The stability of habitat conditions in littoral zones of navigated rivers is strongly affected by shipping induced waves and water displacements. In particular, the increase of variability in flow ...conditions diminishes the suitability of these habitats for juvenile fishes. Recently, a novel ecosystem based river management strategy has resulted in the replacement of traditional river training structures (i.e., groynes) by longitudinal training dams (LTDs), and the creation of shore channels in the river Waal, the main, free-flowing and intensively navigated distributary of the river Rhine in the Netherlands. It was hypothesized that these innovative LTDs mitigated the effects of shipping on fishes by maintaining the natural variability of habitat conditions in the littoral zones during ship passages whereby shore channels served as refugia for juvenile fishes. Measurements of abiotic conditions showed a significantly lower water level fluctuation and significantly higher flow stability in shore channels compared to groyne fields. Flow velocity did not differ, nor did the variation in flow velocity fluctuation during ship passage between these habitats. Densities of fish were found to be significantly higher in the littoral zones of shore channels compared to nearby groyne fields. Moreover, electrofishing along the inner side of the newly constructed LTD showed a significant linear relationship between fish density and distance from highly dynamic in- and outflow sections and to lowered inflow sections in the LTD. Results of our field sampling clearly indicate successful ecological rehabilitation of littoral zones that coincides with a facilitation of navigation in the main river channel and increased flood safety.
Display omitted
•Impacts of passing ships on abiotic conditions in the littoral zone of rivers were reduced in shore channels behind LTD.•Flow stability was enhanced in the shore channel along the LTD compared to traditional groyne fields.•Fish densities in the littoral zone of the LTD shore channel were significantly higher compared to traditional groyne fields.•Fish densities in stony habitats along the LTD increased linearly with distance to dynamic sections (such as in- and outlet).•LTDs allow for ecological rehabilitation of littoral zones of navigated rivers while enabling multiple uses and flood safety.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Riverine ponds, which are formed and sustained through sediment erosion and deposition, are key habitats for enhancing biodiversity in river reaches. The objective of this study was to understand the ...roles of traditional river-training wooden structures called “seigyu” on the formation of ponds on nonvegetated bars. Here, the spatial and temporal patterns of the flow and bedform coupled with pond formations for several flood events were assessed. The surface flow patterns were monitored by an unmanned aerial vehicle (UAV) and evaluated by large-scale particle image velocimetry (LSPIV); the maximum flow velocities were 1.3 m s−1 and 1.9 m s−1 during floods when seigyu units were partially and fully submerged, respectively. Although the overall mean flow velocity was greater for the latter events, the spatial variation in flow velocity and dissipation rate of turbulent kinetic energy (TKE) around seigyu was greater for the former events. Such flow patterns affected both bed formation and ecological habitats; ponds were formed at locations beside and behind seigyu, where the flow converged and bed scouring occurred during floods. The frequency and size of ponds around seigyu increased in the early half of the season, and they decreased in the other half when floods were greater in magnitude, which suggests that the bed scouring effect of seigyu was greater in flood stages with partial than fully submergence. Although the bar ponds lack shade to temper the effects of incident light and atmospheric conditions, the ponds displayed smaller daily oscillations in temperature than did the main river, probably due to hyporheic water supply to the ponds. Because many aquatic species cannot tolerate extremely high temperatures in summer, the generation and maintenance of deeper ponds by scouring with sufficient water exchange with the hyporheic zone can be key to enhancing colonization by various aquatic species.
Display omitted
•Flow behavior around river training structures were monitored by UAV during floods.•Flow was diverted and converged due to the structures in partially submerged floods.•The ponds developed by bed sours around the structures on a bar after the floods.•The ponds were filled by sand and dewatered after fully submerged floods.•Water temperature fluctuation was smaller for the ponds than river main flow.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Sedimentation at intakes of drinking water treatment plants (DWTPs) clogs intake pipe inlets causing interruption of water supply and serious pump abrasion. It occurs due to river flow velocity (FV) ...decline which causes flow inability to carry sediment particles. On the other hand, high velocities increase water turbidity because they induce flow turbulence that diffuses bed sediment particles over the water depth. The diffusion causes turbid water withdrawal and consequent high treatment running cost. This paper aims to adjust FVs near DWTP intakes using river training works (TWs) to control sedimentation and turbidity. Road El-Farag DWTP intake was taken as a case study. Groin construction and riverbed dredging were proposed as effective TWs. A 2-D mathematical model (SMS) was used to simulate different scenarios of the TWs. The simulations aimed to increase the FVs near the intake area provided that they neither allow sedimentation nor bed scour. The study area with FVs ranging from 0.025 to 0.40 was simulated in a physical flume to investigate the corresponding water turbidity (WT) values. A Jar test was conducted to find a relationship between WT and alum doses at different FVs. This relationship determines the optimum alum dose that can minimize turbidity. SMS and flume simulations revealed that positioning of groins on the river bank opposite to the intake area combined with dredging near the intake managed to increase FVs that can prevent sedimentation and bed scour. Finally, a mathematical relationship between alum doses and FVs was established.
The largest ongoing river training project in Switzerland, the so-called Third Correction of the Rhone in the Valais, builds on nature-based solutions (river enlargements and renaturation) while ...official documents and discourses also refer to an ill-defined notion of “sustainable security” and the goal of controlling floods. Drawing on qualitative data from stakeholder interviews and analysis of official documents, this paper examines the concept of sustainable security, as it is applied to the river project in terms of a balance between security and environmental concerns, the relationship between the three pillars of sustainability, and the opportunities of the population to debate the spatial development of the Rhone Valley. We argue that legal provisions, the dominance of security concerns and technocratic framings of the project foreclose more substantive political debate on the sustainable future of the hydrosocial territory of the Rhone Valley.
Spur-dikes are efficient hydraulic structures that are made for numerous purposes. They have one end on the stream bank and another extending into the current. As a result of the existing spur-dikes ...in the stream course, the local scour phenomena usually occur around them, leading to several predicaments which have been of great concern to the hydraulic engineers. For the present work, laboratory experiments were carried out to measure the scour depths around several spur-dikes located at different distances for the V-shaped one. The experiments were conducted using physical models installed in a non-curved flume with a bed with uniform cohesion-less sediment of a medium particle size (d50 = 0.7 mm). All the models were operated under the subcritical flow of clear-water conditions. The investigations include three spur-dikes (1, 2 and 3) and three distances between them (1, 1.5 and 2 of spur-dike length) as two countermeasures to minimize the local scour depths. The results showed that an increasing number of spur-dikes and the distances between them would decrease the scour depths within the limit of the present study. The experimental data were used to create a new formula of R2 = 0.954 that reflects a good agreement with the experimentally observed results.
To date, no survey on the diverse channel patterns existing prior to the major phase of river regulation in the mid‐19th–early 20th century has been elaborated at the scale of the whole European ...Alps. The present paper fills this knowledge gap. The historical channel forms of the 143 largest Alpine rivers with catchments larger than 500 km2 (total length 11,870 km) were reconstructed based on maps dating from the 1750s to 1900. In the early 19th century, one‐third of the large Alpine rivers were multi‐channel rivers. Single‐bed channels oscillating between close valley sides were also frequent in the Alps (28%). Sinuous and even more so meandering channels were much rarer. Historical river patterns generally followed an upstream–downstream gradient according to slope condition, floodplain width and distance from the sources. The local occurrence of certain channel patterns, however, primarily reflected the tectonic/orographic conditions. Multi‐channel reaches were widespread within the whole Alpine area, alternating with confined and oscillating reaches. This demonstrates that most areas were mainly transport‐limited rather than supply limited. Sinuous and meandering reaches were more frequent in the north‐eastern Alps and were characterized by lower denudation rates and less sediment delivery.
Channel straightening caused the loss of about 510 km of river course length, equivalent to 4.3% of the historical extent. Multi‐channel stretches are currently a mere 15% of their historical length, and 45% of the larger Alpine rivers are intensively channelized or have been transformed into reservoirs. Channelization measures differed from one country to another. Human pressures directly affected both local channel geometry and the upstream controls (i.e., sediment supply). Accordingly, individual multi‐channel reaches also evolved into single‐thread channels without any local human interventions.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
River training structures are conventionally used to improve river stability and ecological conditions and to protect the upstream instream infrastructures from scour and erosion. A submerged weir is ...a typical river training structure usually built downstream of bridges for grade control. Flow over the weir can cause local scour, destabilizing both the structure and the trained river reach. It is therefore important for safe design to estimate the scour accurately and understand the effects of an upstream bridge pier on local scour at submerged weirs. This study describes experiments on the scour process at a submerged weir with an upstream bridge pier, varying the distance L between the two. In this study, 56 experiments were conducted using uniform coarse sand with a median grain size d50 = 0.85 mm in a sediment‐recirculating flume. For clear‐water scour, the experiments showed that the bedform induced by the pier scour process creates a scour‐and‐fill process upstream of the submerged weir; and the upstream pier can also affect the scour downstream of the submerged weir, through two mechanisms: (i) upstream sediment replenishment and (ii) flow section constriction. The mechanisms (i) and (ii) can reduce and increase the downstream clear‐water scour depth at the submerged weir, respectively. For live‐bed scour, a pier upstream can reduce and increase the scour depth upstream and downstream of the submerged weir, respectively. Based on the experimental data, the dependence of the scour depth at the submerged weir on L is evaluated.
Key Points
Experimental data of the scour at submerged weirs with an upstream circular bridge pier are provided
The effects of bridge piers on the scour process at downstream river training structures (submerged weir as an example) are illuminated
The quantitative impacts of upstream bridge piers on the scour depth at submerged weirs for different separation distances are evaluated
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
PDF
