Numerical morphodynamic models provide scientific frameworks for advancing our understanding of r... more Numerical morphodynamic models provide scientific frameworks for advancing our understanding of river systems. The research on involved topics is an important and socially relevant undertaking regarding our environment. Nowadays numerical models are used for different purposes, from answering questions about basic morphodynamic research to managing complex river engineering problems. Due to increasing computer power and the development of advanced numerical techniques, morphodynamic models are now more and more used to predict the bed patterns evolution to a broad spectrum of spatial and temporal scales. The development and the success of application of such models is based upon a wide range of disciplines from applied mathematics for the numerical solution of the equations to geomorphology for the physical interpretation of the results. In this light we organized this special issue (SI) soliciting multidisciplinary contributions which encompass any aspect needed for the development and applications of such models. Most of the papers in the SI stem from contributions to session HS9.5/GM7.11 on numerical modelling and experiments in river morphodynamics at the European Geosciences Union (EGU) General Assembly held in Vienna, April 27th to May 2nd 2014.
The construction of dams affects water and sediment supply to the downstream river reach, which t... more The construction of dams affects water and sediment supply to the downstream river reach, which then adjusts itself to the new state by changing its slope, planimetry, reference width, and water depth. This work deals with the assessment of the long-term planimetric adaptation of meandering rivers after upstream dam construction. In particular, the work, which is now in its preliminary phase, aims at anticipating the changes that will occur on the meandering Ribb River (Ethiopia) a long time after the completion of the Ribb Dam. To analyze the effects of dams and generalize the results, two additional case studies are considered: the Tana River (Kenya) and the Blue Nile River (Sudan). These two rivers have been affected by dams for a long time already, whereas more dams are planned or in construction. The effects of large dams on these three rivers will be analyzed and compared, and based on the findings a methodology for the prediction of the effects of planned dams on the downstre...
Recently, engineers propose building longitudinal training walls instead of traditional transvers... more Recently, engineers propose building longitudinal training walls instead of traditional transverse groynes to enhance river navigation or free water inlets at low flow conditions and at the same time maintain the channel conveyance during high flows. For example, the main low-flow stream of the Tra Khuc River in the middle of Vietnam, does not follow the same route year after year causing problems to the inlets of irrigation channel systems along this river. Engineers would like to build longitudinal training walls to stabilize the main stream during low flows without affecting the flood conveyance on rainy season. Another example is along the well-trained Waal River, Dutch authorities are considering substituting the old groynes with longitudinal training walls to obtain an improved navigation channel, while preserving the river conveyance capacity during floods. However, whether longitudinal training walls are indeed effective in achieving the goals and whether they may also produ...
Managing river bars can reduce costs and optimize river engineering works to free water intakes, ... more Managing river bars can reduce costs and optimize river engineering works to free water intakes, enhance navigation and improve ecosystems. This work explores ways to locally suppress alternate bars by either narrowing a finite river reach or imposing symmetry of flow and bed topography at a given cross-section. This work explores also the possibility of restoring alternate and central bars by channel widening, a practice that is often implemented in river rehabilitation projects. The investigation is based on the application of a two-dimensional depth-averaged hydro-morphodynamic model, previously validated on field data and experimental observations. Numerical results suggest that it is possible to achieve a bar-free reach by narrowing the channel for a distance equal to ten times the original width. Moreover, channel widening from either a stable bar-free or an alternate-bar dominated channel leads to a compound bar mode of coexisting alternate and central bars. Although the nume...
Bars are large sediment deposits in river channels emerging at low flows with wavelength and heig... more Bars are large sediment deposits in river channels emerging at low flows with wavelength and height scales of the order of channel width and flow depth, respectively. They consist of recurring sequences of erosion holes and deposition fronts and develop due to morphodynamic instability of flat river beds. Bars create problems to river navigation, intakes, and cause bank erosion, making their morphological study and management an important part of river engineering and rehabilitation works. As rivers normally have both fine and coarse sand, studying the development and characteristics of bars should include both bed and suspended sediment processes. However, most theories for bar instability are based on bed load transport, assuming an immediate adaptation of sediment transport to the local flow conditions. Only a few theoretical works focus on the effects of suspended sediment transport on bars. Moreover, experiments showing the effects of suspended sediments are still lacking. This...
The most common way to represent vegetation in numerical models is to simplify their geometry as ... more The most common way to represent vegetation in numerical models is to simplify their geometry as a collection of uniformly distributed identical cylindrical stems. However, the implications of this assumption are still unknown. This work attempts to represent the effects of several kinds of submerged vegetation on the water flow with uniformly distributed cylinders in a laboratory flume with a movable sand-bed. We considered rigid and flexible artificial plants and real vegetation, with diverse densities and heights and under different flows. We compared water level measurements with estimations by a hydraulic roughness model. We add a description of the observed sediment transport and bed form development. 1 INTRODUCTION The morphological evolution of river systems is strongly influenced by the presence of vegetation (Hickin [1]). By providing additional drag, plants increase the local hydraulic roughness, decrease flow velocity, bed shear stress and sediment transport, and promote...
From the rich biodiversity that the Middle Zambezi sub-catchment supports, both Zambia and Zimbab... more From the rich biodiversity that the Middle Zambezi sub-catchment supports, both Zambia and Zimbabwe have established National Parks, with Mana Pools National Park, Sapi and Chewore safari areas being designated as UNESCO World Heritage Site in 1984 (UNESCO World Heritage Centre 1992-2013). The habitat sustenance depends on the river channels and the associated morphological features with the flood and recession interactions, whose modification can lead to negative environmental consequences. The research work in the area has the key objective to investigate the state of the river and its flood plain environment in terms of surface and ground water flow and morphological variation, for both the pre and post hydropower situations, and the associated impacts on the floodplain tree species the Faidherbia albida. This tree is of vital importance for the local wild life, since its leaves and fruits constitute an important food source during the dry season. In the last decades, however, th...
Numerical morphodynamic models provide scientific frameworks for advancing our understanding of r... more Numerical morphodynamic models provide scientific frameworks for advancing our understanding of river systems. The research on involved topics is an important and socially relevant undertaking regarding our environment. Nowadays numerical models are used for different purposes, from answering questions about basic morphodynamic research to managing complex river engineering problems. Due to increasing computer power and the development of advanced numerical techniques, morphodynamic models are now more and more used to predict the bed patterns evolution to a broad spectrum of spatial and temporal scales. The development and the success of application of such models is based upon a wide range of disciplines from applied mathematics for the numerical solution of the equations to geomorphology for the physical interpretation of the results. In this light we organized this special issue (SI) soliciting multidisciplinary contributions which encompass any aspect needed for the development and applications of such models. Most of the papers in the SI stem from contributions to session HS9.5/GM7.11 on numerical modelling and experiments in river morphodynamics at the European Geosciences Union (EGU) General Assembly held in Vienna, April 27th to May 2nd 2014.
The construction of dams affects water and sediment supply to the downstream river reach, which t... more The construction of dams affects water and sediment supply to the downstream river reach, which then adjusts itself to the new state by changing its slope, planimetry, reference width, and water depth. This work deals with the assessment of the long-term planimetric adaptation of meandering rivers after upstream dam construction. In particular, the work, which is now in its preliminary phase, aims at anticipating the changes that will occur on the meandering Ribb River (Ethiopia) a long time after the completion of the Ribb Dam. To analyze the effects of dams and generalize the results, two additional case studies are considered: the Tana River (Kenya) and the Blue Nile River (Sudan). These two rivers have been affected by dams for a long time already, whereas more dams are planned or in construction. The effects of large dams on these three rivers will be analyzed and compared, and based on the findings a methodology for the prediction of the effects of planned dams on the downstre...
Recently, engineers propose building longitudinal training walls instead of traditional transvers... more Recently, engineers propose building longitudinal training walls instead of traditional transverse groynes to enhance river navigation or free water inlets at low flow conditions and at the same time maintain the channel conveyance during high flows. For example, the main low-flow stream of the Tra Khuc River in the middle of Vietnam, does not follow the same route year after year causing problems to the inlets of irrigation channel systems along this river. Engineers would like to build longitudinal training walls to stabilize the main stream during low flows without affecting the flood conveyance on rainy season. Another example is along the well-trained Waal River, Dutch authorities are considering substituting the old groynes with longitudinal training walls to obtain an improved navigation channel, while preserving the river conveyance capacity during floods. However, whether longitudinal training walls are indeed effective in achieving the goals and whether they may also produ...
Managing river bars can reduce costs and optimize river engineering works to free water intakes, ... more Managing river bars can reduce costs and optimize river engineering works to free water intakes, enhance navigation and improve ecosystems. This work explores ways to locally suppress alternate bars by either narrowing a finite river reach or imposing symmetry of flow and bed topography at a given cross-section. This work explores also the possibility of restoring alternate and central bars by channel widening, a practice that is often implemented in river rehabilitation projects. The investigation is based on the application of a two-dimensional depth-averaged hydro-morphodynamic model, previously validated on field data and experimental observations. Numerical results suggest that it is possible to achieve a bar-free reach by narrowing the channel for a distance equal to ten times the original width. Moreover, channel widening from either a stable bar-free or an alternate-bar dominated channel leads to a compound bar mode of coexisting alternate and central bars. Although the nume...
Bars are large sediment deposits in river channels emerging at low flows with wavelength and heig... more Bars are large sediment deposits in river channels emerging at low flows with wavelength and height scales of the order of channel width and flow depth, respectively. They consist of recurring sequences of erosion holes and deposition fronts and develop due to morphodynamic instability of flat river beds. Bars create problems to river navigation, intakes, and cause bank erosion, making their morphological study and management an important part of river engineering and rehabilitation works. As rivers normally have both fine and coarse sand, studying the development and characteristics of bars should include both bed and suspended sediment processes. However, most theories for bar instability are based on bed load transport, assuming an immediate adaptation of sediment transport to the local flow conditions. Only a few theoretical works focus on the effects of suspended sediment transport on bars. Moreover, experiments showing the effects of suspended sediments are still lacking. This...
The most common way to represent vegetation in numerical models is to simplify their geometry as ... more The most common way to represent vegetation in numerical models is to simplify their geometry as a collection of uniformly distributed identical cylindrical stems. However, the implications of this assumption are still unknown. This work attempts to represent the effects of several kinds of submerged vegetation on the water flow with uniformly distributed cylinders in a laboratory flume with a movable sand-bed. We considered rigid and flexible artificial plants and real vegetation, with diverse densities and heights and under different flows. We compared water level measurements with estimations by a hydraulic roughness model. We add a description of the observed sediment transport and bed form development. 1 INTRODUCTION The morphological evolution of river systems is strongly influenced by the presence of vegetation (Hickin [1]). By providing additional drag, plants increase the local hydraulic roughness, decrease flow velocity, bed shear stress and sediment transport, and promote...
From the rich biodiversity that the Middle Zambezi sub-catchment supports, both Zambia and Zimbab... more From the rich biodiversity that the Middle Zambezi sub-catchment supports, both Zambia and Zimbabwe have established National Parks, with Mana Pools National Park, Sapi and Chewore safari areas being designated as UNESCO World Heritage Site in 1984 (UNESCO World Heritage Centre 1992-2013). The habitat sustenance depends on the river channels and the associated morphological features with the flood and recession interactions, whose modification can lead to negative environmental consequences. The research work in the area has the key objective to investigate the state of the river and its flood plain environment in terms of surface and ground water flow and morphological variation, for both the pre and post hydropower situations, and the associated impacts on the floodplain tree species the Faidherbia albida. This tree is of vital importance for the local wild life, since its leaves and fruits constitute an important food source during the dry season. In the last decades, however, th...
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Papers by Alessandra Crosato