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991.
992.
Flash floods represent one of the deadliest and costliest natural disasters worldwide. The hydrological analysis of a flash flood event contributes in the understanding of the runoff creation process. This study presents the analysis of some flash flood events that took place in a complex geomorphological Mediterranean River basin. The objective of the present work is to develop the thresholds for a real‐time flash flood forecasting model in a complex geomorphological watershed, based on high‐frequency data from strategically located hydrological and meteorological telemetric stations. These stations provide hourly real‐time data which were used to determine hydrological and meteorological parameters. The main characteristics of various hydrographs specified in this study were the runoff coefficients, lag time, time to peak, and the maximum potential retention. The estimation of these hydrometeorological parameters provides the necessary information in order to successfully manage flash floods events. Especially, the time to peak is the most significant hydrological parameter that affects the response time of an oncoming flash flood event. A study of the above parameters is essential for the specification of thresholds which are related to the geomorphological characteristics of the river basin, the rainfall accumulation of an event, the rainfall intensity, the threshold runoff through karstic area, the season during which the rainfall takes place and the time intervals between the rainstorms that affect the soil moisture conditions. All these factors are combined into a real‐time‐threshold flash flood prediction model. Historical flash flood events at the downstream are also used for the validation of the model. An application of the proposed model is presented for the Koiliaris River basin in Crete, Greece. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
993.
Nathan Alec Conroy Brent David Newman Jeffrey Martin Heikoop George Bradford Perkins Xiahong Feng Cathy Jean Wilson Stan Duane Wullschleger 《水文研究》2020,34(3):749-764
Land surface models and Earth system models that include Arctic landscapes must capture the abrupt hydrological transitions that occur during the annual thaw and deepening of the active layer. In this work, stable water isotopes (δ2H and δ18O) are used to appraise hydrologically significant transitions during annual landscape thaw at the Barrow Environmental Observatory (Utqiaġvik, Alaska). These hydrologically significant periods are then linked to annual shifts in the landscape energy balance, deduced from meteorological data and described by the microclimatic periods: Winter, Pre-Melt, Melt, Post-Melt, Summer, and Freeze-Up. The tight coupling of the microclimatic periods with the hydrological transitions supports the use of microclimatic periods as a means of linking polygonal surface water hydrology to meteorological datasets, which provides a mechanism for improving the representation of polygonal surface water hydrology in process-based models. Rayleigh process reconstruction of the isotopic changes revealed that 19% of winter precipitation was lost to sublimation prior to melting and that 23% of surface water was lost to evaporation during the first 10 days post-melt. This agrees with evaporation rates reported in a separate study using an eddy covariance flux tower located nearby. An additional 17% was lost to evaporation during the next 33 days. Stable water isotopes are also used to identify the dominant sources of surface water to various hydrogeomorphological features prevalent in polygonal terrain (a lake, a low centre polygon centre, troughs within the rims of low centre polygons, flat centre polygon troughs, a high centre polygon trough, and drainages). Hydrogeomorphologies that retained significant old water or acted as snow drifts are isotopically distinct during the Melt Period and therefore are easily distinguished. Biogeochemical changes related to the annual thaw are also reported and coupled to the hydrological transitions, which provides insight into the sources and sinks of these ions to and from the landscape. 相似文献
994.
Inferring autogenically induced depositional discontinuities from observations on experimental deltaic shoreline trajectories 下载免费PDF全文
Palaeo shoreline is a commonly used proxy for palaeo sea level, but only if deposition is continuous and constant will shoreline trajectory T(l) completely capture sea‐level time‐series E(t). Artificial deltas were generated in the Eurotank flume facility under stepwise tectonic subsidence, periodic sea‐level fluctuation and two periodic water‐discharge scenarios, one in‐phase and the other out‐of‐phase with sea level. Independent input variables tectonic subsidence Y, sea level E and water discharge Q (controlling sediment supply S) were varied and dependent output variable shoreline trajectory T was monitored. These experiments confirm that deposition is discontinuous even for continuous sediment supply, and this hinders the inference of sea‐level curve from shoreline trajectory. These results justify the here‐developed methodology for converting shoreline trajectory from the space domain to the time domain, thereby improving the accuracy of the inferred sea‐level curve. 相似文献
995.
Regionalisation of the parameters of the log‐Pearson 3 distribution: a case study for New South Wales,Australia 下载免费PDF全文
The index flood method is widely used in regional flood frequency analysis (RFFA) but explicitly relies on the identification of ‘acceptable homogeneous regions’. This paper presents an alternative RFFA method, which is particularly useful when ‘acceptably homogeneous regions’ cannot be identified. The new RFFA method is based on the region of influence (ROI) approach where a ‘local region’ can be formed to estimate statistics at the site of interest. The new method is applied here to regionalize the parameters of the log‐Pearson 3 (LP3) flood probability model using Bayesian generalized least squares (GLS) regression. The ROI approach is used to reduce model error arising from the heterogeneity unaccounted for by the predictor variables in the traditional fixed‐region GLS analysis. A case study was undertaken for 55 catchments located in eastern New South Wales, Australia. The selection of predictor variables was guided by minimizing model error. Using an approach similar to stepwise regression, the best model for the LP3 mean was found to use catchment area and 50‐year, 12‐h rainfall intensity as explanatory variables, whereas the models for the LP3 standard deviation and skewness only had a constant term for the derived ROIs. Diagnostics based on leave‐one‐out cross validation show that the regression model assumptions were not inconsistent with the data and, importantly, no genuine outlier sites were identified. Significantly, the ROI GLS approach produced more accurate and consistent results than a fixed‐region GLS model, highlighting the superior ability of the ROI approach to deal with heterogeneity. This method is particularly applicable to regions that show a high degree of regional heterogeneity. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
996.
997.
George C. Lee 《地震工程与工程振动(英文版)》2008,7(3):I0001-I0001
During the past several months, we have been considering "Special Issues" on a variety of topics for the journal of Earthquake Engineering and Engineering Vibration. We are pleased to announce that the December 2008 issue will be 相似文献
998.
999.
This study presents ductility demand spectra for single degree of freedom (SDOF) systems under multiple near- and far-fault seismic ground motions. The main innovation has to do with the quantification of the seismic sequence effect directly into ductility demands, a phenomenon which has not been studied in the past. Due to lack of real seismic sequences records, this paper examines only artificial sequences, where they have been generated by a rational and random combination of real single events. A statistical investigation of more than 120 millions dynamic inelastic analyses is conducted to obtain expressions for the ductility demands, in terms of the period of vibration, the viscous damping, the post-yield stiffness and the force reduction factor. It is found that due to the seismic sequence effect, it is certainly insufficient to consider only the ‘design earthquake’, since this traditional hypothesis leads to underestimated ductility demands and therefore to underestimated structural damage. 相似文献
1000.
Orissa is an important area for gem variety of corundum deposits in India. Spectroscopic studies, such as ESR, OAS on samples from Sardapur, Orissa, were carried out to ascertain the colour cause of corundum. Electron spin resonance (ESR) spectroscopic study was carried out on the samples to detect the presence of paramagnetic ions i.e. Fe2+, Fe3+, Ti4+, Cr3+ and V3+ etc. The variable temperature experiment carried out to observe the effect of heating on peak valence state change in paramagnetic ions. Samples were cut and polished to obtain the optical absorption spectrum (OAS) to detect the colour causing transition ions/defect centres. The samples of gem variety were step heated up to 300°C for colour enhancement studies. EPMA analysis has revealed the low chromium concentration in the rubies. The varying hues of red in the corundum are due to the presence of bivalent and trivalent iron and charge transfer process along with Cr3+ absorption in the 550 nm region. 相似文献