Investigations du caractère multifractal des débits maximaux annuels de crue / Investigation of multifractality of maximum annual flood discharges

Abstract

Abstract The multifractal analysis of maximum annual flood discharges at 55 stations of the Tunisian gauging network allows one to associate the various statistical moments of surface discharges of the basins through a scale-invariant law. On this basis, a random cascades model is identified. The scale-invariant law obtained for extreme values represents a theoretical foundation for empirical models proposed since the 1960s which link extreme values, and their associated hazards, with surfaces of drainage areas.     

Sediment delivery processes and chemical transport in a small forested basin/Processus de production sédimentaire et transport chimique dans un petit bassin versant forestier

Abstract

Because the properties of eroded soil affect the deposition phenomena and transport capacity of chemical materials by eroded particles, recent research is trying to link the grain-size distribution of the eroded sediment to that of the original soil in order to explain the enrichment of chemical content of the sediment with the respect to the parent soil. In this study, the spatial distribution of nitrogen, phosphorus and total organic carbon was firstly deduced using the measurements carried out in 47 soil samples distributed over a forested basin together with a kriging interpolation method. Then the load of each chemical was calculated at morphological unit and basin scales using the above-mentioned spatial distributions and sediment yield values calculated by the SEDD (SEdiment Delivery Distributed) model, which couples the universal soil loss equation with a spatial disaggregation criterion of sediment delivery processes. Finally, at basin scale, a new expression of the enrichment ratio of a given chemical was applied.     

A reservoir flood forecasting and control system for China / Un système chinois de prévision et de contrôle de crue en barrage

Abstract

Abstract Reservoirs play a vital role in flood prevention and disaster relief in China. The objectives of the project described in this study were to establish a reservoir flood forecasting and control system and to design and develop corresponding application software. This paper introduces the current reservoir flood control and operation practice with this system in China. Using modern integration technologies, an application software for this Reservoir Flood Forecasting and Control System (RFFCS) has been developed and updated since 1995. The structure of the system and its main functions, telemetric data acquisition and processing, the hydrological database, flood forecasting, and reservoir operation components are described in detail. The working environment, key technologies and standardization design are emphasized. Having been successfully applied to 212 reservoirs in China, the software has proved to be reliable and user-friendly. In its latest version, the software supports reservoir flood forecasting and flood dispatch decisions. The future research direction and the extension of the software function are also discussed.     

Tracer tests in fractured rocks with a new fluorescent dye—pyrene-1,3,6,8-tetra sulphonic acid (PTS) / Tests de traçage en roches fracturées avec un nouveau produit fluorescent—l'acide pyrène 1.3.6.8 tétra sulfonique (PTS)

Abstract

Two multi-tracer tests were performed in fissured rocks accessible in underground laboratories to examine a new fluorescent dye: pyrene-1,3,6,8-tetra sulphonic acid (PTS). The first test was carried out at the Lindau Rock Laboratory (LRL), Germany, in a highly permeable ore dike, and the second, at the Grimsel Test Site (GTS), Switzerland, in a heterogeneous granite fault zone (AU 126). At the LRL new tracer was injected together with uranine in a convergent flow field (monopole test), and slightly different tracer breakthrough curves were observed according to different diffusion coefficients of both tracers. The matrix porosity calculated with the aid of the one-dimensional (1-D) single-fissure dispersion model (SFDM) agrees well with that found in earlier tracer tests and with measurements performed on core samples. At the GTS, the PTS tracer was applied together with pyranine in two-well injection–withdrawal (dipole) tests. Both tracers yielded identical tracer concentration curves, which confirm their conservative behaviour. Mathematical simulations performed with the aid of a 3-D numerical model (FRAC3DVS) yielded equally good fits for different sets of parameters, independent of whether matrix porosity was included or neglected. That lack of unique solution and the difficulty in observing the influence of matrix diffusion result from a wide distribution of the transit times of particular streamlines, which is characteristic for injection–withdrawal tests. However, both tracer tests clearly indicated that the new tracer (PTS) behaves conservatively at high pH values and can be successfully used for groundwater labelling.     

Remote sensing algorithms for monitoring eutrophication in Ishizuchi storm water reservoir in Kochi Prefecture,Japan / Algorithmes de télédétection pour la surveillance de l'eutrophisation du réservoir d'orage d'Ishizuchi dans la Préfecture de Kochi,Japon

Abstract

Remote sensing technology is being conceived as a cost-effective tool to monitor the eutrophication problem in shallow inland lakes and reservoirs. The objective of this study is to develop hyperspectral remote sensing algorithms for chlorophyll and accessory pigments retrieval in the Ishizuchi Reservoir in Japan. The laboratory reflectance data of 207 field samples with manipulated pigment and suspended sediment concentrations were measured between 400 and 700 nm with a hyperspectral spectroradiometer, and integrated into 60 contiguous narrow bands. Band ratio and spectral absorption algorithms were developed by regression analysis with the observed chlorophyll measurements, and their estimation accuracies were evaluated using the RMSE of the estimates. Algorithms developed from spectral absorption ratios a(675 nm)/a*(675 nm) for five different classes of total pigment concentrations were more accurate than the algorithms based on band ratios R_rs (538 nm)/R_rs (488 nm), R_rs (581 nm)/R_rs (463 nm) and R_rs (674 nm)/R_rs (622 nm) as a result of removing the influence of overlapping absorption and scattering by water molecules and suspended solids from total absorption spectra.     

Simple water balance modelling of surface reservoir systems in a large data-scarce semiarid region / Modélisation simple du bilan hydrologique de systèmes de réservoirs de surface dans une grande région semi-aride pauvre en données

Abstract

Abstract Water resources in dryland areas are often provided by numerous surface reservoirs. As a basis for securing future water supply, the dynamics of reservoir systems need to be simulated for large river basins, accounting for environmental change and an increasing water demand. For the State of Ceará in semiarid Northeast Brazil, with several thousands of reservoirs, a simple deterministic water balance model is presented. Within a cascade-type approach, the reservoirs are grouped into six classes according to storage capacity, rules for flow routing between reservoirs of different size are defined, and water withdrawal and return flow due to human water use is accounted for. While large uncertainties in model applications exist, particularly in terms of reservoir operation rules, model validation against observed reservoir storage volumes shows that the approach is a reasonable simplification to assess surface water availability in large river basins. The results demonstrate the large impact of reservoir storage on downstream flow and stress the need for a coupled simulation of runoff generation, network redistribution and water use.     

Changes of the 0°C isotherm and the equilibrium line altitude in central Chile during the last quarter of the 20th century / Changements de l'isotherme 0°C et de la ligne d'équilibre des neiges dans le Chili central durant le dernier quart du 20ème siècle

Abstract

An overall retreat of glaciers has been observed in the Andes of central Chile during the last ~100 years. Precipitation is mainly of frontal origin and concentrates in winter months. Analysis of precipitation data shows a decrease until 1976, an increase thereafter north of 34°S and a decrease south of 34°S, but overall no significant trends during the last quarter of the 20th century. Analysis of radiosonde data of central Chile shows mid-tropospheric warming with an elevation increase of the 0°C isotherm of 122 ± 8 m and 200 ± 6 m in winter and summer, respectively, during the 27-year period between 1975 and 2001. The results point to a snowline elevation increase in the region during the last quarter of the 20th century and a concurrent rise of the equilibrium line altitude (ELA) and suggest that mid-troposphere warming is the main cause for glacier retreat in central Chile.     

Modelling the temporal variation in snow-covered area derived from satellite images for simulating/forecasting of snowmelt runoff in Turkey/Modélisation de la variation temporelle de la surface enneigée à partir d'images satellitaires pour la simulation/prévision de l'écoulement de fonte nivale en Turquie

Abstract

Monitoring the change of snow-covered area (SCA) in a basin is vitally important for optimum operation of water resources, where the main contribution comes from snowmelt. A methodology for obtaining the depletion pattern of SCA, which is based on satellite image observations where mean daily air temperature is used, is applied for the 1997 water year and tested for the 1998 water year. The study is performed at the Upper Euphrates River basin in Turkey (10 216 km²). The major melting period in this basin starts in early April. The cumulated mean daily air temperature (CMAT) is correlated to the depletion of snow-covered area with the start of melting. The analysis revealed that SCA values obtained from NOAA-AVHRR satellite images are exponentially correlated to CMAT for the whole basin in a lumped manner, where R ² values of 0.98 and 0.99 were obtained for the water years 1997 and 1998, respectively. The applied methodology enables the interpolation between the SCA observations and extrapolation. Such a procedure reduces the number of satellite images required for analysis and provides solution for the cloud-obscured images. Based on the image availability, the effect of the number of images on the quality of snowmelt runoff simulations is also discussed. In deriving the depletion curve for SCA, if the number of images is reduced, the timing of image analysis within the snowmelt period is found very important. Analysis of the timing of satellite images indicated that images from the early and middle parts of the melt period are more important.     

Improving generalization of artificial neural networks in rainfall–runoff modelling / Amélioration de la généralisation de réseaux de neurones artificiels pour la modélisation pluie-débit

Abstract

Artificial neural networks (ANNs) are general-purpose techniques that can be used for nonlinear data-driven rainfall–runoff modelling. The key issue to construct a good model by means of ANNs is to understand their structural features and the problems related to their construction. Indeed, the quantity and quality of data, the type of noise and the mathematical properties of the algorithm for estimating the usual large number of parameters (weights) are crucial for the generalization performances of ANNs. However, it is well known that ANNs may suffer from poor generalization properties due to the high number of parameters and non-Gaussian data noise. Therefore, in the first part of this paper, the features and problems of ANNs are discussed. Eight Avoiding Overfitting Techniques are then presented, considering that these are methods for improving the generalization of ANNs. For this reason, they have been tested on two case studies—rainfall–runoff data from two drainage basins in the south of Italy—in order to gain insight into their properties and to investigate if there is one that absolutely gives the best performance.     

大陆造山带区调填图中几个地质问题及其研究方法探讨

对我国区调填图工作历程与现状进行概述基础上,对造山带的主要特点,构造岩片的含义,构造岩片填图法的理论依据、基本工作程序及实施要点作了论述;对造山带中常见的"混杂岩"、强烈构造变形变质的层状变质岩、穹隆状变质地质体的主要特征、产出的地质构造条件及其成因机制等进行了较全面总结和分析;建议将"混杂岩"和"穹隆状变质地质体"分别划分为蛇绿混杂岩、火山混杂岩、滑积混杂岩、构造混杂岩和变质核杂岩、花岗岩底辟穹隆(岩浆核杂岩)、片麻岩穹隆、构造穹隆等类型。