Hydraulic visibility: Using satellite altimetry to parameterize a hydraulic model of an ungauged reach of a braided river

What hydraulic information can be gained from remotely sensed observations of a river's surface? In this study, we analyze the relationship between river bed undulations and water surfaces for an ungauged reach of the Xingu River, a first‐order tributary of the Amazon river. This braided reach is crosscut more than 10 times by a ENVISAT (ENVironmental SATellite) track that extends over 100 km. Rating curves based on a modeled discharge series and altimetric measurements are used, including the zero‐flow depth Z ₀ parameter, which describes river's bathymetry. River widths are determined from JERS (Japanese Earth Ressources Satellite) images. Hydrodynamic laws predict that irregularities in the geometry of a river bed produce spatial and temporal variations in the water level, as well as in its slope. Observation of these changes is a goal of the Surface Water and Ocean Topography satellite mission, which has a final objective of determining river discharge. First, the concept of hydraulic visibility is introduced, and the seasonality of water surface slope is highlighted along with different flow regimes and reach behaviors. Then, we propose a new single‐thread effective hydraulic approach for modeling braided rivers flows, based on the observation scales of current satellite altimetry. The effective hydraulic model is able to reproduce water surface elevations derived by satellite altimetry, and it shows that hydrodynamical signatures are more visible in areas where the river bed morphology varies significantly and for reaches with strong downstream control. The results of this study suggest that longitudinal variations of the slope might be an interesting criteria for the analysis of river segmentation into elementary reaches for the Surface Water Ocean Topography mission that will provide continuous measurements of the water surface elevations, the slopes, and the reach widths.     

Investigation of the ingrowth of radioactive daughters of in Mediterranean sapropels as a potential dating tool

Five different sapropels (S1, S3–S6) from two sites (2750 m and 3308 m water depth) in the eastern Mediterranean were analysed for C_org content and specific activities of , , and . Anoxia in the sapropel sediments during or shortly after deposition leads to U enrichment, and the observed excess of over activity is consistent with a seawater source for authigenic U. In certain cases, the U profile shape in and around the sappropels is interpreted to indicate that oxidation shortly after sapropel formation has caused a post-depositional downwards migration of both U isotopes. Systematic variability of the activity ratio across the sapropel units indicates that a different diagenetic process has also led to preferential relocation of produced in situ from the parent. The construction of quasi-isochrons in successively older sapropel units demonstrate that radioactive secular equilibrium is approached by a systematic ingrowth of over time from the marked initial disequilibrium between and the U isotopes. The effects of post-depositional diagenesis violate the isochron model boundary conditions, however, and lead to a deviation of the isochron ages from the expected stratigraphic ages. Following assessment of each data point, some improvements in the calculated ages were achieved in one case by exclusion from the calculations of those points most severely affected by open system behaviour.     

The residual cosmic ray modulation at the 1954 solar minimum

Analysis of the anomalous solar diurnal variation in cosmic rays at the 1954 solar minimum yields an estimate of the residual solar modulation present at that time. The data are consistent with a modulation parameter M in the range 0.6 < M 1.5 GV. Reasons are given for preferring a value in the upper half of this range.     

The heliocentric radial gradient in cosmic ray density and the ‘swinson’ sidereal time variation

The sidereal time variation reported by Swinson depends on the existence of a heliocentric radial gradient of cosmic ray density in the rigidity range ? 100 GV and appears because of the inclination of the axis of rotation of the Earth to the normal to the ecliptic plane. It is sensitive to the polarity of the interplanetary magnetic field. Meson detectors on the surface of the Earth near the equator and at shallow underground depths can be used to measure this effect.In this paper results obtained at Makerere on the Earth's surface and at Kilembe (50 m.w.e.) in Uganda, East Africa, are compared with data previously reported by Swinson from Chacaltaya (25 m.w.e.) and Embudo (40 m.w.e.).From the relationship between the sidereal time variation and the heliocentric radial gradient it is concluded that the data are consistent with a local radial gradient of ($\text{(41 ± 8)}\text{P)}\text{\% A.U.}{}^{\mathrm{?1}}$ in the rigidity range 15 < P ? 100 GV during 1967–1971, a period including the most recent solar maximum. This estimate is consistent with modulation theory and the prevailing power spectrum in the interplanetary magnetic field.The Swinson effect is not appreciable at depths of more than 50 m.w.e. underground.     

Community volunteer assessment of recreational water quality in the Hutt River,Wellington

ABSTRACT

Water is an important component of many recreational opportunities and New Zealand invests significant resources in recreational water quality (RWQ) monitoring to assess risks to public health. However, monitoring primarily focuses on microbiological hazards and RWQ is considerably broader than this. The goal of this study was to take a comprehensive approach to evaluating RWQ while exploring the potential for greater public involvement in monitoring. A popular river swimming site was co-monitored weekly by volunteers and a council field officer. The attributes monitored–water temperature, visual clarity, benthic cyanobacteria and filamentous periphyton cover, E. coli and rubbish–were identified from a volunteer workshop. There was good concordance between volunteer and council data suggesting that volunteer measurements can be considered reliable. This highlights the potential for volunteers, with professional support, including training and quality assurance, to extend council RWQ surveillance to additional monitoring sites while improving public engagement on water management.     

Complex Rays and Wave Packets for Decaying Signals in Inhomogeneous,Anisotropic and Anelastic Media

Diffraction and anelasticity problems involving decaying, evanescent or inhomogeneous waves can be studied and modelled using the notion of complex rays. The wavefront or eikonal equation for such waves is in general complex and leads to rays in complex position-slowness space. Initial conditions must be specified in that domain: for example, even for a wave originating in a perfectly elastic region, the ray to a real receiver in a neighbouring anelastic region generally departs from a complex point on the initial-values surface. Complex ray theory is the formal extension of the usual Hamilton equations to complex domains. Liouville's phase-space-incompressibility theorem and Fermat's stationary-time principle are formally unchanged. However, an infinity of paths exists between two fixed points in complex space all of which give the same final slowness, travel time, amplitude, etc. This does not contradict the fact that for a given receiver position there is a unique point on the initial-values surface from which this infinite complex ray family emanates. In perfectly elastic media complex rays are associated with, for example, evanescent waves in the shadow of a caustic. More generally, caustics in anelastic media may lie just outside the real coordinate subspace and one must trace complex rays around the complex caustic in order to obtain accurate waveforms nearby or the turning waves at greater distances into the lit region. The complex extension of the Maslov method for computing such waveforms is described. It uses the complex extension of the Legendre transformation and the extra freedom of complex rays makes pseudocaustics avoidable. There is no need to introduce a Maslov/KMAH index to account for caustics in the geometrical ray approximation, the complex amplitude being generally continuous. Other singular ray problems, such as the strong coupling around acoustic axes in anisotropic media, may also be addressed using complex rays. Complex rays are insightful and practical for simple models (e.g. homogeneous layers). For more complicated numerical work, though, it would be desirable to confine attention to real position coordinates. Furthermore, anelasticity implies dispersion so that complex rays are generally frequency dependent. The concept of group velocity as the velocity of a spatial or temporal maximum of a narrow-band wave packet does lead to real ray/Hamilton equations. However, envelope-maximum tracking does not itself yield enough information to compute synthetic seismograms. For anelasticity which is weak in certain precise senses, one can set up a theory of real, dispersive wave-packet tracking suitable for synthetic seismogram calculations in linearly visco-elastic media. The seismologically-accepiable constant-Q rheology of Liu et al. (1976), for example, satisfies the requirements of this wave-packet theory, which is adapted from electromagnetics and presented as a reasonable physical and mathematical basis for ray modelling in inhomogeneous, anisotropic, anelastic media. Dispersion means that one may need to do more work than for elastic media. However, one can envisage perturbation analyses based on the ray theory presented here, as well as extensions like Maslov's which are based on the Hamiltonian properties.