Water Resources Research Act Program

Details for Project ID 2020ID165B

Quantifying bed architecture and interstitial processes within granular sediment beds by laser induced fluorescence

Institute: Idaho
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $15,000 Total Non-Federal Funds: $30,002

Principal Investigators: Ralph Budwig

Abstract: Surface waters interact with bed sediments creating an in-stream-pore water exchange known as hyporheic flow. This exchange is the key mechanism for transporting solutes and particles between surface and subsurface waters with important consequences on both surface and subsurface water quality. For instance, heavy metal contaminates in lake and stream beds and seafloors can be released in the surface water due to solution of heavy metal in the anoxic portion of the sediments. The ability to measure the flow paths and monitor biological activities within sediments is paramount to better constrain, model and predict these processes. However, current techniques do not allow direct measurement of intra-gravel flows that have been predicted by numerical modeling. Thus, the scope of this research is to provide a new economical, efficient and non-invasive method to measure bed architecture and interstitial flows hydraulics. This research is fundamental to developing a new methodology that will help to address key issues concerning water quality: (i) nutrient fate in water bodies, (ii) heavy metal fate and storage in water body sediments, (iii) near-surface sediment biogeochemical processes, (iv) water and solute exchange at the water sediment interface, (v) aquatic vegetation growth and development, (vi) studying redd internal flow structure and its relationship to sustenance of embryos, and (vii) studying the movement of organisms in a sediment bed.Hyporheic processes are ubiquitous from inland waters to oceans with important implications for any science and application in those environments. This research will provide a methodology that will support the many disciplines studying processes within sediments soils and at the water-sediment interface.We propose to test the use of Quantitative Planar Laser-Induced Fluorescence (QPLIF) to determine both bed architecture and pore fluid velocities in a simulated riverine sediment bed flow. During the past year, we developed and tested a new transparent sediment simulant. We formed a bed of irregularly shaped grains made of THV (a fluorocarbon plastic) with refractive index of 1.36 and specific gravity of 1.93, similar to natural sediment. Thus, for the first time, we applied Refractive Index Matching (RIM) with sediment simulant and with a safe, biologically friendly and non-toxic fluid that can mimic both fresh and salt waters. We then applied Particle Image Velocimetry (PIV) to determine both bed architecture and pore velocity field. These results are currently being prepared for publication and are encouraging, but have also highlighted some limitations. One difficulty encountered in using PIV to determine the pore velocity field was the build-up of seeding particles on the surfaces of sediment simulant grains (PIV requires that the fluid be seeded with micron size tracer particles called seeding particles). This bed contamination can obstruct laser light illumination of the grain bed and, in addition, as it progresses, can fill pore spaces and thus alter the pore flow characteristics of the bed. Thus, to avoid bed contamination, we propose applying QPLIF to measure the pore fluid velocities. In this approach, dye molecules are used as the tracer rather than micron sized particles. The dye is injected at points of interest in the bed and is then traced by taking images of the dye as it moves through the bed. In addition to measuring the pore fluid velocities, the contrast between dyed fluid and the sediment simulant grains, which have no dye molecules, is used to determine grain-fluid boundaries, and ultimately the architecture of the entire grain bed.The steps to attain the goal of the project are to:(1) Create a physical model of riverine sediment bed flow with THV sediment simulant (2) Develop methods to apply quantitative PLIF (QPLIF) to physical model(3) Conduct QPLIF experiments(4) Perform image analysis to obtain planar pore fluid velocities and bed architecture (5) Refine results (including validation) and prepare them for publication.