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Major River Systems (major + river_system)
Selected AbstractsGeomorphic constraints on the active tectonics of southern TaiwanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007Lucy A. Ramsey SUMMARY Taiwan is a region of rapid active tectonics, yet the study of the tectonic processes that shape the interior of the island is difficult due to the high rates of erosion and dense vegetation. We use digital topography to look for indications of active deformation preserved in the local geomorphology. In particular, anomalies in the regional pattern of drainage are used to infer zones of enhanced tectonic activity. The apparent anticlockwise rotation of major river systems in plan view indicates the presence of a diffuse zone of left-lateral shear running down the southeastern side of Taiwan. Asymmetries in the catchments of individual drainage basins show the influence of varying rates of uplift across southern Taiwan, with the most rapid uplift close to Taitung at the indentation point of the Luzon arc with the Chinese continental margin. Our interpretations, though based predominantly on remote-sensing observations, are consistent with the available field evidence. This study demonstrates the usefulness of drainage basins as tectonic markers in the quantification of regional strain and uplift, which may have wider applicability in other deforming parts of the world. [source] Stable isotopes in the source waters of the Yamuna and its tributaries: seasonal and altitudinal variations and relation to major cationsHYDROLOGICAL PROCESSES, Issue 17 2002Tarun K. Dalai Abstract Water samples from the Yamuna and its tributaries, one of the major river systems draining the Himalaya, have been analysed for their stable oxygen and hydrogen isotopes during three seasons (summer, monsoon and post-monsoon). The data show clear seasonal and altitudinal variations; waters from higher altitudes and those collected during monsoon season are characterized by relatively depleted isotopic composition. Regression analysis of ,D,,18O data of samples collected during summer and monsoon seasons shows that the slope of the best-fit lines are nearly identical to those of precipitation at New Delhi for the same period. The similarity in their slopes suggests that the isotopic composition of precipitation contributing water to these rivers are reasonably well preserved in both monsoon and non-monsoon seasons, however, during the non-monsoon period both rainfall and river waters carry signatures of evaporation. The ,deuterium excess' in river waters during the three seasons though overlap with each other, the values during October are higher. This can be understood in terms of recycled moisture contributions to precipitation. The ,altitude effect' for ,18O in these waters is determined to be 0·11, per 100 m, a factor of about two less than that reported for the Ganga source waters from similar altitudinal range. The variability in altitude effects in rivers draining the Himalaya seems to be controlled by the ,amount effect' associated with the monsoon. The significant spatial variability in altitude effect in these river basins, which are a few hundred kilometers apart, suggests that reconstruction of palaeoelevation in the Himalaya, based on ,18O-altitude gradients, would depend critically on its proper assessment in the region. This study has established a relationship between total cation abundance and ,18O in waters of the Yamuna mainstream; total cations (corrected for cyclic components) double for a 1·4 km decrease in altitude as the Yamuna flows downstream. Copyright © 2002 John Wiley & Sons, Ltd. [source] TREE RING RECONSTRUCTIONS OF STREAMFLOW FOR THREE CANADIAN PRAIRIE RIVERS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 3 2003Roslyn A. Case ABSTRACT: Information regarding long term hydrological variability is critical for the effective management of surface water resources. In the Canadian Prairie region, growing dependence on major river systems for irrigation and other consumptive uses has resulted in an increasing vulnerability to hydrological drought and growing interprovincial tension. This study presents the first dendrochronological records of streamflow for Canadian Prairie rivers. We present 1,113-year, 522-year, and 325-year reconstructions of total water year (October to September) streamflow for the North Saskatchewan, South Saskatchewan, and Saskatchewan Rivers, respectively. The reconstructions indicate relatively high flows during the 20th Century and provide evidence of past prolonged droughts. Low flows during the 1840s correspond with aridity that extended over much of the western United States. Similarly, an exceptional period of prolonged low flow conditions, approximately 900 A.D. to 1300 A.D., is coincident with evidence of sustained drought across central and western North America. The 16th Century megadrought of the western United States and Mexico, however, does not appear to have had a major impact on the Canadian rivers. The dendrohydrological records illustrate the risks involved if future water policy and infrastructure development in the Canadian Prairies are based solely on records of streamflow variability over the historical record. [source] Mixed method approaches to the investigation and mapping of buried Quaternary deposits: examples from southern EnglandARCHAEOLOGICAL PROSPECTION, Issue 2 2007Martin R. Bates Abstract The lower reaches of major river valleys usually present archaeologists with considerable problems where thick sequences of stratified alluvium bury archaeology. These situations are typical of the lower reaches of major river systems that are currently under intense pressure from urban development where the archaeological resource is consequently at risk. Here we demonstrate how mixed method approaches, utilizing a range of borehole methods, cone penetration testing and surface and subsurface geophysics coupled with microfossil assessment (Foraminifera/Ostracoda), can be used to model these deposits and predict locations and depths at which important archaeological remains may be located. The novelty of this approach is not in the application of individual techniques to the problem but in the combined methodology, which enables a structured and cost effective programme of works to be formulated and provides the best chance to understand the subsurface. Although this approach has been developed to facilitate the location of archaeological sites buried at depth within the route corridor of development projects it is also suitable for locating fossil-bearing sequences and mapping stratigraphical units in Quaternary science. We demonstrate the approach using two examples from southern England. Copyright © 2007 John Wiley & Sons, Ltd. [source] | |||||||||||||