The application of caesium‐137 measurements to investigate floodplain deposition in a large semi‐arid catchment in Queensland,Australia: a low‐fallout environment

Floodplains comprise geomorphologically important sources and sinks for sediments and associated pollutants, yet the sedimentology of large dryland floodplains is not well understood. Processes occurring on such floodplains are often difficult to observe, and techniques used to investigate smaller perennial floodplains are often not practical in these environments. This study assesses the utility of ¹³⁷Cs inventory and depth‐profile techniques for determining relative amounts of floodplain sedimentation in the Fitzroy River, northeastern Australia; a 143 000 km² semi‐arid river system. Caesium‐137 inventories were calculated for floodplain and reference location bulk soil cores collected from four sites. Depth profiles of ¹³⁷Cs concentration from each floodplain site and a reference location were recorded. The areal density of ¹³⁷Cs at reference locations ranged from 13 to 978 Bq m^–2 (0–1367 Bq m^–2 at the 95% confidence interval), and the mean value ± 2 (standard error of the mean) was 436 ± 264 Bq m^–2, similar to published data from other Southern Hemisphere locations. Floodplain inventories ranged from 68 to 1142 Bq m^–2 (0–1692 Bq m^–2 at the 95% confidence interval), essentially falling within the range of reference inventory values, thus preventing calculation of erosion or deposition. Depth‐profiles of ¹³⁷Cs concentration indicate erosion at one site and over 66 cm of deposition at another since 1954. Analysis of ^239+240Pu concentrations in a depositional core substantiated the interpretation made from ¹³⁷Cs data, and depict a more tightly constrained peak in concentration. Average annual deposition rates range from 0 to 15 mm. The similarity between floodplain and reference bulk inventories does not necessarily indicate a lack of erosion or deposition, due to low ¹³⁷Cs fallout in the region and associated high measurement uncertainties, and a likely influence of gully and bank eroded sediments with no or limited adsorbed ¹³⁷Cs. In this low‐fallout environment, detailed depth‐profile data are necessary for investigating sedimentation using ¹³⁷Cs. Copyright © 2009 John Wiley & Sons, Ltd.     

Developing channel and floodplain dimensions with limited data: a case study in the Amazon Basin

This research builds on the concept of hydraulic geometry and presents a methodology for estimating bankfull discharge and the hydraulic geometry coefficients and exponents for a station using limited data; only stage‐discharge and Landsat imagery. The approach is implemented using 82 streamflow gauging locations in the Amazon Basin. Using the estimated values for the hydraulic geometry relations, bankfull discharge, discharge data above bankfull and upstream drainage area at each site, relationships for estimating channel and floodplain characteristics as a function of drainage area are developed. Specifically, this research provides relationships for estimating bankfull discharge, bankfull depth, bankfull width, and floodplain width as a function of upstream drainage area in the Amazon Basin intended for providing reasonable cross‐section estimates for large scale hydraulic routing models. The derived relationships are also combined with a high resolution drainage network to develop relationships for estimating cumulative upstream channel lengths and surface areas as a function of the specified minimum channel width ranging from 2 m to 1 km (i.e. threshold drainage areas ranging from 1 to 431,000 km²). At the finest resolution (i.e. all channels greater than 2 m or a threshold area of 1 km²), the Amazon Basin contains approximately 4.4 million kilometers of channels with a combined surface area of 59,700 km². The intended use of these relationships is for partitioning total floodable area (channels versus lakes and floodplain lakes) obtained from remote sensing for biogeochemical applications (e.g. quantifying CO₂ evasion in the Amazon Basin). Copyright © 2011 John Wiley & Sons, Ltd.     

Large‐scale modelling of channel flow and floodplain inundation dynamics and its application to the Pantanal (Brazil)

For large‐scale sites, difficulties for applying coupled one‐dimensional (1D)/2D models for simulating floodplain inundation may be encountered related to data scarcity, complexity for establishing channel–floodplain connections, computational cost, long duration of floods and the need to represent precipitation and evapotranspiration processes. This paper presents a hydrologic simulation system, named SIRIPLAN, developed to accomplish this aim. This system is composed by a 1D hydrodynamic model coupled to a 2D raster‐based model, and by two modules to compute the vertical water balance over floodplain and the water exchanges between channel and floodplain. Results are presented for the Upper Paraguay River Basin (UPRB), including the Pantanal, one of the world's largest wetlands. A total of 3965 km of river channels and 140 000 km² of floodplains are simulated for a period of 11 years. Comparison of observed and calculated hydrographs at 15 gauging stations showed that the model was capable to simulate distinct, complex flow regimes along main channels, including channel‐floodplain interactions. The proposed system was also able to reproduce the Pantanal seasonal flood pulse, with estimated inundated areas ranging from 35 000 km² (dry period) to more than 120 000 km² (wet period). Floodplain inundation maps obtained with SIRIPLAN were consistent with previous knowledge of Pantanal dynamics, but comparison with inundation extent provided by a previous satellite‐based study indicates that permanently flooded areas may have been underestimated. The results obtained are promising, and further work will focus on improving vertical processes representation over floodplains and analysing model sensitivity to floodplain parameters, time step and precipitation estimates uncertainty. Copyright © 2010 John Wiley & Sons, Ltd.     

The influence of vertical water balance on modelling Pantanal (Brazil) spatio‐temporal inundation dynamics

The current benchmark approach for mathematical modelling of floodplain hydrologic regime consists of dynamically coupling one‐dimensional (1D) and two‐dimensional (2D) models for flow routing along the main channel and the floodplain, respectively. For large‐scale sites, floodplain inundation may spread over hundreds of square kilometres and may last for many months and even influence seasonal floods in following years. This paper aims at evaluating the effect of vertical water balance representation on modelling a large‐scale floodplain. The Pantanal wetland (140 000 km²; Brazil) is simulated using a 1D/2D coupled model approach, which also considers the representation of vertical water processes over the floodplain. Four scenarios are simulated: Baseline (the reference scenario), NoVertBal (in which the vertical water balance over floodplain is turned off) and ETp+1 and ETp?1 scenarios, characterized by artificially increasing or decreasing daily potential evapotranspiration (ETp) by 1 mm, respectively. The results showed that the effect of the vertical water processes scenarios on channel flow is directly dependent on the lateral exchange of water between the channel and floodplain in the upstream river reach. This influence is stronger when there is a gain of water from the floodplain to the channel. The inclusion of these vertical water processes into floodplain modelling was essential to represent the process of wetting and drying, this effect being more relevant for areas not directly connected to main channels, which is a characteristic of the Pantanal region. Copyright © 2013 John Wiley & Sons, Ltd.     

内蒙古察干淖尔盐湖29-8ka时段的湖面波动

以内蒙古锡林郭勒盟苏尼特右旗的察干淖尔盐湖为研究对象,利用OSL(Optically Stimulated Luminescence)测年技术和DEM(Digital Elevation Model)数字高程模型,重建湖面波动历史,探讨湖泊形成与环境变化过程.通过对察干淖尔盐湖周边大量的野外考察,发现湖泊周围存在海拔高程为1020、978和973 m的三级古湖岸阶地,其OSL测年结果分别为29.2±1.3、18.4±0.8及8.2 8.0 ka.通过湖岸阶地高程恢复的上述3个时期的古湖面积分别为3600、500和400 km~2.与现今的干旱盐湖景观迥然不同.     

TerEx Toolbox for semi‐automated selection of fluvial terrace and floodplain features from lidar

Terraces and floodplains are important indicators of near‐channel sediment dynamics, serving as potential sediment sources and sinks. Increasing availability of high resolution topography data over large areas calls for development of semi‐automated techniques for identification and measurement of these features. In this study we introduce a novel tool that accommodates user‐defined parameters including, a local‐relief threshold selected by a variable‐size moving window, minimum area threshold, and maximum distance from the channel to identify and map discrete terrace and floodplain surfaces. Each of the parameters can easily be calibrated for a given watershed or reach. Subsequently, the tool automatically measures planform area, absolute elevation, and height relative to the local river channel for each terrace polygon. We validate the tool in two locations where terrace maps were previously developed via manual digitization from lidar and extensive field mapping campaigns. The tool is also tested on six different types of rivers to provide examples of starting selection parameters, and to test effectiveness of the tool across a wide range of landscapes. Generally, the tool provides a high quality draft map of terrace and floodplain surfaces across the wide range of environmental conditions for which it has been tested. We find that the tool functions best in catchments where the terraces are spatially extensive, with distinct differences between the terrace and floodplain. The most challenging environments for semi‐automated terrace and floodplain mapping include steep catchments with dense riparian vegetation, and very small terraces (~10 m² in areal extent). We then apply the tool to map terraces and floodplains in the Root River watershed, southeastern Minnesota and generate exceedance plots for terrace heights. These plots provide a first pass analysis to indicate the tributaries and reaches of the river where terraces constitute a significant source of sediment. Copyright © 2013 John Wiley & Sons, Ltd.     

The distribution of tephra deposits and reconstructing the parameters of 1973 eruption on Tyatya Volcano,Kunashir I., Kuril Islands

We studied the distribution of tephra deposits discharged by the basaltic (52–54% SiO₂) explosive eruption of 1973 on Tyatya Volcano (Kunashir I., Kuril Islands). We made maps showing lines of equal tephra thickness (isopachs) and lines of maximum size of pyroclastic particles (isopleths). These data were used to find the parameters of explosive activity using the standard techniques for each of the two phases of this eruption separately. The first, phreatomagmatic, phase discharged 0.008 km³ of tephra during the generation of maars on the volcano’s northern slope. The tephra mostly consisted of fragmented host rocks with admixtures of fragments of low vesiculated juvenile basalt. The phase lasted 20 hours, the rate of pyroclastic discharge was 2 × 10⁵ kg/s; the eruptive plume reached heights of 4–6 km with wind speeds within 10 m/s. The second, magmatic, phase discharged 0.07 km³ of tephra during the generation of the Otvazhnyi scoria cone on the volcano’s southeastern slope. The tephra mostly consisted of juvenile basaltic scoria. The highly explosive Plinian part of this phase lasted 36 hours, the rate of pyroclastic discharge was 8 × 10⁵ kg/s; the eruptive plume reached heights of 6–8 km with wind speeds of 10–20 m/s. The total tephra volume discharged by the eruption was approximately 0.08 km³; the total amount of ejected pyroclastic material (including the resulting monogenic edifices) was 0.11 km³; the volume of erupted magma was 0.05 km³ (the conversion was based on 2800 kg/m³ density); the volcanic explosivity index, or VEI, was 3. The production rate of the Tyatya plumbing system is estimated as 3 × 10⁵ m³ magma per annum.     

Seasonal inundation patterns in two large savanna floodplains of South America: the Llanos de Moxos (Bolivia) and the Llanos del Orinoco (Venezuela and Colombia)

Inundation patterns in two of the largest savanna floodplains of South America were studied by analysis of the 37‐GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer (Nimbus‐7 satellite). Flooded area was estimated at monthly intervals for January 1979 through to August 1987 using mixing models that account for the major landscape units with distinctive microwave emission characteristics. Results are presented separately for five subregions in each of the two floodplain regions to show the spatial as well as temporal variability in inundation patterns. The total area inundated during the 9 years varied between 2069 and 78 460 km² in the Llanos de Moxos (also spelled as Mojos; median area, 23 383 km²) and 1278 and 105 454 km² in the Llanos del Orinoco (median, 25 374 km²), not including the open‐water area of permanent lakes and river channels. The correlation between flooded area and river stage was used to extend the inundation records over a 30‐year period in the Moxos (1967–97) and a 58‐year period (1927–85) in the Orinoco. Interannual variability in inundation is greater in the Moxos than the Orinoco. Comparison of these data, however, with a previously published analysis of the Pantanal wetland shows that inundation patterns in these two floodplain regions are not as variable across years as they are in the Pantanal. Copyright © 2004 John Wiley & Sons, Ltd.     

Impact of urbanization on suspended sediment and organic matter fluxes from small catchments in Tahiti

This study provides an initial characterization of pollution associated with storm runoff in Tahiti. A thousand floodwater samples were collected from three representative catchments and subsequently analysed. The main pollution parameters chosen were total suspended sediment (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total nitrogen (TN) and Total Phosphorus (TP). First, organic pollution appeared to be related closely to sediment, thus TSS could be used as a global indicator. Next, regression models between an event's TSS load and its hydrological characteristics were used to obtain annual load estimates. Great interannual variability was found to be strongly influenced by the few major floods that occur during the rainy season. Our results also emphasize the importance of the impact of urbanization on solid catchment exportation: from 60 TSS t/km²/year in a natural forested catchment, fluxes reached more than 700 TSS t/km²/year during preparatory urbanization earthworks before stabilizing at 140 TSS t/km²/year in a consolidated urbanized area. Clearly, runoff effects need to be taken into consideration for effective urban planning and for the preservation of the coastal environment in Tahiti. Copyright © 2002 John Wiley & Sons, Ltd.     

Controls on the occurrence and prevalence of floodplain channels in meandering rivers

The process of channelization on river floodplains plays an essential role in regulating river sinuosity and creating river avulsions. Most channelization occurs within the channel belt (e.g. chute channels), but growing evidence suggests some channels originate outside of the channel‐belt in the floodplain. To understand the occurrence and prevalence of these floodplain channels we mapped 3064 km² of floodplain in Indiana, USA using 1.5 m resolution digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) data. We find the following range of channelization types on floodplains in Indiana: 6.8% of floodplain area has no evidence of channelization, 55.9% of floodplains show evidence (e.g. oxbow lakes) of chute‐channel activity in the channel belt, and 37.3% of floodplains contain floodplain channels that form long, coherent down‐valley pathways with bifurcations and confluences, and they are active only during overbank discharge. Whereas the first two types of floodplains are relatively well studied, only a few studies have recognized the existence of floodplain channels. To understand why floodplain channels occur, we compared the presence of channelization types with measured floodplain width, floodplain slope, river width, river meander rate, sinuosity, flooding frequency, soil composition, and land cover. Results show floodplain channels occur when the fluvial systems are characterized by large floodplain‐to‐river widths, relatively higher meandering rates, and are dominantly used for agriculture. More detailed reach‐scale mapping reveals that up to 75% of channel reaches within floodplain channels are likely paleo‐meander cutoffs. The meander cutoffs are connected by secondary channels to form floodplain channels. We suggest that secondary channels within floodplains form by differential erosion across the floodplain, linking together pre‐existing topographic lows, such as meander cutoffs. Copyright © 2016 John Wiley & Sons, Ltd.     

Estimating historic lake stages from one‐time snapshot,the Shuttle Radar Topography Mission of 2000

Lake studies play an important role in water management, ecology and other environmental issues. Monitoring lake stages is typically the first step on the lake studies. However, for the Prairie Pothole Region (PPR) of North America with millions of small lakes and potholes, onsite measurements for lake stages are almost impossible with the conventional gage stations due to the limited accessibility to lakes and the requirement of economical and human resources. To overcome this limitation, we employed the remote‐sensing approach to extract lake stages in PPR for bulk processing. To estimate lake stages, several image‐processing techniques were used with the Shuttle Radar Topography Mission (SRTM) data in January, 2000, a one‐time snapshot useful in historic lake level reconstruction. In this research, image processing techniques, for example, averaging, Fast Fourier Transform (FFT), Lee‐Sigma filtering were applied and masking with Canny Edge Detector (CED) and semi‐automated contouring were developed for lake stage estimation. In terms of simplicity, averaging might be useful if 1·5 m of the local bias for the study area in stage estimates. However, the FFT and Lee‐Sigma methods were slightly better than averaging. Masking with CED and semi‐automated contouring provided outstanding accuracy in the estimation. The masking and contouring methods provided ± 0·5 m of stage differences for relatively large lakes greater than 10 km² when compared with stage reading in spite of their calculation complexities and was shown as the best approaches among implemented methods in this study. Copyright © 2010 John Wiley & Sons, Ltd.     

A method for semi‐automated objective quantification of linear bedforms from multi‐scale digital elevation models

The increasing availability of large, detailed digital representations of the Earth's surface demands the application of objective and quantitative analyses. Given recent advances in the understanding of the mechanisms of formation of linear bedform features from a range of environments, objective measurement of their wavelength, orientation, crest and trough positions, height and asymmetry is highly desirable. These parameters are also of use when determining observation‐based parameters for use in many applications such as numerical modelling, surface classification and sediment transport pathway analysis. Here, we (i) adapt and extend extant techniques to provide a suite of semi‐automatic tools which calculate crest orientation, wavelength, height, asymmetry direction and asymmetry ratios of bedforms, and then (ii) undertake sensitivity tests on synthetic data, increasingly complex seabeds and a very large‐scale (39 000 km²) aeolian dune system. The automated results are compared with traditional, manually derived, measurements at each stage. This new approach successfully analyses different types of topographic data (from aeolian and marine environments) from a range of sources, with tens of millions of data points being processed in a semi‐automated and objective manner within minutes rather than hours or days. The results from these analyses show there is significant variability in all measurable parameters in what might otherwise be considered uniform bedform fields. For example, the dunes of the Rub' al Khali on the Arabian peninsula are shown to exhibit deviations in dimensions from global trends. Morphological and dune asymmetry analysis of the Rub' al Khali suggests parts of the sand sea may be adjusting to a changed wind regime from that during their formation 100 to 10 ka BP. Copyright © 2012 John Wiley & Sons, Ltd.     

Simulating hydrologic and hydraulic processes throughout the Amazon River Basin

Presented here is a model framework based on a land surface topography that can be represented with various degrees of resolution and capable of providing representative channel/floodplain hydraulic characteristics on a daily to hourly scale. The framework integrates two models: (1) a water balance model (WBM) for the vertical fluxes and stores of water in and through the canopy and soil layers based on the conservation of mass and energy, and (2) a routing model for the horizontal routing of surface and subsurface runoff and channel and floodplain waters based on kinematic and diffusion wave methodologies. The WBM is driven by satellite‐derived precipitation (TRMM_3B42) and air temperature (MOD08_M3). The model's use of an irregular computational grid is intended to facilitate parallel processing for applications to continental and global scales. Results are presented for the Amazon Basin over the period Jan 2001 through Dec 2005. The model is shown to capture annual runoff totals, annual peaks, seasonal patterns, and daily fluctuations over a range of spatial scales (>1, 000 to < 4·7M km²). For the period of study, results suggest basin‐wide total water storage changes in the Amazon vary by approximately + /? 5 to 10 cm, and the fractional components accounting for these changes are: root zone soil moisture (20%), subsurface water being routed laterally to channels (40%) and channel/floodplain discharge (40%). Annual variability in monthly water storage changes by + /? 2·5 cm is likely due to 0·5 to 1 month variability in the arrival of significant rainfall periods throughout the basin. Copyright © 2009 John Wiley & Sons, Ltd.     

Rate of floodplain reworking in response to increasing storm‐induced floods,Squamish River,south‐western British Columbia,Canada

Relations among hydroclimatic and channel planform changes on Squamish River are presented for the period 1956–2007. Squamish River basin occupies 3600 km² of mountainous terrain in south‐western British Columbia, about 50 km north of Vancouver. The magnitude, volume and duration of extreme floods (Q ≥ 1500 m³/s) exhibit respective temporal increases of 50, 450 and 300%. The increase in extreme floods is attributed to the intensification of late‐season (August–December) Pacific storms that have produced increases in precipitation amounts, intensity and duration of respectively 340, 200 and 200% over the same period. Changes in floodplain‐surface area calculated from the geographic information system (GIS) differencing of sequential large‐scale aerial photographs indicate that the rate of geomorphic change in Squamish River has accelerated during the 1980s to the mid‐1990s. Among four study reaches of varying planform, erosional, depositional and cumulative changes in floodplain surface‐area have rapidly increased. Channel‐change activity after 1980 has increased by a factor of two to six compared with the period prior to 1980. Erosion is currently outpacing deposition in the majority of study reaches. Although channel geometry generally exhibits no uniform pattern of response to the increase in extreme floods, the meandering reaches have straightened over the duration of the study period. The increase in the magnitude and duration of the annual flood appears to be the principal cause of this recent acceleration of channel change. Copyright © 2010 John Wiley & Sons, Ltd.     

Can channel banks be the dominant source of fine sediment in a UK river?: an example using 137Cs to interpret sediment yield and sediment source

Cultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the caesium‐137 (¹³⁷Cs) inventories of lake and floodplain cores as well as the ¹³⁷Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment. Low ¹³⁷Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. Caesium‐137 activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks. Pre‐1963 sediment yields were approximately 11.2 t km^?2 yr^?1 and post‐1963 was approximately 11.9 t km^?2 yr^?1. The lack of increased sediment yield post‐1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km^?2 yr^?1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material. The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of ¹³⁷Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilization of ¹³⁷Cs from sedimentary deposits. Copyright © 2016 John Wiley & Sons, Ltd.     

Geographical characteristics of China’s wetlands derived from remotely sensed data

In this paper, we report the first wetland mapping of the entire China using Landsat enhanced thematic mapper plus (ETM+) data. These data were obtained from the Global Land Cover Facility at the University of Maryland spanning from 1999 to 2002. A total of 597 scenes of Landsat images were georeferenced and mosaiced. Manual image interpretation of satellite images was aided with elevation data, soil data, land cover/land use data and Google Earth. The minimum mapping unit is 10 pixel × 10 pixel, equivalent...     

Season‐based rainfall–runoff modelling using the probability‐distributed model (PDM) for large basins in southeastern Brazil

Southeastern Brazil is characterized by seasonal rainfall variability. This can have a great social, economic, and environmental impact due to both excessive and deficient water availability. During 2014 and 2015, the region experienced one of the most severe droughts since 1960. The resulting water crisis has seriously affected water supply to the metropolitan region of São Paulo and hydroelectric power generation throughout the entire country. This research considered the upstream basins of the southeastern Brazilian reservoirs Cantareira (2,279 km²; water supply) and Emborcação (29,076 km²), Três Marias (51,576 km²), Furnas (52,197 km²), and Mascarenhas (71,649 km²; hydropower) for hydrological modelling. It made the first attempt at configuring a season‐based probability‐distributed model (PDM‐CEMADEN) for simulating different hydrological processes during wet and dry seasons. The model successfully reproduced the intra‐annual and interannual variability of the upstream inflows during 1985–2015. The performance of the model was very satisfactory not only during the wet, dry, and transitional seasons separately but also during the whole period. The best performance was obtained for the upstream basin of Furnas, as it had the highest quality daily precipitation and potential evapotranspiration data. The Nash–Sutcliffe efficiency and logarithmic Nash–Sutcliffe efficiency were 0.92 and 0.93 for the calibration period 1984–2001, 0.87 and 0.88 for the validation period 2001–2010, and 0.93 and 0.90 for the validation period 2010–2015, respectively. Results indicated that during the wet season, the upstream basins have a larger capacity and variation of soil water storage, a larger soil water conductivity, and quicker surface water flow than during the dry season. The added complexity of configuring a season‐based PDM‐CEMADEN relative to the traditional model is well justified by its capacity to better reproduce initial conditions for hydrological forecasting and prediction. The PDM‐CEMADEN is a simple, efficient, and easy‐to‐use model, and it will facilitate early decision making and implement adaptation measures relating to disaster prevention for reservoirs with large‐sized upstream basins.     

Sediment production in large gullies of the Mediterranean area (NE Spain) from high‐resolution digital elevation models and geographical information systems analysis

Recent studies in the Mediterranean area have shown gully erosion to have a very significant contribution to total soil loss. In the Penedès vineyard region (NE Spain), between 15 and 27% of the land is affected by large gullies and gully‐wall retreat seems to be an ongoing process. Multi‐date digital elevation model (DEM) analysis has allowed computation of sediment production by gully erosion, showing that the sediment production rates are very high by the, up‐to‐date, usual global standards. Here, we present a study carried out using large‐scale multi‐date (1975 and 1995) aerial photographs (1 : 5000 and 1 : 7000) to monitor sediment yield caused by large gullies in the Penedès region (NE Spain). High‐resolution DEMs (1 m grid) were derived and analysed by means of geographical information systems techniques to determine the gully erosion rates. Rainfall characteristics within the same study period were also analysed in order to correlate with the soil loss produced. Mass movement was the main process contributing to total sediment production. This process could have been favoured by rainfalls recorded during the period: 58% of the events were of an erosive character and showed high kinetic energy and erosivity. A sediment production rate of 846 ± 40 Mg ha^?1 year^?1, a sediment deposition rate of 270 ± 18 Mg ha^?1 year^?1 and a sediment delivery ratio of 68·1% were computed for a gully area of 0·10 km². The average net erosion within the study period (1975–95) was 576 ± 58 Mg ha^?1 year^?1. In comparison with other methods, the proposed method also includes sediment produced by processes other than only overland flow, i.e. downcutting, headcutting, and mass movements and bank erosion. Copyright © 2003 John Wiley & Sons, Ltd.     

AntarcticaLC2000: The new Antarctic land cover database for the year 2000

Antarctica plays a key role in global energy balance and sea level change. It has been conventionally viewed as a whole ice body with high albedo in General Circulation Models or Regional Climate Models and the differences of land cover has usually been overlooked. Land cover in Antarctica is one of the most important drivers of changes in the Earth system. Detailed land cover information over the Antarctic region is necessary as spatial resolution improves in land process models. However, there is a lack of complete Antarctic land cover dataset derived from a consistent data source. To fill this data gap, we have produced a database named Antarctic Land Cover Database for the Year 2000 (AntarcticaLC2000) using Landsat Enhanced Thematic Mapper Plus (ETM+) data acquired around 2000 and Moderate Resolution Imaging Spectrometer (MODIS) images acquired in the austral summer of 2003/2004 according to the criteria for the 1:100000-scale. Three land cover types were included in this map, separately, ice-free rocks, blue ice, and snow/firn. This classification legend was determined based on a review of the land cover systems in Antarctica (LCCSA) and an analysis of different land surface types and the potential of satellite data. Image classification was conducted through a combined usage of computer-aided and manual interpretation methods. A total of 4067 validation sample units were collected through visual interpretation in a stratified random sampling manner. An overall accuracy of 92.3% and the Kappa coefficient of 0.836 were achieved. Results show that the areas and percentages of ice-free rocks, blue ice, and snow/firn are 73268.81 km² (0.537%), 225937.26 km² (1.656%), and 13345460.41 km² (97.807%), respectively. The comparisons with other different data proved a higher accuracy of our product and a more advantageous data quality. These indicate that AntarcticaLC2000, the new land cover dataset for Antarctica entirely derived from satellite data, is a reliable product for a broad spectrum of applications.