Upstream from a dam reservoir, river hydrodynamics may be directly changed by temporary inundation driven by the reservoir. This triggers morphological river changes which may additionally modify the ...initial hydrodynamics, even at the time when backwater inundation does not occur (indirect effects of backwater). We verified these hypotheses, applying two-dimensional hydraulic modelling of flood flows to a section of the mountainous Dunajec River upstream from the Czorsztyn Reservoir. The modelling was performed for small, medium and large floods, and hydraulic conditions were compared between the scenarios with lacking and maximum backwater inundation and between the river reaches subjected to backwater inundation and unaffected by backwater fluctuations. Direct effects of reservoir level fluctuations were limited to the reach subjected to backwater inundation during floods and comprised: significantly increased water depth and decreased flow velocity and bed shear stress in the channel and on the floodplain, as well as a re-established hydrological connectivity between the channel and floodplain during small and medium floods. Indirect effects of backwater inundation reflected channel widening and bed aggradation that triggered a positive feedback with changes in hydrodynamics, mostly by reducing the velocity of flood flows in the channel zone. These latter changes occurred on a longer distance upstream from the reservoir than the backwater reach itself, and they modified the river hydrodynamics even when backwater inundation did not occur. We propose a conceptual model which indicates that changes of mountain rivers upstream from dam reservoirs are driven by modified hydrodynamics and lead to different morphological adjustments than those induced by waters underloaded with sediment downstream from dams. Changes in hydrodynamics and the associated morphological and sedimentary adjustments of mountain rivers recorded upstream from dam reservoirs may locally mitigate impacts of channelization and channel incision on riverine and riparian ecosystems of these rivers.
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•Effects of backwater inundation on river hydrodynamics upstream from dam reservoir were investigated.•Hydraulic modelling of flood flows in backwater and control reaches and with/without backwater inundation was performed.•Backwater inundation increases water depth and decreases velocity and bed shear stress of the channel and floodplain flows.•Backwater-induced morphological river changes additionally modify river hydrodynamics.•Conceptual model of hydrodynamics–morphology adjustments downstream and upstream of a dam reservoir was presented.
•First un-biased hydraulic model for middle reach of the Congo.•Floodplain-channel interactions occur extensively along the middle reach.•Constrictions have a modest impact on celerity but are ...important for inundation.•Exchange of water from channel to floodplain is a major source of water in areas.
In this paper we attempt to produce a first hydrodynamic model of the middle reach of the Congo river system in order to understand what controls this river’s unique bimodal flood pulse. The model covers the area between Kisangani and Kinshasa on the main stem and includes the major tributaries and the Cuvette Centrale wetland, one of the world’s largest and most understudied lowland regions. A mixture of in-situ discharges and modelled discharge from a basin-wide catchment hydrology model were used to force a four-kilometre resolution hydrodynamic simulation developed using the LISFLOOD-FP model. River channels are represented as sub-grid scale features and their width is therefore decoupled from that of the over-lying floodplain grid. Unknown channel friction and bathymetry parameters were calibrated using ERS-2 and Envisat satellite altimetry measurements of channel water level. The calibrated model simulated channel water surface elevations across the domain with a bias and root mean square error of 0.185 and 0.842 m respectively. The value for root mean squared error is close to that obtained for comparisons of ERS-2 and Envisat satellite altimetry to in-situ water elevation data in similar basins (0.79 m and 0.47 m respectively). The model results imply that the bimodal annual pattern of Congo river discharge is predominantly a hydrological rather than hydraulically-controlled feature, with the channel-floodplain interactions and river constrictions having only a modest impact on the flood wave propagation. Nevertheless, and counter to current understanding, we find that interactions between channels and floodplains do however occur extensively, with over 2100 km of the 13,000 km of channel network in the model identified as zones where water is actively exchanged between channels and floodplains. Whilst the water volume that is exchanged with the floodplain is substantially less than for other large rivers, our results imply that channel-floodplain interactions are a significant feature of Congo flood wave propagation. Overall the model provides insights into the hydraulics of this understudied system that can next be tested both in the field and through more detailed modelling studies.
The state of Tamilnadu is located along the south west of Indian peninsula. The state has nearly 40 river basin and most of them are seasonal. The river Thamirabarani is one of the perennial rivers ...covering 3 districts namely Tenkasi, Tirunelveli and Tuticorin. The river originates from the eastern side of the west coast and confluences with Bay of Bengal at a village called Punnakayal in Tuticorin district. The Thamirabarani river is known for its irrigation potential in the upper reaches. By the time it reaches the lower end, the flow is very low. The east coast is well known for its littoral drift which is dominantly towards the north direction. The village is famous for its fishing potential. The study area of Punnakayal is influenced by two monsoons namely south west and north east. Due to absence of high flow in the non-monsoon period, the estuaries are highly blocked by sand bar formation. Because of this sand bar formation, the fisherman find it difficult to go in to deep sea during low tide time. Hence studies were made and remedial measures were suggested and completed. The details of hydrologic analyses, hydraulic modelling, hydrodynamic studies, assessment of littoral drift remedial measures and post project performance are detailed in the paper.
FLOOD HAZARD IN THE CITY OF CHEMORA (ALGERIA) SAMI, Guellouh; ABDELWAHHAB, Filali; YAHYAOUI, Habibi ...
Analele Universităţii din Oradea. Seria Geografie,
06/2021, Letnik:
31, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Floods become major concerns in most gobe regions due to socio-economic and environmental consequences caused by these phenomena in recent decades. Most Algerian cities are exposed to flood risks and ...suffered from its consequences. The purpose of this paper is the spatialization of flood hazard in the city of Chemora (Algeria) by hydraulic modelling in a GIS environment whose objective is prevention, which requires a set of hydrological and hydraulic informations in order to achieve a comprehensive and effective management.
•We propose a new practice for flood hazard mapping in presence of multiple gauging stations.•The method uses an original interpolation/assignation coded algorithm for multiple probability models ...fusion.•The use of LiDAR data and multiple probability models increases the reliability of the hazard map.•The method has the potential to support flood hazard mapping over large areas.•Comparison with 2D hydraulic simulation confirm the high performance of the proposed approach.
Hazard mapping is essential for risk assessment and mitigation measurement design in flood prone areas. In Europe, long-term fluvial stage data, acquired since the 18th century, represent a resource of fundamental importance in this perspective, especially where rivers monitoring is completed by multiple stations distributed along the course. In these conditions, a major challenge is represented by the possibility of incorporating multiple probability models, representative of river dynamics at different distance from the mouth, in flood hazard estimation over so large areas. In this paper, we propose a new procedure of hazard estimation based on LiDAR derived flood inundation model and multiple hydrometric time series that, using a specifically developed algorithm/code of interpolation/assignation of multiple probability models, has the potential to work at local to national scale providing reliable estimation also in presence of urban areas. We applied the developed procedure and associated algorithm/code to a selected study area in southern Italy, recently hit by a destructive flood event, and quantitatively evaluate model performance. Confidence interval computation provides an overview of uncertainty related to flood magnitude estimation by extreme value analysis, indicating a substantial uncertainty related to 500 years flood magnitude estimation. Sensitivity analysis indicates a high degree of robustness of the developed procedure. Result validation through comparison against the observed 2015 flood event indicates that the method has the potential to support flood hazard analysis at regional to national scale. Limits of method application are related to the basic assumption of stationarity of hydrologic time series that might be considered too “simplicistic” in a changing climate also related to the limited length of some time series that only in few cases have no discontinuities. The absence of propagation modelling as part of the estimation procedure might be considered as an additional limit since in complex topographic and hydrological conditions it might provide a better evaluation of flood hazard. However, comparison of the 500 years flood derived from our procedure and 500 years flood scenarios derived by 2D hydraulic simulations indicate the capabilities of our procedure in identifying area floodable by specific events with only local overestimation that generally increase safety in human life protection perspective. This confirms the potential of considering multiple probability models distributed along the river course in flood hazard estimation perspective and indicate that our procedure can be a valid alternative to simulation based flood hazard estimation procedures.
•A dynamic GIS-based pluvial flood and damage model, FloodStroem, is developed.•FloodStroem routes water through a surface network of bluespots and flow paths.•FloodStroem computes spatial and ...temporal development dynamically as well as damage costs.•Simulation time is five orders of magnitude faster than for a hydrodynamic model.•FloodStroem tends to underestimate flooding upstream and overestimate downstream.
Due to climate change and urbanization, urban flood modelling has become an increasingly important tool in assessing flooding and associated damage costs. However, large computational demands of state-of-the art hydrodynamic flood models makes multiple and real-time simulations unfeasible. This study presents a fast-dynamic GIS-based flood model, FloodStroem. FloodStroem generates a surface network of depressions (bluespots) and flow paths, and routes surcharged water from a subsurface drainage model through the network resulting in flood depth maps and associated damage costs. FloodStroem is tested on three sub-catchments in Elster Creek Catchment, Melbourne, Australia and benchmarked against the 2D distributed hydrodynamic model MIKE 21 and two other simplified models, RUFIDAM and CA-ffé. FloodStroem is robust to the number of bluespots included. For the three sub-catchments, FloodStroem can reproduce flooding time, pattern, depth, and damage costs sufficiently, but has a tendency to underestimate flooding upstream and overestimate flooding downstream. Performance is best for the large, steep sub-catchments and largest rainstorms, where FloodStroem performs better than the two other simplified models. The Critical Success Index (CSI) ranges from 23% for a 5-year storm event in a flat catchment to 65% for a 100-year return period for a steeper catchment. With respect to simulation time, FloodStroem is five orders of magnitude faster than the 2D hydrodynamic model, and 33 times faster when including the entire model setup time, which has potential for further reduction by optimization of the workflow.
Here we present an original approach to generate 2D high detail riverbed based on a drone photogrammetric survey, and RTK bathymetry measurements for Mera river in the Italian Alps. The aim is to ...better represent macro-roughness and riverbed structure of the river, also extending it to an ungauged area. Specifically, we apply a step-by-step approach. I) Depth and average slope of the riverbed were calculated from bathymetry data. II) Thus, a trapezoidal channel with constant slope and variable width was defined using the drone images. III) Riffle-pool sequence was assessed as a function of river width and applied to the generated channel. IV) Finally, the semi-random Perlin Noise was added to recreate riverbed irregularities in the natural stream. HEC-RAS 2D hydraulic software was then implemented to assess spatialized water depth and velocity. The proposed methodology could be quite relevant in river hydraulics to decouple roughness coefficient from water submergence, and in Physical Habitat Simulation Model (PHABSIM), where the dependency of the output is not linear with hydraulic parameters (i.e. water depth and velocity). Indeed, we apply PHABSIM for a case study of a stretch of the river and results are compared with a previous environmental study for Mera river.
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•A new methodology to generate 2D riverbed is presented.•Point cloud bathymetry is used to model riffle-pool sequence.•Drone data are used to recreate riverbed in ungauged area.•Perlin noise is included to mimic the riverbed irregularities.•Habitat Suitability is studied basing on generated river topography.
Surface irrigation is a widely utilized method for agricultural irrigation, but it often suffers from low conveyance efficiency. Improving flow conditions in surface irrigation systems is crucial for ...enhancing water distribution and optimizing crop production. This study presents a comprehensive hydraulic modelling approach aimed at improving flow conditions in irrigation canals. The analysis focuses on the Doho Rice Irrigation Scheme in Uganda and utilizes the HEC-RAS hydraulic model. Different canal conditions, including desilting and vegetation clearing, concrete lining, plastic lining, and brick lining, are evaluated for their impact on flow dynamics. The findings reveal that all four canal conditions lead to significant improvements in flow conditions compared to the current state of the canal. Plastic lining emerges as the most effective solution, resulting in a remarkable 48 % improvement in flow conditions. Concrete lining follows closely with a 37 % improvement, while brick lining shows a 39 % enhancement. Desilting and vegetation clearing contribute to a 20 % improvement in flow conditions. These results underscore the potential of hydraulic modelling in guiding the design and management of irrigation canals to ensure sustainable water use practices.
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