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River action and control
Published in F.G. Bell, Geological Hazards, 1999
Straight streams possess essentially straight banks, having a sinuosity of less than 1.5, but flow between the banks is not necessarily straight. Turbulent flow does not move water in a straight line, because secondary currents develop with transverse flow producing various bedforms, pools and riffles. A pool is a deep reach, whereas a riffle is shallower with elongated sediment bars. Each succeeding riffle in a downstream direction slopes alternately towards the opposite bank. The form of the riffle can become relatively fixed in position as a node of accumulation, and particles that compose the bar are intermittently moved from one riffle to the next with each succeeding flood flow. The spacing of pools and riffles is normally 5 to 8 times channel width.
Water Ecology
Published in Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2020
As mentioned, lotic (washed) habitats are characterized by continuously running water of current flow. These running water bodies, have typically three zones: riffle, run, and pool. The riffle zone contains faster flowing, well-oxygenated water, with coarse sediments. In the riffle zone, the velocity of the current is great enough to keep the bottom clear of silt and sludge, thus providing a firm bottom for organisms. This zone contains specialized organisms, which are adapted to live in running water. For example, organisms adapted to live in fast streams or rapids (trout) have streamlined bodies, which aid in their respiration and in obtaining food (Smith, 1996). Stream organisms that live under rocks to avoid the strong current have flat or streamlined bodies. Others have hooks or suckers to cling or attach to a firm substrate to avoid the washing-away effect of the strong current. The run zone (or intermediate zone) is the slow-moving, relatively shallow part of the stream with moderately low velocities and little or no surface turbulence. The pool zone of the stream is usually a deeper water region where the velocity of water is reduced and silt and other settling solids provide a soft bottom (more homogeneous sediments), which is unfavorable for sensitive bottom dwellers. The decomposition of some of these solids causes a lower amount of DO. Some stream organisms spend some of their time in the rapids part of the stream and other times can be found in the pool zone (trout, for example). Trout typically spend about the same amount of time in the rapids zone pursuing food as they do in the pool zone pursuing shelter.
Introduction
Published in Frank R. Spellman, The Science of Water, 2020
But to see the rest of the story we need to look at the pool’s outlet, and where its flow enters the main river. This is the riffle—a shallow place where water runs fast and is disturbed by rocks. Only organisms that cling very well, such as net-winged midges, caddisflies, stoneflies, some mayflies, dace, and sculpins, can spend much time here, and the plant life is restricted to diatoms and small algae. Riffles are a good place for mayflies, stoneflies, and caddisflies to live because they offer plenty of gravel to hide.
Bulk Flow Characteristics of a Gravel Bed River with Instream Emergent Vegetation
Published in ISH Journal of Hydraulic Engineering, 2023
Sadegh Derakhshan, Hossein Afzalimehr, Vijay P. Singh
Subtracting the vegetative and grain friction from the total friction factor leads to a value of f = 0.09 which is due to the bed irregularities of the river reach in the vegetated region. The bed elevation profiles in the longitudinal direction at the center of the channel are drawn for the vegetated (Figure 4a) and unvegetated segments of the reach and (Figure 4b), as can be observed from Figure 4a, no specific bedforms can be detected in the longitudinal direction of the channel except for a few minor irregularities. In the spanwise direction, however, a central bar as characterized by (Crosato and Mosselman 2020), was apparent in the beginning of the reach (Figure 5a), moreover, a transverse bar as characterized by (Crosato and Mosselman 2020) can be seen in Section 2 (Figure 5b), these bars and the irregularities of the bed are likely to be the cause of f ′′ = 0.09 in the vegetated segment of the reach. For the unvegetated segment (from Section 3 to 4), subtracting the grain roughness from the total friction leads to an amount of f ′′ = 0.3 for the bed form friction. A pool-riffle like bedform was observed at the end of the river reach (Figure 4b), furthermore, by examining the general shape of the cross-Section 4 (Figure 5d), a transverse bar can be delineated. The pool-riffle bedform and the transverse bar and the general irregularities of the bed are the main source of friction in the unvegetated part of the river and grain roughness makes up only 16% of the total friction.
Chinook Salmon habitat evolution following river restoration, drought, and flood
Published in Journal of Ecohydraulics, 2022
Rocko A. Brown, Kirsten Sellheim, Jesse T. Anderson, Joseph E. Merz
Patterns of velocity generally follow those of Shields stress, with the upper section having lower velocity than the lower section (Figure 11A). At the spawning flow, thalweg velocities never exceed 1 m/s in the upper section but are on average 0.3 m/s higher in the lower section. These differences between the two sections increase to 0.57 and 0.46 m/s, at the bankfull and flood flow, respectively. Spawning flow velocities are focused on riffle crests and at the bankfull and flood flow some areas of peak velocity shift from the riffles to the adjacent pools, demonstrating the presence of velocity reversals (Figure 11B). For example, the island-riffle complex is a zone of peak thalweg velocity at the low flow but at the bankfull flow the velocity in the upstream pool exceeds the riffle velocity (Figure 11C). The central island riffle, however, is always a zone of peak velocity and the upstream pool never approaches the magnitude of velocity in the riffles. The broad riffle does not show a clear reversal, but velocities in the adjacent pools are within ∼ 0.2 m/s of the riffle at the flood flow, interpreted as velocity convergence.
Target species selection and design of fish habitat suitability curves in the Ayuquila-Armería River, western Mexico
Published in International Journal of River Basin Management, 2021
Demetrio Meza Rodríguez, Luis Manuel Martínez Rivera, Norman Mercado-Silva, Diego García de Jalón Lastra, Carlos Alonso González, Ángel Aguirre García
The proposed suitability curves for the three species showed differences related to adaptations for the use of habitat. Agonostomus monticola preferred zones that were deeper and with faster flows than the other two species. Such zones are characteristic of areas of rapids found on the river. The curves of A. zonistius for depth (0.56 m) and velocity (0.57 m s−1) presented lower values than those of A. monticola. Previous studies conducted by Lyons and Mercado-Silva (2000) indicated that A. zonistius avoids areas with velocities greater than 0.75 m s−1, and the results of this study suggest that this species is found in depths from 0.42 to 0.73 m and flow velocities from 0.60 to 0.68 m s−1. The depths and velocities defined for this species match the characteristics of riffle zones and shallow rapids in the river.