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Computational hydrodynamics based flow accumulation models to identify urban waterlogging at deltaic plain using GIS
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机译：Computational hydrodynamics based flow accumulation models to identify urban waterlogging at deltaic plain using GIS
The gradient for any point on the land surface can be calculated using the digital-elevation model. Only some empirical correlations are available to determine gradients. Therefore, the prime objective of the present study is to find an improved method for accurately determining gradients on a plain surface that can help identify key areas affected by run-off, subsequent flow accumulation, and waterlogging. Here, Kolkata city as a deltaic plain surface is selected for this study. Grid sizes of up to 600 m x 600 m are used on the DEM map to calculate the run-off pattern using four techniques (a) D8 algorithm, and (b) second-order, (c) third-order, (d) fourth-order finite differences of computational hydrodynamics. After gradient estimations, the run-off pattern is determined from relatively higher to lower gradient points. Based on such run-off pattern, waterlogging points are accurately determined. All results, thereafter, are compared with the actual waterlogging map of Kolkata. The D8 algorithm and fourth-order finite-difference techniques are found as the most accurate while determining the waterlogging areas of a plain surface. Next, true gradients of identified waterlogging points are calculated to determine the relationship and error between the true and calculated gradient using various statistical analysis methods. The relationship between true and calculated gradients is observed from weak to strong when the D8 algorithm is replaced by the newly introduced fourth-order finite difference technique. Better accuracy and stronger relationships can be achieved using a smaller grid size.
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