EurOCEAN 2000 - Vlaams Instituut voor de Zee

• Historic bathymetric chart analysis by WHOI and SOES for a 300 year period suggests
that the number of inlets in the Ria Formosa system may be increasing over time while
computer modelling of the lagoon system by WHOI shows that the lagoon can be divided
into three largely separate hydrodynamic cells. Lagoon modelling by HIDROMOD and
LU shows that the Barra Nova Inlet is ebb dominant, which will assist longshore easterly
movement by wave action, and that more tidal water is drawn to the Inlet from the western
part of the lagoon than from channels to the east.
• Analysis of recent hydrographic charts by UALG and computer modelling by
HIDROMOD and LU shows that the erosion that has occurred on the inside of the
Peninsula de Ancão near the Barra Nova Inlet is a consequence of the re-direction of tidal
flow in the lagoon by the opening of the new Inlet.
• Use of models of aeolian sand transport by LERG has shown that significant sand
movement from the beach dunes to the lagoon only occurs during high storm events (1-2
per year) and that transport is very sensitive to the state of the dune vegetation.
• Use of bathymetric surveys of the Ancão beaches combined with fluorescent tracer
studies by UB and UALG has shown that the easterly moving longshore sand transport is
trapped by the Barra Nova's ebb shoal, which has also received material from the eroded
area on the lagoon side of the Peninsula de Ancão. Sediment transport calculations by UB
using engineering formulae show realistic comparison with sediment movement on the
ebb shoal system as determined by tracer studies.
• Computer modelling of sediment movements in the Barra Nova vicinity by KU and LU
show a complex pattern of deposition on ebb and flood shoals and rapid erosion of beachsize
sand from the Inlet channel. The nett ebb loss of sand through the inlet is confirmed
by LU computations of bedload sediment movements, which represents the dominant
mode of transport until major cliff erosion of medium-sized sand on the downcoast Ile de
Barreta occurs, which computer modelling suggests disperses rapidly to the ebb and flood
shoal areas. The effect of wave action in the inlet cross-section has been shown by LU to
reduce the nett ebb loss of sand.
• Computer modelling of flow patterns through the Barra Nova Inlet by KU, LNEC and LU
show the presence of tide and wave-induced gyre-circulations in the Inlet flow crosssection
on both flood (Ancão side) and ebb (Barreta side) phases of the tide.
• Computer modelling of wave transformations from offshore to the Inlet by LU, KU,
LNEC, IMAR show major reduction in wave heights (60-70%) due to depth limitations
and refraction in the Inlet.
• Computer modelling of tidal currents by KU and LU together with CCMS-POL barge
observations show maximum ebb tidal currents of between 2.5-3.5 m/s through the Inlet
with lower values (some 60-75%) on flood tides. The models also show good agreement
with surface currents measured by JCU's COSRAD radar system.
• Direct calculations of sediment transport by CCMS-POL based on measurement of ripple
migrations in the Inlet from a jack-up barge using sonar shows good comparisons with
engineering transport equations, while prediction of bed form sizes by LU's engineering
bedform model shows similar values to CCMS-POL's measurements: features not
predicated by existing engineering equations used for design purposes.
• Much of the Project's remote sensing equipment has been found to produce reliable results
during storm conditions: BLISS (UP), STABLE (CCMS-POL) bed tripods offshore; S4
current meters (UB) inshore; automatic tracer vehicles in the inter-tidal zone (UB, UALG);
the use (CCMS-POL) of a jack-up barge (SEACORE Ltd) in the Inlet itself; X-Band radar
(CCMS-POL) on the barge for waves as well as ECM's , SONTEK ADVs and ADCPs
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