River engineering

About: River engineering is a research topic. Over the lifetime, 435 publications have been published within this topic receiving 10286 citations. The topic is also known as: Channelisation.

Decadal-Scale Variations of Thalweg Morphology and Riffle–Pool Sequences in Response to Flow Regulation in the Lowermost Mississippi River

Abstract: The lowermost Mississippi River (LMR) is one of the largest deltaic systems in North America and one of the heavily human-manipulated fluvial river systems. Historic hydrographic surveys from the mid-1900s to the early 2010s were used to document the thalweg morphology adjustments, as well as the riffle–pool sequences. Extensive aggradation was observed during 1950s to 1960s, as the Atchafalaya River was enlarging before the completion of the Old River Control Structure (ORCS). Following the completion of the ORCS, reductions in sediment input to the LMR resulted in net degradation of the thalweg profile patterns since the mid-1960s except for the 1992–2004 period. Different flood events that supplied sediment might be the cause of upstream aggradation from 1963–1975 and net aggradation along the entire reach from 1992–2004. Furthermore, the change pattern of thalweg profiles appear to be controlled by backwater effects, as well as the Bonnet Carre spillway opening. Results from riffle–pool sequences reveal that the averaging Ws ratios (length to channel width) are 6–7, similar to numerous previous studies. Temporal variations of the same riffles and pools reveal that aggradation and degradation might be heavily controlled by similar factors to the thalweg variations (i.e., sediment supply, backwater effects). In sum, this study examines decadal-scale geomorphic responses in a low-lying large river system subject to different human interventions, as well as natural flood events. Future management strategies of this and similar river systems should consider recent riverbed changes in dredging, sediment management, and river engineering.

Spatio-temporal Patterns of River Water Quality in the Semiarid Northeastern Brazil

Abstract: Non-perennial rivers have attracted significant attention due to the progressive increase in water demand and pollution, river engineering side effects and climate change. The present study investigates the interannual, seasonal and spatial variability of nine water quality variables (pH, colour, turbidity, biochemical oxygen demand, total phosphorus, total inorganic nitrogen, chlorophyll-a, total solids and thermotolerant coliforms) from 93 monitoring river sites distributed over 11 watersheds in the highly populated Brazilian semiarid region. Shapiro–Wilk and Kruskal–Wallis tests were applied for assessing data normality and statistical differences, respectively. Additionally, principal component analysis (PCA) was performed for comparison between temporal and spatial data sets, while the Standardized Precipitation Index (SPI) was used to characterize meteorological drought. The results revealed that spatial variability is more evident than temporal variability. In the temporal scale, the interannual variability is more relevant than the seasonal one. The discharge of wastewater seems to attenuate a seasonal hydrological effect on water quality. There is a deterioration of water quality in most watersheds in the drier years, even in the rainy season. This is especially for colour, total phosphorus, total inorganic nitrogen and thermotolerant coliforms. The abrupt transition from dry to wet years also played an important role in changes in river water quality. This study provides new insights for the understanding of the water quality patterns in non-perennial rivers. In addition, we go on to identify important aspects for the management of these water sources, such as the need for wastewater discharge guidelines within scope of each watershed, and restrictions on the use of soil and water in the driest periods.

Optimum design of large flood relief culverts under the A89 motorway in the Dordogne—Isle confluence plain

Abstract: The planned A89 motorway will go through the Dordogne — Isle confluence plain, which is regularly flooded under the effect of both river discharges and ocean tides. Hydraulic transparency of the motorway embankment was one of the prerequisites imposed by the French government. In order to optimize the cost/efficiency ratio of large culverts located under the motorway, their position and size had to be determined with great accuracy. This task has been fulfilled thanks to complementary sophisticated physical scale models and 2-D numerical models. The schematization principles adopted in the 2-D numerical model concerning bridge pier grouping were validated using the physical scale model. The finite element TELEMAC-2D code was used to draw up the optimum design of this river engineering scheme. TELEMAC-2D solves the 2-D Shallow Water equations on non-structured grids in the presence of alternately dry and wet beds. The 2-D numerical modelling based on high quality topographic data allows considerable improvements to be made in the computation of flood flows in a flat valley, as compared with traditional one-dimensional techniques. Near flood relief culverts in particular, the various physical effects contributing to the overall head loss can be distinguished: bottom roughness, medium size bed variations, strong curvature of the streamlines and vortices behind abutments. The hydraulic impact of the optimum solution has been studied under different aspects (rise of maximum flood levels, increase in maximum velocity, changes in the water flow patterns, submersion time of flooded land, modification of flood routing characteristics) for a wide range of flood hydrological events. Copyright © 2000 John Wiley & Sons, Ltd.