Sediment budgeting of short-term backfilling processes: The erosional collapse of a Carolingian canal construction     

Johannes Schmidt  Lukas Werther  Johannes Rabiger-Völlmer  Franz Herzig  Birgit Schneider  Ulrike Werban  Peter Dietrich  Stefanie Berg  Sven Linzen  Peter Ettel  Christoph Zielhofer 《地球表面变化过程与地形》2020,45(14):3449-3462

Sediment budgeting concepts serve as quantification tools to decipher the erosion and accumulation processes within a catchment and help to understand these relocation processes through time. While sediment budgets are widely used in geomorphological catchment-based studies, such quantification approaches are rarely applied in geoarchaeological studies. The case of Charlemagne's summit canal (also known as Fossa Carolina) and its erosional collapse provides an example for which we can use this geomorphological concept and understand the abandonment of the Carolingian construction site. The Fossa Carolina is one of the largest hydro-engineering projects in Medieval Europe. It is situated in Southern Franconia (48.9876°N, 10.9267°E; Bavaria, southern Germany) between the Altmühl and Swabian Rezat rivers. It should have bridged the Central European watershed and connected the Rhine–Main and Danube river systems. According to our dendrochronological analyses and historical sources, the excavation and construction of the Carolingian canal took place in AD 792 and 793. Contemporary written sources describe an intense backfill of excavated sediment in autumn AD 793. This short-term erosion event has been proposed as the principal reason for the collapse and abandonment of the hydro-engineering project. We use subsurface data (drillings, archaeological excavations, and direct-push sensing) and geospatial data (a LiDAR digital terrain model (DTM), a pre-modern DTM, and a 3D model of the Fossa Carolina] for the identification and sediment budgeting of the backfills. Dendrochronological findings and radiocarbon ages of macro remains within the backfills give clear evidence for the erosional collapse of the canal project during or directly after the construction period. Moreover, our quantification approach allows the detection of the major sedimentary collapse zone. The exceedance of the manpower tipping point may have caused the abandonment of the entire construction site. The spatial distribution of the dendrochronological results indicates a north–south direction of the early medieval construction progress. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Tutorial: unified 1D inversion of the acoustic reflection response     

Evert Slob  Kees Wapenaar  Sven Treitel 《Geophysical Prospecting》2020,68(5):1425-1442

Acoustic inversion in one-dimension gives impedance as a function of travel time. Inverting the reflection response is a linear problem. Recursive methods, from top to bottom or vice versa, are known and use a fundamental wave field that is computed from the reflection response. An integral over the solution to the Marchenko equation, on the other hand, retrieves the impedance at any vertical travel time instant. It is a non-recursive method, but requires the zero-frequency value of the reflection response. These methods use the same fundamental wave field in different ways. Combining the two methods leads to a non-recursive scheme that works with finite-frequency bandwidth. This can be used for target-oriented inversion. When a reflection response is available along a line over a horizontally layered medium, the thickness and wave velocity of any layer can be obtained together with the velocity of an adjacent layer and the density ratio of the two layers. Statistical analysis over 1000 noise realizations shows that the forward recursive method and the Marchenko-type method perform well on computed noisy data.  相似文献   

Rainfall Variability in Murang'a District, Kenya: Meteorological Data and Farmers' Perception   总被引：2，自引：0，他引：2  

Mira Ovuka  & Sven Lindqvist 《Geografiska Annaler: Series A, Physical Geography》2000,82(1):107-119

This study examines meteorological data and farmers' perception of rainfall in the Central Highlands of Kenya. Rainfall data from five meteorological stations during the period from 1947 to 1996 were analysed on an annual and a monthly basis. Daily data exist from 1957 and analyses from 1957 to 1996 were done on a daily basis. Discussions were held with 60 farmers about rainfall and its variation. Ten of these farmers were interviewed with a questionnaire about rainfall. Analysing annual precipitation and rain periods gave no clear trends over the study period. Results from analysing the growing seasons for maize, the main annual crop, and periods during which maize plants are sensitive to drought showed decreasing trends in rainfall amounts for the study period. Results from the interviews indicate that most of the farmers think rainfall has decreased over the last 40 years. Farmers'perceptions of rainfall are related to periods when the main food and annual crop require water and not to the periods scientists often analyse, i.e. annual and rain periods. More research and better advice from agricultural extension workers to farmers are necessary to enable this area to sustain itself in sufficient food production if the decreasing trends during the growing seasons and drought-sensitive periods continue.  相似文献   

Basic limnological characteristics of the shallow eutrophic lake Grimnitzsee (Brandenburg, Germany)     

Frank Gervais  Sven Berger  Ilka Schnfelder  Renate Rusche 《Limnologica》1999,29(2):105

The medium shallow lake Grimnitzsee (maximum depth: 9.9 m; mean depth: 4.6 m; area: 7.7 · 10⁶ m²) which is situated in the biosphere reserve “Schorfheide-Chorin” in northern Brandenburg (Germany) was studied in 1994 and 1995. A bathymetric map of Grimnitzsee is given for the first time. The lake is usually polymictic although in 1994 and 1995 relatively long summer stratification was observed due to very high global radiation input. Nutrient concentration, light climate, oxygen status, phytoplankton biomass and the species composition of littoral diatoms characterize the lake as eutrophic. Special features deducible from the lake's polymictic character were the multiple development of aerobic or anaerobic strata above the sediment, the fast recovery of silicon concentration in the water column after diatom sedimentation, the importance of resuspension for the success of planktonic diatom populations, and an only moderate correlation between chlorophyll a concentration and light attenuation as well as seston dry weight probably due to the influence of suspended particles.  相似文献   

Validation of GOME total ozone by means of the Norwegian ozone monitoring network     

G. Hansen  A. Dahlback  F. Tønnessen  T. Svenøe 《Annales Geophysicae》1999,17(3):430-436

The Global Ozone Monitoring Experiment (GOME) onboard the ERS-2 satellite has been in operation since July 1995. The Norwegian ground-based total ozone network has played an important role both in the main validation during the commissioning phase and in the validation of upgraded versions of the analysis algorithms of the instrument. The ground-based network consists of various spectrometer types (Dobson, Brewer, UV filter instruments). The validation of the second algorithm version used until January 1998 reveals a very good agreement between GOME and ground-based data at solar zenith angles <60° and deviations of GOME total ozone data from ground-based data of up to ±60 DU (∼20%) at zenith angles ≥60°. The deviations strongly depend on the season of the year, being negative in summer and positive in winter/spring, The deviations furthermore show a considerable scattering (up to ±25 DU in monthly average values of 5° SZA intervals), even in close spatial and temporal coincidence with ground-based measurements, especially in the high Arctic. The deviations are also dependent on the viewing geometry/ground pixel size with an additional negative offset for the large pixels used in the backswath mode and at solar zenith angles ≥85°, compared to forward-swath pixels.  相似文献   

Can climate variability information constrain a hydrological model for an ungauged Costa Rican catchment?          下载免费PDF全文

Beatriz Quesada‐Montano  Ida K. Westerberg  Diana Fuentes‐Andino  Hugo G. Hidalgo  Sven Halldin 《水文研究》2018,32(6):830-846

Long‐term hydrological data are key to understanding catchment behaviour and for decision making within water management and planning. Given the lack of observed data in many regions worldwide, such as Central America, hydrological models are an alternative for reproducing historical streamflow series. Additional types of information—to locally observed discharge—can be used to constrain model parameter uncertainty for ungauged catchments. Given the strong influence that climatic large‐scale processes exert on streamflow variability in the Central American region, we explored the use of climate variability knowledge as process constraints to constrain the simulated discharge uncertainty for a Costa Rican catchment, assumed to be ungauged. To reduce model uncertainty, we first rejected parameter relationships that disagreed with our understanding of the system. Then, based on this reduced parameter space, we applied the climate‐based process constraints at long‐term, inter‐annual, and intra‐annual timescales. In the first step, we reduced the initial number of parameters by 52%, and then, we further reduced the number of parameters by 3% with the climate constraints. Finally, we compared the climate‐based constraints with a constraint based on global maps of low‐flow statistics. This latter constraint proved to be more restrictive than those based on climate variability (further reducing the number of parameters by 66% compared with 3%). Even so, the climate‐based constraints rejected inconsistent model simulations that were not rejected by the low‐flow statistics constraint. When taken all together, the constraints produced constrained simulation uncertainty bands, and the median simulated discharge followed the observed time series to a similar level as an optimized model. All the constraints were found useful in constraining model uncertainty for an—assumed to be—ungauged basin. This shows that our method is promising for modelling long‐term flow data for ungauged catchments on the Pacific side of Central America and that similar methods can be developed for ungauged basins in other regions where climate variability exerts a strong control on streamflow variability.  相似文献   

Evaluation and modification of some empirical and semi-empirical approaches for prediction of area-storage capacity curves in reservoirs of dams     

Issa E.Issa  Nadhir Al-Ansari  Govand Sherwany  Sven Knutsson 《国际泥沙研究》2017,32(1)

The storage capacity of reservoirs is gradually reduced due to sediment accumulation that causes changes in the area-storage capacity (ASC) curves.Establishing these curves and predicting their future change is an important issue for planners,designers and operators of dams.Many empirical and semiempirical approaches have been suggested for establishing and predicting the future changes for these curves.In this study four empirical and semi-empirical methods were evaluated and three of them were modified to be used for the prediction of changes in the ASC curves due to sedimentation,based on the existing sedimentation survey data for 11 reservoirs in the USK For evaluation,these approaches were reviewed and used to determine sedimentation depth and establishing the ASC curves for the Mosul dam reservoir (MDR),which is the biggest hydraulic structure on the River Tigris in northern Iraq.MDR started operating in 1986 with a storage capacity of 11.11 km3 and a water surface area 380 km2 at normal operation stage (330 m a.s.l.).The results obtained from these methods were evaluated using observed bathymetric survey data that had been collected in 2011 after 25 years of the operation of the dam.The evaluation results showed three methods had presented more accurate results for estimating water depth or sedimentation depth at dam site with percentage error about 1.06-3.30％.Whilst for establishing ASC curves,one method presented good agreement result with survey data.Furthermore,ASC and sedimentation depths at dam site of MDR for periods 50,75,100 and 125 years were estimated using the modified approaches and the area reduction method.The results of the modified methods provided reasonable agreement when compared with the area reduction method proposed by the U.S.Bureau of Reclamation and the agreement became better with an increase in time period.  相似文献   

The impact of interactive visualization on trade-off-based geospatial decision-making     

Goran Milutinović  Ulla Ahonen-Jonnarth  Stefan Seipel  Sven Anders Brandt 《International journal of geographical information science》2019,33(10):2094-2123

In a previous work we developed GISwaps, a novel method for geospatial decision-making based on Even Swaps. In this paper, we present the results of an evaluation of a visualization framework integrated with this method, implemented within a decision support system. This evaluation is based on two different studies. In the quantitative study, 15 student participants used GISwaps with no visual features, and 15 participants used GISwaps with the integrated visual framework, as the tool in a solar farm site location case study. The results of the quantitative evaluation show positive impact of the visualization in terms of increased coherency in trade-offs. The results also show a statistically significant difference in average trade-off values between the groups, with users from the non-visual group setting on average 20% higher trade-off values compared with the users in the visual group. In the qualitative study, we had one expert in GIS, two experts in decision-making and two experts in solar energy as a focus user group. Data in this study were obtained by observations and semi-structured interviews with the participants. The impact of the visualization framework was assessed positively by all participants in the expert group.  相似文献   

Complementing the European earth observation and geographic information body of knowledge with a business‐oriented perspective     

Barbara Hofer  Sven Casteleyn  Estefanía Aguilar‐Moreno  Eva‐Maria Missoni‐Steinbacher  Florian Albrecht  Rob Lemmens  Stefan Lang  Jochen Albrecht  Martyna Stelmaszczuk‐Grska  Glenn Vancauwenberghe  Aida Monfort‐Muriach 《Transactions in GIS》2020,24(3):587-601

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