Spatial Resolution Digital Elevation Model Research Articles

Hydrological assessment and management implications for the ancient Nabataean flood control system in Petra, Jordan

Evaluating the function and effectiveness of the Nabatean flash flood management system in Petra requires both insight into the nature and extent of the system as well as its hydrological information. Studies of runoff and flooding in semi-arid mountainous regions with high potential for flash floods, such as Petra, can be limited by the lack of any runoff measurements as well as low-resolution rainfall and terrain data. Wadi Hremiyyeh is a small catchment that flows into the Treasury Plaza and is responsible for much of the flooding that occurs there. Half meter spatial-resolution digital elevation model (DEM) was built for this catchment using unmanned aerial vehicles (UAV) surveying, which was useful in determining the exact sites of terraces built by the Nabataeans for flood management. Rainfall data from the nearby Wadi Musa station was supplemented with a new station installed through this project for continuous precipitation measurements at the site. New water level meters specifically designed for that purpose were installed within the main channel. Four of the ancient Nabataean and post Nabataean check dams were restored. Data collected from the 2019–2020 rainy season created an understanding of the rain-runoff conditions at the site and was utilized in constructing and calibrating hydrological models using HEC-HMS and HEC-RAS software. The function and the effectiveness of the rebuilt terraces were evaluated. The models suggest that terraces are effective at delaying the flood peak time (up to 25-minute delay for an 18 dam setup) and at reducing the actual amount of water arriving downstream (13.5% volume reduction). Similar results can be observed for lower frequency flood analysis, in which the models also show effectiveness of these interventions. Modeling of a large dam, rather than the smaller terraces and check dams, shows that such an intervention would result in a reduction of 30.5% in peak flow but a delay of the peak of merely 14 min. While Petra was the venue for this work, its techniques and suggested parameters are applicable to cases of similar arid and semi-arid mountainous regions that are subjected to flash floods.

Digital Elevation Models of Rockfalls and Landslides: A Review and Meta-Analysis

The scope of this paper is to summarize previous research pertaining to the use of digital elevation models (DEMs) and digital terrain models (DTMs) in the study of rockfalls and landslides. Research from 1983 to 2020 was surveyed in order to understand how the spatial resolution of DEMs and DTMs affects landslide detection, validation, and mapping. Another major question examined was the relationship between the DEM resolution and the extent of the rockfall or landslide event. It emerged from the study that, for landslides, the majority of researchers used DEMs with a spatial resolution of between 10 m and 30 m, while for rockfalls, they used DEMs with a spatial resolution of between 5 m and 20 m. We concluded that DEMs with a very high resolution (less than 5 m) are suitable for local-scale occurrences, while medium-resolution (from 20 m to 30 m) DEMs are suitable for regional-scale events. High resolution is associated with high accuracy and detailed structural characteristics, while medium accuracy better illustrates the topographic features. A low pixel size (more than 90 m) is not recommended for this type of research. Susceptibility maps, inventory maps, hazard risk zones, and vulnerability assessments are some of the main tools used in landslide/rockfall investigations, and topographic indexes, methods, models, and software optimize the reliability of the results. All of these parameters are closely related to DEMs and DTMs as the cell size affects the credibility of the final outcome.

New pedotransfer approaches to predict soil bulk density using WoSIS soil data and environmental covariates in Mediterranean agro-ecosystems.

For the estimation of the soil organic carbon stocks, bulk density (BD) is a fundamental parameter but measured data are usually not available especially when dealing with legacy soil data. It is possible to estimate BD by applying pedotransfer function (PTF). We applied different estimation methods with the aim to define a suitable PTF for BD of arable land for the Mediterranean Basin, which has peculiar climate features that may influence the soil carbon sequestration. To improve the existing BD estimation methods, we used a set of public climatic and topographic data along with the soil texture and organic carbon data. The present work consisted of the following steps: i) development of three PTFs models separately for top (0-0.4 m) and subsoil (0.4-1.2 m), ii) a 10-fold cross-validation, iii) model transferability using an external dataset derived from published data. The development of the new PTFs was based on the training dataset consisting of World Soil Information Service (WoSIS) soil profile data, climatic data from WorldClim at 1 km spatial resolution and Shuttle Radar Topography Mission (SRTM) digital elevation model at 30 m spatial resolution. The three PTFs models were developed using: Multiple Linear Regression stepwise (MLR-S), Multiple Linear Regression backward stepwise (MLR-BS), and Artificial Neural Network (ANN). The predictions of the newly developed PTFs were compared with the BD calculated using the PTF proposed by Manrique and Jones (MJ) and the modelled BD derived from the global SoilGrids dataset. For the topsoil training dataset (N = 129), MLR-S, MLR-BS and ANN had a R2 0.35, 0.58 and 0.86, respectively. For the model transferability, the three PTFs applied to the external topsoil dataset (N = 59), achieved R2 values of 0.06, 0.03 and 0.41. For the subsoil training dataset (N = 180), MLR-S, MLR-BS and ANN the R2 values were 0.36, 0.46 and 0.83, respectively. When applied to the external subsoil dataset (N = 29), the R2 values were 0.05, 0.06 and 0.41. The cross-validation for both top and subsoil dataset, resulted in an intermediate performance compared to calibration and validation with the external dataset. The new ANN PTF outperformed MLR-S, MLR-BS, MJ and SoilGrids approaches for estimating BD. Further improvements may be achieved by additionally considering the time of sampling, agricultural soil management and cultivation practices in predictive models.

Cross Section Intervals of Flood Intervals of Flood Inundation Mapping at Ungauged Area

Digital Elevation Models (DEMs) are essential to present the continuous surface elevation and is used for flood mapping. The use of different cross-section intervals obtained from the various spatial resolution of DEMs will affect the flood depth and inundation area estimation. Therefore, a comparison study is carried out to investigate the effect of cross-section intervals on flood expansion and flood depth which is simulated using one dimensional (1D) HEC-RAS model at Padang Terap River, Malaysia. Two digital elevation models (DEMs) imageries, Interferometry Synthetic Aperture Radar (IFSAR) and Shuttle Radar Topography Mission (SRTM) are used in this study. The result was evaluated using likelihood measures (F-statistics, root mean square error (RMSE), and mean absolute error). The findings reveal the IFSAR DEM with cross-section interval 50 m has higher F-statistics of 70% on flood inundation estimation. By proposing the methodology, flood mapping can be provided accurately by considering the error that exist in the Geographical Information System (GIS) spatial context.

Effects of neighborhood analysis window forms and derivative algorithms on the soil aggregate stability – Landscape modeling

One of the most important factors in soil-landscape analysis can be the operational scale applied for mathematical calculations of terrain attributes. This study aimed to investigate the effects of different calculation patterns on terrain attributes and soil aggregate stability-landscape modeling at the subwatershed scale. For this purpose, four terrain attributes (slope gradient, slope aspect, plan curvature, and profile curvature) were calculated by two derivative algorithms (Evans-Young and Zevenbergen-Thorne) from a one-meter digital elevation model (DEM), using two neighborhood shapes (square and circular) with ten different neighborhood scales (from 5 m to 50 m). The regression tree model was used for modeling, and Kruskal-Wallis test was performed for determining significant differences in the terrain attributes across different calculation patterns. The results showed that the curvature attributes were mostly sensitive to the type of calculation pattern rather than the slope attributes. In calculation patterns, the neighborhood scale was the most important factor, which influenced differences in terrain attributes more than the neighborhood shape or type of derivative algorithm. The terrain attributes, calculated by the Evans-Young algorithm, were more distinct between circular and square neighborhoods, compared to attributes calculated by the Zevenbergen-Thorne algorithm, because of the difference in the polynomial type. Investigation of the relationship between the aggregate stability and terrain attributes indicated the great importance of the neighborhood scale. Differences in the R-squared values of models indicated that the type of derivative algorithms and the neighborhood shape could have remarkable effects on the soil-landscape models. Overall, the present results revealed that differences in calculation patterns had considerable effects on the soil-landscape analysis, although the results might be influenced by changes in the spatial resolution of DEM.

Morphometric evolution of Everest region debris-covered glaciers

Debris-covered glaciers in the central Himalaya have now experienced several decades of sustained ice loss, manifested predominantly in glacier surface lowering. In particular, glacier surfaces of low longitudinal gradient and low ice surface velocity have developed locally complex surface topographies and undergone profound changes in supraglacial hydrology. In this study we examine the development of complex ice surface topography across six debris-covered glaciers in the Everest region over the last four decades via a new metric of glacier surface relief applied to Digital Elevation Models (DEMs). We focus in on Khumbu Glacier, and use fine spatial and temporal resolution DEMs covering a period of 28 months to quantify the contemporary contribution of ice cliff and supraglacial pond expansion to overall mass loss from stagnant areas of ice. On the broader scale, we find three common long-term changes in glacier surface topography, (1) glacier-wide expansion of high relief topography in response to ice cliff and supraglacial pond network evolution, (2) up-glacier expansion of high local relief zones that may be caused by differential sub-debris melt beneath thin debris, and (3) increase in glacier surface relief proximal to glacier termini caused by supraglacial stream incision where linked proglacial-supraglacial hydrological networks exist. Overall, we contend that these topographic measurements will be important for understanding glacier surface water storage and also the energy balance of a debris-covered glacier surface, both of which could exacerbate future ice loss and downstream meltwater supply.

Geomorphometric Characterization and Analysis of the Bued Watershed Using Advanced Spaceborne Thermal Emission and Reflection Radiometer – Global Digital Elevation Model V3 through Geospatial Techniques

The present study analyzed and quantified the linear, areal, and relief geomorphometric aspects of the Bued Watershed in Benguet, Philippines using a 30-m spatial resolution digital elevation model. The study was carried out using geospatial techniques to describe the hydrogeological processes acting on the watershed including its landforms, geologic structure, and terrain features that are relevant in watershed conservation and natural resources management. The study site has a total area of 146.46 km² and a basin length of 23.38 km. Based on the linear parameters, it has four stream orders generated using a 1.5-ha critical source area (CSA). Stream order three, with a total of three stream segments, contributes much higher sediment loads to the Bued River. These stream segments are also controlled by geologic structures with a high possibility of flash floods during a high rainfall intensity. For the areal parameters, the study area was categorized as medium-watershed and less elongated. It has a low drainage density value (1.16 km/km²), which is characterized by a good vegetative cover. The study site has permeable subsurface material and lower relief, which turns out to have a more infiltration capacity. Whereas the drainage texture and form factor values (0.812 km and 0.27, respectively) described the study area with a lower peak flow of longer duration, these values indicate that the flood flows are easier to control. The linear parameters showed that most of the Bued Watershed area (44%) is located at an elevation of > 1000 masl with moderate to steep slopes, which make it more susceptible to erosions and landslides. This is consistent with the relief ratio and relative relief results (0.08 and 0.03, respectively), which suggest that the area is vulnerable to erosion.

Accuracy Assessment of Spatial Interpolation Methods to Derives DEMs of Small Islands with Relative Topographic Variations

Responding to Climate Change in Small Island Developing States (SIDS), accurate Digital Elevation Model (DEM) can support the Sea level Rise (SLR) scenarios and sequenceit is impacts on coastal zone for proper adaptation. The DEM accuracy may vary to a certain degree following different interpolation algorithms and the data acquisition method. Indeed, numerous mathematical interpolation methods have been developed on spatial interpolation for topographic information densification and DEM restitution. The aim of this study focuses on the accuracy assessment of high spatial resolution DEM (at 2.5 m pixel size) regenerated from high topographic contour lines map at scale of 1:5,000 applying four different interpolation algorithms. Three deterministic methods were considered including the IDW with variable and fixed parameters, the Spline with regular and tension conditions, and the Natural Neighbor. While, for stochastic methods, the ordinary and simple Kriging were analyzed according to the semi-variogram adjustment considering five mathematical functions: Stable, Circular, Spherical, Exponential and Gaussian. For validation purposes, a datasets of 400 ground control points (GCPs) uniformly distributed over the study site, to cover all the existing altitude classes, were used. These were measured using Differential Global Position System (DGPS) with ± 1 cm and ± 2 cm for planimetric and altimetric accuracies, respectively. The results obtained show that ordinary and simple kriging methods, based on the exponential function, achieved a similar DEMs restitution with the best RMSE (± 0.65 m), which proved to be less than the tolerance or the total deviation (± 0.78 m). Consequently, these two Kriging methods are more accurate for DEM production for small island applications such as the evaluation of coastal zones vulnerability to SLR, flooding, detection of topographic features and hydrological modeling.

Active Tectonics and Earthquake Geology Along the Pallatanga Fault, Central Andes of Ecuador

Based on new geological data and the analysis of a 4 m spatial resolution Digital Elevation Model (DEM), we provide a detailed and comprehensive description of section of the Chingual Cosanga Pallatanga Puna Fault System, a major active fault system in Ecuador. This work allows estimating new slip rates and large earthquakes parameters (displacement, recurrence) along a ∼100 km-long section of the continental-scale dextral shear zone that accommodates the extrusion of the North Andean Sliver with respect to the South America continental Plate. We focus on the NE-SW Pallatanga strike-slip fault zone and related contractional and transcurrent features that extend to the north in the Inter-Andean valley and the Cordillera Real, respectively. The detailed analysis of the available DEM allowed mapping a series of lineaments at the regional scale and along the entire fault system. Field studies on key areas show valley deflections, aligned and elongated hills of Tertiary or Quaternary sediments, as well as faulted Holocene deposits and even preserved coseismic free-face ruptures in some places. Such morphological anomalies strongly suggest that those landscape scars represent long-living (Holocene to historical times) earthquake faults. Altogether, these new data confirm that very large crustal earthquakes (M∼7.5) have been generated along the fault system, probably during multiple segment ruptures. This conclusion agrees with reports of large earthquakes during historical times (post-1532 CE) in 1698, 1797, and 1949. They all occurred in the vicinity of the Pallatanga fault, causing catastrophic effects on environmental and cultural features. Based on new sample dating of both soils and volcanic series, we infer that the NE-SW dextral Pallatanga fault slips at rates ranging from ∼2 to 6 mm/yr for southern and central strands of the studied area, respectively. Further north, surface faulting is distributed and the deformation appears to be partitioned between sub-meridian fault-related folds (∼2 mm/yr) and NE- SW strike-slip fault(s), like the ∼1 mm/yr Pisayambo Fault that ruptured the surface in 2010. All this information offers the opportunity to size the earthquake sources for further seismic hazard analyses.

The influence of DEM spatial resolution on landslide susceptibility mapping in the Baxie River basin, NW China

The selection of an appropriate map resolution is highly important for landslide susceptibility assessment. No consistent objective criteria, however, are currently applied to the choice of map resolution. This research, in conjunction with slope units, explores the effect of digital elevation model (DEM) resolution on susceptibility modelling using three statistical models (frequency ratio, index of entropy, and weight of evidence). Seven different spatial resolutions (30, 40, 50, 60, 70, 80, and 90 m) and three statistical models are investigated. For each resolution, we compare the performance of the three models using area under curve (AUC) analysis. The results show that, independent of the statistical models, the best performances are produced at 70 m DEM resolution. This highlights that finer resolutions do not necessarily lead to higher predictive accuracy in landslide susceptibility mapping. Rather, the frequency ratio model seems to be optimal for the coarser resolutions (i.e. 70, 80, and 90 m).

Accuracy assessment of the CARTOSAT DEM using robust statistical measures

CARTOSAT-1-derived 10 m spatial resolution digital elevation model (DEM) for entire India was compiled for several applications. Overall assessment of the accuracy of this product requires additional regional studies involving ground truth control points and accuracy verification methods with a higher level of precision, such as the global positioning system (GPS).The study presented in this paper compares the accuracy of CARTOSAT-1 datasets with respect to eight sites over different terrains in India with the same GPS system. Robust statistical analysis including mean errors, standard deviation error, root mean square error (RMSE), skewness, kurtosis measures and Shapiro–Wilk’s normality test were used for evaluating error. The results of this study show a linear trend between the DEM and the ground control points (GCP). The mean error is very high in highlands ranging up to − 14.06 m, whereas in moderate terrain it ranges around 2.65 m and in the lowland about 1.20 m. RMSE ranges up to 28.82 m in rugged high-altitude topographies, 6.24 m in moderate and 1.98 m in low-altitude regions. However, this study shows that CARTODEM is one of the finest DEM that can be used for the Indian subcontinent as it works more accurately over plain and moderately undulating lands.

Impact of Spatial Resolution of Digital Elevation Model on Landslide Susceptibility Mapping: A Case Study in Kullu Valley, Himalayas

Landslides are one of the most damaging geological hazards in mountainous regions such as the Himalayas. The Himalayan region is, tectonically, the most active region in the world that is highly vulnerable to landslides and associated hazards. Landslide susceptibility mapping (LSM) is a useful tool for understanding the probability of the spatial distribution of future landslide regions. In this research, the landslide inventory datasets were collected during the field study of the Kullu valley in July 2018, and 149 landslide locations were collected as global positioning system (GPS) points. The present study evaluates the LSM using three different spatial resolution of the digital elevation model (DEM) derived from three different sources. The data-driven traditional frequency ratio (FR) model was used for this study. The FR model was used for this research to assess the impact of the different spatial resolution of DEMs on the LSM. DEM data was derived from Advanced Land Observing Satellite-1 (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) ALOS-PALSAR for 12.5 m, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global for 30 m, and the Shuttle Radar Topography Mission (SRTM) for 90 m. As an input, we used eight landslide conditioning factors based on the study area and topographic features of the Kullu valley in the Himalayas. The ASTER-Global 30m DEM showed higher accuracy of 0.910 compared to 0.839 for 12.5 m and 0.824 for 90 m DEM resolution. This study shows that that 30 m resolution is better suited for LSM for the Kullu valley region in the Himalayas. The LSM can be used for mitigation and future planning for spatial planners and developmental authorities in the region.

Applications of SPOT-7 tri-stereo imagery in deriving the surface topography and mass changes of glaciers in Indian Himalaya

The present study describes the application of satellite images of SPOT 7, acquired on 10 October 2014 for producing the high spatial resolution digital elevation models of five glaciers in the Indian Himalaya. For data processing, we applied a Semi-Global Matching algorithm deployed in LPS- ERDAS. Ground control points were also used for validation, which were obtained during the autumn of 2014. Then, precise estimate are derived for the glacier area, the terminus elevation, the areas of supraglacial debris and the areas of proglacial lakes. Further, the ASTER (obtained in 2011) and SRTM V3 (of 2000) elevation models were used in conjunction with the generated SPOT-7 DEM to estimate the glaciers mass balance between 2000, 2011 and 2014. Mass balance was observed negative for all five glaciers, but the mass loss decreased from the mean of –0.99 ± 0.27 m.w.e.a−1 in 2000–2011 to –0.61 ± 0.31 m.w.e.a−1 from 2011 to 2014.

Effects of DEM Source, Spatial Resolution and Drainage Area Threshold Values on Hydrological Modeling

Automated computation of hydrological and morphometric parameters of any watershed are not only depended on Digital Elevation Model (DEM) resolution but also affected by their sources and drainage Area Threshold Value (ATV). In present study, the effects of different resolution of freely available DEMs are analysed in QSWAT model at different ATVs. The performance of QSWAT model and processing time were also evaluated. DEM derived from ASTER, CARTOSAT and SRTM were used at 30, 90 and 180 m spatial resolutions with six different ATV’s, in QSWAT model. Result shows that DEM resolutions and ATVs have significant impacts on hydrological and morphometric parameters. QSWAT output like sub-basin count and surface runoff were less impacted by DEM resolutions while these components were affected by ATV, while HRU counts and sediment yield were affected by DEM resolution. It was also observed that fine resolution DEM increases processing time at smaller threshold values as compared to coarser resolution DEM. Result of this study could be used for selection of optimum DEM resolution and ATV.

Wetland Classification with Multi-Angle/Temporal SAR Using Random Forests

To better understand and mitigate threats to the long-term health and functioning of wetlands, there is need to establish comprehensive inventorying and monitoring programs. Here, remote sensing data and machine learning techniques that could support or substitute traditional field-based data collection are evaluated. For the Bay of Quinte on Lake Ontario, Canada, different combinations of multi-angle/temporal quad pol RADARSAT-2, simulated compact pol RADARSAT Constellation Mission (RCM), and high and low spatial resolution Digital Elevation and Surface Models (DEM and DSM, respectively) were used to classify six land cover classes with Random Forests: shallow water, marsh, swamp, water, forest, and agriculture/non-forested. Results demonstrate that high accuracies can be achieved with multi-temporal SAR data alone (e.g., user’s and producer’s accuracies ≥90% for a model based on a spring image and a summer image), or via fusion of SAR and DEM and DSM data for single dates/incidence angles (e.g., user’s and producer’s accuracies ≥90% for a model based on a spring image, DEM, and DSM data). For all models based on single SAR images, simulated compact pol data generally achieved lower accuracies than quad pol RADARSAT-2 data. However, it was possible to compensate for observed differences through either multi-temporal/angle data fusion or the inclusion of DEM and DSM data (i.e., as a result, there was not a statistically significant difference between multiple models). With a higher repeat-pass cycle than RADARSAT-2, RCM is expected to be a reliable source of C-band SAR data that will contribute positively to ongoing efforts to inventory wetlands and monitor change in areas containing the same land cover classes evaluated here.

High spatial resolution digital elevation model (DEM) production using different interpolations techniques

DEMs, thus, simply regular grids of elevation measurements over the land surface.The aim of the present work is to produce high resolution DEM for certain investigated region (i.e. Baghdad University Campus\ college of science). The easting and northing of 90 locations, including the ground-base and buildings of the studied area, have been obtained by field survey using global positioning system (GPS). The image of the investigated area has been extracted from Quick-Bird satellite sensor (with spatial resolution of 0.6 m). It has been geo-referenced and rectified using 1st order polynomial transformation. many interpolation methods have been used to estimate the elevation such as ordinary Kriging, inverse distance weighted (IDW) and natural neighbor methods. The mosaic algorithm has then been applied between the base and building layers of studied area in order to perform the final DEM. The accuracy assessments of the interpolation methods have been calculated using the root-mean-square-error (RMSE) criterion. Finally, the estimated DEMs have been used to constructing 3-D views of the original image.

Influence of digital elevation model resolution on rockfall modelling

Spatial models are an effective tool for determining potential rockfall source, transit and deposit areas. The reliability of the final rockfall modelling results depends on the quality of the input data, which is mostly based on the digital elevation model (DEM). The spatial resolution of the DEM holds key information about the main morphological properties of the surface, which is crucially important when modelling this kind of geomorphological phenomenon. Therefore, this article studies the influence of DEM spatial resolution on the modelling of rockfall source, transit and deposit areas. Modelling was carried out at five different DEM spatial resolutions available for Slovenia (1 m, 5 m, 12.5 m, 25 m and 100 m). Rockfall source areas were identified using a geomorphometric approach based on a high resolution DEM and a geographical information system. Rockfall transit and deposit areas were modelled using the Conefall computer program, which is designed to estimate potential rockfall risk areas. The area of study was the municipality of Vipava (107.4 km2) in Slovenia, EU. A spatial resolution of 1 m was chosen as a reference layer to which all modelling results of the other spatial resolutions were compared. Validation of modelling included rockfall source area comparison with orthorectified aerial images and location collection of silent witnesses (rock deposits) in the field for estimating maximum runout zones. The modelling results indicate that a spatial resolution of 1 m is the most suitable for modelling on a local scale; resolutions of 5, 12.5 and 25 m can be used for modelling on a regional scale (depending on the purpose of the modelling results); and a resolution of 100 m should not be used for rockfall modelling. Major differences between spatial resolutions can be observed when modelling rockfall source areas, i.e. in areas with the most diverse topography, while in deposit areas the observed differences are smaller due to the less rugged surface.

Evaluation of TanDEMx and SRTM DEM on watershed simulated runoff estimation

In hydrological models, digital elevation models (DEMs) are being used to extract stream network and delineation of the watershed. DEMs represent elevation surfaces of earth landscape. Spatial resolution refers to the dimension of the cell size representing the area covered on the ground. Spatial resolution is the main parameter of a DEM. The grid cell size of raster DEM has significant effects on derived terrain variables such as slope, aspect, curvature, the wetness index, etc. Selection of appropriate spatial resolution DEM depends on other input data being used in the model, type of application and analysis that needs to be performed, the size of the database and response time. Each DEM contains inherent errors due to the method of acquisition and processing. The accuracy of each DEM varies with spatial resolution. The present paper deals with Shuttle Radar Topography Mission (SRTM), TerraSAR-X add-on for Digital Elevation Measurements (TanDEM DEMs) and compares their watershed delineation, slope, stream network and height with ground control points. It was found that the coarse resolution DEM-derived attributes and terrain morphological characteristics were strongly influenced by DEM accuracy. The objective of the present study is to investigate the impact of DEM resolution on topographic parameters and runoff estimation using TanDEM-12, TanDEM-30 and SRTM-90 m with the Soil and Water Assessment Tool. The analysis of the results using different DEM resolutions gave a varied number of sub-basins, Hydrological Response Units (HRUs) and watershed areas. The results were optimum at a specific threshold value as extraction of drainage network has a significant influence on simulated results. The accuracy of DEM is important, as the source of construction of DEM is the main factor causing uncertainty in the output. The results showed variable amounts of runoff at the watershed level, which may be attributed to varied stream lengths, minimum and maximum elevations and sub-basin areas.

Numerical Modeling of Flow Patterns Applied to Analysis of Susceptibility to Movements of the Ground

Mass movements in deformed areas of natural relief deformed by seismotectonic factors are one of the most destructive and recurrent natural hazards in the Republic of Ecuador, especially during intense rain periods, the El Niño phenomenon, or due to earthquakes such as the one that occurred on 16 April 2016 in the Ecuadorian coastline. This study proposes the application of Hydrological Model D8 and its derived morphometric parameters like slope, orientation of the slope, and curvatures, extracted from the high spatial resolution Digital Elevation Model (DEM), implemented in programs such as Rockworks 7 (gridzo), SURFER (downwards slope), ArcView (flowacc), and SAGA (curvatures) to obtain runoff flow, structural geological lineaments, and superficial deformations of the topographic relief that are the origin of erosion, superficial landslides, lateral propagation, of the rock–soil complex, mass flows, and deep gravitational deformations. This methodology has been validated in three locations with intense deformations: two in Ecuador and one in Spain. The DEM were obtained from the Ecuadorian Spatial Institute (ESI) (spatial resolution of 10 m), the Rural Technological Infrastructure and Information National System (SIGTIERRAS) (spatial resolution of 5 m), and the Council of Andalusia (spatial resolution of 5 m).

DEVIATION BETWEEN HILL SLOPE ESTIMATION METHODS AND THE ROLE OF DEM SPATIAL RESOLUTION. COMPARATIVE STUDY IN A GIS ENVIRONMENT

Three methods are descibed between the most frequently used for the estimation of hill slope from digital elevation models (DEM), the 'd8' method (Travis et al. 1975), Horn's method (1981) and Zevenbergen and Thorne method (1987), are described. Also a new approach was examined introduced by Tarboton (1997) called 'd-infinite' method. In order to investigate the spatial distribution of deviations between the examined methods, a statistical analysis was performed in a GIS environment. The magnitude of the differences between the methods was determined by calculating the RMSEr (Root Mean Square Error), while the degree of their equivalence was expressed by the linear correlation factor (r). Most deviations were located in areas of high relief, whereas the most interesting fact was that each method overestimates or underestimates the slope in very specific morphological structures, e.g. along watersheds, streams and generally in some types of morphological discontinuities. Finally, the DEM spatial resolution effect was explored on the estimated slope values using the selected methods. Regardless the method used, a general tendency of underestimating slope values by decreasing the DEM resolution was observed. The degree of divergences between these was also highly depended on the change of spatial resolution. Thus, the importance of defining a suitable resolution for each application should be addressed.