The concept of dominant discharge applied to two gravel-bed streams in relation to channel stability thresholds     

Paul Carling 《地球表面变化过程与地形》1988,13(4):355-367

Dominant discharge may be defined as that discharge which transports most bed sediment in a stream that is close to steady-state conditions. The concept is examined in relation to two single thread gravel-bedded streams. One stream is alluvial and free to adjust its geometry whilst in the other, channel capacity and form are partially constrained by cohesive till-banks and a heavily compacted bed. The total quantity of bedload and its calibre were measured for every flood over a six year period, so that the relationship between the grain-size of bedload and the most effective discharge could be examined in the context of thresholds for channel change. The dominant discharge concept was applicable to the alluvial stream in that the bankfull value is an effective discharge for maintaining channel capacity. The concept applied less well to the ‘non-alluvial’ stream. Although in both streams the bankfull value was exceeded for less than 0.34 per cent of the time, overbank flows are important in instigating channel change. It is only during overbank flows that the largest bed material is entrained in quantity. For within-channel flows a threshold separates flows which winnow fine matrix from those which entrain the finer bed gravels. This threshold occurred at 60 per cent bankfull. It was concluded that the dominant discharge concept can be applied to streams close to steady-state which are alluvial, competent, and free to adjust their boundaries. An important proviso is that two channel-stability domains can be recognized. These domains represent channel maintenance and channel adjustment and are defined by intrinsic thresholds in the bed material entrainment function.  相似文献   

Bedload transport in two gravel-bedded streams     

P. A. Carling 《地球表面变化过程与地形》1989,14(1):27-39

Bedload transport measurements in two upland streams are considered as a function of the excess stream power exerted on the bed by the flow. During low flows when the framework gravels remain undisturbed, fine sediments are winnowed from the bed-surface layer once a threshold of 3·4 W m^?2 is exceeded and the transport rate is strongly supply limited. However for stream powers in excess of 15 W m^?2 framework gravels are mobilized and the efficiency of the transport process approaches a local maximum of about 1 per cent for discharges up to 2/3 of bankfull. An inverse depth dependence in the efficiency of the transport process was noted but although bedload calibre increased as a function of discharge its influence on efficiency could not be demonstrated. However it was suspected that the size-sorting relationships of the bed-material in a number of rivers in relation to the transport efficiency might profitably be examined further.  相似文献   

The next time you are asked to review a manuscript for the journal… and other musings…     

Paul Carling  Peter Swart 《Sedimentology》2007,54(6):1223-1224

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The morphodynamics of fluvial sand dunes in the River Rhine, near Mainz, Germany. II. Hydrodynamics and sediment transport   总被引：1，自引：0，他引：1  

Carling  Williams  Gölz  & Kelsey 《Sedimentology》2000,47(1):253-278

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Hydrodynamic interpretation of a boulder berm and associated debris-torrent deposits     

P.A. Carling 《Geomorphology》1987,1(1)

The hydrodynamic environment associated with a boulder berm is reconstructed from the geometry and sedimentology of the berm and associated debris-torrent deposits. Berms may result from a variety of hydrodynamic scenarios but in this instance the berm was associated with flow separation downstream of an abrupt change in channel morphology. Sediment fabric analyses are summarized particularly as eigenvalues and these data compared with the fabric of debris flows and clear-water gravel deposits. Although data are few, the eigenvalue results can be interpreted consistently as reflecting a transition between the end members of a sediment fabric continuum.The value of detailed studies of berm geometry and sedimentology is discussed with reference to their hydraulic significance. This latter aspect is important for palaeo-discharge reconstruction of both Newtonian and non-Newtonian flows.  相似文献   

Hydraulic model calibration for extreme floods in bedrock‐confined channels: case study from northern Thailand     

R. L. Kidson  K. S. Richards  P. A. Carling 《水文研究》2006,20(2):329-344

Palaeoflood reconstructions based on stage evidence are typically conducted in data‐poor field settings. Few opportunities exist to calibrate the hydraulic models used to estimate discharge from this evidence. Consequently, an important hydraulic model parameter, the roughness coefficient (e.g. Manning's n), is typically estimated by a range of approximate techniques, such as ‘visual estimation’ and semi‐empirical equations. These techniques contribute uncertainty to resulting discharge estimates, especially where the study reach exhibits sensitivity in the discharge–Manning's n relation. We study this uncertainty within a hydraulic model for a large flood of known discharge on the Mae Chaem River, northern Thailand. Comparison of the ‘calibrated’ Manning's n with that obtained from semi‐empirical equations indicates that these underestimate roughness. Substantial roughness elements in the extra‐channel zone, inundated during large events, contribute significant additional sources of flow resistance that are captured neither by the semi‐empirical equations, nor by existing models predicting stage–roughness variations. This bedrock channel exhibits a complex discharge–Manning's n relation, and reliable estimates of the former are dependent upon realistic assignment of the latter. Our study demonstrates that a large recent flood can provide a valuable opportunity to constrain this parameter, and this is illustrated when we model a palaeoflood event in the same reach, and subsequently examine the magnitude–return period consequences of discharge uncertainty within a flood frequency analysis, which contributes its own source of uncertainty. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Soil erosion and conservation on land cultivated and drained for afforestation     

P. A. Carling  M. S. Glaister  T. P. Flintham 《水文研究》1993,7(3):317-333

Erosion of soil from pre-afforestation plough furrows has been measured on four soil types in Scotland for 12 to 18 month periods between 1987 and 1990. Rainfall-run-off was also measured at one site. Run-off is directly proportional to furrow length and rainfall intensity, and for a wide range of intensities (typically > 6 mm hr^?1) small amount of soil is flushed out of the furrows. However, for furrow spacings of 3.8 m, a critical downslope run-off increment associated with significant soil loss is of the order of 25 cm³ s^?1 m^?1, which is in accord with a storm of five years return period and a maximum intensity of 25 mm hr^?1. The total run-off volume for any hydrograph is commensurate with the total rainfall in the rainstorm — typically 40–80% by the hydrograph peak and approaching 100% by the end of the hydrograph; i.e. long term storage is negligible. A positive relationship was recorded between furrow length, slope angle and sediment yield, with deposition predominating in furrows less than 30 m in length on slopes less than a few degrees. Soil loss is proportional to the excess streampower expended by the run-off with an exponent in the range 1–1.5. For the soils examined, significant differences in soil loss when comparing sites for low power expenditure become undifferentiated at high power expenditures. For the rainfall regimes monitored, maximum soil losses were in the region of 40 kg per meter run-length of furrow, when soil peds were ripped from the bed. Laboratory data concerning the critical erosion threshold power and shear stress to erode soil peds are in general accord with the threshold furrow run-lengths defined using the field data for a five year storm and the soil losses observed.  相似文献   

Bibliography     

E. B. Carling  Z. Kopal  S. H. Tellier 《Earth, Moon, and Planets》1989,46(1):31-105

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Factors controlling the temporal variability in dissolved oxygen regime of salmon spawning gravels          下载免费PDF全文

D. A. Sear  I. Pattison  A. L. Collins  M. D. Newson  J. I. Jones  P. S. Naden  P. A. Carling 《水文研究》2014,28(1):86-103

Dissolved oxygen (DO) plays a critical role in the development of the juvenile stages of benthic spawning fish and salmonids in particular. Factors influencing the DO regime within spawning gravels include the accumulation of fine sediment, penetration of groundwater or surface water into the gravels, thermal regime, and the consumption of oxygen by sediment and its associated organic fractions. In this field study, we quantify the DO regime within an artificial salmon redd at high temporal resolution. The environment within the redd is shown to be complex, with large variations in DO. Application of a numerical model (SIDO‐UK) enables for the first time, the quantification of the relative contributions to DO consumption from thermal regime, sediment accumulation and sediment oxygen demand. Sediment accumulation is shown to have a minor impact on DO in the redd whereas upwelling groundwater is identified as the most likely cause of the major changes in DO. Bed mobility has a minor impact on DO regime of the redd. The effects of fine sediment and oxygen supply on salmon embryo survival are estimated. Implications for river catchment management and prospects for future research are discussed. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies     

James Q.Feng  C.F.Gallo 《中国天文和天体物理学报》2011,(12)

We present an efficient,robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies.With appropriate mathematical treatments,the apparent numerical difficulties associated with singularities in computing elliptic integrals are completely removed.Using a boundary element discretization procedure,the governing equations are transformed into a linear algebra matrix equation that can be solved by straightforward Gauss elimination in one step without further ...  相似文献