A mixing-length model for predicting vertical velocity distribution in flows through emergent vegetation     

PAWEŁ M. ROWIŃSKI  JANUSZ KUBRAK 《水文科学杂志》2013,58(6):893-904

Abstract

The vertical profiles of streamwise velocities are computed on flood plains vegetated with trees. The calculations were made based on a newly developed one-dimensional model, taking into account the relevant forces acting on the volumetric element surrounding the considered vegetation elements. A modified mixing length concept was used in the model. An important by-product of the model is the method for evaluating the friction velocities, and consequently bed shear stresses, in a vegetated channel. The model results were compared with the relevant experimental results obtained in a laboratory flume in which flood plains were covered by simulated vegetation.  相似文献   

Evaluation of grain shear stresses required to initiate movement of particles in natural rivers     

F. Petit 《地球表面变化过程与地形》1990,15(2):135-148

Shear stresses were evaluated at different sites on two rivers. The first (the Rulles) is characterized by a pebbly bedload and a meandering bed with riffles and pools. The second (the Rouge Eau) has mainly a sandy rippled bed where meandering is well developed but also flat gravelly sectors without meandering system. Shear stresses calculated from friction velocities (τ*) using a redefined y₁ roughness height parameter were compared with total shear stresses calculated from the energy grade line and the hydraulic radius (τ), Divergence between these shear stresses seems to increase in the presence of bedforms and large-scale irregularities of the channel. The τ*/τ ratio is close to 0·5 in the gravelly sector of the Rouge Eau and reaches 0·65 in the riffles of the Rulles (generally located at the inflexion point of the meanders), while it is less than 0·3 in the pools of the same river (located in the loops) and only 0·2 in the sandy rippled sector of the Rouge Eau. Grain and bedform shear stresses were evaluated at these same sites by different methods. The grain shear stress (τ') represents on average 30 per cent of the total shear stress in the riffles of the Rulles and the gravelly sector of the Rouge Eau, but less than 15 per cent in the pools in the Rulles and the sandy sectors of the Rouge Eau. However, it emerges from experiments conducted with marked pebbles and in situ observations of erosion and transport of sandy and gravelly particles, that the grain shear stresses are underestimated and cannot explain the movements and modifications actually observed. Conversely, shear stresses calculated from friction velocities at the sites where erosion actually occurred (or failed to occur despite very high velocities) provide a better explanation of the observed movements.  相似文献   

Evaluation of temporal concentration profiles for ungauged rivers following pollution incidents     

Adam P. Piotrowski  Jaroslaw J. Napiorkowski  Pawel M. Rowinski  Steve G. Wallis 《水文科学杂志》2013,58(5):883-894

Abstract

In order to predict the impact of pollution incidents on rivers, it is necessary to predict the dispersion coefficient and the flow velocity corresponding to the discharge in the river of interest. This paper explores methods for doing this, particularly with a view to applications on ungauged rivers, i.e. those for which little hydraulic or morphometric data are available. An approach based on neural networks, trained on a wide-ranging database of optimized parameter values from tracer experiments and corresponding physical variables assembled for American and European rivers, is proposed. Tests using independent cases showed that the neural networks generally gave more reliable parameter estimates than a second-order polynomial regression approach. The quality of predictions of temporal concentration profiles was heavily influenced by the accuracy of the velocity prediction.

Citation Piotrowski, A. P., Napiorkowski, J. J., Rowinski, P. M. & Wallis, S. G. (2011) Evaluation of temporal concentration profiles for ungauged rivers following pollution incidents. Hydrol. Sci. J. 56(5), 883–894.  相似文献   

Accuracy,reproducibility and sensitivity of acoustic Doppler technology for velocity and discharge measurements in medium-sized rivers     

S. Song  B. Schmalz  G. Hörmann  N. Fohrer 《水文科学杂志》2013,58(8):1626-1641

Abstract

With increased interest and requirements in surface water quality and hydrodynamics, additional information is needed about water flow in streams. The mobile OTT Qliner with acoustic Doppler technology (ADQ) provides a highly efficient and accurate way of collecting this information. For this study we completed 366 measurements of flow velocity, water depth and discharge with ADQ from September 2010 to June 2011 at 174 cross-sections in eight catchments of different sizes located in northern Germany, central Germany and southeastern China. The measurements were used to study the accuracy, reproducibility and sensitivity of the device, and to improve the hydrodynamic sampling for medium-sized rivers and channels by investigating its internal settings. The observations reported clearly show that the results of flow average, profile, layer and point values obtained with the ADQ compare very well with those of electromagnetic or ultrasonic devices. In general, the average flow velocity gives the highest agreement. Vertical velocity has a better quality than the layer velocity, which indicates a greater precision in the horizontal than in the perpendicular direction. Point velocity, the composite of vertical velocity and layer velocity, has intermediate precision. Tests on internal settings revealed that measurement is more sensitive to cell size than to time interval setting. A cell size to depth ratio of between 0.1 and 0.2 m produced the highest reliability. A measurement period of 30 s is needed for velocities faster than 0.3 m/s; for shallow and slow-flowing rivers, an interval of 50 s or even greater is recommended. The closer the measured points were to the river bank or bed, the greater the measurement error. The river bed can also influence the measurement more distinctly than the river bank.

Editor D. Koutsoyiannis; Associate editor A. Montanari

Citation Song, S., Schmalz, B., Hörmann, G., and Fohrer, N., 2012. Accuracy, reproducibility and sensitivity of acoustic Doppler technology for velocity and discharge measurements in medium-sized rivers. Hydrological Sciences Journal, 57 (8), 1626–1641.  相似文献   

Comparison of direct statistical and indirect statistical-deterministic frameworks in downscaling river low-flow indices     

Deepti Joshi  Andre St-Hilaire  Taha B. M. J. Ouarda  Anik Daigle  Nathalie Thiemonge 《水文科学杂志》2013,58(11):1996-2010

ABSTRACT

This work explores the ability of two methodologies in downscaling hydrological indices characterizing the low flow regime of three salmon rivers in Eastern Canada: Moisie, Romaine and Ouelle. The selected indices describe four aspects of the low flow regime of these rivers: amplitude, frequency, variability and timing. The first methodology (direct downscaling) ascertains a direct link between large-scale atmospheric variables (the predictors) and low flow indices (the predictands). The second (indirect downscaling) involves downscaling precipitation and air temperature (local climate variables) that are introduced into a hydrological model to simulate flows. Synthetic flow time series are subsequently used to calculate the low flow indices. The statistical models used for downscaling low flow hydrological indices and local climate variables are: Sparse Bayesian Learning and Multiple Linear Regression. The results showed that direct downscaling using Sparse Bayesian Learning surpassed the other approaches with respect to goodness of fit and generalization ability.