Low-relief Regions Research Articles

Spatial patterns of landslides in a modest topography of the Ozark and Ouachita Mountains, USA

Controls on landslides vary as a function of landscape and regional activity. For example, low-relief, woodland regions have slope gradients, soil types, and substrate lithologies that contrast with steeper mountainous regions prone to rock fall and debris flows. Similarly, regional variations in precipitation, earthquakes, and other impacts on landslide surfaces create regional variations in landslide properties. While the controls on landslide characteristics have been extensively studied for high-relief coastal and tectonically active regions, controls on low-relief landslides have received comparatively less attention. We focus here on a part of the Ozark and Ouachita Mountains in the US southern mid-continent to explore such characteristics of landslides and potential controls in low-relief regions. The area exhibits frequent landslides in soil-covered low-relief forested hillslopes. We evaluated the frequency-size scaling of landslides occurred during periods of different earthquake frequency and precipitation amount (pre- and post-2005). We also produced maps of landslide susceptibility based on random forest machine learning applied to remotely sensed data. We found that landslides are clustered mostly in upland hillslopes, and that small landslides dominate the area, quantified by a landslide frequency-size distribution fitting a double Pareto curve. Additionally, the overall landslide frequency, and potentially the porportion of smaller landslides relative to the larger ones, significantly increased after 2005, the period during which the area also experienced increased induced seismicity and extreme storm events. Approximately 94 % of historical landslides were within random-forest-classified high-landslide probability (probability > 0.5) zones, coinciding with moderate to steep (18° ± 9°) and convergent upland slopes underlain by shale and sandstone. Anomalously high frequency landslides appear to result from triggering by extreme weather, human-induced earthquake activity, and human-induced hillslope modification.

Impacts of a century of land‐use change on the eutrophication of large, shallow, prairie Lake Manitoba in relation to adjacent Lake Winnipeg (Manitoba, Canada)

Abstract Evaluation of large lake response to centennial changes in land use and climate can be complicated by high spatial and hydrological complexity within their catchments, particularly in regions of low relief. Furthermore, large lakes can exhibit abrupt changes in structure and function that obscure causes of eutrophication. We provide the first quantification of historical trends in lake production, cyanobacterial abundance, sediment geochemistry and diatom composition since c. 1800 in Lake Manitoba, the 29th largest lake in the world, and compared them to Lake Winnipeg, a morphologically similar, adjacent basin with a 10‐fold larger catchment and an abrupt increase in production around 1990. Before 1900, Lake Manitoba was mesotrophic, with low sedimentary concentrations of carbon, phosphorus, nitrogen, cyanobacteria and algal pigments, as well as assemblages of low‐light‐adapted benthic diatoms. Analysis of pigment time‐series with hierarchical generalised additive models revealed that Lake Manitoba eutrophied during 1900–1930 as a consequence of the development of intensive agriculture within its local catchment, but thereafter exhibited stable cyanobacterial densities with limited expansion of N2‐fixing cyanobacteria despite persistent eutrophication. Lake Manitoba did not undergo an abrupt change as seen in Lake Winnipeg. These findings suggest that catchment size had little influence on water quality degradation and that nutrient influx from proximal agricultural sources was sufficient to initially degrade these large prairie lakes. The abrupt change in Lake Winnipeg around 1990 required additional intensification of local land use that did not occur in the Lake Manitoba catchment.

Topographic disequilibrium, landscape dynamics and active tectonics: an example from the Bhutan Himalaya

Abstract. The quantification of active tectonics from geomorphological and morphometric approaches commonly implies that erosion and tectonics have reached a certain balance. Such equilibrium conditions are however rare in nature, as questioned and documented by recent theoretical studies indicating that drainage basins may be perpetually re-arranging even though tectonic and climatic conditions remain constant. Here, we document these drainage dynamics in the Bhutan Himalaya, where evidence for out-of-equilibrium morphologies have for long been noticed, from major (> 1 km high) river knickpoints and from high-altitude low-relief regions in the mountain hinterland. To further characterize these morphologies and their dynamics, we perform field observations and a detailed quantitative morphometric analysis using χ plots and Gilbert metrics of drainages over various spatial scales, from major Himalayan rivers to their tributaries draining the low-relief regions. We first find that the river network is highly dynamic and unstable, with much evidence of divide migration and river captures. The landscape response to these dynamics is relatively rapid. Our results do not support the idea of a general wave of incision propagating upstream, as expected from most previous interpretations. Also, the specific spatial organization in which all major knickpoints and low-relief regions are located along a longitudinal band in the Bhutan hinterland, whatever their spatial scale and the dimensions of the associated drainage basins, calls for a common local supporting mechanism most probably related to active tectonic uplift. From there, we discuss possible interpretations of the observed landscape in Bhutan. Our results emphasize the need for a precise documentation of landscape dynamics and disequilibrium over various spatial scales as a first step in morpho-tectonic studies of active landscapes.

Tectonic geomorphology and active faults in the Bolivian Amazon

The Bolivian Amazon foreland basin is controlled by i) the sediment input from the Andes and the topographic load; ii) the basinal uplift in the forebulge; and iii) the uplifting Fitzcarrald Arch in the north. These boundary conditions should lead to bending and active faulting of the crust. However, although the presence of active faults has been inferred from geomorphological studies, neither seismicity studies nor geodetic methods and geomorphological constraints have been successful in identifying active faults so far. Reasons for this are mainly the dense vegetation and the extremely dynamic fluvial landscape of the Bolivian Amazon. In this study we use the TanDEM-X and SRTM digital elevation models to show that there are at least five faults, several tens of kilometres long, that are active. We present offset measurements from fault scarps and combine these data with river system analyses. Our results suggest that tilting of tectonic blocks occurred in the Late Pleistocene or Holocene. The reversal of fluvial longitudinal profiles and incipient creek erosion inside paleochannels, markers of young tectonic activity, allow us to reconstruct the tilting directions. We find two orthogonal main faulting directions: WNW-ESE trending faults parallel to the Andean uplift and NNE-SSW trending faults tangent to the bulge of the uplifting Fitzcarrald Arch. Thus, our study area records the interplay between these two main drivers of crustal deformation. We show that some fault scarps were caused by large single earthquakes with magnitudes of around M W 7, while others have recorded multiple strong seismic events. These magnitudes exceed by far the magnitudes known from instrumental seismicity in the last 40 years. Our results shed light on the seismic hazard of the region and highlight that catastrophic river course changes due to sudden uplift in this low-relief region are an underestimated hazard. • We have identified four previously unknown active faults in the Bolivian Amazon. • These faults suggest that here neotectonics are driven by the interplay between the forebulge and the Fitzcarrald Arch. • Faults and tilting blocks control the evolution of the fluvial landscape of the Bolivian Amazon. • Seismic risk in the Bolivian Amazon is higher than previously thought.

Mapping soil organic carbon stock by hyperspectral and time-series multispectral remote sensing images in low-relief agricultural areas

High-precision digital soil organic carbon (SOC) stocks mapping is very important for agricultural production management and global carbon cycle. The spatial heterogeneity of farmland SOC is not only influence by the environmental factors of soil formation but also the management practices of tillage, fertilization, and irrigation. However, the traditional modeling covariates of digital soil mapping, such as terrain factors, land use types and climate factors have weak spatial variations in low-relief agricultural areas, and they cannot reflect the large spatial variation of SOC. Thus the time-series multispectral remote sensing images will be used for mapping soil properties in low relief regions in this study, meanwhile a new collaborative verification strategy was put forward to evaluate the spatial distribution characteristics of soil maps. The current study was performed in a nearly flat agricultural region southeast of Iowa (with an area of approximately 385.45 ha), where 195 surface soil samples (0–15 cm) were collected. A hyperspectral image (Headwall-Hyperspec, 380–1700 nm) and the time-series multispectral remote sensing images of Sentinel 2 and Landsat 8 were used to construct the prediction models of SOC stock and its relevant soil properties of SOC and soil bulk density (SBD) through partial least square regression (PLSR) and extreme learning machine (ELM) models. The collected soil samples and evaluation indexes of root mean square error (RMSE), R2, and ratio of performance to interquartile range (RPIQ) were used to evaluate the model performance. Results are as follows: (1) hyperspectral images were successfully used to predict the SOC stock, SOC, and SBD through PLSR and ELM, while ELM (RPIQ = 2.03, 1.97, 1.64) outperformed PLSR (RPIQ = 1.83, 1.97, 1.53); (2) the time-series multispectral remote sensing images of Sentinel 2 and Landsat 8 can reflect the spatial distribution characteristics of the SOC stock, SOC and SBD by PLSR and ELM, but the combination of Sentinel 2 images and ELM obtained the best prediction results (RPIQ = 1.45, 1.25, 1.26); and (3) the differences of the soil maps predicted by the hyperspectral image and time-series multispectral remote sensing images were small, and the largest percentage errors nearly appeared on the edges of the farmland patches owing to mixed pixels. This study further confirmed the good prediction abilities of the time-series multispectral remote sensing images in low relief farmland regions. Lastly, this mapping strategy can provide additional valuable information for agricultural management and carbon cycle.

The Baker Creek Research Watershed: Streamflow data highlighting the behaviour of an intermittent Canadian Shield stream through a wet–dry–wet cycle

AbstractBaker Creek drains water from subarctic Canadian Shield terrain comprised of a mix of exposed Precambrian bedrock, lakes, open black spruce forest and peat filled depressions. Research in the catchment has focused on hydrological processes at the hillslope and catchment scales. Streamflow is gauged from several diverse sub‐catchments ranging in size from 9 to 155 km2. The period of record (2003–2019) of streamflow from these sub‐catchments extends from 12 to 17 years, and these data are the focus of this note. Such data are unique in this remote region. 2003–2019 was a period that included both historic wet and dry conditions. Observations during such a diversity of conditions are helping to improve understanding of how stream networks that drain this landscape expand and contract in response to short and long hydroclimatic cycles. These data from a distinctly cold and dry region of low relief, thin soils, exposed bedrock and permafrost are a valuable contribution to the global diversity of research catchment data.

A model for faults to link the Neogene reservoirs to the Paleogene organic-rich sediments in low-relief regions of the south Bohai Sea, China

Fault acts as an important vertical migration conduit for hydrocarbons in rift basins and can transport hydrocarbons from deep-buried organic-rich sediments to shallow-buried coarse-grained sequences. Such migration process is expected, but generally needs to pass through thick mudstone intervals and its controlling factors are not well understood. The low-relief regions of the south Bohai Sea in the Bohai Bay rift basin, comprising both Paleogene and Neogene hydrocarbon traps, can act as a good case study for the factors controlling the hydrocarbon transporting capacity of faults. By comparing the hydrocarbon generation potential of source rocks in different formations, we confirm that the hydrocarbons trapped in the Neogene traps mainly originate from the Eocene Shahejie Formation, and need to pass through a thick Oligocene regional caprock. Hydrocarbon fluid inclusions within the Neogene reservoir sandstones indicate two major hydrocarbon charging events in the middle Pliocene to Quaternary, based on which we chose the T02 seismic marker bed to calculate fault displacement. Seismic profiles show that Neogene hydrocarbon-charged traps are commonly linked to faults with large-amount displacement, where the regional caprock has a limited thickness. Using statistics of the Neogene charged traps in a regional 3D seismic grid, we draw the minimum fault displacement for hydrocarbon migration in the Laizhouwan Sag at 53.6 m and in the Huanghekou Sag at 56 m, and the biggest caprock thickness for hydrocarbon migration in the Laizhouwan Sag at 240.7 m and in the Huanghekou Sag at 320.2 m. These observations emphasize the coupling of fault displacement and regional caprock thickness controlling the hydrocarbon transporting capacity of faults in a rift basin.

Hydrologic connectivity determines dissolved organic matter biogeochemistry in northern high‐latitude lakes

AbstractNorthern high‐latitude lakes are undergoing climate‐induced changes including shifts in their hydrologic connectivity with terrestrial ecosystems. How this will impact dissolved organic matter (DOM) biogeochemistry remains uncertain. We examined the drivers of DOM composition for lakes in the Yukon Flats Basin in Alaska, an arid region of low relief that is characteristic of over one‐quarter of circumpolar lake area. Utilizing the vascular plant biomarker lignin, chromophoric dissolved organic matter (CDOM), and ultrahigh‐resolution mass spectrometry, we interpreted DOM compositional changes using lake‐water stable isotope (δ18O‐H2O) composition as a proxy for lake hydrologic connectivity with the landscape. We observed a relative decrease in CDOM in more hydrologically isolated lakes (enriched δ18O‐H2O) without a corresponding decrease in dissolved organic carbon (DOC) concentration. Although DOC and CDOM were weakly correlated, a significant positive relationship between lignin and CDOM (r2 = 0.67) demonstrates that optical parameters are useful for estimating lignin concentration and thus vascular plant contribution to lake DOM. Indicators of allochthonous DOM, including lignin carbon normalized yields, CDOM aromaticity proxies, and relative abundances of polyphenolic and condensed aromatic compound classes, were negatively correlated with δ18O‐H2O (r2 > 0.45), suggesting there is little allochthonous DOM supplied to many of these hydrologically isolated lakes. We conclude that decreased lake hydrologic connectivity, driven by ongoing climate change (i.e., decreased precipitation, warming temperatures), will reduce allochthonous DOM contributions and shift lakes toward lower CDOM systems with ecosystem‐scale ramifications for heat transfer, photochemical reactions, productivity, and ultimately their biogeochemical function.

An integrated evaluation of the National Water Model (NWM)–Height Above Nearest Drainage (HAND) flood mapping methodology

Abstract. Flood maps are needed for emergency response, research, and planning. The Height Above Nearest Drainage (HAND) technique is a low-complexity, terrain-based approach for inundation mapping using elevation data, discharge–height relationships, and streamflow inputs. The recent operational capacities of the NOAA National Water Model (NWM) and preprocessed HAND products from the University of Texas offer an operational framework for real-time and forecast flood guidance across the US. In this study, we evaluate the integrated National Water Model –Height Above Nearest Drainage (NWM–HAND) flood mapping approach using 28 remotely sensed inundation maps and 54 reach-level catchments. The results show the NWM–HAND method tends to underpredict inundated cells in 4th-order and lower-order reaches but does better with a slight tendency to overpredict in high-order reaches. An evaluation of the roughness coefficient used in the production of synthetic rating curves suggests it is the most important parameter for correcting these errors. Persistent inaccuracies do occur when NWM streamflow predictions are substantially biased (>60 % mean absolute error between NWM and observed streamflow) and in regions of low relief. Overall, the NWM–HAND method does not accurately capture inundated cells but is quite capable of highlighting regions likely to be at risk in 4th-order streams and higher. While NWM–HAND should be used with caution when identifying flood boundaries or making decisions of whether a cell is dry or wet, its applicability as a high-level guidance tool along larger rivers is noteworthy.

DIGITAL SOIL MAPPING USING GEOMORPHOMETRIC ANALYSIS AND CASE-BASED FUZZY LOGIC APPROACH

Abstract. In low relief region such as plains, applied digital soil mapping has a controvertible issue, therefore, this study was aimed to digital mapping of soil classes at family levels by appropriate Geomorphometric variables along with fuzzy logic with area of 16,600 hectares in Qazvin Plain. Based on the geomorphologic map, the plain and pen plain are dominant landscape units. In this regards, 61 soil profiles were dogged. According to the expert’s opinion, covariates including diffuse insolation, standardized height, catchment area, valley depth and multiresolution valley bottom flatness (MrVBF) had the most important in order to generating soil map. Also, 19 fuzzy soil class maps were generated through using sample-based in ArcSIE software. Validation were carried out using achieved overall accuracy (OA) and Kappa index through error matrix. Subsequently, both ignorance and exaggerating uncertainty of hardened soil map were also done. The results showed that 19 soil families class were found. Accordingly, OA and the Kappa index were 54% and 46% respectively. The uncertainty of ignorance and exaggeration were obtained from 0 to 0.64 and 0 to 1, respectively. Moreover, the results indicated that exaggerated uncertainty was the highest in the northern and the lowest in the southern regions. Generally, applied geomorphometric parameters had the specific importance in the low relief areas for mapping of soils that have not been assessed properly so far.

Planform geometry and relief characterization of drainage networks in high-relief environments: An analysis of Chilean Andean basins

Drainage network types give indications of the landscape evolution processes and the lithologic and structural conditions that produced them. Moreover, drainage network attributes affect the hydrologic response of basins. Several network types have been identified through visual inspection and, more recently, through quantitative methods developed and applied primarily on relatively low-relief regions. These methods have not been tested in high-relief environments where other factors can control network evolution and other network types may exist. In this work, we study the occurrence of network types in high-relief environments and their potential identification through quantitative classification methods. We analyze 29 high-relief basins in the Chilean Andean region. After exploring the contextual properties (geological, climatic and landcover) of these networks, we calculate several metrics describing their horizontal and vertical attributes and benchmark them against those for network types in low-relief regions. Results show that the high-relief networks have three different types (herringbone, barbed, and high-relief pinnate), which differ in terms of their contextual properties as well as their horizontal and vertical attributes. Classification trees built using only vertical attributes have accuracies of 93% and 84% when differentiating among the high- and low-relief networks, respectively. Furthermore, an overall accuracy of 91% is reached when classifying the entire set of high- and low-relief networks with a combination of vertical and horizontal attributes. Overall, we conclude that classification of drainage patterns through vertical and horizontal attributes is feasible and more accurate than with horizontal attributes alone.

Influence of Ultrafine-Grained Structure on the Kinetics and Fatigue Failure Mechanism of VT6 Titanium Alloy

The kinetics and mechanism of fatigue failure of the VT6 titanium alloy (composition, wt %: 5.95 V, 5.01 Al, 89.05 Ti) in the initial (hot-rolled) coarse-grained (CG) state and after equal-channel angular pressing (ECAP) in the ultrafine-grained state (UFG) are investigated. ECAP is performed using billets of the mentioned alloy 20 mm in diameter and 100 mm in length preliminarily subjected to homogenizing annealing. Then, quenching in water is performed from 960°C with holding for 1 h, tempering at 675°C for 4 h, and ECAP at 650°C (route Bс, φ = 120°, number of passes n = 6). The fine alloy structure after ECAP is investigated by transmission electron microscopy at an accelerating voltage of 200 kV. To determine alloy hardness, a Time Group TH 300 hardness meter is used. Static tensile tests are performed for round samples 5 mm in diameter using a Tinius Olsen H50KT universal testing machine. The extension velocity is 5 mm/min. Fatigue tests are performed using prismatic samples 10 mm in thickness at 20°C according to the three-point bending test using an Instron 8802 installation. It is shown that, under the same loading conditions, the fatigue life of alloy samples (the number of cycles before failure) in the initial CG state is higher than that of the alloy samples in the UFG state. It is shown that the number of cycles before fatigue-crack nucleation was at a level of 19–23% of the total sample longevity, regardless the alloy state. The straight-linear segment in kinetic diagrams of the alloy fatigue failure is approximated by the Paris equation. It is revealed that the propagation rate of the fatigue crack in the alloy with an UFG structure is somewhat higher than in the alloy with a CG structure. The microrelief of fatigue cleavages of the VT6 alloy both in the CG and UFG state can be characterized as scaly with fatigue grooves on the scale surface. A low-relief region 4–6 μm in length can be observed in the failure region of the samples with an UFG structure. The microrelief of the rupture region is pit, irrespective of the alloy state.

Improving the Accuracy of Open Source Digital Elevation Models with Multi-Scale Fusion and a Slope Position-Based Linear Regression Method

The growing need to monitor changes in the surface of the Earth requires a high-quality, accessible Digital Elevation Model (DEM) dataset, whose development has become a challenge in the field of Earth-related research. The purpose of this paper is to improve the overall accuracy of public domain DEMs by data fusion. Multi-scale decomposition is an important analytical method in data fusion. Three multi-scale decomposition methods—the wavelet transform (WT), bidimensional empirical mode decomposition (BEMD), and nonlinear adaptive multi-scale decomposition (N-AMD)—are applied to the 1-arc-second Shuttle Radar Topography Mission Global digital elevation model (SRTM-1 DEM) and the Advanced Land Observing Satellite World 3D—30 m digital surface model (AW3D30 DSM) in China. Of these, the WT and BEMD are popular image fusion methods. A new approach for DEM fusion is developed using N-AMD (which is originally invented to remove the cycle from sunspots). Subsequently, a window-based rule is proposed for the fusion of corresponding frequency components obtained by these methods. Quantitative results show that N-AMD is more suitable for multi-scale fusion of multi-source DEMs, taking the Ice Cloud and Land Elevation Satellite (ICESat) global land surface altimetry data as a reference. The fused DEMs offer significant improvements of 29.6% and 19.3% in RMSE at a mountainous site, and 27.4% and 15.5% over a low-relief region, compared to the SRTM-1 and AW3D30, respectively. Furthermore, a slope position-based linear regression method is developed to calibrate the fused DEM for different slope position classes, by investigating the distribution of the fused DEM error with topography. The results indicate that the accuracy of the DEM calibrated by this method is improved by 16% and 13.6%, compared to the fused DEM in the mountainous region and low-relief region, respectively, proving that it is a practical and simple means of further increasing the accuracy of the fused DEM.

Using TanDEM-X Pursuit Monostatic Observations with a Large Perpendicular Baseline to Extract Glacial Topography

Space-based Interferometric Synthetic Aperture Radar (InSAR) applications have been widely used to monitor the cryosphere over past decades. Owing to temporal decorrelation, interferometric coherence often severely degrades on fast moving glaciers. TanDEM-X observations can overcome the temporal decorrelation because of their simultaneous measurements by two satellite constellations. In this study, we used the TanDEM-X pursuit monostatic mode with large baseline formation following a scientific phase timeline to develop highly precise topographic elevation models of the Petermann Glacier of Northwest Greenland. The large baseline provided the advantage of extracting topographic information over low relief areas, such as the surface of a glacier. As expected, coherent interferometric phases (>0.8) were well maintained over the glaciers, despite their fast movement, due to the nearly simultaneous TanDEM-X measurements. The height ambiguity, which was defined as the altitude difference corresponding to a 2π phase change of the flattened interferogram, of the dataset was 10.63 m, which was favorable for extracting topography in a low relief region. We validated the TanDEM-X derived glacial topography by comparing it to the SAR/Interferometric radar altimeter observations acquired by CryoSat-2 and the IceBridge Airborne Topographic Mapper laser altimeter measurements. Both observations showed very good correlation within a few meters of the offsets (−12.5~−3.1 m), with respect to the derived glacial topography. Routine TanDEM-X observations will be very useful to better understand the dynamics of glacial movements and topographic change.

Predicting soil organic carbon concentrations in a low relief landscape, eastern Iran

Understanding the spatial distribution of soil organic carbon (SOC) concentrations in arid areas is necessary for the management of these regions. In the present study, the distribution of SOC concentrations was investigated using digital soil mapping for an area of ~41,000 ha in Zahak county, Sistan and Baluchestan province, eastern Iran. 417 soil samples were collected from 0 to 30 cm depth across a 750 m by 750 m grid. Random Forest (RF) technique was used to model soil organic carbon (SOC) concentrations. Topographic and remote sensing indices, and land use and soil texture fractions maps were used as environmental variables. 10-fold cross-validation was used to evaluate models. Results showed that the mean SOC concentration is very low with a value of 0.33%. The most important variables for predicting SOC concentration variations were the clay map, Landsat 8 bands 7, 4, 6, 3 and distance from the river. Remote sensed data showed high potential to predict SOC in this low relief region. Root mean square error (RMSE) and mean absolute error (MAE) were 0.21 and 0.16%, respectively. We concluded that soil clay content, agricultural management, and the processes of wind erosion and deposition determine the SOC distribution in Zahak region, eastern Iran. The predicted map is consistent with the realities of the study area. These maps could be used in comprehensive planning to improve SOC in the study area.

Landslide susceptibility and risk assessment in a non-mountainous region – a case study of Koronowo, northern Poland

The study deals with landslide threats in a low-relief region which exemplifies an area rarely perceived as prone to such geohazards. Actually, in the gently undulated landscape in the vicinity of Koronowo at the Brda River (South Pomeranian Lake District, northern Poland) intensified landsliding was observed in the recent years. The field mapping and examination of air photos showed that endangered terrains are fairly extensive and cannot be limited to initially identified slope failure incidences (hot-spots). The devised landslide susceptibility and hazard map is an outcome of predictive modelling using empirical likelihood ratio function ( LR ) with respect to seven evidential layers: elevation, slope angle, slope aspect, flow accumulation, surface deposits, depth to glacial raft, land cover as well as the landslide scars. The values of potential losses were calculated based on the mapped land-use categories and current market prices of estates and services. The final map, which resulted from combining landslide hazard with potential losses, shows damage propensity in a spatial scale of the town surroundings. It is meant as a supportive tool for decision-making with regard to allocating funds for stabilization measures or planning placement of new investments. On this background, stabilization solutions for selected sites are assessed in a cost-benefit context.

Hydrologic implications of smoldering fires in wetland landscapes

AbstractSmoldering fires in organic soils have negative effects on air quality and motorist safety as well as global implications from their release of large quantities of refractory C. However, the ecological implications of their occurrence are relatively unexplored despite their potential importance to the management of wetland ecosystems. We developed a conceptual model of the ecohydrologic implications of peat-consuming fires that explores the interactive effects of fire, hydrology, and C dynamics on hydrology. We modify an existing wetland hydrology model parameterized with climate, soil, and spatial data from a low-relief region in southern Florida (USA) to explore hypothesized pyrogeomorphic changes to upland water table elevation, wetland inundation (depth and hydroperiod), and groundwater exchange as a function of fire severity (area and depth of burn). Smoldering fires increase hydroperiod and storage in organic soils in burned wetlands by changing soil elevation. After fire, negative feedbacks...

Morphometric Analysis of a Shakkar River Catchment Using RS and GIS

Employing Remote Sensing (RS) and Geographical Information System (GIS), morphometric analysis was carried out for Shakkar River catchment (area = 2220 km2) using satellite imageries and topographic maps on a scale map of 1:50,000 to determine its drainage characteristics. Exhibiting a dendritic drainage pattern, the drainage density of the study area varies from 2.84 to 3.67 km/km 2 which observed that area is highly permeable and structurally controlled. The bifurcation ratio varies from 3.49 to 5.52 and the elongation ratio vary from 0.47 to 1.00, whereas value nearing 1 are typical of region of low relief. The area is delineated in 8 sub watershed. The morphometric analysis reveals that sub-watershed 3 show lower value of Drainage density and Stream Frequency, Sub-watershed 6 shows low value Compactness Constant and sub-watershed 7 show lower value of Circulatory Ratio and Form factor. The relief aspect lower in the subwatershed 2. And the values of Average slope vary from 9.27 to 88.50%. This study of morphometric analysis characterizes the watershed and helps to understand the hydrological behaviour of the Shakker river catchment.

Effect of DEM data resolution on low relief region sub-watershed boundaries delineating using of SWAT model and DEM derived from CARTOSAT-1 (IRS-P5), SRTM and ASTER

Watersheds are natural integrators of hydrological, biological, and geological processes and as such require an integrated approach to data analysis and modeling, which usually starts delineating accurately a polygon vector layer of watershed boundaries as input. In that way, Garrah sub-watershed in Shahjahanpur district of U.P., India, had been isolated with the objective of evaluate the accuracy of sub-watershed boundaries derived from three different sources: One was delineated by 2.6 m resolution CARTOSAT-1 DEM (IRS-P5) and other two were derived from a 30 m ASTER DEM and a 90 m SRTM DEM, using the Soil and Water Assessment Tool (SWAT) model. In this analysis we found that the accuracy of CARTOSAT-1 DEM is so best for accurate delineation of a sub-watershed in the management of the watershed, and the coarse spatial resolution SRTM DEM (90 m) performed much better and significantly than the high spatial resolution ASTER DEM (30 m) it’s cause of the errors in the ASTER DEM, map algebra was used to define where the “Fill” tool had filled the sinks finding that the errors in the stream network occurred where some especially large fills had occurred. Not only the visual interpretation of the produces figures indicate the SRTM DEM delineated sub-watershed as relatively more accurate from ASTER DEM delineated sub-watershed boundaries, also statistics for the SRTM DEM elevation turned in significantly higher than that of the ASTER DEM. Overall SRTM DEMs offer more precise elevations while, ASTER DEMs offer more details. Therefore, the accuracy of the sub-watershed delineation depends on the first place on the accuracy of the DEM.

Assessing Impact of Flood on River Dynamics and Susceptible Regions: Geomorphometric Analysis

Natural climatic hazards like flood, an important hydro-geomorphic process of earth’s surface, have different regional and local impacts with significant socio-economic consequences. Similar was the case in Gujarat State, India during last week of June 2005. This study is about assessing the impact of Gujarat flood on river dynamics. It deals with extraction of water bodies information using radiance image and standard water indices i.e., Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI) for pre- and post-flooding periods. Geomorphometric analysis along with drainage network extraction was done using two different Digital Elevation Models (DEMs) i.e., Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) and Shuttle Radar Topographic Mission (SRTM) and compared. Finally, depressions mapping and comparative analysis of magnitude and directional change of drainage networks was carried out. Results confirmed better accuracy of MNDWI in separating water bodies. The water bodies area increased by 10.4 % in post-flood monsoon compared to pre-flood monsoon and by 3.8 % in post-flood dry season compared to pre-flood dry season. Geomorphometric analysis indicated that ASTER DEM gave more values of maximum slope, average slope, and standard deviation as compared to SRTM. Aspects distribution algorithm did not work well in low relief regions. The drainage network generated using SRTM DEM was more accurate. The depressions identified were more susceptible to flood events. Change analysis of drainage network (deviating 100–300 m) indicated that 5.22 % points deviated between October, 2004 and 2005 and 3.18 % between February, 2005 and 2006.