528
J. Ojeda Zújar et al.
analysis of samples since 1988 has provided an important and substantial database
which, up to a point, shows the improvements made in water quality in this part of the
Andalucian coast. Nonetheless the thorough use of this information is, on occasion,
somewhat hampered by the nature of the sampling process.
1) the littoral zone and the interior of the estuary are treated as independent
areas, so the sampling days were different and, at times, far apart
2) sampling days were not chosen according to the hydrodynamic situation (e.g.
tidal coefficient) but rather according to the availability of staff and boat
3) the sample points were based solely on visual reference points
4) the time of sampling was not recorded so that it is not possible to relate the
sample to the exact state of the tide, only to a general statement of high or low
tide. The time taken to sample the estuary sites meant that it was impossible
for all to be taken at the top or bottom of the tide. Moreover knowing the
time of sampling and thus the sequence would help to interpret the data in
relation to water mass movement in response to the tide
In a zone such as we are considering, in which the water dynamics are
complex and the tidal currents reach a considerable speed (0.56m/sec - an average
water mass displacement of 6km. in each half-tide cycle.) all the aforementioned
characteristics of the sampling process mean that the available information leaves
much to be desired, notably:i) the distribution of sample sites may not fully represent the estuary because of
significant absences such as the El Burro and Punta Umbria channels, the upper
sector of the Odiel and Tinto channels, the main channel mouth etc.
ii) taking the samples in different hydrodynamic circumstances means that
comparability is lost
Clearly, a better awareness of the dynamics of the estuary and the disposition of the
different water masses in various synoptic situations could help to improve the
consistency and representativeness of the sampling process. Therefore the aim of this
project is to evaluate the potential contribution of remote sensing to enhancing
sampling representativeness both:
J. Ojeda Zújar et al.
analysis of samples since 1988 has provided an important and substantial database
which, up to a point, shows the improvements made in water quality in this part of the
Andalucian coast. Nonetheless the thorough use of this information is, on occasion,
somewhat hampered by the nature of the sampling process.
1) the littoral zone and the interior of the estuary are treated as independent
areas, so the sampling days were different and, at times, far apart
2) sampling days were not chosen according to the hydrodynamic situation (e.g.
tidal coefficient) but rather according to the availability of staff and boat
3) the sample points were based solely on visual reference points
4) the time of sampling was not recorded so that it is not possible to relate the
sample to the exact state of the tide, only to a general statement of high or low
tide. The time taken to sample the estuary sites meant that it was impossible
for all to be taken at the top or bottom of the tide. Moreover knowing the
time of sampling and thus the sequence would help to interpret the data in
relation to water mass movement in response to the tide
In a zone such as we are considering, in which the water dynamics are
complex and the tidal currents reach a considerable speed (0.56m/sec - an average
water mass displacement of 6km. in each half-tide cycle.) all the aforementioned
characteristics of the sampling process mean that the available information leaves
much to be desired, notably:i) the distribution of sample sites may not fully represent the estuary because of
significant absences such as the El Burro and Punta Umbria channels, the upper
sector of the Odiel and Tinto channels, the main channel mouth etc.
ii) taking the samples in different hydrodynamic circumstances means that
comparability is lost
Clearly, a better awareness of the dynamics of the estuary and the disposition of the
different water masses in various synoptic situations could help to improve the
consistency and representativeness of the sampling process. Therefore the aim of this
project is to evaluate the potential contribution of remote sensing to enhancing
sampling representativeness both: