Replication dataset for "Fine sediment in mixed sand-silt environments impact bedform geometry by altering sediment mobility"

This is the data underlying the publication "Fine sediment in mixed sand-silt environments impact bedform geometry by altering sediment mobility".It consists of the laser scanner data (elevation scans of the bedforms), the ubertone data (velocity profiles), and the corresponding scripts to read out the data from the source files.<br>Abstract: Geometric characteristics of subaqueous bedforms, such as height, length and leeside angle, are crucial for determining hydraulic form roughness and interpreting sedimentary records. Traditionally, bedform existence and geometry are predicted with phase diagrams and empirical equations, primarily based on uniform, cohesionless sediments. However, mixtures of sand, silt and clay are common in deltaic, estuarine, and lowland river environments, where bedforms are ubiquitous. The exact influence of these mixed sediments on bedform dimensions remains unknown. Here, we investigate the impact of fine sand and silt in sand-silt mixtures on bedform geometry, based on laboratory experiments conducted in a 15 m long tilting, recirculating flume. We systematically varied the content of sand and silt for different discharges, and we utilised a UB-Lab 2C (a type of acoustic Doppler velocimeter) to measure flow velocity profiles. The final bed geometry was captured using a line laser scanner. Our findings reveal that the response of bedforms to mixtures is not straightforward and depends on several factors, including bimodality-driven bed mobility and cohesiveness. When fine, non-cohesive material (fine sand or coarse silt) is mixed with the base material, the hiding-exposure effect comes into play, resulting in enhanced mobility of the coarser material and leading to an increase in dune length. However, the addition of weakly-cohesive fine silt reduces the mobility, suppressing dune height and length. Finally, at the transition from the dune regime to upper stage plane bed, the bed becomes unstable and bedform heights vary over time. The composition of the bed material does not significantly impact the hydraulic roughness, but mainly affects roughness via the geometry of the bedforms, especially the leeside angle.

本数据集为论文《混合砂-粉砂环境中的细颗粒沉积物通过改变沉积物活动性调控床形几何特性》的支撑数据。数据集包含激光扫描仪数据（床形高程扫描数据）、ubertone测速数据（流速剖面数据）以及用于从源文件中读取数据的配套脚本。
摘要：水下床形的几何特征（如高度、长度及背坡角）是确定水力形态粗糙度、解读沉积记录的关键参数。传统上，床形的存在与否及其几何特征主要基于均匀非黏性沉积物，通过相图与经验公式进行预测。然而，在三角洲、河口及低地河流等普遍发育床形的环境中，砂、粉砂与黏土的混合沉积物极为常见。这类混合沉积物对床形尺寸的确切影响仍不明晰。本研究基于15米长可倾斜循环水槽开展的室内实验，探究砂-粉砂混合物中的细砂与粉砂对床形几何特征的影响。本研究针对不同流量系统调控砂与粉砂的占比，并采用UB-Lab 2C（声学多普勒测速仪的一种）测量流速剖面。最终采用线激光扫描仪采集床面的最终几何形态。研究结果表明，床形对混合沉积物的响应并非简单线性，而是受多重因素调控，包括双模态驱动的床面活动性与沉积物黏结性。当细颗粒非黏性物质（细砂或粗粉砂）与基底沉积物混合时，掩蔽-暴露效应会发挥作用，使粗颗粒沉积物的活动性增强，进而导致沙丘长度增加。但添加弱黏结性细粉砂则会降低床面活动性，抑制沙丘的高度与长度增长。最终，在从沙丘流态向上部平面床流态过渡的阶段，床面会失稳，床形高度随时间产生波动。床面沉积物的组成对水力粗糙度并无显著影响，而主要通过床形的几何特征（尤其是背坡角）调控粗糙度。