Use of Systematic, Palaeoflood and Historical Data for the Improvement of Flood Risk Estimation. Review of Scientific Methods

The catastrophic floods recently occurring in Europe warn of the critical need forhydrologic data on floods over long-time scales. Palaeoflood techniques provideinformation on hydrologic variability and extreme floods over long-time intervals(100 to 10,000 yr) and may be used in combination with historical flood data (last1,000 yr) and the gauge record (last 30–50 yr). In this paper, advantages anduncertainties related to the reconstruction of palaeofloods in different geomorphologicalsettings and historical floods using different documentary sources are described.Systematic and non-systematic data can be combined in the flood frequency analysisusing different methods for the adjustment of distribution functions. Technical toolsintegrating multidisciplinary approaches (geologic, historical, hydraulic and statistical)on extreme flood risk assessment are discussed. A discussion on the potential theoreticalbases for solving the problem of dealing with non-systematic and non-stationary data ispresented. This methodology is being developed using new methodological approachesapplied to European countries as a part of a European Commission funded project (SPHERE).     

DInSAR analysis of ALOS PALSAR images for the assessment of very slow landslides: the Tena Valley case study

In this work we analyse the performance of advanced land observing satellite (ALOS) phased array type L-band syntetic aperture radar (PALSAR) images for mapping and monitoring of very slow landslides using conventional differential interferometry in the Tena Valley (Central Pyrenees, Spain). These results are compared with those retrieved in previous works where multi-band advanced differential interferometric synthetic aperture radar (DInSAR) analysis was performed for the same area using PSI techniques. The study area is largely underlain by slates (ca. 80 %) where large deep-seated very slow earth flows are dominant. The results reveal that DInSAR analysis is able to measure displacements of landslides with a greater spatial coverage than PSI analysis, but for a lower amount of them (nine against 51). Overall, the combination of the DInSAR and multi-band PSI analysis permitted to map and monitor 68 % of the landslides in Tena Valley. From this amount, 63 landslides are considered as active. The main advantage of DInSAR with respect to PSI analysis is the capability to detect faster movements (up to 145 cm?year^?1) derived from the 46 days interferograms. That is the case of Sextas and La Selva landslides where an acceleration of the moving mass was measured after intense rainfall periods producing major damages to linear infrastructures. The combination of measured displacement from ALOS interferograms, with the observed damages on the A-136 road, was useful to assess the potential damage that could cause these slow movements. In general, it is demonstrated that even though PSI analysis provides a better performance in terms of landslide mapping, L-band DInSAR analysis provides an added value for landslide hazard assessment through radar remote sensing. For this reason it is necessary to encourage the launch of new satellite missions similar to ALOS PALSAR that could operate with shorter revisiting time periods.     

Resistivity and induced polarization response of a thin sheet

The relevant potential theory is given for a current point source in the presence of a conductive slab embedded in a homogeneous host region of infinite extent. The thin sheet representation is obtained from the exact integral formulation by a simple mathematical limit process. The same result is also deduced directly at the outset by applying a thin sheet boundary condition. The apparent resistivity for a two electrode array is then computed for the case where the bore hole intersects the thin sheet at right angles. The corresponding results for the dilution factor, relevant to the induced polarization response, are also obtained. It is shown that the apparent resistivity and the dilution factor are constant when the potential and the current electrode straddle the sheet but there is a characteristic decrease as the electrodes move away from the sheet.     

Phosphorus in granitic rocks of Colombia

One hundred and three samples of granitic rock taken systematically from the Andean part of Colombia reveal that the observed variation in phosphorus content reflects the variation observed for the wholerock chemical composition. This relationship was established using a form of trend analysis termed COMTRENA and information-theory statistics.     

New rurality and the experience of place: the small rural locality of La Niña,Buenos Aires,Argentina

This paper presents a cultural geographic approach for understanding local social processes of territorial re-appropriation taking place in response to non-local forces and interests. This approach is applied to the small rural locality of La Niña, in Buenos Aires Province, Argentina. The small village of La Niña is currently in a locally-led process of recovering from a recent depopulation trend caused mainly by the irruption of transnational agribusiness. As economic opportunities have dwindled in the last decades, more recently local inhabitants and new settlers have set forth diverse strategies aimed at mitigating the effects of depopulation on the social structure. We focus our attention on the way the living experience of place is involved in all these strategies. We contend that despite economic and cultural homogenization caused by globalization, the experience of place is a permanent though ever-changing aspect of social life. Our research was based on archival and hemerographic surveys and ethnographic field techniques, encompassing participatory observation, semistructured and in-depth interviews with social and government leaders and local producers as well as field landscape appraisals.     

Energy Expenditure and Geomorphic Work of the Cataclysmic Missoula Flooding in the Columbia River GGorge,USA

Cataclysmic releases from the glacially dammed Lake Missoula, producing exceptionally large floods, have resulted in significant erosional processes occurring over relatively short time spans. Erosional landforms produced by the cataclysmic Missoula floods appear to follow a temporal sequence in many areas of eastern Washington State. This study has focused on the sequence observed between Celilo and the John Day River, where the erosional features can be physically quantified in terms of stream power and geomorphic work. The step-backwater calculations in conjunction with the geologic evidence of maximum flow stages, indicate a peak discharge for the largest Missoula flood of 10 × 10⁶m³s⁻¹. The analysis of local flow hydraulics and its spatial variation were obtained calculating the hydrodynamic variables within the different segments of a cross-section. The nature and patterns of erosional features left by the floods are controlled by the local hydraulic variations. Therefore, the association of local hydraulic parameters with erosional and depositional flood features was critical in understanding landform development and geomorphic processes. The critical stream power required to initiate erosion varied for the different landforms of the erosional sequence, ranging from 500 W m⁻² for the streamlined hills, up to 4500 W m⁻² to initiate processes producing inner channels. Erosion is possible only during catastrophic floods exceeding those thresholds of stream power below which no work is expended in erosion. In fact, despite the multiple outbursts which occurred during the late Pleistocene, only a few of them had the required magnitude to overcome the threshold conditions and accomplish significant geomorphic work. © 1997 by John Wiley & Sons, Ltd.     

Geomorphology of a sand wave in lower Chesapeake Bay,Virginia, U.S.A.

Morphologic and sedimentologic studies of a single sand wave within a sand wave field in the lower Chesapeake Bay suggest that the bedform was originally formed by ebb currents, and is presently in static equilibrium with the circulation pattern. In this report, the concept of solitary sand wave is introduced to describe the state of a sand wave when further evolution of the sedimentary structure is mostly independent of adjacent bedforms. This concept can be applied to several bedforms in the area that are isolated from others by flats. A particular sand wave that is included in this category is discussed.Contribution number 79, Instituto Argentino de Oceanografia.