Spillway design floods in Sweden: I. New guidelines

Abstract

The new Swedish guidelines for the estimation of design floods for dams and spillways are presented, with emphasis on high-hazard dams. The method is based on a set of regional design precipitation sequences, rescaled for basin area, season and elevation above sea level, and a full hydrological model. A reservoir operation strategy is also a fundamental component of the guidelines. The most critical combination of flood generating factors is searched by systematically inserting the design precipitation sequence into a ten year climatological record, where the initial snowpack has been replaced by a statistical 30-year snowpack. The new guidelines are applicable to single reservoir systems as well as more complex hydroelectric schemes, and cover snowmelt floods, rain floods and combinations of the two. In order to study the probabilities of the computed floods and to avoid regional inconsistencies, extensive comparisons with observed floods and frequency analyses have been carried out.     

Description de deux nouvelles Cyclotelles (Bacillariophyceae) de milieux alcalins et eutrophes:Cyclotella costei nov. sp. etCyclotella wuethrichiana nov. sp.

Two new species of the genus Cyclotella are presented which have been discovered during ecological and paleoecological research studies in the littoral zone of two small alkaline eutrophic lakes in France (Lake Paladru) and in Switzerland (Lake Le Loclat). These new species are namedCyclotella costei nov. sp. andCyclotella wuethrichiana nov. sp.     

Effects of F,B2O3 and P2O5 on the solubility of water in haplogranite melts compared to natural silicate melts

The effects of F, B₂O₃ and P₂O₅ on the H₂O solubility in a haplogranite liquid (36 wt. % SiO₂, 39 wt. % NaAlSi₃O₈, 25 wt. % KAlSi₃O₈) have been determined at 0.5, 1, 2, and 3 kb and 800, 850, and 900°C. The H₂O solubility increases with increasing F and B content of the melt. The H₂O solubility increase in more important at high pressure (2 and 3 kb) than at low pressure (0.5 kb). At 2 kb and 800°C, the H₂O solubility increases from 5.94 to 8.22 wt. % H₂O with increasing F content in the melt from 0 to 4.55 wt. %, corresponding to a linear H₂O solubility increase of 0.53 mol H₂O/mol F. With addition of 4.35 wt. % B₂O₃, the H₂O solubility increases up to 6.86 wt. % H₂O at 2 kb and 800°C, corresponding to a linear increase of 1.05 mol H₂O/mol B₂O₃. The results allow to define the individual effects of fluorine and boron on H₂O solubility in haplogranitic melts with compositions close to that of H₂O-saturated thermal minima (at 0.5–3 kb). Although P has a dramatic effect on the phase relations in the haplogranite system, its effect on the H₂O solubility was found to be negligible in natural melt compositions. The concominant increase in H₂O solubility and F can not be interpreted on the basis of the available spectroscopic data (existence of hydrated aluminofluoride complexes or not). In contrast, hydrated borates or more probably boroxol complexes have been demonstrated in B-bearing hydrous melts.     

Desertification,famine, and the 1988 rainfall —

The 1988 good rainy season in the Sudan raised the hopes that desertification/land degradation and shortage of food so markedly observed in Western Sudan have been elevated. This was particularly so as large quantities of grains were produced in the mechanized rain-fed agricultural schemes in the clay plains of Eastern Sudan. But the field work carried by the author in the Umm Ruwaba district of Kordofan region in July/August 1989 shows that, although there has been some improvement in the crop production situation, desertification/land degradation and shortage of food produced locally are still prevailing in the district. The people are still living below the poverty line, but they are able to cope because of remittances from members of the families working abroad and because of donations of food by some world organizations.     

Intercrystalline cation partitioning between minerals of the triplite-zwieselite-magniotriplite and the triphylite-lithiophilite series in granitic pegmatites

Minerals of the triphylite-lithiophilite, Li(Fe, Mn)PO₄, and the triplite-zwieselite-magniotriplite series, (Mn, Fe, Mg)₂PO₄F, occur in the late stage period of pegmatite evolution. Unfortunately, neither are the genetic relationships between these phosphates fully understood nor are thermodynamic data known. Consequently, phosphate associations and assemblages from 8 granitic pegmatites — Clementine II, Rubicon II and III, and Tsaobismund (Namibia); Hagendorf-Süd and Rabenstein (Germany); Valmy (France); Viitaniemi (Finland) — have been tested for compositional zoning and intercrystalline partitioning of main elements by electron microprobe techniques. Although the selected pegmatites display varying degrees of fractionation, and the intergrowth textures indicate different genetic relationships between the phosphates, the plots of mole fractions X _Fe=Fe/(Fe+Mn+Mg+Ca), X _Mn=Mn/(Fe+Mn+Mg+Ca), and X _Mg=Mg/(Fe+Mn+Mg+Ca) can be fitted relatively well with smooth curves in Roozeboom diagrams. Their deviations from symmetrical distribution curves are mainly dependent upon X _Mg or X _Ca, and upon non-ideal solutions. Surprisingly small differences between the partition coefficients were detected for intergrowths of different origin. However, the partitioning of shared components among coexisting phases is clearly dependent upon the conditions of formation. Compositional zoning is observed only when both Fe–Mn phosphates are intergrown mutually or with other Fe–Mn–Mg mineral solid-solutios. Thus, the zoning does not seem to be due to continuous crystallization, but to later diffusion processes. The triplite structure has preference for Mn, Mg, and Ca, while Fe prefers minerals of the triphylite series. A quantification of main element fractionation between minerals of the triphylite and the triplite series is possible in the cases where diffusion can be excluded. For the Fe/(Fe+Mn) ratios of core compositions an equation with a high correlation coefficient (R=0.988) was determined: Fe/(Fe+Mn)_Tr=[Fe/(Fe+Mn)_Li]/{2.737-(1.737)[Fe/(Fe+Mn)_Li]} (Tr=triplite series, Li=triphylite series). Consequently, the Fe/(Fe+Mn) ratio of the triplite series can now also be used in the interpretation of pegmatite evolution, just like that of the triphylite series which has been successfully applied in the past.     

The origin of the high-K latites from Camp Creek,Arizona: constraints from experiments with variable fO2 and a_{{\text{H}}_{\text{2}} {\text{O}}}

Near-liquidus melting experiments were performed on a high-K latite at fO₂'s ranging from iron-wustite-graphite (IWG) to nickel-nickel oxide (NNO) in the presence of a C-O-H fluid phase. Clinopyroxene is a liquidus phase under all conditions. At IWG , the liquidus at 10 kb is about 1,150° C but is depressed to 1,025° C at NNO and . Phlogopite and apatite are near-liquidus phases, with apatite crystallizing first at pressures below 10 kb. Phlogopite is a liquidus phase only at NNO and high . Under all conditions the high-K latites show a large crystallization interval with phlogopite becoming the dominant crystalline phase with decreasing temperature. Increasing fO₂ affects phlogopite crystallization but the liquidus temperature is essentially a function of . The chemical compositions of the near-liquidus phases support formation of the high-K latites under oxidizing conditions (NNO or higher) and high . It is concluded from the temperature of the H₂O-saturated liquidus at 10 kb, the groundmass: crystal ratio and presence of chilled latite margins around some xenoliths that the Camp Creek high-K latite magma passed thru the lower crust at temperatures of 1,000° C or more.     

Multispectral remote sensing of biomass burning in West Africa

Remote sensing measurements provide a vauable means of determining the extent of burning areas and of estimating the overall distribution of pollutant sources (identified from experimental studies) in time and space. This distribution has to be taken into account in the boundary conditions of chemistry atmospheric models.Recent methods developed for the remote sensing of active fires in tropical or temperated forest zones, have been found to be completely inadequate for fire detection on West African savannas. In order to accurately estimate the active fire distribution in the function of different sorts of West African savannas (Sahelian, Sudanian and Guinean) and forests, a multispectral methodology has been developed based on NOAA/11-AVHRR satellite data, with the purpose of eliminating as much as possible the problems related to large surface heterogeneity, confusion and bias, produced by clouds, smoke, haze, background emissivities, etc.Unlike other methods, the results show that the multispectral method, in spite of its selectivity, provides realistic results, and does not under- or over-estimate the number of fires that can be sensed by the satellite. Consequently, this methodology is more appropriate than the simplest ones for a systematic sensing of this phenomenon.     

The stratospheric quasi-biennial oscillation observed in the semidiurnal ground pressure data

Ground pressure observations made at Macao (22^○N, 113^○E) from 1953 to 1991 are analyzed and compared with the stratospheric quasi-biennial oscillation (QBO) data obtained during the same interval. The periods of the two phenomena and their time evolution are found to be close to each other. Furthermore, the time series of the stratospheric winds and the S2(p) QBO signature are highly correlated, thus confirming earlier analysis. On this basis, pressure measurements obtained at Batavia (now Djakarta: 6^○S, 107^○E) from 1870 to 1944 are used to trace back the QBO phenomenon before the advent of systematic stratospheric balloon measurements. The inferred period, which varies between 25 and 32 months, suggests that the QBO has been present in the atmosphere at least since 1870.     

Detailed gravity study of the offshore structure of Piton de la Fournaise volcano,Reunion Island

We present an interpretation of gravity data acquired in 1984 by the French R/V Jean Charcot on the submarine part of the eastern flank of Piton de la Fournaise volcano. We comment on the Bouguer anomaly map and give a quantitative interpretation of three gravity profiles. The main results are that a gravity high over Grand Brûlé, the lower subaerial part of the eastern flank, does not extend far offshore and that an anomalous topographic feature, discovered in 1982 on the submarine eastern flank, is characterized by a large negative anomaly. We propose three hypotheses to explain the origin of this anomaly, i. e., it marks the site of a new volcano, or it is a consequence of lateral volcanism from a volcano older than Piton de la Fournaise, or more probably, it represents a great landslide deposit.     

Authigenic smectite on diatom frustules in Bolivian saline lakes

Observation under the electron microscope of diatom frustules from Bolivian Altiplano saline lakes shows that many of these are coated with particles occurring as tiny sheets. The frustules can be found to be almost completely replaced by these sheets. Isolated sheet aggregates seem to have resulted from completely transformed frustules. Section observations of altered frustules bear out that the sheets have grown from biogenic silica through replacement. Selected area diffraction, dark field observation, microdiffraction, and elemental microanalysis show that the particles on the diatom frustules consist of a poorly crystallized MG-smectite.The unambiguous localisation of this authigenesis allows us to reconstruct its hydrochemical and sedimentological environment. Observation of the most recent lake sediments has pointed out that at least two main conditions are required for this authigenesis at 5°C: saturation with respect to amorphous silica, and a pH above 8.2. Variations in the Mg concentration have no significant effect.