Abstract
Fluorescent tracers have been widely used in hydrology. Recently, quinine started to be used as a fluorescent tracer for estimating the velocity of surface sheet flows over various soil surface conditions and environments. In the present work, the visibility of the fluorescent tracer (quinine) was assessed for various applications’ forms of the tracer (liquid, ice cube with quinine and soaked sponge). The brightness intensity of all tracer forms was estimated for different hydraulic conditions (hydrostatic, linear, and rotational flows) and for clear water, and water with medium and high suspended sediment loads. Results show that, when used as a flow velocity tracer, liquid quinine solution has to be applied carefully into the water and should better be used on sheet flows, shallow overland flows or shallow still waters. Its visibility in deep and muddy flows is insufficient for surface velocity estimations. The sponge soaked with quinine solution, which partially floats, is better visible in clear waters or low-medium suspended sediment loads, regardless of the water depth. However, for high turbulence and rotational flows, the soaked sponge sinks and is no longer visible. The ice cubes showed better visibility in all tested flow water depths and suspended sediment loads, although, in very shallow depths (of millimetres), ice cubes cannot be used because they might not follow adequately the fluid motion, which also applies to the sponge.
Keywords:
hydrologic tracers; flow visualization; flow velocities; free surface water flows
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Source: elaborated by the authors.
Source: elaborated by the authors.Note: The size of the ice and sponge was approximately 0.040 × 0.035 × 0.010 m3.
Source: elaborated by the authors.Note: The sketch is not to scale (laboratory flume dimension: 0.15 m wide and 4.00 m long).
Source: elaborated by the authors.Note: H is the depth of water in the cylinder (H = 0.10 m, before starting the rotation) and ω is the angular velocity.
Source: elaborated by the authors.Note: The images are top views of the water surface, where the tracers were applied.
Source: elaborated by the authors.Note: ND means no data (tracer could not be detected).
Source: elaborated by the authors.Note: The horizontal axes distance is expressed in pixels.
Source: elaborated by the authors.Note: The zero of the x-axis contains the brightest pixel of each of the tracer plumes, with this axis supporting the representation of the variation of the tracer brightness intensity across transects identified for each of the plumes of the various tracer forms (liquid, ice, and sponge). Regardless of the actual positioning of the tracer plume in the image, for the ice blocks and sponges, the transects were defined along the longest dimension of their rectangular shape, containing the brightest pixel; for the liquid tracer, imaginary circles were superimposed to the plumes, and the transects contained the circles’ centre and the brightest pixel in each image. The graph shows the mean values of three replicates.
Source: elaborated by the authors.Note: The water depth was 0.01 m and the flow velocity was approximately 0.10 m∙s-1.
Source: elaborated by the authors.Note: Two superimposed images are represented in each panel, for a time lapse Δt = 1 s. In the graphs, the water movement is from left to right. Flow velocity was approximately 0.02 m∙s-1. In the horizontal axes, the “distance” is expressed in pixels. Vertical scales are not the same in the three graphs, but, overall, the colour scale used is the same.
Source: elaborated by the authors.Note: The liquid quinine tracer form was not visible, and the soaked sponge brightness is strongly reduced for the high suspended load.
Source: elaborated by the authors.Note: The liquid and soaked sponge quinine tracer forms were not visible. The water column depth in the initial static condition was 0.10 m.