Measurements of Turbulence Structure in a Compound Channel

Mirosław‐Świątek

2018

Water

This study investigates the effect of the Digital Terrain Model (DTM) uncertainty effect on the output of a 1D flow model. The analysis is performed for the lowland river Biebrza, covered with dense wetland vegetation, with a high uncertainty of terrain elevations. The DTM uncertainty is modeled in two ways: (1) accounting for the uncertainty spatial dependency on the basis of the correlogram function and (2) neglecting the correlation of the elevation points. The model explanation of water levels improves when elevation uncertainty is being included. Without the elevation uncertainty, the model provided a good fit only for peak flows, with uncertainty also representation of lower flows is better. It was shown that the correlation of the elevation uncertainty had a noticeable effect on the modeling outcomes, especially for near bankfull flows, where for the uncorrelated case water levels were underestimated by 5 cm, comparing to the correlated case. The effect was also present for inundation extents, obtained by an interpolation of computed water levels. The correlation of the elevation uncertainty strongly affects estimates of standard deviations of computed water levels, which were almost twice smaller when correlation was neglected. In the result, only when the correlation of the elevation uncertainty was included, it was possible to obtain confidence bands that enclosed observation points.

Section: Introductionmentioning

confidence: 99%

Impact of Uncertainty of Floodplain Digital Terrain Model on 1D Hydrodynamic Flow Calculation

Mirosław‐Świątek

2018

Water

“…A brief concept of the Pasche method is provided by Pasche (1984) and Pasche and Rouvé (1985), and a detailed description of the algorithm used herein is provided in Kozioł et al (2004). The model describes the discharge capacity of the compound cross section with rigid vegetation, derived for steady flow conditions.…”

Section: Pasche and Mertens Methodsmentioning

confidence: 99%

“…The experiments were conducted at the Warsaw University of Life Sciences (WULS-SGGW) using a physical model of a compound channel with rigid cylinders simulating vegetation. A detailed description of the data set can be found in Kozioł and Kubrak (2015), Kozioł (2013), Kubrak et al (2019a), and Kubrak et al (2019b).…”

Section: Flume Experimentsmentioning

confidence: 99%

Predicting discharge capacity of vegetated compound channels: uncertainty and identifiability of one-dimensional process-based models

Hydrol. Earth Syst. Sci.

Västilä

Kozioł

et al. 2020

Self Cite

Abstract. Despite the development of advanced process-based methods for estimating the discharge capacity of vegetated river channels, most of the practical one-dimensional modeling is based on a relatively simple divided channel method (DCM) with the Manning flow resistance formula. This study is motivated by the need to improve the reliability of modeling in practical applications while acknowledging the limitations on the availability of data on vegetation properties and related parameters required by the process-based methods. We investigate whether the advanced methods can be applied to modeling of vegetated compound channels by identifying the missing characteristics as parameters through the formulation of an inverse problem. Six models of channel discharge capacity are compared in respect of their uncertainty using a probabilistic approach. The model with the lowest estimated uncertainty in explaining differences between computed and observed values is considered the most favorable. Calculations were performed for flume and field settings varying in floodplain vegetation submergence, density, and flexibility, and in hydraulic conditions. The output uncertainty, estimated on the basis of a Bayes approach, was analyzed for a varying number of observation points, demonstrating the significance of the parameter equifinality. The results showed that very reliable predictions with low uncertainties can be obtained for process-based methods with a large number of parameters. The equifinality affects the parameter identification but not the uncertainty of a model. The best performance for sparse, emergent, rigid vegetation was obtained with the Mertens method and for dense, flexible vegetation with a simplified two-layer method, while a generalized two-layer model with a description of the plant flexibility was the most universally applicable to different vegetative conditions. In many cases, the Manning-based DCM performed satisfactorily but could not be reliably extrapolated to higher flows.

“…Nezu and Nakagawa (1993) proposed the equations describing relative turbulence intensity distributions in single channels for a steady and uniform 2D flow. However, the conditions of water flow after a water plant or in a compound channel are significantly different and very complex (Ali et al, 2014;Czernuszenko et al, 2007;Dargahi, 2003;Kozioł, 2013Kozioł, , 2015Kozioł and Kubrak, 2015;Kozioł et al 2016;Mazurczyk, 2007;Nezu and Nakagawa, 1993;Nikora et al, 1994;Oliveto and Comuniello, 2009;Oliveto et al, 2011;Pagliara and Palermo, 2013;Rowiński et al, 1998;Rowiński et al, 2002;Shiono and Knight, 1991;Siniscalchi et al, 2012). The turbulence generation produces fluctuations of the flow velocity associated with big vortices, and the turbulent energy is converted into an energy cascade to smaller scale eddies until it is dissipated into heat by the molecular viscosity (Nezu and Nakagawa, 1993).…”

Section: Introductionmentioning

confidence: 99%

“…According to Nikora et al (1994), the spatial scales ranging from L/h = 0.1 to the scales on the order of twice or even three times the depths of the stream and results agree closely with the measured data of Yokosi (1967), McLean and Smith (1979), Nikora (1985) and Grinwald and Nikora (1988). In open channels, for different roughness of the channel without and with vegetated floodplains, the variability of macroeddies was analyzed in the research papers: Rowiński et al (2002), Rowiński and Mazurczyk (2006), Czernuszenko et al (2007), Mazurczyk (2007), Kozioł (2000Kozioł ( , 2008Kozioł ( , 2015, Kozioł and Kubrak (2015).…”

Section: Introductionmentioning

confidence: 99%

Turbulence intensity and spatial scales of turbulence after hydraulic jump over scour hole in rectangular channel

Kozioł

Urbański

Journal of Hydrology and Hydromechanics

et al. 2017

Abstract:The study presents experimental investigations of spatial turbulence intensity and scales of turbulent eddies (macroeddies) in a rectangular channel and the impact of the hydraulic jump on their vertical and streamwise distributions over a flat and scoured bed. The results of four tests and two different discharge rates are presented. Intensive mixing caused by the hydraulic jump has an impact on the instantaneous velocity, turbulence intensity and sizes of macroeddies, as well as their vertical and longitudinal distributions along the channel. The largest differences in turbulence characteristics were reported directly after the hydraulic jump, above the eroded bed. The interaction between the stream of the increased turbulence and the bed is a direct cause of formation of scour downstream water structures, which has a great effect on overall flow characteristics. The scour hole that arose downstream the jump moderated, in a small degree, the turbulence intensity at its end. Just next to the hydraulic jump only the small longitudinal relative sizes of macroeddies were present, while at the end of the analyzed reach, downstream of the scour, the relative scale reached around 1.5 depth of the stream.