Showing papers on "River engineering published in 2011"

The sedimentary response to a pioneer geo-engineering project: Tracking the Kander River deviation in the sediments of Lake Thun (Switzerland)

Abstract: Human activities such as river corrections and deviations, lake-level regulations and installations of hydropower plants affect and often strongly modify natural processes in lacustrine systems. In 1714, the previously bypassing Kander River was deviated into peri-alpine Lake Thun. This pioneering geo-engineering project, the first river correction of such dimensions in Switzerland, doubled the water and sediment input to the lake. In order to evaluate the sedimentary consequences of the Kander River deviation, the lacustrine sediments were investigated using a combined approach of high-resolution (3AE5 kHz) reflection seismic data and sediment cores (maximum length 2AE5 m). The significance of this study is increased by the possible hazard represented by ammunition dumped into the lake (from 1920 to 1960) and by the recent installation of a gas pipeline on the lake floor in 2007/2008. The first 130 years after the river deviation were dominated by an extremely high sediment input, which led to the frequent occurrence of subaquatic mass movements. Slope failures primarily occur due to rapid sediment accumulation, but were occasionally triggered in combination with earthquake-induced shocks and lake-level fluctuations. After 1840, massmovement activity and sedimentation rates decreased due to a reduced sediment input as the Kander River adjusted to its new base level and, to a smaller degree, by further engineering of the Kander River bed and gravel withdrawal at the Kander Delta. A further consequence of the Kander River deviation is that the shores around Lake Thun have been more frequently affected by flooding due to the increased water input. In the time span from 1850 to 2006, six historically and/or instrumentally documented flood events could be correlated to flood turbidites in the sediment cores. This study demonstrates the significant usefulness of lacustrine sediments, not only in archiving natural hazards and human impact but also in assessing the consequences of future anthropogenic interventions on lacustrine systems.

The Influence of Floodplain Vegetation Succession on Hydraulic Roughness: Is Ecosystem Rehabilitation in Dutch Embanked Floodplains Compatible with Flood Safety Standards?

Abstract: Here, we show for one of the Dutch Rhine River branches that large-scale riverine ecosystem rehabilitation and related vegetation succession may lead to up to 0.6 m higher river flood levels, because of increased hydraulic roughness. We hydraulically modeled future succession stages of embanked floodplain vegetation, following from present ecosystem rehabilitation plans for the 124-km-long river IJssel, and found flood levels exceeding the safety levels (related to dike heights). Our models take into account river engineering measures that are presently carried out, aimed at enhancing the river discharge capacity in order to meet required safety standards. Our study shows that there is a pressing need for integrated hydraulic-ecological evaluation of river engineering measures and ecosystem rehabilitation plans in the Rhine embanked floodplains. An important conclusion also is that hydraulic evaluation of planned vegetation goals only is inadequate, because flow resistance of preceding succession stages may be higher.

No Longer “Bullying the Rhine:” Giving Narrative a Place in Flood Management

Abstract: In this paper we explore whether today multiple sources of reasoning are being considered in the discourse of flood management. We examine whether stakeholders are considered and served as an audience of partners in managing rivers. To this end, we reviewed sources of reasoning that people living in river basins use for handling floods and mitigating flood risk. We focus on texts dealing with lowland flooding, taking as an example the Rhine River in historical times and in the present. Our review of river management documentation revealed that the scheme that guides engineers', policy makers', and administrators' actions toward rivers is shifting from correcting rivers toward accommodating their needs for flood plains—while still controlling the rivers. In current European river management reports we found elements of narrative side by side with formal scientific fact reporting.

Robust prediction of hydraulic roughness

Abstract: : OVERVIEW: The National River Restoration Science Synthesis (NRRSS) demonstrated that, in 2007, river and stream restoration projects and funding were at an all time high and increasing exponentially (Bernhardt et al. 2007). Increasingly, these restoration projects rely on soft engineering techniques involving planting riparian vegetation to alter channel and floodplain hydraulics or geomorphology. The ability to quantify the influence of vegetation on channel and floodplain hydraulics, in particular hydraulic roughness, is critical for flood control concerns; however, diversity of vegetation type and behavior makes this parameter very difficult to quantify repeatedly and accurately. A fundamental concept of hydraulic theory in the context of river engineering is the influence of boundary conditions on flow through natural environments. This technical note presents a tool for estimating hydraulic roughness from boundary conditions in rivers. Hydraulic roughness, or resistance, is herein defined as the primary factor influencing retarding or resisting forces exerted by channel boundaries on stream flow. Calculation of hydraulic resistance is not a trivial matter due to the multitude of factors influencing roughness (e.g., bed material, bed forms, crosssectional and planform variability, vegetation, etc.). This document will present a theory of hydraulic resistance estimation, a synthesis of many resistance estimation techniques into a spreadsheet model, and an application of said model to Ham Branch, a tributary of the Trinity River. The diversity of methods applied in the model will allow users to isolate effects of diverse contributions to roughness (e.g., grain v. vegetative) and create a weight-of-evidence for an estimation of hydraulic roughness.

The Hydrodynamics and Morphodynamics of Rivers

Abstract: Rivers are a crucial part of the water cycle on the Earth. They transport water and sediment over many scales from the Amazon River to a small stream or ditch. The necessity of water to human existence means that civilization has always been intimately connected to rivers. They are used for water supply, agriculture through irrigation or flood plain cultivation, industry, transport, recreation, and even as discharge routes for polluted water. This close connection brings risks as well as benefits. Dangers include erosion, flood risk, and health risk. Benefits and dangers mean that human society has adapted rivers and floodplains over many centuries. Human intervention has accelerated since the industrial revolution and in many cases, such changes have been unsustainable, leading to severe negative impacts. The latter have led to a change from a paradigm of river engineering to one of river management, where there is greater attention paid to the effects at different scales and to working with natural processes. This move to greater sustainability has also brought in perspectives from ecology and the concept of environmental water allocation. In addition to the physical aspects of rivers, they also have great significance in cultural, political, and religious terms. All these reasons mean that modern river management must involve a wide range of stakeholders. In order to manage our rivers we need an understanding of the fundamental processes that govern their shape, processes, and impacts. This requires an understanding of the behavior of rivers at a range of scales, both spatial and temporal. This chapter outlines this understanding by looking at the various scales. This presents the state of the art of scientific understanding and then put forward issues that need to be addressed in the future.

Run of River Bulk Hydroelectric Generation from the Congo River without a Conventional Dam

Abstract: The paper discusses harvesting the Congo River for bulk hydroelectric generation based on run of river, low head generation technology, as employed at the existing Inga 2 power station in the Democratic Republic of Congo. The evolutionary approach builds on existing infrastructure.The results show that the footprint is much smaller than that which employs a conventional dam. The environmental impact is minimized. These collectively will contribute to lower capital costs. In summary, 10,000 cm³/sec of constant river flow will produce 5,000 MW of base power. On average, the constant recorded flow of the river is 30,000 cm³/sec and a total of 15,000 MW of base power generation is possible.

Preliminary study on accumulated influence of the bankline use on flood control in the middle and lower reaches of the yangtze river

Abstract: Based on the analysis of the present situation and existing problems of the bankline use in the middle and lower reaches of the Yangtze River,with the mathematical model research method,taken bridges in Wuhan river reach and dock groups in Yangzhong river reach as examples,the calculation of accumulated influence on river flood water level and flow field by lots of wading engineering groups were carried out.Results showed that the flood water level and velocity influence were accumulated after the wading engineering groups built and the influence of wading engineering groups was much larger than that of single engineering.When the influence was increased to the extent,it would do harm to the river regime and flood carrying capacity.In the end,some suggestions are given,such as the bridge density and dock group scale should be controlled reasonable,the principle of the bankline use should be put forward,river engineering design should be regulated,and River regulation should be strengthened,in order to minimize the cumulative effects of flood control.

Modelling of urban flooding due to yangtze river dike break

Abstract: A computational case study is presented of the flooding in urban Jiujiang due to the Yangtze River dike break in August 1998. A shallow water hydrodynamic model was deployed based on the weighted average flux – total variation diminishing (WAF-TVD) finite volume algorithm. A series of numerical modelling was conducted to identify the influences of the mesh resolution and model parameterisation on the flood propagation. Three mesh resolutions (2, 5 and 10 m) were used, and spatially distributed roughness was specified based on land-use classification. Due to the highly irregular topography and densely distributed buildings, the flood propagation is largely hindered. The numerical results show that an area of merely 6 km2 was inundated at 6 h following the dike break with a discharge of 400 m3/s. Mesh resolution and roughness parameterisation have considerable effects on the flood propagation, whereas the impact of turbulent eddy viscosity is negligible. A coarser mesh could result in a larger inundation ar...

Experimental Investigation of Groin Placement On Minimizing River Bank Erosion

Abstract: River banks are exposed to bank erosion and destruction. One of the river engineering goals is t o provide human life requirements and reduce river danger. So spreading extent of this phe nomenon, whose risk and other important factors must be recognized. Using groins is one of the control ways that by accurate design and accurate performance, bank erosion control and field reclamation would be possible. In addition, groin placement has important effect on bank erosion control. The purposes of this research were to survey groin placement on river protection and reduce bank erosion by experimental model. Tests were done by 3 different intervals and 5 discharges. Results showed that in 30 cm with erodible stuff, groin reduced bank erosion, destruction in river bank protection was almost 24-55% and with 15-25 l/s of discharge, bank erosion reduction was about 16.6%. By adding groin at river bank the water surface changes, with increasing discharge water surface first decreases and then increases by adding discharge.

Moveable flood barriers in the Rhine-Meuse estuary

Abstract: It is possible to reduce flood risk in estuaries without having to drastically modify the river banks by levees or to block shipping routes and ecological flows by dams. ‘Storm surge barriers’ close off a river mouth at times of high sea water levels, but keep the river open during calmer times. ‘Moveable river flood barriers’ direct a river towards less urbanised parts of the delta. It is likely that with climate change and continuing economic growth more of these barriers will be built worldwide. The influential Dutch state commission the ‘Delta Commission’ has adopted an idea by Delft University of Technology to flood-proof the Dutch Rhine-Meuse delta by a number of existing and new moveable barriers. These will direct high water flows in desired directions, particularly at times when a storm at sea coincides with high river discharges. This would create a historically complex system of flood defenses, thus needing thorough modelling and more detailed design to evaluate benefits and costs. This paper will compare a number of alternatives as follows: locate the various barriers on different locations, see where additional river widenings would be possible, calculate the remaining required levee modifications (dictated by Dutch national flood law) as a function of sea level rise, determine the effects on urbanisation of the river banks, on shipping, and if possible also on ecological flows. This comparison will in this paper not lead to the ‘best configuration’, but to valuable insight in the system. It appears that improving the high water prediction errors and the location, failure probability, operating regimes and architecture of the barriers will increase benefits and reduce costs of the entire flood protection system. This paper follows from a multidisciplinary, explorative and practically-oriented research project (11 different researchers and consultants) conducted under the Dutch ‘Hotspot Rotterdam - Knowledge for Climate’ programme in 2010.

The Research for Simulation Model of River Eco-Security: A Case Study for Danshui River in Taipei City

Abstract: Urban river eco-security completely reflected continuous mutual impacts and conductions among many factors, such as the increment and the decrement of urban environment pollution, the type of land use, the technology to water conservancy engineering, the policy of ecological conservation. However, our early warning system of urban river eco-security was not perfect. In this study which aims to construct the urban vision for the urban river eco-security structure analysis, quantitative measurement and strategy simulation. This research , construction of five subsystems, “drainage control” ,”purification ability”, “water recycled”, “habitat” and “biomass”. A dynamic model of urban river eco-security forecast and simulation system was constructed by system dynamics software Vensim DSS 5.9. The error value between simulation and real situation are few to prove the model is effective .The study results indicate that the eco-security for Danshui River is going to biomass raising, drainage raising, Habitat increasing and pollution reducing. The cogitation has integrated by system dynamic model which coming together to form precaution,water use,conservation and ecological restoration. It is clear that urban river eco-security model may provide an alternative choice of urban river Engineering Construction decision and correspond to the direction of sustainable city.

Assessment of Urban River Eco-Security: An Integrated Index and Forecast Modeling System

Abstract: It is clear that urban river eco-security model may provide an alternative choice of urban river Engineering Construction decision and correspond to the direction of sustainable city. Our goal is to provide a framework to conceptualize the impacts of various urban river eco-security development strategies over a time scale of several decades, while taking into account interactions and feedback loops between various criteria to the fullest extent allowed by available data and theory. Flooding is serious natural disaster, but there is a lack of integrated strategy on urban river ecosystem management in Taiwan. This study aims to construct a integrated index formwork by function and goal of eco-security of urban river. The other purposes of this research are apply the System Dynamics to understand the trend on forecast modeling. Formulate a system dynamics model to simulate the trend of Tamsui River Eco-Security. This research , construction of five subsystems, “discharge security” ,” purification security”, “water security”, “habitat security” and “biosecurity”. The error value between simulation and real situation are few to prove the model is effective .The study results indicate that the eco-security for Danshui River is going to biomass raising, drainage raising, habitat increasing and pollution reducing. The cogitation has integrated by system dynamic model which coming together to form precaution, water use, conservation and ecological restoration to keep the sustainability of urban nature resources by the research.

Modelling of overbank flow structures in meandering channels

Abstract: Overbank flow in a meandering channel displays a complex coherent flow structure resulting from the interplay between the floodplain and main channel flows. Understanding and modeling such coherent flow structure are of great importance for addressing river engineering and management issues where the design solutions are required to retain natural channel features and to maintain a balance between environmental, ecological and amenity issues. In recent years, numerical models have increasingly been used for river flow modeling in order to understand their flow behavior. The main aim of this paper is to predict and investigate the overbank flow behavior in the physical model of meandering channels using three-dimensional (3D) numerical model. The performance of the model is first assessed by comparing predicted results with the limited experimental data. The experiment data were obtained from a 1:5 scale physical model of the River Blackwater and a flume study in Loughborough University. The predicted distributions of the streamwise velocity, secondary vectors, turbulent parameters and bed shear stress are used to investigate the coherent flow structures along the channel, in both the horizontal and inclined floodplain cases and main channel mobile sand bed case. The results show that the three-dimensional model predicts the coherent flow structures reasonably well.

Research on the Engineering Management Reform of the Yellow River

Abstract: For further improving and perfecting the level of engineering management, the engineering management database of Yellow River is established, which is an effective means to realize the share and distributed storage of basin engineering management information and serves the function of regulating development of the Yellow River engineering management. At the same time, the system framework of new management mode is established preliminarily and the level of engineering management is reformed dramatically.