Resolution DEM Research Articles

The impact of DEM resolution on landslide susceptibility modeling

The impact of DEM resolution on landslide susceptibility modeling

Global sensitivity analysis in hydrodynamic modeling and flood inundation mapping

Flood simulation with two-dimensional hydrodynamic models is subject to different sources of uncertainties in model configuration, boundary conditions, and model parametrization. HEC-RAS 2D is a widely used hydrodynamic model. Here, we assess the sensitivity of the HEC-RAS 2D to its configuration factors and parameters. We evaluate the impacts of different model configuration factors, including the floodplain and channel roughness coefficients, terrain and mesh size, as well as river boundary conditions on the dynamic of water levels, maximum water level, and flood extent, and determine the importance of these contributing factors for reliable flood inundation modeling using both variogram and variance-based analyses. For our case study, we found that depending on the perturbation scale, the performance measure, and the predicted output, the sensitivity to input factors changes. While for simulation of water level dynamics, the DEM and mesh resolutions are the most important factors, for flood extent mapping the floodplain roughness coefficient and the upstream boundary condition are the key factors. In addition, our analyses indicated that for a reliable simulation of maximum flood water level, modelers need to spend resources on the calibration of floodplain roughness coefficient while using fine DEM and mesh resolutions. Here, we also investigate the role of computational time interval and mesh resolution on the model's run time and accuracy. Our results suggested that reducing the computational time interval has minimum impact, as it increases the model run time without much improving the model accuracy.

Model-based assessment of shallow landslides susceptibility at a petrochemical site in Brazil

The Serra do Mar mountain range is the main site of shallow-landslides occurrence in Brazil. The application of physically-based models is an effective method to predict landslide susceptibility, which is of great importance in hazard assessments and urban-planning studies. Thus, the objective of this study is to compare landslide susceptibility scenarios created with SHALSTAB and SINMAP at two large watersheds (Mogi and Perequê) in Cubatão, Latin America’s largest petrochemical site. Model calibration is based on the landslide scars inventory of the 1985 event, the geotechnical parameters derived from soil samples and the topography sourced from a 5 m resolution DEM. Using the Receiver Operating Characteristics (ROC) analysis to assess model performance, SHALSTAB emerges as the best-fit model for both watersheds due to higher concentration of landslide scars in unstable areas (true positive results) and higher global accuracy. Even though SINMAP had similar degree of success, it was slightly less accurate and failed more often in the identification of potentially unstable areas. Comparative performance studies of physically-based models are fundamental to support effective and reliable hazard assessments in mountain regions, providing an outlook in how to proceed with more detailed studies.

Evaluating the effect of DEM resolution on performance of cartographic depth-to-water maps, for planning logging operations

Reliable and accurate soil moisture maps are needed to minimise the risk of soil disturbance during logging operations. Depth-to-water (DTW) maps extracted from digital elevation models have shown potential for identifying water flow paths and associated wet and moist areas, based on surface topography. We have examined whether DEMs from airborne LiDAR data with varying point density can improve performance of DTW maps in planning logging operations. Soil moisture content was estimated on eight sites after logging operations and compared to DTW maps created from DEMs with resolutions of 2 m, 1 m, and 0.5 m. Different threshold values for wet soil (1 m and 1.5 m depth to water) were also tested. The map performances, measured by accuracy (ACC) and Matthews Correlation Coefficient (MCC), changed slightly (79%, 81% and 82% and 0.33, 0.26 and 0.30 respectively) when DEM resolutions varied from 2 m to 1 m, and 0.5 m. The corresponding values when the DTW threshold value for wet/dry soil changed from 1 m to 1.5 m were 70%, 72%, 71% and 0.38, 0.41 and 0.39. LiDAR-based DEM resolutions of 1–2 m were found to be sufficient for extraction of DTW maps during planning of logging operations, when knowledge about soil hydrological features, associated wet and moist areas, and their connectivity is beneficial.

Joint Effects of the DEM Resolution and the Computational Cell Size on the Routing Methods in Hydrological Modelling

Natural disasters, including droughts and floods, have caused huge losses to mankind. Hydrological modelling is an indispensable tool for obtaining a better understanding of hydrological processes. The DEM-based routing methods, which are widely used in the distributed hydrological models, are sensitive to both the DEM resolution and the computational cell size. Too little work has been devoted to the joint effects of DEM resolution and computational cell size on the routing methods. This study aims to study the joint effects of those two factors on discharge simulation performance with two representative routing methods. The selected methods are the improved aggregated network-response function routing method (I-NRF) and the Liner-reservoir-routing method (LRR). Those two routing methods are combined with two runoff generation models to simulate the discharge. The discharge simulation performance is evaluated under the cross combination of four DEM resolutions (i.e., 90 m, 250 m, 500 m, and 1000 m) and fifty-six computational cell sizes (ranging from 5 arc-min to 60 arc-min). Eleven years of hydroclimatic data from the Jianxi basin (2000–2010) and the Shizhenjie basin (1983–1993) in China are used. The results show that the effects of the DEM resolution and the computational cell size are different on the I-NRF method and the LRR method. The computational cell size has nearly no influence on the performance of the I-NRF methods, while the DEM resolution does. On the contrary, the LRR discharge simulation performance decreases with oscillating values as the computational cell size increases, but is hardly affected by the DEM resolution. Furthermore, the joint effects of the DEM resolution and the computational cell size can be ignored for both routing methods. The results of this study will help to establish the appropriate DEM resolution, computational cell size, and routing method when researchers build hydrological models to predict future disasters.

Effect of DEM resolution in flood modeling: a case study of Gorganrood River, Northeastern Iran

Effect of DEM resolution in flood modeling: a case study of Gorganrood River, Northeastern Iran

Calculation of runoff computation cost and sensitivity analysis of topological attributes

Computation cost and sensitivity of the simulated results to the input parameters are the essential targets in this study. The impact of different DEMs with various sources and cell -sizes are studied on the output accuracy of the hydrological model. Evaluation of the most influential input parameters is conducted by employing Sequential Uncertainties Fitting Ver. 2 algorithms on the performance of the SWAT model. The simulation time is calculated in each case, and the trade-off between the output accuracy and the computation time is discussed. Zarrineh River watershed in Iran has been studied as a case study. The outcomes indicate that the reach lengths, reach slopes, the number of sub-basins and the amount of HRUs are the most influential parameter in runoff simulation by the SWAT model, and they differ by changing the DEM source and resolution. Simulated results over-predict the runoff during low precipitation periods and under-predict it during high precipitation seasons. The accuracy of simulated results decreases by reducing the DEM resolution, and ten times reduction of the DEM resolution generally leads to a 50% increase of error while decreasing the simulation time by eight times. The results show that the fine resolution of the input data enhances the performance of the SWAT model in the prediction of a few parameters such as the runoff yield, the hydrological response, and estimating the terrain morphology. The SWAT model has the best performance while using the DEM generated from the TOPO1:25000 as the input with 0.79, 0.79, −13.57 for the NSE, R2, PBIAS, respectively. The results can be employed to estimate the impact of low-resolution input data on the simulated result and reduce the computation time by decreasing the input DEM resolution with only a minor reduction of accuracy.

Landslide susceptibility assessment using AHP model and multi resolution DEMs along a highway in Manipur, India

Landslide susceptibility assessment using AHP model and multi resolution DEMs along a highway in Manipur, India

A Simple Method of Mapping Landslides Runout Zones Considering Kinematic Uncertainties

Landslides can be triggered by natural and human activities, threatening the safety of buildings and infrastructures. Mapping potential landslide runout zones are critical for regional risk evaluation. Although remote sensing technology has been widely used to discover unstable areas, an entire landslide runout zone is difficult to identify using these techniques alone. Some simplified methods based on empirical models are used to simulate full-scale movements, but these methods do not consider the kinematic uncertainties caused by random particle collisions in practice. In this paper, we develop a semi-empirical landslide dynamics method considering kinematic uncertainties to solve this problem. The uncertainties caused by the microtopography and anisotropy of the material are expressed by the diffusion angle. Monte Carlo (MC) simulations are adopted to calculate the probability of each cell. Compared with the existing Flow-R model, this method can more accurately and effectively estimate runout zones of the Yigong landslide where random particle collisions are intense. Combining the D-InSAR technique, we evaluate the runout zones in the Jinsha River from June 2019 to December 2020. This result shows that the method is of great significance in early warning and risk mitigation, especially in remote areas. The source area of the landslide and DEM resolution together affect the number of MC simulations required. A landslide with a larger volume requires a larger diffusion angle and more MC simulations.

Methods of modeling and mapping of the soil bulk density: a case study from Chernivtsi region, Ukraine

Soil monitoring programs in many countries often do not measure such an indicator as soil bulk density. At the same time, modern problems of assessing the condition of the soil cover require its use in soil management of agricultural landscapes. We see the solution to this problem in geospatial modeling. We have developed a technique for simulating soil bulk density, the algorithm of which consists of five stages: the creation of model maps of agro-industrial soil groups, modeling of a clay content map, construction of a map of humus content, selection of empirical dependences of soil bulk density on humus and clay content with evaluation reliability of these dependencies and their implementation in GRASS GIS and, finally, cartographic modeling of the spatial continuous distribution of soil bulk density. At the same time, parameters for improving the quality of methods modeling and mapping the soil bulk density were established. First of all, this is an increase in the sampling dataset of density, humus, and clay content to improve the reliability of the selected regression formula. It is also an improvement in the quality of spatial modeling of the humus content using geostatistical methods or modeling. To improve the clay content map, it is necessary to increase the resolution of DEM and predictors, to choose more accurate sources of DEM and prediction algorithms. The application of the presented methodology is shown in a part of Chernivtsi region, Ukraine, with the possibility of use on the scale of the entire country. URL: https://www.gcass.science.upjs.sk/

Influence of DEM resolution on landslide hazard assessment (a case study in Sapa district, Laocai province, Vietnam)

Influence of DEM resolution on landslide hazard assessment (a case study in Sapa district, Laocai province, Vietnam)

3D MODELING AND ASSESSMENT OF FLOOD RISK ZONES USING GIS AND REMOTE SENSING IN CATCHMENT AREA TERENGGANU, MALAYSIA

The application of 3D GIS has enabled better representation and visualization of flood events than previous 2D maps. Flooding is common in the Terengganu basin. Flash floods occur most of the year during the monsoon season, which lasts from November to January. Flooding along riverbanks is mainly affected by heavy rainfalls of 2500mm to well over 3500mm per year. This has significant impacts on environmental resources such as land use/land cover, local soil types and slopes. The study area of Kuala Terengganu was particularly affected by heavy rains and flash floods during the monsoon season. ASTER DEM resolution 5m converted to ArcScene 10.3 using ArcGIS 10.3 and 3D software. In recent years, flood monitoring methods have been developed that can predict water flow and associated risks and hazards. 3D visualization techniques include remote sensing such as satellite imagery and geographic information systems “GIS”. and LiDAR modeling

Technological features of distribution between river basins using GIS technologies (based on the example of r. Brusnytsya)

Formulation of the problem. The catchment area and surface runoff volume – morphometric parameters calculated from digital terrain models – are widely used in geographic information analysis of the area. They are attributed to the block of hydrological parameters, where they are basic concepts. The emergence and widespread usage of GIS tools has greatly simplified this labor-intensive process. However, the complexity of the applied algorithms forms the sensitivity of the models to the entered parameters, the values of most of which are selected by the user through numerous attempts and tests. The research methodology. The study examines the most common GIS tools from many existing ones that support hydrology tools – ArcGIS, Global Mapper, SAGA GIS, Surfer. Finding out the principles of operation of hydrological tools in different GIS environments and the applied algorithms was one of the goals, the solution of which was revealed in the process of research methodology. The same set of initial data obtained as a result of vectorization of relief elements of a fragment of a topographic map of the research territory is used for all software. The digital terrain model was prepared taking into account the requirements and features of hydrologically correct models. The initial data were checked for topological correctness. In order to determine the influence of separate DEM on the results of the boundaries, its modeling was performed in three versions – 10 × 10 m; 25 × 25 m; 50 × 50 m. According to the same algorithm in each of the GIS tools, the boundaries of the basins were selected. The obtained map metrics were entered into comparative tables, and in some cases were subject to correlation analysis. As a result of studies. The correct location and accurate plotting of the catchment areas of water bodies on the cartographic material has a decisive influence on the accuracy of determining their areas. No direct relationship was found between the effect of the DEM resolution on the results of modeling the boundaries of catchment areas. However, the resolution of the DEM affects the detail of the hydrographic network. It is established that for the same parameter ( ), there is a linear relationship between the cell size and the total length of the river network within the studied basins. Despite the study of hydrological modeling algorithms used in GIS tools, the most difficult is the special sensitivity of the models to the entered parameters. A correlation (very high level of connection) has been established, which consists in reducing the length and number of selected objects of watercourses with increasing the threshold value of the amount of runoff ( ). The scientific novelty. The obtained results are aimed at increasing the accuracy of modeling the boundaries of catchment basins and calculating the derived hydrographic parameters. They can be used to generalize hydrographic network objects within dedicated catchments and to achieve a reasonable degree of cartographic compliance and detail depending on the objectives and scope of research. The practical significance. Thus, both the resolution of the DEM and the value of the runoff threshold have a direct impact on the derived hydrographic parameters (for example, the density of the river network).

A Systematic Analysis of the Interaction between Rain-on-Grid-Simulations and Spatial Resolution in 2D Hydrodynamic Modeling

A large number of 2D models were originally developed as 1D models for the calculation of water levels along the main course of a river. Due to their development as 2D distributed models, the majority have added precipitation as a source term. The models can now be used as quasi-2D hydrodynamic rainfall–runoff models (‘HDRRM’). Within the direct rainfall method (‘DRM’), there is an approach, referred to as ‘rain-on-grid’, in which input precipitation is applied to the entire catchment area. The study contains a systematic analysis of the model behavior of HEC-RAS (‘Hydrologic Engineering Center—River Analysis System’) with a special focus on spatial resolution. The rain-on-grid approach is applied in a small, ungauged, low-mountain-range study area (Messbach catchment, 2.13 km2) in Central Germany. Suitable model settings and recommendations on model discretization and parametrization are derived therefrom. The sensitivity analysis focuses on the influence of the mesh resolution’s interaction with the spatial resolution of the underlying terrain model (‘subgrid’). Furthermore, the sensitivity of the parameters interplaying with spatial resolution, like the height of the laminar depth, surface roughness, model specific filter-settings and the precipitation input-data temporal distribution, is analyzed. The results are evaluated against a high-resolution benchmark run, and further criteria, such as 1. Nash–Sutcliffe efficiency, 2. water-surface elevation, 3. flooded area, 4. volume deficit, 5. volume balance and 6. computational time. The investigation showed that, based on the chosen criteria for this size and type of catchment, a mesh resolution between 3 m to 5 m, in combination with a DEM resolution from 0.25 m to 1 m, are recommendable. Furthermore, we show considerable scale effects on flooded areas for coarser meshing, due to low water levels in relation to topographic height.

Using Unmanned Aerial Vehicle and LiDAR-Derived DEMs to Estimate Channels of Small Tributary Streams

Defining stream channels in a watershed is important for assessing freshwater habitat availability, complexity, and quality. However, mapping channels of small tributary streams becomes challenging due to frequent channel change and dense vegetation coverage. In this study, we used an Unmanned Aerial Vehicle (UAV) and photogrammetry method to obtain a 3D Digital Surface Model (DSM) to estimate the total in-stream channel and channel width within grazed riparian pastures. We used two methods to predict the stream channel boundary: the Slope Gradient (SG) and Vertical Slope Position (VSP). As a comparison, the same methods were also applied using low-resolution DEM, obtained with traditional photogrammetry (coarse resolution) and two more LiDAR-derived DEMs with different resolution. When using the SG method, the higher-resolution, UAV-derived DEM provided the best agreement with the field-validated area followed by the high-resolution LiDAR DEM, with Mean Squared Errors (MSE) of 1.81 m and 1.91 m, respectively. The LiDAR DEM collected at low resolution was able to predict the stream channel with a MSE of 3.33 m. Finally, the coarse DEM did not perform accurately and the MSE obtained was 26.76 m. On the other hand, when the VSP method was used we found that low-resolution LiDAR DEM performed the best followed by high-resolution LiDAR, with MSE values of 9.70 and 11.45 m, respectively. The MSE for the UAV-derived DEM was 15.12 m and for the coarse DEM was 20.78 m. We found that the UAV-derived DEM could be used to identify steep bank which could be used for mapping the hydrogeomorphology of lower order streams. Therefore, UAVs could be applied to efficiently map small stream channels in order to monitor the dynamic changes occurring in these ecosystems at a local scale. However, the VSP method should be used to map stream channels in small watersheds when high resolution DEM data is not available.

Post‐fire management effects on sediment (dis)connectivity in Mediterranean forest ecosystems: Channel and catchment response

AbstractForest fires and post‐fire practices influence sediment connectivity (SC). In this study, we use the ‘aggregated index of connectivity’ (AIC) to assess SC in five Mediterranean catchments (198–1090 ha) affected by a wildfire in 2012 in south‐eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post‐fire management, and 2 years after the fire including all practices (hillslope barriers, check‐dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)‐derived digital elevation model (DEM, 2 m × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AICOUT), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non‐nested catchments comparable (AICN‐OUT). The output analysis includes the SC distribution along the catchments and at local scale (929 sub‐catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area‐specific sediment yield (SSY) at 10 new (built after post‐fire practices) concrete check‐dams located in the catchments (SSY = 1.94 Mg ha−1 yr−1; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AICN‐OUT. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post‐fire practices that reduced SC ( = − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC ( = + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AICN‐OUT at sub‐catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AICN‐OUT. However, the coarse DEM resolution explained the lack of effect of the rock check‐dams – located on the secondary channels – on AICN‐OUT. AICN‐OUT proved to be a useful tool for decision making in post‐fire restoration, but an optimal input data is still necessary to refine calculations.

An Enhanced Double-Filter Deep Residual Neural Network for Generating Super Resolution DEMs

High-resolution DEMs are important spatial data, and are used in a wide range of analyses and applications. However, the high cost to obtain high-resolution DEM data over a large area through sensors with higher precision poses a challenge for many geographic analysis applications. Inspired by the convolution neural network (CNN) excellent performance in super-resolution (SR) image analysis, this paper investigates the use of deep residual neural networks and low-resolution DEMs to generate high-resolution DEMs. An enhanced double-filter deep residual neural network (EDEM-SR) method is proposed, which uses filters with different receptive field sizes to fuse and extract features and reconstruct a more realistic high-resolution DEM. The results were compared with those generated with the bicubic, bilinear, and EDSR methods. The numerical accuracy and terrain feature preserving effects of the EDEM-SR method can generate reconstructed DEMs that better match the original DEMs, show lower MAE and RMSE, and improve the accuracy of the terrain parameters. MAE is reduced by about 30 to 50% compared with traditional interpolation methods. The results show how the EDEM-SR method can generate high-resolution DEMs using low-resolution DEMs.

Revisited sediment budget with latest bathymetric data in the highly altered Yangtze (Changjiang) Estuary

Most river-deltas of the world have been extremely altered by anthropic activities, where a regime shift from net accretion into net erosion may have occurred. In this study, subtidal morphodynamic variations in the Yangtze Estuary (YE) are elaborately analyzed for their causalities using high resolution DEM data from bathymetric surveys conducted every two years from 2007 to 2019; sediment budgetary balance in the estuary has been updated accordingly with mean annual depositional/erosional sediment amounts. The results show that subtidal channel erosion has occurred almost over the whole YE with a mean annual erosional rate of −5.59 cm/yr during the study period. Peak erosion occurred both in the South Branch and the delta front with mean annual erosional rates of −12.64 cm/yr and −8.11 cm/yr, respectively. The erosion lessened in the middle estuary where sandy shoals prevail, and a net accretive rate of 3.13 cm/yr was solely measured at the Chongming shoal. Negative correlation between estuarine erosional volume and riverine sediment discharge demonstrates the great impact of upstream hydro-engineering projects on estuarine morphodynamic change, but large-scale estuarine engineering projects also exert remarkable influence on local morphodynamics, evidenced by the presence of deep erosional belts near the projects. Annually eroded sediment amounts were estimated as 166 Mt/yr and 206 Mt/yr in the distributary channels and the delta front during the period 2007–2019, and the former was almost offset by recent sand mining amount of 143 Mt/yr from the distributary channels for land reclamation. Moreover, contemporary eroded sediment mass and sand mining amount from the tidal river reach between Datong and Xuliujing were reckoned as 77 Mt/yr and 44 Mt/yr, respectively. Our analysis further show that recently 124 Mt/yr and 153 Mt/yr of sediment discharge into the tidal river reach at Datong station and the YE at Xuliujing station account for merely 27.5% and 37.7% of their corresponding values before the 1990s, respectively. Annual sediment amount bypassing the estuary into the open sea has decreased by 37.8% from pre-1990s 370 Mt/yr to recent 140 Mt/yr, leading to recently severe erosion in the delta front. It is therefore highlighted that the estuarine system in response to natural and anthropogenic pressures is very dynamic, and the impacts of various engineering projects in the source-to-sink system should be fully taken into consideration when predicting its morphodynamic response in the estuary.

Estimation of Hydrologic Simulation in Upstream of KRS Reservoir using SWAT Model

The simulation of hydrologic response of a watershed system using hydrologic models involves calibration and validation process. Carrying out these processes, indeed requires an intensive knowledge on the parameters that impact the hydrologic process in that particular system. In this study, Soil and Water Assessment Tool (SWAT) model was used to simulate the streamflow for upstream of Krishna Raja Sagar (KRS) reservoir, Karnataka, India for the period from 1982-2014. Sensitivity analysis, calibration and validation was carried out using SWAT CUP (SWAT-calibration and uncertainty program) along with SUFI-2 algorithm (sequential uncertainty fitting-version 2) for monthly time scale. The computational efficiency and performance of the model was evaluated using statistical metrics including Nash-Sutcliffe (NS), Coefficient of determination (R2) and Percent bias (P-bias), p factor and r factor. Sensitivity of the parameters were analysed by performing one-at-a-time technique. Calibration of the model was carried out for a period of 10 years i.e., 2002-2011 and validation period was 3 years i.e., 2012-2014 which is one-third of the calibration time period. Using 90 m resolution DEM, landuse and soil maps, observed and 0.25° gridded rainfall along with other observed weather data. NS and R2 for calibration and validation period were 0.62, 0.67 and 0.60, 0.60, respectively. Thus, result indicates that SWAT model can be further used to assess the impacts of management scenarios as it effectively simulated the hydrologic response in the KRS catchment.

SUITABLE DEM ASSESSMENT STUDY FOR DATA SCARCE CITIES TOWARDS URBAN EXTREME AND NUISANCE FLOOD MAPPING

Abstract. The high-resolution accurate topography data should be used for extreme and nuisance flood inundation modeling and mapping in cities, but not available for many cities, including most developed countries. It is necessary to study and identify an alternate open-source topographic model that satisfies high-resolution topography datasets’ conditions. We analyzed the open-source DEMs visually, elevation histogram statistics, streams and watershed identification, contour statistics, Topographic Wetness Index, and vertical accuracy of other medium-resolution DEMs compared with high-resolution LiDAR data over New York City to determine alternative open-source Digital Elevation Model in the context of urban flood modeling. In high urban sprawl areas, in the context of flood mapping, our findings have shown that the medium resolution DEMs predicted similar to high-resolution DEMs with the same linear errors around RMSE 25–35ft and LE90 30–40ft. Overall, the ALOS AW3D performed better than other open-source DEMs. Even though SRTM predicted well, it inducted smoothness in DEM where more buildings were located. It noted that ALOS PALSAR DEM is not suitable for any urban studies. ASTER DEM has also shown good agreement with LiDAR and observed elevations, but it induced by noise while processing. Finally, it can be suggested that the ALOS AW3D can be used as an alternative source for urban flood modeling which represented footprints of buildings even though it performed average in vertical accuracy.