DEM Of Difference Research Articles

Estimation of small-scale soil erosion in laboratory experiments with Structure from Motion photogrammetry

The quantitative estimation of changes in terrain surfaces caused by water erosion can be carried out from precise descriptions of surfaces given by means of digital elevation models (DEMs). Some stages of water erosion research efforts are conducted in the laboratory using rainfall simulators and soil boxes with areas less than 1m2. Under these conditions, erosive processes can lead to very small surface variations and high precision DEMs are needed to account for differences measured in millimetres. In this paper, we used a photogrammetric Structure from Motion (SfM) technique to build DEMs of a 0.5m2 soil box to monitor several simulated rainfall episodes in the laboratory. The technique of DEM of difference (DoD) was then applied using GIS tools to compute estimates of volumetric changes between each pair of rainfall episodes. The aim was to classify the soil surface into three classes: erosion areas, deposition areas, and unchanged or neutral areas, and quantify the volume of soil that was eroded and deposited. We used a thresholding criterion of changes based on the estimated error of the difference of DEMs, which in turn was obtained from the root mean square error of the individual DEMs. Experimental tests showed that the choice of different threshold values in the DoD can lead to volume differences as large as 60% when compared to the direct volumetric difference. It turns out that the choice of that threshold was a key point in this method. In parallel to photogrammetric work, we collected sediments from each rain episode and obtained a series of corresponding measured sediment yields. The comparison between computed and measured sediment yields was significantly correlated, especially when considering the accumulated value of the five simulations. The computed sediment yield was 13% greater than the measured sediment yield. The procedure presented in this paper proved to be suitable for the determination of sediment yields in rainfall-driven soil erosion experiments conducted in the laboratory.

Recent movement of the Late Pleistocene Shoushan slump, southwestern Taiwan, based on landform surveys

This study aims to investigate and to analyze the recent complex mass movements of Shoushan in Kaohsiung City, southwestern Taiwan, by the short-term global positioning system (GPS) survey and the comparison of elevation data from different sources. Landform change is derived from difference of 5-m digital elevation models (DEMs), i.e., the DEMs of difference (DoD), which are abstracted from 1:5000 scale contour maps dating to 1978 and 1998. The spatial distribution of elevation change within the study area is visualized and delineated by the threshold value of 2.5 m which is resulted from the error level of contour maps. The GPS survey of benchmarks is deployed to infer the short-term surface movement in the study area, and to argue with the results of DoD analysis. To ensure the reliability of GPS field measurements, a 6-h static surveying procedure is applied to each benchmark with the reference GPS station being positioned in a tectonically stable location close to the study area. Based on the GPS survey results and the DoD analysis, the study identifies the development of several secondary slumps on the main body of the huge slump. The secondary slumps are characterized by relatively slow movements with diverse directions.

Inland thinning on the Greenland ice sheet controlled by outlet glacier geometry

Greenland’s contribution to future sea-level rise remains uncertain and a wide range of upper and lower bounds has been proposed. These predictions depend strongly on how mass loss—which is focused at the termini of marine-terminating outlet glaciers—can penetrate inland to the ice-sheet interior. Previous studies have shown that, at regional scales, Greenland ice sheet mass loss is correlated with atmospheric and oceanic warming. However, mass loss within individual outlet glacier catchments exhibits unexplained heterogeneity, hindering our ability to project ice-sheet response to future environmental forcing. Using digital elevation model differencing, we spatially resolve the dynamic portion of surface elevation change from 1985 to present within 16 outlet glacier catchments in West Greenland, where significant heterogeneity in ice loss exists. We show that the up-glacier extent of thinning and, thus, mass loss, is limited by glacier geometry. We find that 94% of the total dynamic loss occurs between the terminus and the location where the down-glacier advective speed of a kinematic wave of thinning is at least three times larger than its diffusive speed. This empirical threshold enables the identification of glaciers that are not currently thinning but are most susceptible to future thinning in the coming decades. Greenland’s ice loss depends on propagation of mass loss from the marine glacier termini to the interior. An analysis of surface elevation change in 16 glacier catchments shows that the up-glacier extent of thinning is limited by glacier geometry.

Mapping of coastal landforms and volumetric change analysis in the south west coast of Kanyakumari, South India using remote sensing and GIS techniques

The coastal landforms along the south west coast of Kanyakumari have undergone remarkable change in terms of shape and disposition due to both natural and anthropogenic interference. An attempt is made here to map the coastal landforms along the coast using remote sensing and GIS techniques. Spatial data sources, such as, topographical map published by Survey of India, Landsat ETM+ (30m) image, IKONOS image (0.82m), SRTM and ASTER DEM datasets have been comprehensively analyzed for extracting coastal landforms. Change detection methods, such as, (i) topographical change detection, (ii) cross-shore profile analysis, (iii) Geomorphic Change Detection (GCD) using DEM of Difference (DoD) were adopted for assessment of volumetric changes of coastal landforms for the period between 2000 and 2011. The GCD analysis uses ASTER and SRTM DEM datasets by resampling them into common scale (pixel size) using pixel-by-pixel based Wavelet Transform and Pan-Sharpening techniques in ERDAS Imagine software. Volumetric changes of coastal landforms were validated with data derived from GPS-based field survey. Coastal landform units were mapped based on process of their evolution such as beach landforms including sandy beach, cusp, berm, scarp, beach terrace, upland, rockyshore, cliffs, wave-cut notches and wave-cut platforms; and the fluvial landforms. Comprising of alluvial plain, flood plains, and other shallow marshes in estuaries. The topographical change analysis reveals that the beach landforms have reduced their elevation ranging from 1 to 3m probably due to sediment removal or flattening. Analysis of cross-shore profiles for twelve locations indicate varying degrees of loss or gain of coastal landforms. For example, the K3-K3′ profile across the Kovalam coast has shown significant erosion (−0.26 to −0.76m) of the sandy beaches resulting in the formation of beach cusps and beach scarps within a distance of 300m from the shoreline. The volumetric change of sediment load estimated based on DoD model depict a loss of 241.69m3/km2 for 62.82km2 of the area and land gain of 6.96m3/km2 for 202.80km2 of the area during 2000–2011. However, an area of 26.38km2 unchanged by maintaining equilibrium in sediment budgeting along the coastal stretch. The study apart from providing insight into the decadal change of coastal settings also supplements a database on the vulnerability of the coast, which would help the coastal managers in future.

Geomorphic study of seismically active areas using remote sensing data. Case of the Gorny Altai (Siberia) affected by the 2003 Altai earthquake

This paper shows that a multitemporal, multiscale, and multisource remote sensing dataset represents an efficient tool for studying morphotectonics in seismically active areas, with an application in Siberia. The focus is placed on the use of high resolution imagery including Corona, Orbview 3, Ikonos 2 (available on Google Earth), and Landsat images combined with four different digital elevation models (DEMs) built using various satellite data. DEMs are the version 2 SRTM 3 arc-second and version 3 SRTM 1 arc-second released by USGS, the X-SAR DEM, and the version 2 Aster GDEM.In the specific case of the Gorny Altai, the remote sensing dataset composed of DEMs and satellite images provide relevant evidence of the geomorphological consequences of the 2003 Altai earthquake characterized by large landslides, block tilting, and ground-cracks. Ikonos imagery reveals the en-échelon faults compatible with a dextral strike-skip faulting. Archive satellite data allow us detecting new faults generated by the earthquake, but also the pre-existing fault network, with a specific emphasis on the use of Corona archive from the 1960’s. The best global DEMs (SRTM 1 arc-second and Aster GDEM) are well-correlated. Generally, the Aster GDEM presents a lower horizontal accuracy than the SRTM DEM, whereas the vertical accuracy is relatively similar. In the case of the largest landslide induced by the 2003 Altai earthquake (about 1 km2), the comparison of the pre-seismic topographic profile obtained by SRTM and the post-seismic topographic profile obtained by Aster GDEM is of great interest. Following the landslide episode, it allows us defining a zone of depletion and a zone of accumulation. The limit between the hard Palaeozoic rocks (sandstone, etc.) and the loose Quaternary sediments appears clearly as a zone of weakness. Before the 2003 earthquake, a round track was already detected in the Corona images, corresponding either to an old landslide or a precursor stage of the major landslide.More generally, the dextral strike-slip faulting is accompanied by the uplift of the northeastern segment, close to the Chagan Uzun block. In the Kuskunnur-Taltura-Chagan river area, this uplift is revealed by the abnormal elevation of the Kuskunnur river compared to the elevation of the Taltura river. The present geomorphological study is a complement to dendrochronological and radiocarbon dating of earthquake triggered landslides, rockfalls and seismically cut fossil soils.

Feasibility of High-Resolution Soil Erosion Measurements by Means of Rainfall Simulations and SfM Photogrammetry

The silty soils of the intensively used agricultural landscape of the Saxon loess province, eastern Germany, are very prone to soil erosion, mainly caused by water erosion. Rainfall simulations, and also increasingly structure-from-motion (SfM) photogrammetry, are used as methods in soil erosion research not only to assess soil erosion by water, but also to quantify soil loss. This study aims to validate SfM photogrammetry determined soil loss estimations with rainfall simulations measurements. Rainfall simulations were performed at three agricultural sites in central Saxony. Besides the measured data runoff and soil loss by sampling (in mm), terrestrial images were taken from the plots with digital cameras before and after the rainfall simulation. Subsequently, SfM photogrammetry was used to reconstruct soil surface changes due to soil erosion in terms of high resolution digital elevation models (DEMs) for the pre- and post-event (resolution 1 × 1 mm). By multi-temporal change detection, the digital elevation model of difference (DoD) and an averaged soil loss (in mm) is received, which was compared to the soil loss by sampling. Soil loss by DoD was higher than soil loss by sampling. The method of SfM photogrammetry-determined soil loss estimations also include a comparison of three different ground control point (GCP) approaches, revealing that the most complex one delivers the most reliable soil loss by DoD. Additionally, soil bulk density changes and splash erosion beyond the plot were measured during the rainfall simulation experiments in order to separate these processes and associated surface changes from the soil loss by DoD. Furthermore, splash was negligibly small, whereas higher soil densities after the rainfall simulations indicated soil compaction. By means of calculated soil surface changes due to soil compaction, the soil loss by DoD achieved approximately the same value as the soil loss by rainfall simulation.

Mapping snow depth in open alpine terrain from stereo satellite imagery

Abstract. To date, there is no definitive approach to map snow depth in mountainous areas from spaceborne sensors. Here, we examine the potential of very-high-resolution (VHR) optical stereo satellites to this purpose. Two triplets of 0.70 m resolution images were acquired by the Pléiades satellite over an open alpine catchment (14.5 km2) under snow-free and snow-covered conditions. The open-source software Ame's Stereo Pipeline (ASP) was used to match the stereo pairs without ground control points to generate raw photogrammetric clouds and to convert them into high-resolution digital elevation models (DEMs) at 1, 2, and 4 m resolutions. The DEM differences (dDEMs) were computed after 3-D coregistration, including a correction of a −0.48 m vertical bias. The bias-corrected dDEM maps were compared to 451 snow-probe measurements. The results show a decimetric accuracy and precision in the Pléiades-derived snow depths. The median of the residuals is −0.16 m, with a standard deviation (SD) of 0.58 m at a pixel size of 2 m. We compared the 2 m Pléiades dDEM to a 2 m dDEM that was based on a winged unmanned aircraft vehicle (UAV) photogrammetric survey that was performed on the same winter date over a portion of the catchment (3.1 km2). The UAV-derived snow depth map exhibits the same patterns as the Pléiades-derived snow map, with a median of −0.11 m and a SD of 0.62 m when compared to the snow-probe measurements. The Pléiades images benefit from a very broad radiometric range (12 bits), allowing a high correlation success rate over the snow-covered areas. This study demonstrates the value of VHR stereo satellite imagery to map snow depth in remote mountainous areas even when no field data are available.

MONITORING OF FLUVIAL TRANSPORT IN THE MOUNTAIN RIVER BED USING TERRESTRIAL LASER SCANNING

The fluvial transport is the surface process that has a strong impact on the topography changes, especially in mountain areas. Traditional hydrological measurements usually give a good understanding of the river flow, however, the information of the bedload movement in the rivers is still insufficient. In particular, there is limited knowledge about the movement of the largest clasts, i.e. boulders. This investigation addresses mentioned issues by employing Terrestrial Laser Scanning (TLS) to monitor annual changes of the mountain river bed. The vertical changes were estimated based on the Digital Elevation Model (DEM) of difference (DoD) while transported boulders were identified based on the distances between point clouds and RGB-coloured points. Combined RGB point clouds allowed also to measure 3D displacements of boulders. The results showed that the highest dynamic of the fluvial process occurred between years 2012-2013. Obtained DoD clearly indicated alternating zones of erosion and deposition of the sediment finer fractions in the local sedimentary traps. The horizontal displacement of the rock material in the river bed showed high complexity resulting in the displacement of large boulders (major axis about 0.8 m) for the distance up to 2.3 m.

MONITORING OF FLUVIAL TRANSPORT IN THE MOUNTAIN RIVER BED USING TERRESTRIAL LASER SCANNING

Abstract. The fluvial transport is the surface process that has a strong impact on the topography changes, especially in mountain areas. Traditional hydrological measurements usually give a good understanding of the river flow, however, the information of the bedload movement in the rivers is still insufficient. In particular, there is limited knowledge about the movement of the largest clasts, i.e. boulders. This investigation addresses mentioned issues by employing Terrestrial Laser Scanning (TLS) to monitor annual changes of the mountain river bed. The vertical changes were estimated based on the Digital Elevation Model (DEM) of difference (DoD) while transported boulders were identified based on the distances between point clouds and RGB-coloured points. Combined RGB point clouds allowed also to measure 3D displacements of boulders. The results showed that the highest dynamic of the fluvial process occurred between years 2012-2013. Obtained DoD clearly indicated alternating zones of erosion and deposition of the sediment finer fractions in the local sedimentary traps. The horizontal displacement of the rock material in the river bed showed high complexity resulting in the displacement of large boulders (major axis about 0.8 m) for the distance up to 2.3 m.

Impacts of DEM uncertainties on critical source areas identification for non-point source pollution control based on SWAT model

The impacts of different digital elevation model (DEM) resolutions, sources and resampling techniques on nutrient simulations using the Soil and Water Assessment Tool (SWAT) model have not been well studied. The objective of this study was to evaluate the sensitivities of DEM resolutions (from 30m to 1000m), sources (ASTER GDEM2, SRTM and Topo-DEM) and resampling techniques (nearest neighbor, bilinear interpolation, cubic convolution and majority) to identification of non-point source (NPS) critical source area (CSA) based on nutrient loads using the SWAT model. The Xiangxi River, one of the main tributaries of Three Gorges Reservoir in China, was selected as the study area. The following findings were obtained: (1) Elevation and slope extracted from the DEMs were more sensitive to DEM resolution changes. Compared with the results of the 30m DEM, 1000m DEM underestimated the elevation and slope by 104m and 41.57°, respectively; (2) The numbers of subwatersheds and hydrologic response units (HRUs) were considerably influenced by DEM resolutions, but the total nitrogen (TN) and total phosphorus (TP) loads of each subwatershed showed higher correlations with different DEM sources; (3) DEM resolutions and sources had larger effects on CSAs identifications, while TN and TP CSAs showed different response to DEM uncertainties. TN CSAs were more sensitive to resolution changes, exhibiting six distribution patterns at all DEM resolutions. TP CSAs were sensitive to source and resampling technique changes, exhibiting three distribution patterns for DEM sources and two distribution patterns for DEM resampling techniques. DEM resolutions and sources are the two most sensitive SWAT model DEM parameters that must be considered when nutrient CSAs are identified.

Thematic Map Construction of Erosion and Deposition in Rivers Using GIS-based DEM Comparison Technique

Rivers refer to either natural or artificial structures whose primary functions are flood control and water conservation. Due to recent localized torrential downpours led by climate change, large amounts of eroded soil have been carried away, forming deposits downstream, which in turn degrades the capacity to fulfill these functions. To manage rivers more effectively, we need data on riverbed erosion and deposition. However, environmental factors make it challenging to take measurements in rivers, and data errors tend to prevent researchers from grasping the current state of erosions and deposits. In this context, the aim of the present study is to provide basic data required for river management. To this end, the author made annual measurements with a Real-time Kinematic-Global Positioning System (RTK-GPS) and a total station in Pats Cabin Canyon, Oregon, United States, and also prepared thematic maps of erosion and deposition thickness as well as water depth profiles based on a GIS spatial analysis. Furthermore, the author statistically analyzed the accuracy of three dimensional (3D) measurement points and only used the data that falls within two standard deviations (i.e. ±2σ). In addition, the author determined a threshold for a DEM of Difference (DoD) by installing measurement points in the rivers and taking measurements, and then estimated erosion and deposition thickness within a confidence interval of ±0.1m. Based on the results, the author established reliable data on river depth profiles and thematic maps of erosion and deposition thickness using pre-determined work flows. It is anticipated that the riverbed data can be utilized for effective river management.

Effects of different boundary conditions and palaeotopographies on the onshore response of tsunamis in a numerical model – A case study from western Greece

Hydrodynamic numerical models are essential in modern tsunami hazard assessment. They allow the economical simulation of possible tsunami scenarios for areas at risk and provide reliable and detailed insights into local onshore dynamics. This is especially true when simulations are calibrated with field traces of past tsunami inundation events. Following this approach, the current study focuses on palaeotsunami events indicated by sedimentary and geomorphological field traces in the northern Gulf of Kyparissia (NW Greece). Based on three different digital elevation models (DEM) – reflecting the recent and two palaeotopographies – various tsunami wave constellations according to the solitary and N-wave theory are numerically simulated. The main objective is to investigate the effects of both, different palaeotopographies and boundary conditions on the tsunami onshore response in the numerical model.Tsunami landfall related to N-waves is found to be considerably stronger compared to solitary waves. This phenomenon, known as the N-wave effect, is demonstrated for the first time in a specific study area. Inundation dynamics are even stronger affected by the different palaeotopographies, which is due to substantial vertical crust movements in the northern Gulf of Kyparissia considered in the palaeo-DEMs. By applying different waveforms and palaeotopographies, the model achieves close agreement with field observations, altogether revealing a significant tsunami hazard for the Gulf of Kyparissia, which is in contrast to conventional numerical studies of the area. The marked differences between the presented scenarios emphasise the need to consider a wide variety of possible hydrodynamic boundary conditions and probable topographical conditions in order to find scenarios in plausible accordance with palaeotsunami field traces. Once a plausible scenario is found it can be applied to the recent topography in view of a reliable modern hazard assessment.

Assessment of erosion and deposition in steep mountain basins by differencing sequential digital terrain models

Digital elevation models (DEMs) built from repeated topographic surveys permit producing DEM of Difference (DoD) that enables assessment of elevation variations and estimation of volumetric changes through time. In the framework of sediment transport studies, DEM differencing enables quantitative and spatially-distributed representation of erosion and deposition within the analyzed time window, at both the channel reach and the catchment scale. In this study, two high-resolution Digital Terrain Models (DTMs) derived from airborne LiDAR data (2m resolution) acquired in 2005 and 2011 were used to characterize the topographic variations caused by sediment erosion, transport and deposition in two adjacent mountain basins (Gadria and Strimm, Vinschgau - Venosta valley, Eastern Alps, Italy). These catchments were chosen for their contrasting morphology and because they feature different types and intensity of sediment transfer processes. A method based on fuzzy logic, which takes into account spatially variable DTMs uncertainty, was used to derive the DoD of the study area. Volumes of erosion and deposition calculated from the DoD were then compared with post-event field surveys to test the consistency of two independent estimates. Results show an overall agreement between the estimates, with differences due to the intrinsic approximations of the two approaches. The consistency of DoD with post-event estimates encourages the integration of these two methods, whose combined application may permit to overcome the intrinsic limitations of the two estimations. The comparison between 2005 and 2011 DTMs allowed to investigate the relationships between topographic changes and geomorphometric parameters expressing the role of topography on sediment erosion and deposition (i.e., slope and contributing area) and describing the morphology influenced by debris flows and fluvial processes (i.e., curvature). Erosion and deposition relations in the slope-area space display substantial differences between the Gadria and the Strimm basins. While in the former erosion and deposition clusters are reasonably well discriminated, in the latter, characterized by a complex stepped structure, we observe substantial overlapping. Erosion mostly occurred in areas that show persistency of concavity or transformation from convex and flat to concave surfaces, whereas deposition prevailingly took place on convex morphologies. Less expected correspondences between curvature and topographic changes can be explained by the variable sediment transport processes, which are often characterized by alternation of erosion and deposition between different events and even during the same event.

Potential of UAVs for Monitoring Mudflat Morphodynamics (Application to the Seine Estuary, France)

Intertidal mudflats play a critical role in estuarine exchange, connecting marine and continental supplies of nutrients and sediments. However, their complex morphodynamics, associated with a wide range of physical and biological processes, are still poorly understood and require further field investigation. In addition, mudflats are challenging areas for Structure-from-Motion (SfM) photogrammetric surveys. Indeed, the mudflats generally hold back residual tidal water, which can make stereo restitution particularly difficult because of poor correlations or sun-glint effects. This study aims to show the potential of light UAVs (Unmanned Aerial Vehicles) for monitoring sedimentary hydrodynamics at different spatial scales in a silty estuary. For each UAV mission an orthophotograph and a Digital Elevation Model (DEM) are computed. From repeated surveys the diachronic evolution of the area can be observed via DEM differencing. Considering the ground texture in such a context, the stereo restitution process is made possible because of the high spatial resolution of the UAV photographs. Providing a synoptic view as well as high spatial resolution (less than 4 cm), the UAV dataset enables multi-scale approaches from the study of large areas to the morphodynamics of smaller-scale sedimentary structures and the morphodynamics impact of plant ground cover.

Digital Elevation Model Differencing and Error Estimation from Multiple Sources: A Case Study from the Meiyuan Shan Landslide in Taiwan

In this study, six different periods of digital terrain model (DTM) data obtained from various flight vehicles by using the techniques of aerial photogrammetry, airborne LiDAR (ALS), and unmanned aerial vehicles (UAV) were adopted to discuss the errors and applications of these techniques. Error estimation provides critical information for DTM data users. This study conducted error estimation from the perspective of general users for mountain/forest areas with poor traffic accessibility using limited information, including error reports obtained from the data generation process and comparison errors of terrain elevations. Our results suggested that the precision of the DTM data generated in this work using different aircrafts and generation techniques is suitable for landslide analysis. Especially in mountainous and densely vegetated areas, data generated by ALS can be used as a benchmark to solve the problem of insufficient control points. Based on DEM differencing of multiple periods, this study suggests that sediment delivery rate decreased each year and was affected by heavy rainfall during each period for the Meiyuan Shan landslide area. Multi-period aerial photogrammetry and ALS can be effectively applied after the landslide disaster for monitoring the terrain changes of the downstream river channel and their potential impacts.

Surface elevation and mass changes of all Swiss glaciers 1980–2010

Abstract. Since the mid-1980s, glaciers in the European Alps have shown widespread and accelerating mass losses. This article presents glacier-specific changes in surface elevation, volume and mass balance for all glaciers in the Swiss Alps from 1980 to 2010. Together with glacier outlines from the 1973 inventory, the DHM25 Level 1 digital elevation models (DEMs) for which the source data over glacierized areas were acquired from 1961 to 1991 are compared to the swissALTI3D DEMs from 2008 to 2011 combined with the new Swiss Glacier Inventory SGI2010. Due to the significant differences in acquisition dates of the source data used, mass changes are temporally homogenized to directly compare individual glaciers or glacierized catchments. Along with an in-depth accuracy assessment, results are validated against volume changes from independent photogrammetrically derived DEMs of single glaciers. Observed volume changes are largest between 2700 and 2800 m a.s.l. and remarkable even above 3500 m a.s.l. The mean geodetic mass balance is −0.62 ± 0.07 m w.e. yr−1 for the entire Swiss Alps over the reference period 1980–2010. For the main hydrological catchments, it ranges from −0.52 to −1.07 m w.e. yr−1. The overall volume loss calculated from the DEM differencing is −22.51 ± 1.76 km3.

Monitoring channel responses to flood events of low to moderate magnitudes in a bedrock-dominated river using morphological budgeting by terrestrial laser scanning

Changes to channel morphology reflect geomorphic work by flood events of differing magnitude and frequency. Advances in remote sensing and digital terrain processing now allow for sophisticated analysis of spatial and temporal changes in erosion and deposition. Although the morphological budgeting approach using digital elevation models of difference has been widely applied to track volume estimation of changes to erosion and deposition over time, appraisals of geomorphic effectiveness in high-energy confined and partly confined channels are still lacking. This study applied terrestrial laser scanning to monitor three reaches of the Liwu River, a bedrock-dominated river in eastern Taiwan, from 2009 to 2012, to investigate channel responses to flood events of low to moderate magnitude and appraise their geomorphic effectiveness. Variability in geomorphic effectiveness reflected valley confinement and the composition/configuration of geomorphic units on the channel bed. Annual low magnitude flood events reworked gravel and sand deposits, creating local scour and fill (<0.5m in depth) in the confined and in the unconfined reaches. Lower unit stream power in the wider, less-confined reach resulted in longer intervals between phases of boulder reworking relative to the confined reach. Bedrock exposure and stable sediment storage units in the confined reach restricted changes to channel pattern. Successive moderate and low magnitude events in 2012 created an evident erosion of 7556m3 (~1m in depth) and were able to modify channel configuration in partly confined and unconfined reaches. Frequent changes of scour/fill position on the channel bed indicate that the Liwu River is highly sensitive to flood events of low to moderate magnitude. This reflects an active orogenic river system that is characterized by a steep channel and narrow valley floors with limited accommodation space but abundant sediment.

10 year mass balance by glaciological and geodetic methods of Glaciar Bahía del Diablo, Vega Island, Antarctic Peninsula

AbstractWe present new glacier mass-balance field data from Glaciar Bahía del Diablo, Vega Island, northeastern Antarctic Peninsula. The results provided here represent glacier mass-balance data over a 10 year period (2001–11) obtained by the glaciological and geodetic methods relying on field measurements. Glacier surface digital elevation models (DEMs) were obtained in 2001 and 2011 from a kinematic GPS field survey with high horizontal and vertical accuracies. In situ mass-balance data were collected from yearly stake measurements. The results attained by the two methods agree, which may be considered a measure of their accuracy. A cumulative mass change of –1.90 ± 0.31 m w.e. over the 10 year period was obtained from the annual mass-balance field surveys. The total mass change derived from DEM differencing was –2.16 ± 0.23 m w.e.

Evaluating topographic wetness indices across central New York agricultural landscapes

Abstract. Accurately predicting soil moisture patterns in the landscape is a persistent challenge. In humid regions, topographic wetness indices (TWIs) are widely used to approximate relative soil moisture patterns. However, there are many ways to calculate TWIs and very few field studies have evaluated the different approaches – especially in the US. We calculated TWIs using over 400 unique formulations that considered different digital elevation model (DEM) resolutions (cell size), vertical precision of DEM, flow direction and slope algorithms, smoothing via low-pass filtering, and the inclusion of relevant soil properties. We correlated each TWI with observed patterns of soil moisture at five agricultural fields in central NY, USA, with each field visited five to eight times between August and November 2012. Using a mixed effects modeling approach, we were able to identify optimal TWI formulations applicable to moderate relief agricultural settings that may provide guidance for practitioners and future studies. Overall, TWIs were moderately well correlated with observed soil moisture patterns; in the best case the relationship between TWI and soil moisture had an average R2 and Spearman correlation value of 0.61 and 0.78, respectively. In all cases, fine-scale (3 m) lidar-derived DEMs worked better than USGS 10 m DEMs and, in general, including soil properties improved correlations.

Downstream Effects of Recent Reservoir Development on the Morphodynamics of a Meandering Channel: Savery Creek, Wyoming, USA

AbstractRecent reservoir construction on Savery Creek provided an opportunity to examine the downstream effects of a dam on a small, meandering channel. The new dam, completed in 2005, modified the flow regime by reducing the magnitude of spring peaks and increasing baseflows, including a second period of high discharge in the fall. A time series of remotely sensed data spanning 1980–2011 was used to measure lateral migration rates, quantify areas of erosion and deposition, and map spatial patterns of channel change. Both migration rates, and gross erosion and deposition increased during the post‐dam era, although 2 years of exceptionally large snowmelt runoff also occurred during this time. Net sediment flux inferred from the image time series was negative for both the upper and lower reaches for the first photo pair after the dam's completion but became positive for the most recent photos. Detailed topographic surveys of five individual meander bends were used to produce digital elevation models of difference and infer bed material transport rates. For three sites located in the upper reach, downstream increases in transport rate implied a sediment deficit satisfied through channel incision and/or bank erosion. For two sites in the lower reach where sediment supply was greater, larger values of gross erosion were balanced by enhanced deposition and transport rates stabilized or increased along each bend. Together, these results suggest that Savery Creek has entered a period of adjustment as the channel adapts to altered, dam‐regulated supplies of water and sediment. Copyright © 2014 John Wiley &amp; Sons, Ltd.