Field surveys

TASK 2. FIELD SUSVEYS

Objective:

Realisation of tidal cycle surveys and long-term deployments to elucidate the transverse structure of exchange flows and water density fields.

Field setup  (see figure beside):

  • Tidal cycle surveys: Ship borne ADCP measurements + CTD vertical profiles across the channel during 2 semi-diurnal tidal cycles (25 hours) at spring and neap tides. The survey will be conduct at 2 transects simultaneously (using 2 boats), one near the mouth and one at 20-30 km upstream.After each tidal cycle surveys, the salinity will be measured along the estuary at high water slack.
  • Long-term (2 months) bed moorings:
    • ADCPs CTDs across the channel close to the tidal cycle transects location.
    • CTDs along the estuary (every 5 km from the mouth to 40 km).

Expected results

  • Spatial and temporal variability of flow and density fields.
  • Quantification of along and across-estuary gradients.

Study area showing the Guadiana River’s watershed (a) and stations distribution along the estuary (b): the 2 transects for tidal cycle surveys are indicated in red, the 2 ADCP+CTD cross-channel moorings in green, and the 7 CTD moorings along the channel with blue triangles. The bathymetric cross-sections at the lower and mid-estuary appear in (c) with rough indication of the ADCP+CTD cross channel moorings (green squares).