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.

Effect of the barrage and embankments on flooding and channel avulsion case study Koshi River, Nepal

Abstract: Humans have utilized water resources for millennia by modifying natural river courses and such interventions have greatly influenced not only river flows and sediment fluxes, but also the overall river morphology. Situated in the Nepal's eastern Ganges region, the braided Koshi River is unique among the other rivers, because of the high frequency of channel avulsion and other morphological changes, such as: channel migration, channel width adjustment. This study examines effect of the Koshi barrage and related embankments on flooding and channel avulsion in Koshi River. In particular, it tries to explain the avulsion that occurred in 2008, studying the role of the Koshi barrage, and related embankments, constructed near the border between Nepal and India in 1963. Series of satellite images and historical maps show overall sedimentation, especially in the western side of the river channel, which lead to the shifting of the Koshi River towards the east (almost 6 km) during around 40 years period, since the construction of the barrage, although before, shifting toward the west. The barrage was constructed at eastern side of the river channel within two embankments, leading to sedimentation in western side, since river is flowing short courses. Sediment deposition upstream of the barrage brought to the conditions that lead to dike breaching in 2008. During the 2008 flooding event, huge amounts of previously deposited sediment were eroded from the river bed upstream of the barrage. The resulting bed lowering means a gain of time to prevent a similar event in the future, since new space for sediment inside the embankments system has been created. So, this time, estimated in 40-50 years, can be used to take proper river engineering measures.

Experimental Analysis of River Evolution with Riparian Vegetation

Abstract: Studying the effects of different riparian vegetation densities on river channel evolution has practical significance for predicting the river channel evolution process during flood periods and ecological river engineering via the artificial planting of vegetation. In this study, we simulated the formation and evolution processes of river channels under different riparian vegetation coverage rates in laboratory conditions. The riparian vegetation coverage rates were set as 0, 20, 40 and 80%, on unilateral and bilateral sides of a river channel bank. Given the same flow and sediment boundary conditions, experiments were carried out in a 4 × 1.5 m tank. This paper focuses on the comparative analysis of main stream stability characteristics, bend migration characteristics, river bank erosion characteristics and sediment transport intensity. The results showed that different amounts of riparian vegetation cover created different characteristics of river channel evolution and strongly impacted the stability of the banks and bed. River channel evolution under unilateral vegetation cover is often accompanied by alternate development of the main stream and branch, and the bend stability under unilateral riverbank vegetation cover is worse than under bilateral cover. For a bilateral vegetation-covered river channel, a narrow and deep regime channel more easily forms with a higher vegetation coverage rate; the curvature of the stable river bend is smaller, but the adaptation period of the flow to the river channel bed increases. Planting of riparian vegetation played a positive role in the erosion resistibility, which effectively reduced the lateral migration rate of the riverbank. The higher the vegetation coverage rate, the greater the flow shear stress needed for the same river channel migration rate. While effectively reducing lateral migration, riparian vegetation coverage increased the vertical migration and led to a trend in overall scour depth along the riverbank.

Study for restoration using field survey and geoinformatics of the kolong river, assam, india

Abstract: River engineering and the subsequent loss and fragmentation of Riparian habitats during recent centuries have had serious impacts on aquatic ecosystem. The Kolong River of Nagaon, Assam, India has also faced serious penalty of one of such radical engineering approach where the mouth of the river in Jakhalabandha was permanently closed during the year 1964 by constructing an earthen embankment across it, viz. the Hatimura dyke, with the chief objective of protecting Nagaon town against flood. The act of blocking has shattered the natural flow regime of the entire river leaving it in a moribund state. Here we briefly summarize the existing scenario of the study area with an emphasis on a possible river restoration technique. Seven well distributed sampling stations were selected for the study purpose. Water quality and hydrological parameters were determined using standard procedures. Base map, drainage map and landuse/land-cover map of the study area were prepared (Database: Survey of India Topological sheets, LANDSAT satellite imagery and IRS LISS-III satellite imagery) for acquiring a broad apparition about the geo-environmental setting of the study area. Results of the present study reveal the fact that a restoration paradigm is essential for management of the river’s health and ecosystem. A framework of the restoration program is discussed.

Feedback Mechanism in Bifurcating River Systems: the Effect on Water-Level Sensitivity

Abstract: Accurate and reliable estimates of water levels are essential to assess flood risk in river systems. In current practice, uncertainties involved and the sensitivity of water levels to these uncertainties are studied in single-branch rivers, while many rivers in deltas consist of multiple distributaries. In a bifurcating river, a feedback mechanism exists between the downstream water levels and the discharge distribution at the bifurcation. This paper aims to quantify the sensitivity of water levels to main channel roughness in a bifurcating river system. Water levels are modelled for various roughness scenarios under a wide range of discharge conditions using a one-dimensional hydraulic model. The results show that the feedback mechanism reduces the sensitivity of water levels to local changes of roughness in comparison to the single-branch river. However, in the smaller branches of the system, water-level variations induced by the changes in discharge distribution can exceed the water-level variations of the single-branch river. Therefore, water levels throughout the entire system are dominated by the conditions in the largest branch. As the feedback mechanism is important, the river system should be considered as one interconnected system in river maintenance of rivers, flood-risk analyses, and future planning of river engineering works.