Hydrodynamic, Morphological and Environmental Effects of the River Engineering Approach to Flood Alleviation and Navigation on the Amazon – Lab Report Example

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The paper “ Hydrodynamic, Morphological and Environmental Effects of the River Engineering Approach to Flood Alleviation and Navigation on the Amazon”   is an informative version of a lab report on engineering and construction. The hydrodynamic, morphological, and environmental effects of the traditional river engineering approach to flood alleviation and navigation on the Amazon river. There are various options for sustainable river engineering under ISIS include simple flood rooting, unsteady 3-dimensional flow, steady and unsteady 2-D flow, steady and unsteady quasi 2- D flow, steady 1-D flow, and unsteady 1-D flow. Steady and unsteady 2D and quasi-2D flow models are typically used to assess the water levels and discharges during floods in compound river channels where flow occurs in both the main channel and on the flood plains.

The quasi 2D approach is usually to couple a 1D model of the main channel with a series of cells representing the flood plains, whereby each cell is modeled as a level-pool reservoir with weir-type spilling to allow flow to enter or exit the cell. The momentum transfer between the main channel and flood plain is not represented and the flood plain flows are taken as 1D, parallel to the main channel, which results in an approximate estimate of the flow behavior.

The use of the unsteady 2D models takes advantage of the increasing availability of digital ground elevation data but the computational run time is significantly longer than that of quasi-2D and 1D models. Steady one-dimensional flow modeling is used in determining increases in river stage within the main river channel as a result of backwater curves resulting from new bridges, weirs, and intake structures.

Unsteady one-dimensional flow modeling determines the water level and discharges at various locations along the main channel of a river during floods. Unsteady 3D flow modeling may be used in special circumstances to assess local, small-scale flow features. However, the complexity of running the model and the long computational run-times means that 3D modeling is not widely used in practice, and is subject to on-going research and development. These models will succeed when some factors are taken into consideration such as input data, calibration, discretization, and physical processes. Schematization is the process representing features of a river in a model.

In some models, it involves identifying all the positions of river and flood plain cross-sections, and the location of weirs and bridges and the location of any lateral inflows. Discretization refers to the process whereby the cross-sectional data is input to the computational model as a set of spatial coordinates (from which all the hydraulic parameters are calculated). In 1D modeling, the discretization is simplified into channel cross-sections at measured distances (chainages) apart. Each section is represented by a series of channel bed elevations at discrete horizontal distances measured from one edge of the section.

The chosen cross-sections need to be representative of the river reach. Thus between cross-sections, there should not be any large changes in cross-section. Also, the cross-sections should be drawn normal to the general flow direction. This is not a problem for the main channel but is uncertain on the flood plains when using a one-dimensional model. It is very important that the discretized data preserves, as far as possible, both the river and flood plain reach lengths (and hence gradients) and the flood plain volumes.

The computational model consists of adjusting the model parameters such that the model predictions are, as near as possible, in agreement with measured field data. In the case of 1D river models, the principal parameter to be adjusted is the Manning’ s n or roughness height ks  in each model river reach. Given the traditional use of such models in river engineering practice, there is substantial experience, particularly with the use of Manning’ s n, that can be drawn upon. For 2D models, however, the roughness coefficient at a grid point is only applicable to the local bed, rather than a given river cross-section, and this is an area of on-going research.

To calibrate a river model, it is necessary to have recorded values of stage and discharge. Given that the friction coefficient may vary with the stage it is advisable to calibrate the model for a range of stages. Where flood levels are to be predicted it is also important to obtain records of historical floods so that flood plain roughness and flooded areas can also be calibrated.

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