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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Extracting palaeoflood data from coarse-grained Pleistocene river terrace archives: an example from SE Spain
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Extracting palaeoflood data from coarse-grained Pleistocene river terrace archives: an example from SE Spain

机译：从粗粒更新世河阶地层档案中提取古洪水数据：以西班牙东南部为例

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Field-based palaeoflood event reconstruction has the potential to contribute to the development of our understanding of long-term landscape evolution. However, the reconstruction of past flow event histories (magnitude and frequency) over long-term (Quaternary) timescales is fraught with difficulties. Here we make a preliminary exploration of some of the practicalities of flood reconstruction from fluvial terrace archives using commonly available sedimentological and geomorphological observations from a field perspective. We utilize Manning and palaeostage indicators to reconstruct historic events that can be used as benchmarks for a lesser used competence based approach, which is applied to coarse-grained strath terrace deposits. We evaluate the results against gauged records for extreme and catastrophic events that affected the same region in 1973 and 2012. The findings suggest that the competence approach is most effectively applied to terrace deposits if the channel geometry is taken into account when sampling both in cross-section and in longitudinal section and calibrated against the sedimentology for palaeo-flow depth. Problems can arise where constrictive channel geometries allow boulder jams to develop, acting as sediment traps for the coarsest material and leading to downstream boulder starvation'. Useful sites to target for palaeoflood reconstruction, therefore, would be upstream of such constrictive reaches where the coarsest transportable bedload has been effectively trapped. Sites to avoid would be downflow, where the deposited material would poorly represent palaeoflood competence. Underestimation from maximum boulder preservation and limited section exposure issues would appear to outweigh possible overestimation concerns related to fluid density and unsteady flow characteristics such as instantaneous acceleration forces. Flood data derived from river terrace deposits suggests that basal terrace geometries and coarse boulder lags common to many terrace sequences are likely the result of extreme flow events which are subsequently filled by lesser magnitude flood events, in this environmental setting. Copyright (c) 2016 John Wiley & Sons, Ltd.
机译：基于野外的古洪水事件重建有可能促进我们对长期景观演化的理解。然而，在长期（第四纪）时间内重建过去的流事件历史（幅度和频率）充满了困难。在这里，我们从野外角度，利用常用的沉积学和地貌学观测资料，对河流阶地档案库进行洪水重建的一些实用性进行了初步探索。我们利用曼宁和古阶段指标来重建历史事件，这些历史事件可以用作较少使用的基于能力的方法的基准，该方法适用于粗粒岩性阶地沉积物。我们根据针对1973年和2012年影响同一地区的极端和灾难性事件的记录记录评估了结果。研究结果表明，如果在交叉采样中同时考虑通道几何形状，则将能力方法最有效地应用于阶地沉积物剖面和纵剖面，并根据沉积学对古流深进行了校准。如果狭窄的通道几何形状会导致巨石堵塞，从而成为最粗物质的沉积物陷阱并导致下游巨石饥饿，就会出现问题。因此，将目标对准古洪水重建的有用地点将在此类狭窄河段的上游，在该河段，有效地捕获了最粗的可运输床位。要避免的站点将是下游，那里的沉积物将很难代表古洪水的能力。由于最大的巨石保存量和有限的断面暴露问题而导致的低估似乎超过了与流体密度和非稳态流动特性（例如瞬时加速力）有关的可能的高估关注。来自河流阶地沉积物的洪水数据表明，许多阶地序列共有的基底阶地层几何形状和大石砾滞后可能是极端水流事件的结果，随后在这种环境下被较小幅度的洪水事件所填充。版权所有（c）2016 John Wiley＆Sons，Ltd.

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