STRUCTURE AND COMPOSITION OF A WATERSHED-SCALE SEDIMENT INFORMATION NETWORK

A "Watershed-Scale Sediment Information Network" (WaSSIN), designed to complement UNESCO’s International Sedimentation Initiative, was endorsed as an initial project by the World Association for Sedimentation and Erosion Research. WaSSIN is to address global fluvial-sediment information needs through a network approach based on consistent protocols for the collection, analysis, and storage of fluvial-sediment and ancillary information at smaller spatial scales than those of the International Sedimentation Initiative. As a second step of implementation, it is proposed herein that the WaSSIN have a general structure of two components, (1) monitoring and data acquisition and (2) research. Monitoring is to be conducted in small watersheds, each of which has an established database for discharge of water and suspended sediment and possibly for bed load, bed material, and bed topography. Ideally, documented protocols have been used for collecting, analyzing, storing, and sharing the derivative data. The research component is to continue the collection and interpretation of data, to compare those data among candidate watersheds, and to determine gradients of fluxes and processes among the selected watersheds. To define gradients and evaluate processes, the initial watersheds will have several common attributes. Watersheds of the first group will be: (1) six to ten in number, (2) less than 1000 km2 in area, (3) generally in mid-latitudes of continents, and (4) of semiarid climate. Potential candidate watersheds presently include the Weany Creek Basin, northeastern Australia, the Zhi Fanggou catchment, northern China, the Eshtemoa Watershed, southern Israel, the Metsemotlhaba River Basin, Botswana, the Aiuaba Experimental Basin, Brazil, and the Walnut Gulch Experimental Watershed, southwestern United States.     

1) I. A. H. S. / A. I. H. S.

Abstract

A simple method is used to study the response of runoff in the Sahel to climate change. The statistical characteristics of rainfall are calculated over the western part of the Sahel for the period 1961–1990, using the BADOPLU network. Daily rainfall is simulated using a Markov process with Weibull distribution for rainfall depths. Runoff is modelled using a conceptual SCS model and the curve numbers are calculated for West Africa. Climate change is provided by simulations using the Arpège GCM (Scenario A1B), and a perturbation method is used on the parameters which describe the rainfall. Changes in rainfall are assumed to occur through increases in frequency, not intensity. Using Arpège, runoff is mainly found to increase, in depth and in number of events, by the end of the 21st century. Changes in evaporation and land use are not included in the analysis. The impact of this 21st century potential climate change (rainfall) on the runoff is found to be of the same magnitude as the impact of changes in land use.     

Generalized Born inversion of seismic reflection data

Summary . Born inverse methods give accurate and stable results when the source wavelet is impulsive. However, in many practical applications (reflection seismology) an impulsive source cannot be realized and the inversion needs to be generalized to include an arbitrary source function. In this paper, we present a Born solution to the seismic inverse problem which can accommodate an arbitrary source function and give accurate and stable results. It is shown that the form of the generalized inversion algorithm reduces to a Wiener shaping ***filter, which is solved efficiently using a Levinson recursion algorithm. Numerical examples of synthetic and real field data illustrate the validity of our method.     

A Reconnaissance Method for Delineation of Tracts for Regional-Scale Mineral-Resource Assessment Based on Geologic-Map Data

The U.S. Geological Survey (USGS) is proposing to conduct a global mineral-resource assessment using geologic maps, significant deposits, and exploration history as minimal data requirements. Using a geologic map and locations of significant pluton-related deposits, the pluton-related-deposit tract maps from the USGS national mineral-resource assessment have been reproduced with GIS-based analysis and modeling techniques. Agreement, kappa, and Jaccard's C correlation statistics between the expert USGS and calculated tract maps of 87%, 40%, and 28%, respectively, have been achieved using a combination of weights-of-evidence and weighted logistic regression methods. Between the experts' and calculated maps, the ranking of states measured by total permissive area correlates at 84%. The disagreement between the experts and calculated results can be explained primarily by tracts defined by geophysical evidence not considered in the calculations, generalization of tracts by the experts, differences in map scales, and the experts' inclusion of large tracts that are arguably not permissive. This analysis shows that tracts for regional mineral-resource assessment approximating those delineated by USGS experts can be calculated using weights of evidence and weighted logistic regression, a geologic map, and the location of significant deposits. Weights of evidence and weighted logistic regression applied to a global geologic map could provide quickly a useful reconnaissance definition of tracts for mineral assessment that is tied to the data and is reproducible.     

Sedimentological constraints on hydrometeor-enhanced particle deposition: 1992 Eruptions of Crater Peak, Alaska

Water is a dominant component of volcanic clouds and has fundamental control on very fine particle deposition. Particle size characteristics of distal tephra-fall (100s km from source volcano) have a higher proportion of very fine particles compared to predictions based on single particle settling rates. In this study, sedimentological analyses of fallout from for the 18 August and 16–17 September 1992 eruptions of Crater Peak, Alaska, are combined with satellite observations, and cloud trajectory and microphysics modeling to investigate meteorological influences on particle sedimentation. Total grain size distributions of tephra fallout were reconstructed for both Crater Peak eruptions and indicate a predominance of fine particles < 125 μm. Polymodal analysis of the deposits has identified a particle subpopulation with mode ~ 15–18 μm involved in particle aggregation. Accounting for the magmatic water source only, calculated ice water content of the 3.7 hour old September 1992 Spurr cloud was ~ 4.5 × 10^− 2 g m^− 3 (based on an estimated cloud thickness of ~ 1000 m from trajectory modeling). Hydrometeor formation on particles in the volcanic cloud and subsequent sublimation may induce a cloud base instability that leads to rapid bulk (en masse) sedimentation of very fine particles through a mammatus-like mechanism.     

Density and conductivity properties of Na−CO3−Cl−SO4 brine from Mono Lake, California, USA

Relationships among conductivity, temperature, total dissolved solids (TDS), and density were determined for hypersaline brine (TDS, 83 g kg⁻¹) from Mono Lake. A theoretical estimate of density based on ionic composition and calculated partial molar volumes compared well with actual measurements (difference, 390 ppm). However, an empirically derived equation of state based on temperature and conductivity provides the most accurate density estimates (residual errors, 190 ppm) and can be used with data collected with CTD profilers.     

Tsunamis as geological agents

When a tsunami wave series approaches and interacts with a coast, the consequent passage shorewards of great volumes of water and their invasion of the land, especially within bays and up river valleys, results in the disturbance of existing sediment and the removal seawards of land debris and coastal and shallow‐water marine sediments. Tsunami action builds up sequences of peculiar sediments in shallow water; it at least assists in the formation and maintenance of submarine canyons and, through them, produces turbidity currents of a particularly powerful kind. Tsunami action may explain many puzzling sedimentary phenomena, for example, sudden and drastic changes in near‐shore bathymetry; the formation of chaotic sediments such as some paraconglomerates and edgewise conglomerates. It offers solutions to problems arising from the study of turbiditic sequences, both modern and ancient.