New ages from the Mauritanides Belt: recognition of Archean IOCG mineralization at Guelb Moghrein,Mauritania

The Guelb Moghrein Fe oxide–Cu–Au–Co (IOCG) deposit is located in the northern part of the Mauritanides chain at the western edge of the West African Craton. It is commonly held that the orogenic belt has experienced a polyphase tectonothermal evolution, including two Panafrican and one Variscan event. Dating of two distinct morphological types of hydrothermal monazite and xenotime from Guelb Moghrein yielded in situ U–Pb ages of 2492 ± 9 and 1742 ± 12 Myr respectively. Such ages have not been reported previously from the region which is conspicuous by the widespread occurrence of banded iron formations, more akin to Proterozoic or Archean than to Paleozoic settings. The supracrustal rocks are thought, therefore, to represent a greenstone terrane that was mineralized by hydrothermal fluids during the late Archean and reactivated by middle Proterozoic fluid flow. Final emplacement at the current position on the West African Craton was at ～300 Ma during Gondwana–Laurentia collision.     

On the relation between the Sun's (geocentric) angular diameter and the observed (topocentric) ‘drift time’

It is pointed out that the relation between the Sun's geocentric diameter and the so-called drift time observed on the Earth's surface does not depend on topocentric data (distance, declination, parallax, refraction), but only on the geocentric values of distance, declination, and variation of right ascension.     

Comparison of hydrodynamic models of different complexities to model floods with emergency storage areas

A flood emergency storage area (polder) is used to reduce the flood peak in the main river and hence, protect downstream areas from being inundated. In this study, the effectiveness of a proposed flood emergency storage area at the middle Elbe River, Germany in reducing the flood peaks is investigated using hydrodynamic modelling. The flow to the polders is controlled by adjustable gates. The extreme flood event of August 2002 is used for the study. A fully hydrodynamic 1D model and a coupled 1D–2D model are applied to simulate the flooding and emptying processes in the polders and flow in the Elbe River. The results obtained from the 1D and 1D–2D models are compared with respect to the peak water level reductions in the Elbe River and flow processes in the polders during their filling and emptying. The computational time, storage space requirements and modelling effort for the two models are also compared. It is concluded that a 1D model may be used to study the water level and discharge reductions in the main river while a 1D-2D model may be used when the study of flow dynamics in the polder is of particular interest. Further, a detailed sensitivity analysis of the 1D and 1D–2D models is carried out with respect to Manning's n values, DEMs of different resolutions, number of cross-sections used and the gate opening time as well as gate opening/closing duration. Copyright © 2008 John Wiley & Sons, Ltd.     

The effects of spiral arms on the multi-phase ISM

Statistical parameters of the ISM driven by thermal energy injectionsfrom supernova explosions have been obtained from 3D, nonlinear,magnetohydrodynamic, shearing-box simulations for spiral arm andinterarm regions. The density scale height obtained for the interarm regionsis 50% larger than within the spiral arms because of thehigher gas temperature. The filling factorof the hot gas is also significantly larger between the armsand depends sensitively on magnetic field strength.     

Probabilistic flood forecasting for a mountainous headwater catchment using a nonparametric stochastic dynamic approach

Abstract

Hydrological models are commonly used to perform real-time runoff forecasting for flood warning. Their application requires catchment characteristics and precipitation series that are not always available. An alternative approach is nonparametric modelling based only on runoff series. However, the following questions arise: Can nonparametric models show reliable forecasting? Can they perform as reliably as hydrological models? We performed probabilistic forecasting one, two and three hours ahead for a runoff series, with the aim of ascribing a probability density function to predicted discharge using time series analysis based on stochastic dynamics theory. The derived dynamic terms were compared to a hydrological model, LARSIM. Our procedure was able to forecast within 95% confidence interval 1-, 2- and 3-h ahead discharge probability functions with about 1.40 m³/s of range and relative errors (%) in the range [–30; 30]. The LARSIM model and the best nonparametric approaches gave similar results, but the range of relative errors was larger for the nonparametric approaches.

Editor D. Koutsoyiannis; Associate editor K. Hamed

Citation Costa, A.C., Bronstert, A. and Kneis, D., 2012. Probabilistic flood forecasting for a mountainous headwater catchment using a nonparametric stochastic dynamic approach. Hydrological Sciences Journal, 57 (1), 10–25.