Replication dataset for "Fine sediment in mixed sand-silt environments impacts 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形态》"Fine sediment in mixed sand-silt environments impact bedform geometry by altering sediment mobility"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，laser scanner data）、Ubertone数据（速度剖面数据，ubertone data）以及用于从源文件中读取数据的配套脚本。

摘要：水下床形（bedform）的几何特征（包括高度、长度及背坡角度等）是确定水力形态粗糙度、解释沉积记录的核心参数。传统床形存在性及几何形态的预测主要基于均匀无黏性沉积物，通过相图与经验公式实现。然而砂、粉砂与黏土的混合沉积物广泛分布于三角洲、河口及低地河流环境中，床形在这类环境中普遍存在，但此类混合沉积物对床形尺寸的确切影响仍未明确。
本研究依托总长15 m的可倾斜循环水槽（tilting, recirculating flume）开展室内实验，探究砂-粉砂混合体系中细砂与粉砂对床形几何形态的调控作用。实验中系统改变不同流量下砂与粉砂的占比，并采用UB-Lab 2C型二维声学多普勒测速仪（acoustic Doppler velocimeter）测量流速剖面；最终通过线激光扫描仪采集床面最终几何形态数据。
研究结果表明，床形对混合沉积物的响应并非单一模式，其受双模态驱动的沉积物活动性及黏结性等多重因素共同影响。当非黏性细颗粒物质（细砂或粗粉砂）与基底沉积物混合时，掩蔽-暴露效应（hiding-exposure effect）会发挥作用，使粗颗粒物质的活动性增强，进而导致沙丘长度增加。但加入弱黏性细粉砂会降低沉积物活动性，抑制沙丘高度与长度的增长。最后，在从沙丘床态向高流态平面床过渡的阶段，床面会变得不稳定，床形高度随时间发生波动。床面沉积物的组成对水力粗糙度无显著影响，其主要通过床形的几何形态（尤其是背坡角度）间接影响粗糙度。