Summertime conditions of a muddy estuarine environment: the EsCoSed project contribution.

As part of the Estuarine Cohesive Sediments (EsCoSed) project, a field experiment was performed in a highly engineered environment, acting as a natural laboratory, to study the physico-chemical properties of estuarine sediments and the associated hydro-morphodynamics during different seasons. The present contribution focuses on the results obtained from the summertime monitoring of the most downstream part of the Misa River (Senigallia, Italy). The measured hydrodynamics suggested a strong interaction between river current, wave forcing and tidal motion; flow velocities, affected by wind waves traveling upstream, changed significantly along the water column in both direction and magnitude.

Effect of organic matter on estuarine flocculation: a laboratory study using montmorillonite, humic acid, xanthan gum, guar gum and natural estuarine flocs.

Background: Riverine particles undergo a rapid transformation when they reach estuaries. The rapid succession of hydrodynamic and biogeochemical regimes forces the particles to flocculate, settle and enter the sediment pool. The rates and magnitudes of flocculation depend on the nature of the particles which are primarily affected by the types and quantities of organic matter (OM).

The low-frequency sound speed of fluid-like gas-bearing sediments.

The low-frequency sound speed in a fluid-like kaolinite sediment containing air bubbles was measured using an acoustic resonator technique and found to be 114 ms with negligible dispersion between 100 and 400 Hz. The sediment's void fraction and bubble size distribution was determined from volumetric images obtained from x-ray computed tomography scans. A simplified version of Wood's effective medium model, which is dependent only upon the ambient pressure, the void fraction, the sediment's bulk mass density, and the assumption that all the bubbles are smaller than resonance size at the highest frequency of interest, described the measured sound speed.

Evidence of dispersion in an artificial water-saturated sand sediment.

A laboratory experiment was conducted to measure the speed of sound in an artificial water-saturated granular sediment composed of cleaned and sorted medium-grained sand and degassed distilled water. The experiment was conducted within a range of frequencies where dispersion is predicted by a number of existing models. Between 2 and 4 kHz, the sound speed was inferred from measurements of the resonance frequencies of a thin-walled cylindrical container filled with the material.