INDIA (1997 – 2000)

Posted by admin on February 22, 1997

Short description:
INDIA is a three year MAST 3 project focusing attention on a small, highly dynamic, tidal inlet in southern Portugal.

The principal objectives of the INDIA project are:

• to understand interactions between waves, tides and sediments which determine the morphology and stability of tidal inlets and adjacent coastlines;
• to improve numerical models used to predict changes in coastal morphology.

To achieve these objectives the INDIA project will address the following research areas using a combination of fieldwork and computer modelling:

• fundamental sediment transport mechanisms;
• measured and predicted sediment transport rates;
• mechanisms by which sediments by-pass inlets;
• hydrodynamic properties of inlets;
• sediment transport mechanisms and rates through inlets;
• modification of surface wave amplitude, form and direction by the flood and ebb tidal deltas and by the inlet;
• the morphological evolution and dynamics of deltas;
• wave overwash processes;
• aeolian sediment transport rates and dune evolution;
• surf zone processes.

Activities carried out in the first 6 months of the project duration

The activities were concentrated on a mathematical model for the description of sediment transport as bedload and suspended load in a thin layer above bed due to surface waves. The model is an extension of the theoretical concept of moveable seabed developed jointly by IHE and the University of Liverpool, see Kaczmarek & O’Connor (1993a, b) and Kaczmarek et al. (1994). The model has recently been adapted for non-linear (asymmetric) and irregular (random) waves and verified in laboratory conditions by Kaczmarek & Ostrowski (1996a). The present model of seabed dynamics incorporates the solution scheme for determination of bed shear stress due to irregular waves proposed by Kaczmarek & Ostrowski (1995) as well as the aspect of bedload in real sea conditions tested by Kaczmarek & Ostrowski (1996b) on the basis of field results.

To test the model, random series of free stream velocity measured at the top of boundary layer in laboratory conditions were used, previously being explored by Kaczmarek & Ostrowski (1995) in the verification of irregular bed shear stress model. On the basis of each input series, the output series of bed shear stress and bedload rate were computed. Then the statistical and spectral analyses were carried out for all series. Similar procedure was applied in the sediment transport computations for real sea conditions. Here, the input free stream velocities were simulated from the shallow water surface elevation spectra measured at the IHE Coastal Research Facility. In addition, a few bedload series have been computed from water surface elevation series registered by a wave buoy at bigger depth.

On the basis of the computations the proposed theoretical model has been found to be useful in practical applications for the coastal zone. Furthermore, a simplified model version has been formulated, the methodology of which requires regular wave parameters at the input, being representative for irregular wave motion.

The model extension comprises the transport of sediment suspended in a thin layer above sea bed (contact load layer). For this purpose, the use has been made of Deigaard’s (1993) proposal combined with the present approach. The results of computations show that the contribution of suspended load to total sediment transport is extremely small in weak wave conditions while the suspended load transport rate can be 5 times bigger than bedload for extreme storm conditions. A part of the above mentioned findings will be presented at the ICCE in Copenhagen, Kaczmarek & Ostrowski (1998), and published in the conference proceedings.

The model is now available in the form of software package. The usefulness of the package was demonstrated during a meeting of the IHE representatives and the INDIA project co-ordinator at the University of Liverpool in January 1998. At the present stage of the project the model estimations of sediment transport features can be used to plan the experiments and design the measuring devices. The latter has been carried out for the sand trap design proposed at the LIM/UPC laboratory within TMR proposal.