Hydrodynamics of the Instream Flow Environment of a Gravel-Bed River

Abstract

This work was aimed at comparing the instream flow environment of four basic hydromorphological units of a mountain gravel-bed river: pools, runs, riffles and rapids. A survey was performed during the average flow stage on the Skawa River in southern Poland. In the 3.5 km long reach, 31 physical habitats were surveyed: eight pools, eight runs, nine riffles and seven rapids. Using Micro ADV Sontek equipment, instantaneous velocity time series components were measured at eight locations in three positions—z/h = 0.2, 0.4 and 0.6—in each unit. Turbulence descriptors—the mean components of velocity, turbulence intensities calculated as the root mean square of velocity component time series, turbulent kinetic energy TKE, Reynolds shear stresses and standard hydraulic attribute, i.e., Froude number—were estimated. Although there was a wide dispersion of the turbulence variable distributions, a standard tendency of decreased mean velocity and increased turbulence towards the bottom was observed. Most turbulence parameters—streamwise velocity, turbulence intensities, TKE and streamwise-vertical Reynolds shear stresses—reveal differences of instream flow environment between the pools, runs and riffles. In addition, the mean turbulence intensities suggested a 1:2:3:3 proportion of turbulence intensity in pools, runs, riffles and rapids, respectively. Riffles and rapids, in general, have similar turbulence values, whereas rapids are deeper and visually more energetic.

Hydraulic Effect of Vegetation Zones in Open Channels: An Experimental Study of the Distribution of Turbulence

“…However, the minimum turbulence values of Tu do not occur in the center of the channel cross-section, as there is an increase in longitudinal velocity v x and it is a zone of increased stream turbulence. Other researchers have also noted this hydraulic effect of plants [19,[31][32][33][34][35][36][37]51,52].…”

“…To date, many researchers have dealt with the problem of hydraulic flow conditions in rivers. Some of them have also studied the spatial distribution of turbulence [15,17,19,25,[28][29][30][31][32][33][34]38,[51][52][53][54]. However, those studies focused on a completely different factor that affects the distribution of turbulence.…”

“…In those cases, they mainly studied the effect of a very rough, gravelly riverbed on the distribution of turbulence and turbulent kinetic energy (TKE). Even when there were plants in the river (often common river hydrophytes rather than reeds), their hydraulic influence was not dominant as in the case of gravel-bed rivers [17,28,[32][33][34]52]. There are known laboratory studies where the influence of plant zones on stream turbulence and flow conditions was also tested.…”

“…In a mountain riverbed with plants and a gravelly bottom, Wos and Ksiazek (2022) studied the spatial distributions of velocity, turbulence intensity, turbulent kinetic energy TKE, shear stress and Froude number. Although there was a wide dispersion of the turbulence variable distributions, a standard tendency of decreased mean velocity and increased turbulence towards the bottom was observed [32]. Soltani et al (2020), on the other hand, conducted their study of turbulent flow characteristics on the Plusjan River (Iran) with a very rough, gravelly riverbed.…”

Environmental Restoration and Changes of Sediment and Hydrodynamic Parameters in a Section of a Renaturalised Lowland Watercourse

“…These conditions are further influenced by channel structures. The use of seminatural structures such as deflectors improves the hydromorphological conditions of altered watercourses [12], which result in increased habitat diversity in the riverbed [13,14], leading to a rise in hydrobiota biodiversity [15] and an improvement in environmental sustainability [16,17].…”