X-Ray Computed Tomography to Measure Bed Density in Sand Transport

Abstract

This paper reports a new experimental method applying medical X-ray computed tomography (CT) to estimate the bed load in sand transport. A set of current-generated sand ripple experiments were conducted in a small hydraulic flume inserted in the CT scanner. The methodology is based on the measurements of height, velocity, and density of bed forms to estimate bed load. A temporal series of bed topography is first extracted from the CT scan images. The velocity is estimated by tracking the displacement of bed forms from two successive bed topographies. The sand bed density (ρsb) is estimated from the CT scan measurements using a calibration technique. The method measuring ρsb to calculate bed load is validated comparing measurements made with sand traps. The advantages and limitations of the CT method applied to bed-load transport are discussed. Sediment transport is a fundamental physical process in Earth Sciences. It refers to the movement of sediment grains transported by water currents and deposited where or when water flow ends. This cycle seems at first inoffensive but could impact millions of human lives all around the world. River floods, sea-level rise, and storms are likely to modify the landscape of many populated areas located nearby in the next decades. A better understanding of sediment transport processes would greatly benefit our capacity to determine the impact of those extreme events on river and coastal morphology. To achieve this, physical models are used in laboratories to simulate sediment dynamics at a smaller scale. These results help researchers developing numerical models of sediment transport to better predict river dynamics as well as the movement of coastlines. This study is an insight on the application of new laboratory techniques using advanced three-dimensional imaging technique as an effort to contribute to our knowledge of sediment dynamics.