Quantifying concentration and flux of suspended particulate matter through a tidal inlet of the East Frisian Wadden Sea by acoustic doppler current profiling
Cuneo, P.S.; Flemming, B.W. (2000). Quantifying concentration and flux of suspended particulate matter through a tidal inlet of the East Frisian Wadden Sea by acoustic doppler current profiling, in: Flemming, B.W. et al. (Ed.) Muddy coast dynamics and resource management. Proceedings in Marine Science, 2: pp. 39-52
In: Flemming, B.W.; Delafontaine, M.T.; Liebezeit, G. (Ed.) (2000). Muddy coast dynamics and resource management. Proceedings in Marine Science, 2. Elsevier: Amsterdam. ISBN 0-444-50464-8. 294 pp., more
In: Proceedings in Marine Science. Elsevier: New York. ISSN 1568-2692; e-ISSN 2352-2860, more
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| Authors | | Top |
- Cuneo, P.S.
- Flemming, B.W.
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| Abstract |
The seasonal transport of suspended particulate matter through a tidal inlet of the East Frisian Wadden Sea was recorded over complete tidal cycles using a 1.2 MHz acoustic doppler current profiler (ADCP). Suspended sediment concentrations and fluxes were estimated on the basis of the acoustic backscatter and the time-integrated current velocity along a cross-sectional transect of the main channel near the inlet. An optical transmissometer and a centrifuge pump were deployed to collect data and material for compositional analysis and calibration of the ADCP. Analyses of the pump samples revealed that substantial quantities of both fine sand and mud were transported in suspension during peak flow. Under fair weather conditions (wind speeds <4 Bft), maximum concentrations of suspended particulate matter (SPMC) were relatively low (~60 mg 1¹), with no significant net import or export being evident. Under more windy conditions (~6 Bft), the total SPMC more than doubled (>130 mg 1-¹), the concentration of suspended sand increasing by two orders of magnitude. In this case a mean net import of up to 2950 tonnes was recorded over individual tidal cycles, of which up to 1640 tonnes were contributed by the sand fraction, and up to 1310 tonnes by the mud fraction. These results show that calibrated ADCPs can be used to quantify SPM concentrations and net fluxes of particulate matter in tidal channels. It was demonstrated that net transport was strongly dependent on local weather conditions, being evenly balanced during fair weather but showing a net sand-dominated import during more windy conditions. With increasing wind the proportion of suspended sand increased more rapidly than that of mud. It is tentatively suggested that the postulated longterm net export of fine-grained material from the Wadden Sea is linked to episodic storm action. Calibration of ADCPs for different size fractions is recommended. Furthermore, the resolution of the analog-to-digital conversion of the backscattering signal intensity should be upgraded to achieve more precise assessments of SPMC. |
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