology, 1979, 40, 123–138) sediment transport formulae, both based on the stream power theory, were applied to experimental data for sediment transport during overbank flow obtained from the large-scale UK Flood Channel Facility and the small-scale Ulster Channel. Comparisons between different velocity calculation methods were made. A simple calculation method for predicting the main channel mean velocity has been proposed. The Conveyance Estimation System, the Lambert and Myers (Proceedings of the Institution of Civil Engineers, Water, Maritime & Energy, 1998, 130, No. 2, 84–94) method and the new proposed method gave good prediction of the mean main channel velocity and were tested for use with the Ackers and White and Yang sediment transport formulae. Comparisons between computed and measured sediment discharge indicated that the Yang formula used with an accurate velocity prediction me...

Study on Hydro-dynamic Mechanism of Natural Soil Detachment in Loess Region

Abstract: Quantitative simulation on soil detachment rate is the base of process-based soil erosion model development. This study was conducted to analysis hydro-dynamic mechanism of soil detachment process for original soil core in loess region under the large range of flow discharge (0.5~2.0 L/s) and slope gradient (8.8%~46.6%). The results indicated that detachment rate of disturbed soil is more greater than that of original undisturbed soil caused by the disturbance of soil structure. It is necessary to use original undisturbed soil to investigate the mechanism of soil detachment and soil erosion. Soil detachment rate increased with both flow discharge and slope gradient increasing. However, the regression equations were slightly different between each other. Soil detachment rate can be simulated with power function of flow discharge and slope gradient (R~2=0.95). Due to the influence of sediment transport and soil sample disturbance, erodibility parameter of current study was significantly different with the relative results obtained from disturbed soil samples. Therefore, it is necessary to use original soil sample to simulate soil erosion mechanism. Among three current used hydro-dynamic parameters of shear stress, unit stream power, and stream power, there was closely relationship between soil detachment rate and stream power.

Sediment rating curve for the Ganges river

Abstract: In this study, a sediment rating curve for the Ganges river at Hardinge bridge gauge station has been developed by establishing power relations between sediment transport as dependent variable and discharge and unit stream power as independent variables separately. The unit stream power used as independent variable gives an improved curve. The sediment rating curve improves significantly when it is developed by partitioning the data into rising, flood and falling limbs.