Moving sand waves and the overlying tubulent flow were
measured on the Wilga River
in Poland, and the Tirnava Mica and Buzau Rivers in Romania. Bottom elevations
and
flow velocities were measured at six points simultaneously by multi-channel
measuring
systems. From these data, the linear and two-dimensional sections of the
three-dimensional correlation and structure functions and various projections
of
sand wave three-dimensional spectra were investigated.It was found that the longitudinal wavenumber spectra of the sand waves
in the
region of large wavenumbers followed Hino's −3 law
(S(Kx)
∝K−3x)
quite satisfactorily, confirming the theoretical predictions of Hino
(1968) and Jain & Kennedy
(1974). However, in contrast to Hino (1968), the sand wave frequency spectrum
in the
high-frequency region was approximated by a power function with the exponent
−2, while in the lower-frequency region this exponent is close to
−3.A dispersion relation for sand waves has been investigated from analysis
of
structure functions, frequency spectra and the cross-correlation
functions method. For
wavelengths less than 0.15–0.25 of the flow depth, their
propagation velocity C is
inversely proportional to the wavelength λ. When the wavelengths
of spectral
components are as large as 3–4 times the flow depth, no
dispersion occurs. These results
proved to be in good qualitative agreement with the theoretical dispersion
relation
derived from the potential-flow-based analytical models (Kennedy 1969;
Jain &
Kennedy 1974). We also present another, physically-based, explanation of
this
phenomenon, introducing two types of sand movement in the form of sand
waves. The
first type (I) is for the region of large wavenumbers (small wavelengths)
and
the second one (II) is for the region of small wavenumbers (large wavelengths).
The small sand waves move due to the motion of individual sand particles
(type I,
C∝λ−1) while
larger sand waves propagate as a result of the motion of smaller waves
on their
upstream slopes (type II, C∝λ0). Like
the sand particles in the first type, these smaller
waves redistribute sand from upstream slopes to downstream ones. Both types
result
in sand wave movement downstream but with a different propagation velocity.The main characteristics of turbulence, as well as the quantitative
values
characterizing the modulation of turbulence by sand waves, are also presented.
An enzyme-catalyzed process has been used for dioxygen monitoring. The enzymes were two different laccases (p-diphenol:dioxygen oxidoreductases), chosen as catalysts for dioxygen reduction. The laccases were immobilized in a liquid crystalline cubic phase formed with monoolein. The structures of the cubic phases, both with and without enzymes, were established using small-angle X-ray scattering. The catalytic reduction of dioxygen was performed using a glassy carbon electrode modified with cubic phases containing the enzymes. The modified electrode was used as a dioxygen sensing system, based on the increasing reduction current of a suitable electrochemical probe in the presence of dioxygen.
Abstract:The impact of floodplain hydrology on the in-stream dissolved oxygen dynamics and the relation between dissolved oxygen and water temperature are investigated. This has been done by examining the time series of dissolved oxygen and water temperature coupled with meteorological and hydrological data obtained from two lowland rivers having contrasting hydrological settings. Spectral analysis of long-term oxygen variations in a vegetated river revealed a distinct scaling regime with slope '-1' indicating a self-similar behaviour. Identical slopes were obtained for water temperature and water level. The same power-law behaviour was observed for an unvegetated river at small timescales revealing the underlying scaling behaviour of dissolved oxygen regime for different types of rivers and over various time scales. The results have shown that the oxygenation of a vegetated river is strongly related to its thermal regime and flow conditions. Moreover, analysis of short-term fluctuations in the unvegetated river demonstrated that physical factors such as rainfall and backwaters play a substantial role in the functioning of this ecosystem. Finally, the results show that the relation between water temperature and dissolved oxygen concentration at the diurnal timescale exhibits a looping behaviour on the variable plot. The findings of this study provide an insight into the sensitivity of rivers to changing hydro-physical conditions and can be useful in the assessment of environmental variability.
New sustainable, cost-effective solutions are urgently needed for river management since conventional practices have posed serious ecological threats on streams, rivers and the surrounding riparian areas. Besides addressing the societal needs e.g. for flood management, river management should increasingly address the ecosystem requirements for improved water quality and biodiversity. We argue that it is not feasible to solve existing and future river management challenges with intensive restoration projects. Instead, we believe that less resource-intensive solutions using natural channel processes and features, including vegetation, should be investigated. Besides directly supporting biota, aquatic and riparian vegetation traps, takes up and helps to process nutrients and harmful substances, and thus this paper emphasizes vegetation as a tool for nature-based solutions (NBS) in river management. In this paper, emphasis is placed on the usage of vegetation as a NBS in river management. We synthesize findings from key literature, showing that the fate of substances in channel systems is largely controlled by abiotic and biotic processes facilitated and modified by vegetation, including flow hydrodynamics, channel morphology, and sediment transport. Subsequently, we demonstrate how vegetation can be incorporated into channel designs, focusing on a two-stage (compound) design to improve resilience to flooding, control the transport of substances, and enhance the ecological status. As a conclusion, clever use and maintenance of vegetation present unused potential to obtain large-scale positive environmental impacts in rivers and streams experiencing anthropogenic pressures.
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