Showing papers on "River engineering published in 2007"

Urban Rivers: Hydrology, Geomorphology, Ecology and Opportunities for Change

Abstract: This article describes how urban development impacts on the processes that control river geomorphology and influence ecology. At the catchment scale, urban development transforms the hydrological system through construction of impervious surfaces and stormwater drainage systems. River water and sediment quality also are affected by stormwater and waste water drainage and by point and diffuse inputs of pollutants. Within the river channel network, widespread river engineering improves floodwater conveyance but imposes major changes in river network and channel characteristics. The results of an analysis of Urban River Survey data from 143 channel reaches in three European rivers (the River Tame, UK; the River Emscher, Germany; and the River Botic, Czech Republic) are presented to demonstrate the strong influence of river channel engineering on channel structure, physical habitat features and vegetation patterns. This analysis also shows the surprisingly varied character of urban rivers and thus their differential potential to respond to rehabilitation efforts. Because the success of river rehabilitation efforts depend not only on a scientific understanding of form and process within urban river systems but also on the acceptance and support of urban communities and integration within urban design and planning, the article briefly explores the coupling of natural and social science approaches to drive a more sustainable future for rivers in cities.

Revised equations for Manning's coefficient for Sand‐Bed Rivers

Abstract: The procedure for selecting values of Manning n is subjective and requires judgment and skill which are developed primarily through experience. Government agencies and private sectors in developed nations such as the USA are still doing research on predicting n values for rivers. Since flow and boundary roughness vary with river conditions, such research is therefore pertinent for rivers in Malaysia where floods are one of primary concerns. Research on Manning n value was started by River Engineering and Urban Drainage Research Centre (REDAC), Universiti Sains Malaysia (USM) since 2000 at the Kinta River catchment. Further data collections were later made at two other major rivers i.e. Langat River and Kulim River. Two new equations are proposed for determining Manning n for sand‐bed rivers in Malaysia based on 163 data collected from these three rivers. On average, both equations have an error less than 10% in predicting flow discharge for all 163 data.

Ecohydrology, key-concept for large river restoration

Abstract: Successful restoration requires clear goals and objectives to succeed. Possibilities for and constraints of rehabilitation - both from a process-oriented view as well as from the nature conservation perspective differ strongly according to the landscape setting of a particular river segment and to the degree of anthropogenic changes. Large river restoration requires the development of an integrative scientific approach between ecology, hydrology and river engineering. For defining ecological targets and longterm sustainability of restoration programmes two aspects are particularly relevant. First, reference standards must be applied. Reference standards have to be based on the original landscape dynamics as defined by hydrology and bedload transport which resulted in a dynamic equilibrium of fluvial processes, habitat composition and consequently characteristic patterns of biodiversity and biogeochemical processes. The application of reference standards has to follow this cause-effect sequence. A second major requirement, dependent on this cause-effect chain between fluvial dynamics, habitat composition and ecology is the development of a prognostic ecohydrological parameter set which allows an evaluation of restoration scenarios and a prediction of their effects at a range of temporal and spatial scales.

Effects of habitat restoration on the macroinvertebrate fauna in a foreland along the river waal, the main distributary in the rhine delta

Abstract: River engineering in the Rhine delta and water pollution have been major threats for the ecological functioning of the river in The Netherlands. To mitigate effects of river engineering, secondary channel construction in the forelands along the existing distributaries is considered to be an important measure for river restoration. These areas are the remnants of the former Rhine floodplain and the only area where habitat restoration is possible due to the river functions assigned. Secondary channel construction in the area called ‘Gamerensche Waarden’ was taken as an example to show effects of habitat restoration on the macroinvertebrate fauna. Totally 322 macroinvertebrate taxa were found during the monitoring period. During the first 3 years species richness in the area increased rapidly due to colonization processes in the channels following habitat development. After that period total number of taxa found in the channels stabilized at around 170. A clear positive relationship was demonstrated between habitat quality and species richness. Furthermore, the density of exotic species in the secondary channels was less than in the groyne fields of the main channel. The relatively low number of taxa in polluted habitats could be explained by the presence of the PCB 28 congener. Copyright © 2007 John Wiley & Sons, Ltd.

Scour in hydraulic engineering

Abstract: As a result of damage and failures due to undermining of foundations and the blockage of water flow caused by sediment aggradation downstream of scour holes, scour in hydraulic engineering has become an important issue in recent decades. This paper presents recent research on: (a) plunge pool scour in which a variety of effects were investigated; (b) bridge piers for which spatial and temporal scour development was described using particle image velocimetry for a test case; (c) the failure of riprap-protected spur dykes in a straight river reach. In all three fields, the main features of scour are described based on similitude according to Froude—that is, using the densimetric Froude number of the approach flow as the dominant parameter. The large number of parameters involved were controlled with suitable experimental setups allowing for the determination of the governing effects of a scour problem. Results are presented that readily apply to river engineering problems.

Backwater effect due to a single spur dike

Abstract: Spur dikes are river engineering structures that project from the bank of a stream at some angle to the main flow direction. They are principally used for river training and protection of the river...

Numerical Analysis Of Braided Rivers and Alluvial Fan Deltas

Abstract: Understanding the processes of morphological behavior in braided rivers and alluvial fan deltas is very important for river engineering purposes to manage hydraulic structures and prevent disasters from flood, and environmental purposes to maintain river ecosystem. A two-dimensional numerical model was developed to simulate braided rivers and alluvial fan deltas with erodible bed and banks. A moving boundary-fitted coordinate system was employed to calculate water flow, bed change, and bank erosion. CIP (Cubic Interpolated Pseudo-particle) method was used to calculate flow, which introduced little numerical diffusion. Sediment transport equation in the streamline and transverse wise, considering the secondary flow, was used to estimate bed and bank evolution in time. Bank erosion was simulated by following the procedure proposed by Shimizu (2002). Braided river in laboratory was reproduced for verifying the numerical model in the channel filled with nearly uniform sandy materials. Comparison of nu...

Nile river sediment transport simulation (case study: damietta branch)

Abstract: Sediment transport is an important element in the quantitative and qualitative management of river engineering. The rate of sediment transport, at any given river cross section, depends mainly on the availability of the transported material and transport ability of the stream. Many different formulas have been used to predict the amount of sediment discharge in the Nile River, but only few equations give reasonable results compared with field measurements. Some examples of these equations are Ackers and White, Engelund and Hansen and Yang equations. Damietta Branch was selected as a case study for this analysis. This study has been performed to simulate the period from 1982 to 2001 for Damietta Branch. Analysis and comparison of the selected formulas for both trend and value are discussed at each cross section. Keyword: Damietta Branch, Nile River Sediment, Sediment Transport Equation, Sediment Transport Simulation.

Managing River Sediments

Abstract: Sediments play an important role in river engineering and water resources management. In the past, many rivers in developed countries have been engineered by training and regulation works for navigation, hydropower generation and flood protection. In the past decades, municipal and industrial waslewaler discharge and various diffusive sources from agriculture have caused a widespread contamination of river sediments by heavy metals, organic toxicants and agrochemicals. Meanwhile, many historically contaminated sites in rivers are localized and identified as a severe latent hazard for the river ecosystem (see Sect. 1.1.3). Most of the contaminated sites have been detected in low flowing water bodies which are either permanently or temporarily connected to the main river channel such as near bank groyne fields in waterways or harbors, river dead arms, flood plains and last not least flood retention reservoirs (Fig. 2.1). Many deposits are most likely to be resuspended and transported over a long distance by extreme discharges causing contamination of not yet polluted surface water bodies and unpolluted soils subject to flooding.

Perfect morphology of meandering river for middle and lower reaches of Hanjiang River

Abstract: Based on field data and former research,the perfect morphology of meandering river is studied.The perfect morphology of meandering river was influenced not only by flow conditions including flow discharge and slope of river,but also influenced by the constitute and median diameter of river bed.The expression of curvature semidiameter is formed.Based on the field data of the middle and lower reaches of the Hanjing River,an empirical formula is developed.This empirical formula may be helpful both in river engineering and waterway improvement.

Application of MIKE21 Software in Flood Routing of Tidal Rivers: A Case Study of the Zohre River

Abstract: routing is of special importance from different aspects of river engineering such as flood zoning, flood forecasting, etc. There are two methods employed in river flood routing, hydraulic and hydrological. Hydrological methods are used when the river is at low tide and, hence, cannot be employed to analyze floods caused by the tide. Hydraulic methods must be employed in tidal rivers when the direction of the current reverses at high tide. In this research, MIKE21 modeling software was used for the flood routing of the Zohreh tidal river. The model was calibrated by surveying the river, taking samples form the river bed, measuring sea water level and the velocity of the river flow. Analyzing the sensitivity of the model showed that the coefficient of determination, root mean square error and relative error were 0.95, 0.032, and 0.27, respectively, all indicating the efficacy of the model in simulating different parameters such as velocity, flow rate, and water surface profile. The flood routing results of the tidal currents showed that the hydrograph of the influent and effluent to the reach at high tide (when the current direction is from sea to the river) was similar to the normal flood routing of the river, but at low tide (when the current direction is from the sea to the river) influent and effluent hydrograph would not follow the laws of normal flood routing.

Flood control in urban basins using detention ponds comparison to localized river engineering countermeasures; technical report

Abstract: In this paper effects of constructing detention ponds for flood control in basins immediately upstream an urban area, are studied. Comparisons are made between this practice and conventional localized river engineering countermeasures regarding socio-economical aspects. The study is conducted in Abkharvar urban basin in Behbahan city in the Khouzestan Province, in southwestern Iran. Based on the design flood routing, the effects of detention ponds on the dimensions of the conveyance canal are studied. Total costs of flood control alternatives are then compared. Results show that regarding socio-economical issues, detention ponds are superior to conventional localized river engineering and flood control countermeasures for flood control purposes in urban basins.

Modeling of radiation shade fuction considering seasonal change of leaf area index of riparian vegetation

Abstract: Recently, multiple functions of river riparian vegetation are attracted in biological, environmental river engineering field. The decline of riparian vegetation strongly affects the river thermal environment, which also has a large impact on the ecological systems. In this study, a model that relates stream temperature with riparian vegetation was developed. The Nam Song River, which is a tributary of the Nam Ngum River flowing through the Vientiane Metropolis, was selected for field study. Meteorological data (air temperature, relative humidity, wind speed) were used, and the sink or source terms of the heat transfer equation were estimated from that data. NDVI (normalized difference of the vegetation index) remote sensing data was used for estimation of LAI (leaf area index) seasonal change. Simulations were made with several cases of riparian vegetation density, showing that river water temperature is more sensitive to river discharge change in the case of low density condition.

Morphological changes of river due to construction of a port at Baan Paeng

Abstract: The purpose of this paper is to analyze fluvial process and evaluate the impact of a port construction on river by using quasi-two-dimensional GSTARS 2.1 that can simulate the lateral change or river bank failure. The study emphasizes the quantitative influence of construction of the port which obstructs or diverts the flow direction. Furthermore, it shows the efficiency and application of the mathematical model on river engineering especially on the cases that have limited data. The selected case study is the project for surveying and the design of a port at the Mekong River, Amphor Baan Paeng, Nakorn Panom Province. The data of 19 river cross-sections, discharge of water, maximum level of water in 2002 and minimum level of water in 1992 with 20 return periods were used. The results show that the port does not severely affects the changing of the thalweg and the bank of the Mekong River at the project location and nearby areas. Moreover, the scouring or failure of river bank was found to be reduced at some river cross-sections.

Comparison of flow characteristics in a physical model with 1d, quasi-2d, and 2d numerical models in a river reach

Abstract: Numerical models are being used widely in river engineering projects. However, the reliability of these models, minimum field data requirement, and the optimal computational processes are of major concern. This study compares the simulated steady flow parameters from a well-known numerical models with that of a true river physical model. A fixed-bed model is developed for the Nazloo River, IRAN, with horizontal scale of 1:100 and vertical scale of 1:20. Results from HEC-RAS (1D), BRI-STARS (quasi 2D), and FAST-2D (2D) were compared for corresponding flow parameters under similar initial and boundary conditions. This was made for five different flows in three sub-reaches along the river (i.e. downstream of a bridge, bridge reach, upstream of the bridge). The best adapted results were produced by HEC-RAS. BRI-STARS and FAST-2D models took the next ranks respectively. The averaged predictive errors were rated 1.8, 2.2, and 5.5 percent for water surface elevations and 10.2, 9, and 12.6 percent for mean velocities, respectively. The application of each model is recommended in river projects subject to the inclusion of the degree of certainties provided by the present study.