Repeated multibeam echo-sounder surveys can provide information on developing stratigraphy over large areas and during periods when environmental conditions are known. In this study, analysis encompasses 13 time-separated multibeam echo-sounder surveys between 2002 and 2010 of a tidal sand ridge in a macrotidal estuary: Nash Sands, a banner bank in the Bristol Channel (UK). Over the surveyed period, Nash Sands was S-shaped in plan-view, with two en échelon segments separated by a channel (swatchway). Migration of these inflections along the ridge led to deposition of clinoforms up to 5° to 7° steep and 12 to 14 m tall. The clinoforms downlapped onto their substrates or onto cross-sets formed by dunes migrating clockwise around the lower flanks of the ridge. Clinoform topsets were removed or truncated by repeated erosion and/or dune migrations over the ridge crest and replaced with packages of near-horizontal laterally discontinuous irregular beds. Flank dune crests were oriented obliquely to nearly perpendicularly to the clinoforms in all three sets, so the clinoforms developed by oblique−lateral accretion locally. Although one area had strongly eroded in the prior decade during elevated wave conditions, the 2002 to 2010 stratigraphic development revealed a different relationship with extreme wave heights; Nash Sands generally accumulated sand during times of more extreme waves and lost sand during more quiescent conditions. Using also single-beam survey data from 1991 to 2002 to study the ridge morphology over 19 years to 2010, the swatchway was absent in 1991 to 1992 and progressively developed as the ridge sinuosity became more accentuated. Dunes found migrating north-west through the swatchway are potential evidence of a current caused by tidal height differences across the ridge during ebb conditions. The study illustrates how repeated sonar measurements reveal the processes and timescales that lead to the deposition of stratigraphic units.

中文翻译：

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重复高分辨率多波束回声测深仪测量的布里斯托尔海峡（纳什金沙旗岸）潮汐沙脊的动力学和地层学

重复的多波束回声测深调查可以提供有关在大面积和已知环境条件期间发展地层学的信息。在这项研究中，分析包括 2002 年至 2010 年期间对大潮河口的潮汐沙脊进行的 13 次时间分离的多波束回声测深仪调查：Nash Sands，布里斯托尔海峡（英国）的一个横幅银行。在调查期间，纳什桑兹在平面图中呈 S 形，有两个梯队由通道（swatchway）分隔的片段。这些拐点沿山脊的迁移导致高达 5° 至 7° 陡峭和 12 至 14 m 高的斜坡形沉积。斜顶向下重叠在它们的基底上或由沙丘围绕山脊下侧沿顺时针方向迁移形成的交叉组上。山脊顶部反复侵蚀和/或沙丘迁移，去除或截断了斜顶顶，取而代之的是近水平横向不连续不连续不规则床。侧面沙丘嵴在所有三组中均倾斜至几乎垂直于斜坡状，因此斜坡状由局部斜侧吸积发育。尽管在过去的十年中，在海浪高涨的情况下，一个地区受到了强烈的侵蚀，2002 年至 2010 年的地层发展揭示了与极端波高的不同关系；Nash Sands 通常在更极端的波浪期间积累沙子，在更静止的条件下丢失沙子。还使用 1991 年至 2002 年的单波束调查数据研究了 19 年至 2010 年的山脊形态，1991 年至 1992 年没有斯沃琪道，并随着山脊弯曲度变得更加突出而逐渐发展。发现的沙丘通过斯沃琪道向西北迁移，这可能是在退潮条件下由跨越山脊的潮汐高度差异引起的电流的潜在证据。该研究说明了重复声纳测量如何揭示导致地层单元沉积的过程和时间尺度。Nash Sands 通常在更极端的波浪期间积累沙子，在更静止的条件下丢失沙子。还使用 1991 年至 2002 年的单波束调查数据研究了 19 年至 2010 年的山脊形态，1991 年至 1992 年没有斯沃琪道，并随着山脊弯曲度变得更加突出而逐渐发展。发现的沙丘通过斯沃琪道向西北迁移，这可能是在退潮条件下由跨越山脊的潮汐高度差异引起的电流的潜在证据。该研究说明了重复声纳测量如何揭示导致地层单元沉积的过程和时间尺度。Nash Sands 通常在更极端的波浪期间积累沙子，在更静止的条件下丢失沙子。还使用 1991 年至 2002 年的单波束调查数据研究了 19 年至 2010 年的山脊形态，1991 年至 1992 年没有斯沃琪道，并随着山脊弯曲度变得更加突出而逐渐发展。发现的沙丘通过斯沃琪道向西北迁移，这可能是在退潮条件下由跨越山脊的潮汐高度差异引起的电流的潜在证据。该研究说明了重复声纳测量如何揭示导致地层单元沉积的过程和时间尺度。1991 年至 1992 年间，swatchway 不存在，随着山脊弯曲变得更加突出，逐渐发展。发现的沙丘通过斯沃琪道向西北迁移，这可能是在退潮条件下由跨越山脊的潮汐高度差异引起的电流的潜在证据。该研究说明了重复声纳测量如何揭示导致地层单元沉积的过程和时间尺度。1991 年至 1992 年间，swatchway 不存在，随着山脊弯曲变得更加突出，逐渐发展。发现的沙丘通过斯沃琪道向西北迁移，这可能是在退潮条件下由跨越山脊的潮汐高度差异引起的电流的潜在证据。该研究说明了重复声纳测量如何揭示导致地层单元沉积的过程和时间尺度。