Volume 5 [2003]

Currently flood warning in the catchment of the River Cam in Cambridgeshire relies on the issuing of
alerts when the river level at the monitoring station at Byron's Pool, just upstream of Cambridge, reaches
certain pre-determined levels. Warnings are shown to be fairly accurate, but there is very little lead
time between the trigger being exceeded and the commencement of flooding. At present there is no
method used that can forecast in advance when the trigger is likely to be reached.
Three conceptually different methods of forecasting if and when the trigger at Byron's Pool will be
exceeded are presented. The first of these is a simple additive model, in which flows from the three tributaries
that are gauged are summed to give a combined flow. The second method involves the derivation
and application of two transfer function models capable of transforming river levels on the
upstream tributaries to a level at the trigger site. These models are applied both with and without realtime
updating techniques. The third method involves the calibration and application of a lumped rainfall-
runoff model of the whole catchment to Byron's Pool. Two different calibration periods are used,
and the results compared.
The results indicate that the simple additive model, while being better than no model at all, is very inaccurate,
and fails to replicate the hydrograph shape and timing, most likely because of the influence of
an ungauged tributary. The transfer function models perform well, especially when real-time updating
is used. The rainfall-runoff model performs less well, struggling to reproduce the hydrograph shape.
Ôhe main conclusions are that for this site a hierarchy of models may be appropriate, with rainfallrunoff
models providing an early indication of flooding, and transfer function routing models with
updating providing a more accurate forecast, with the additive model as a back up. The importance of
obtaining more data, including validation of ratings, and the future gauging of the ungauged tributary,
is noted throughout this investigation.

The intrusion of salt wedge in rivers is a natural phenomenon, which occurs in many estuaries. Saline
water tends to propagate upstream from the river mouth, due to the limited freshwater and the tidal
and density currents developed, resulting in deterioration of water quality in the lower river reach.
Several methods to control the salt wedge have been employed, including the construction of inflatable
dams or gates. A promising method of control is the use of an air curtain. In this study, a two-dimensional,
laterally averaged numerical model has been developed to describe salt wedge intrusion. This
model provided necessary hydraulic parameters, which were used in air curtain design theory to evaluate
the application of the air curtain method in a particular estuary system. The application takes place
in the estuary of Strymon River in Northern Greece, where the limited discharge of freshwater, mainly
caused by the construction of Kerkini dam, results in the creation and upstream intrusion of a salt
wedge in the summertime, affecting water quality and making water unsuitable for irrigation uses.

The Gulf of Astakos is a very important embayment of the Ionian Sea, as it offers an ideal environment
for extensive aquacultures with tourism, agriculture and commercial activities. In view of the need for
sustainable development of the region, the state of the gulf's quality was assessed on the basis of determinations
of nutrients (NO3
-, NO2
-, PO4
3-, SiO4
4-, and NH4
+) and trace metals (Cd, Cu, Fe, Pb, Ni and
Zn) along with physicochemical parameters in the seawater. The samples were collected in three sampling
cruises during February 2000, May 2000 and July 2000 from ten sampling stations.
Nutrients were determined by standard colorimetric methods UV-Vis, using a Varian spectrophotometer.
Dissolved metals were pre-concentrated using Chelex-100 resin. Particulate metals were
digested following a hot plate digestion in teflon bombs. Metal concentrations were determined by
Flame or Graphite Furnace Atomic Absorption techniques with a Varian spectrometer equipped with
Zeeman background correction according to the concentration levels.
Seasonal fluctuations were recorded in both nutrient and metal concentrations presenting proportional
fluctuations with those of the marine euphotic zones. The reduction of concentrations can be attributed
to the low rainfall seasonal height, the reduced flow of the streams and in the bioaccumulation
and consumption from the phytoplankton cells that bloomed during spring and early summer.

Results of a monitoring project for the water quality of three important rivers of western Greece
(Acheloos, Louros and Acherontas) are presented in this paper. The results include the concentrations
as well as the temporal and spatial distributions of nitrates, nitrites, phosphates, ammonia and dissolved
organic carbon for a period of twelve months (October 2002 to September 2003). Monthly samplings
took place in four sampling sites at the rivers Acheloos and Louros and two at the river Acherontas.
The samples were analyzed by standard spectrophometrical methods.
According to our measurements, Louros is the most polluted river as it concerns nitrogen compounds,
probably due to the increased human activities in its catchment area. It also occasionally accepts pollutants
from the small stream of Vossa.
Although Acheloos is the biggest and most important river for the whole territory, it seems not to be
heavily polluted. The chemical parameters level, indicates the enrichment of its water in nutrients,
from the water of Lisimahia lake that enters the river through the water lock of Dimikos. No significant
inflow of pollutants was observed in river Acherontas, since no remarkable spatial variation
recorded.