O uso dos dados lidar para a compreensão da dinâmica de escoamento e acúmulo de águas em Recife – PE

Os grandes aglomerados urbanos desencadeiam profundas problemáticas de natureza hidroclimática, resultantes principalmente das formas de uso e ocupação do solo. Os padrões hídricos, tais como escoamento e acúmulo de fluxo, são afetados diretamente pelo efeito de impermeabilização do solo decorrente das construções humanas e quando esta estrutura urbana é somada aos eventos climáticos extremos, culminam na ocorrência periódica de inundações. Diante deste contexto, o presente estudo tem como objetivo compreender e identificar os danos hidrológicos decorrentes da concentração urbana, sobre a dinâmica natural do escoamento, a fim de investigar os fatores que provocam estas inundações nas determinadas regiões. A área de estudo do presente trabalho é representada por folhas de amostragem do sensor LiDAR das Regiões político administrativas IV e VI do município do Recife, Pernambuco. Para subsidiar a análise proposta, os modelos digitais de elevação do projeto Pernambuco 3D, provenientes do sensor LiDAR, foram processados em ambiente SIG, e a partir destes dados de alta resolução espacial foi possível analisar detalhadamente as variáveis que propiciam o escoamento superficial e acúmulo de fluxo nas áreas em estudo. Os resultados obtidos para as áreas de amostragem, foram analisados e comparados com as políticas públicas de drenagem urbana e planejamento territorial vigentes, avaliando a relação entre as redes de macro e microdrenagem, com a ocorrência de inundações no meio urbano. The use of lidar data for the understanding of water flow and accumulation dynamics in the Recife – PEA B S T R A C TLarge urban agglomerations result in huge problems of hydroclimatic nature, resulting mainly from the forms of land use and occupation. Water patterns, such as runoff and flow accumulation, are directly affected by the waterproofing effect from human constructions, and when added to the extreme weather events, they culminate in a periodic occurrence of urban floods. The study area of the present work is represented by the LiDAR sensor sampling sheets from the administrative political Regions IV and VI of the municipality of Recife, in Pernambuco. Given this context, the present study aims to understand and identify the hydrological damage caused by the urban concentration on the natural dynamics of runoff, to investigate the factors that cause these floods in that specific region. To subsidize the proposed analysis, the digital elevation models of the Pernambuco 3D project, from the LiDAR sensor, were processed in a GIS environment, and from these high spatial resolution data it was possible to analyze in detail the variables that propitiate surface runoff and flow accumulation in the areas under study. The results obtained for the sampling areas were analyzed and compared with the urban drainage and territorial planning public policies in force, evaluating the relationship between the macro and micro drainage networks, with the occurrence of floods in the urban environment. Keywords: Geoprocessing. remote sensing. urbanization. urban flood. surface runoff.

The Influence of Fracture on the Permeability of Carbonate Reservoir Formation Using Lattice Boltzmann Method

Due to the complex conditions of carbonate reservoir, in this paper, a unified lattice Boltzmann method was used to study the rule of the flow in carbonate reservoir as the foundation. Two group models were designed to simulate the influences of fractures and vugs. In experiments, at first, the model for carbonate reservoir considering different amounts and lengths of fractures was considered. Then, the model was improved by taking the influences of fractures and vugs into consideration. The result from the first group shows that the whole permeability enhanced a lot when multiple fractures form a big one which connects to two boundaries. At the same time, the main result of the other group shows that the main capability of vugs is flow accumulation. Through a series of experiments, the flow rule in carbonate reservoir with vugs and fractures is proved based on LBM theory, which has a huge impact on the study in LBM and researches on carbonate reservoir.

An Approach to Identify Urban Waterlogging on a Deltaic Plain using ArcGIS on CHD based Flow Accumulation Models

The gradient for any point on the land surface can be calculated using the digital-elevation model. Some empirical correlations are available to determine the gradient of any points. A few studies were conducted for hilly forest areas to determine the aspect and gradient of various points using computational hydrodynamics (CHD) based techniques. On a plain surface, the accuracy of such techniques was rarely verified. The application of such techniques for a plain surface is also extremely challenging for its small slope. Therefore, the prime objective of the present study is to find out an advanced technique to more accurately determine the gradient of various points on a plain surface which may help in determining the key areas affected by run-off, subsequent flow accumulation, and waterlogging. Here, Kolkata city as a deltaic plain surface is chosen for this study. Upto 600 m × 600 grid sizes are used on the DEM map to calculate the run-off pattern using a D8 algorithm method and second-order, third-order, and fourth-order finite difference techniques of CHD. After finding out the gradient, the run-off pattern is determined from relatively higher to lower gradient points. Based on the run-off pattern, waterlogging points of a plain surface are precisely determined. The results obtained from all the different methods are compared with one other as well as with the actual waterlogging map of Kolkata. It is found that the D8 algorithm and fourth-order finite-difference-technique are the most accurate while determining the waterlogging areas of a plain surface. Next, true gradients of waterlogging points are calculated manually to compare the calculated gradient points using each method. This is also done to determine the relationship and error between the true and calculated gradient of waterlogged points using various statistical analysis methods. The relationship between true and calculated gradients is observed from weak to strong if the D8 algorithm is replaced by the newly introduced fourth-order finite difference technique. Better accuracy and stronger relationships can be achieved by using a smaller grid size.

Adaptive Determination of the Flow Accumulation Threshold for Extracting Drainage Networks from DEMs

Selecting the flow accumulation threshold (FAT) plays a central role in extracting drainage networks from Digital Elevation Models (DEMs). This work presents the MR-AP (Multiple Regression and Adaptive Power) method for choosing suitable FAT when extracting drainage from DEMs. This work employs 36 sample sub-basins in Hubei (China) province. Firstly, topography, the normalized difference vegetation index (NDVI), and water storage change are used in building multiple regression models to calculate the drainage length. Power functions are fit to calculate the FAT of each sub-basin. Nine randomly chosen regions served as test sub-basins. The results show that: (1) water storage change and NDVI have high correlation with the drainage length, and the coefficient of determination (R2) ranges between 0.85 and 0.87; (2) the drainage length obtained from the Multiple Regression model using water storage change, NDVI, and topography as influence factors is similar to the actual drainage length, featuring a coefficient of determination (R2) equal to 0.714; (3) the MR-AP method calculates suitable FATs for each sub-basin in Hubei province, with a drainage length error equal to 5.13%. Moreover, drainage network extraction by the MR-AP method mainly depends on the water storage change and the NDVI, thus being consistent with the regional water-resources change.

Computational study of a radial flow turbine operates under various pulsating flow shapes and amplitudes

Radial flow turbines are extensively used in turbocharging technology due to their unique capability of handling a wide range of exhaust gas flow. The pulsating flow nature of the internal combustion engine exhaust gases causes unsteady operation of the turbine stage. This paper presents the impact of the pulsating flow of various characteristics on the performance of a radial flow turbine. A three-dimensional computational fluid dynamic model was coupled with a one-dimensional engine model to study the realistic pulsating flow. Applying square wave pulsating flow showed the highest degree of unsteadiness corresponding to 92.6% maximum mass flow accumulation due to the consecutive sudden changes of the mass flow rates over the entire pulse. Although saw-tooth showed a maximum mass flow accumulation value of 88.9%, the mass flow rates entailed gradual change resulted in the least overall mass flow accumulation over the entire pulse. These two extremes constrained the anticipated performance of the radial flow turbine operates under realistic pulsating flow. Such constraints could develop an operating envelop to predict the performance and optimize radial flow turbines' power extraction under pulsating flow conditions.

Setting the Flow Accumulation Threshold Based on Environmental and Morphologic Features to Extract River Networks from Digital Elevation Models

Determining the flow accumulation threshold (FAT) is a key task in the extraction of river networks from digital elevation models (DEMs). Several methods have been developed to extract river networks from Digital Elevation Models. However, few studies have considered the geomorphologic complexity in the FAT estimation and river network extraction. Recent studies estimated influencing factors’ impacts on the river length or drainage density without considering anthropogenic impacts and landscape patterns. This study contributes two FAT estimation methods. The first method explores the statistical association between FAT and 47 tentative explanatory factors. Specifically, multi-source data, including meteorologic, vegetation, anthropogenic, landscape, lithology, and topologic characteristics are incorporated into a drainage density-FAT model in basins with complex topographic and environmental characteristics. Non-negative matrix factorization (NMF) was employed to evaluate the factors’ predictive performance. The second method exploits fractal geometry theory to estimate the FAT at the regional scale, that is, in basins whose large areal extent precludes the use of basin-wide representative regression predictors. This paper’s methodology is applied to data acquired for Hubei and Qinghai Provinces, China, from 2001 through 2018 and systematically tested with visual and statistical criteria. Our results reveal key local features useful for river network extraction within the context of complex geomorphologic characteristics at relatively small spatial scales and establish the importance of properly choosing explanatory geomorphologic characteristics in river network extraction. The multifractal method exhibits more accurate extracting results than the box-counting method at the regional scale.

Effects of Glacial Isostatic Adjustment on Surface Topography, Flow Accumulation, Stream Power & Sediment Transport Indexes in the Canadian Prairies

<p>Glacial Isostatic Adjustment (GIA) induced by the melting of the Pleistocene Ice Sheets causes differential land uplift, relative sea level and geoid changes. Thus, GIA in North America may affect water flow-accumulation and the rate of sedimentation and erosion in the South Saskatchewan River Basin (SSRB), but so far this has not been well investigated.</p><p> </p><p>Our aim here is to use surface topography in the SSRB and simple models of surface water flow to compute flow-accumulation, wetness index, stream power index and sediment transport index - the latter two affect the rates of erosion and sedimentation. Since the river basin became virtually ice-free around 8 ka BP, we shall study the effects of GIA induced differential land uplift during the last 8 ka on these indexes.</p><p> </p><p>Using the present-day surface topography ETOPO1 model, we see that the stream power index and sediment transport index in the SSRB may not be high enough to alter the surface topography significantly today and probably during the last 8 ka except for places around the Rocky Mountains. The effect of using 1 and 3 arc minute grid resolution of the ETOPO1 model does not significantly alter the value of these indexes. However, we note that using 1 arc minute grid is much more computationally intensive, so only a smaller area of the SSRB can be included in the computation.</p><p> </p><p>Next, we assume that sedimentation and erosion did not occur in the SSRB during the last 8 ka BP, and the change in surface topography is only due to GIA induced differential uplift. We use land uplift predicted by a large number of GIA models to study the changes in stream power & sediment transport indexes in the last 8 ka BP. Our base GIA model is ICE6G_C(VM5a). Then we investigate the effects of using uplift predicted by other GIA models that can still fit the observed relative sea level (RSL), uplift rate and gravity-rate-of-change data in North America reasonably well. These alternate GIA models have lateral heterogeneity in the mantle and lithosphere included – in particular we test those that give the largest differential uplift in the SSRB. We found that the effect of these other GIA earth models is not large on the stream power & sediment transport indexes. Finally, we investigate the sensitivity of these indexes on the ice models that are consistent with GIA observations. The results of this study will be useful to our understanding of water flow accumulation, sedimentation and erosion in the past, present and future and for water resource management in North America.</p>

Sediment connectivity in the Koiyavgan glacier's cirques (Adyl-Su river basin, Caucasus, Russia)

<p>The highland cirques mostly created by nivation and glacial exaration take large areas in mountains and have a significant role in the sediment transit of the basins. The approximate view on the connection of cirques and low levels in the sediment flow could be given with the sediment connectivity index analysis. We study the spatial distribution of the index for typical ice cirque – the Koiyavgan cirque near the join of the Main Caucasus Range and its offshoot (the Gumachy range). This area is located in the tops of the Adyl-Su valley (left side of the Baksan river basin). In August 2020, we got a high-resolution orthophoto image (13+ cm) and digital elevation model (27+ cm) from aerial photography. The territory located in the elevation range from 3230 to 4022 m. Geological conditions: gneiss, metamorphic shale and basic dark coloured igneous rocks. There is no developed vegetation cover. Typical post-glacial cirques topography includes (top-down): mountain tops, very steep bedrock slopes, colluvial footslopes and fans, cirques bottom (moraine ridges with dividing valleys, craters from melting of the in-moraine covered ice etc.) with fluvial, avalanche and creep post-shaping, and bottom surface break as analogue of riegels in glacial trough valleys. The connectivity index (CI) after Cavalli et al. [2013] is very dependent on initial DEM resolution, from the method for filling mistaken depressions, from window size for computing intermediate geomorphometric variables (e.g. roughness index), from choice in flow impedance variable, from area coverage and terrain diversity and others. We compute connectivity index with the parameters: 1) DEM resolution – 27 cm; 2) impedance variable – terrain roughness index (standard deviation of elevation) with window 7*7 cells; 3) standard filling method used in the ArcMap (filling local depression without any limitations on maximum depth); 4) range of impedance values before normalization (partially related to area coverage) is from 0 to 72 m. In the some buffers from the channel network the connectivity index generally grows in the top-down direction. Greatest spurt of the CI values relates to the cirques low border - the riegel (3300 m asl). There are two levels characterised with low values of the CI: 3550 m and 3750 m. The first one is backside of cirques bottom with relatively low flow accumulation area and low-moderate slopes (0-25°), the second one is mountain tops with high steep slopes, but with lowest flow accumulation. For different geomorphodynamical zones the threshold of IC where sediment transit turns into sediment accumulation has differ values: for example, -2.3 for colluvial fans and -2.5 for alluvial fans (p-value for differences significance « 0.01). Maximum values of CI (quantile: the top-95%) for accumulative positions again are -1.27 and -0.72. Its means, those accumulative processes areas with different mechanics of the deposition may be delineated with using non-constant CI values only. The potential of sediment flow connectivity modelling for high mountain isn’t exhausted, but its application needs wide discussion and calibration.<br>The study was supported by the Russian Science Foundation (project No. 19-17-00181).</p>

Automatic Extraction of Intermittent Channel Systems of a Low‐Relief, Low‐Gradient Floodplain

<p>Intermittent floodplain channels are low‐relief conduits etched into the floodplain surface and remain dry much of the year. These channels comprise expansive systems and are important because during low‐level inundation they facilitate lateral hydraulic connectivity throughout the floodplain. Nevertheless, few studies have focused on these floodplain channels due to uncertainty in how to identify and characterize these systems in digital elevation models (DEMs). In particular, their automatic extraction from widely available DEMs is challenging due to the characteristically low‐relief and low‐gradient topography of floodplains. We applied three channel extraction approaches to the Congaree River floodplain DEM and compared the results to a channel reference map created through numerous field excursions over the past 30 years. The methods that we tested are based on flow accumulation area, topographic curvature, and mathematical morphology, or the D8, Laplacian, and bottom‐hat transform (BHT), respectively. Of the 198 km of reference channels the BHT, Laplacian, and D8 extracted 83%, 71%, and 23%, respectively, and the BHT consistently had the highest agreement with the reference network at the local (5 m) and regional (10 km) scales. The extraction results also include commission “error”, augmenting the reference map with about 100 km of channel length. Overall, the BHT method provided the best results for channel extraction, giving over 298 km in 69 km2 with a detrended regional relief of 1.9 m.</p>