Volume 14 [2012]

Systematic measurements of sediment transport rates and water discharge were conducted in the
Nestos River (Greece), at a place located between the outlet of Nestos River basin and the river
delta. This basin area is about 838 km2 and lies downstream of the Platanovrysi Dam. Separate
measurements of bed load transport and suspended load transport were performed at certain cross
sections of the Nestos River.
In this study, relationships between sediment transport rates and stream discharge for the Nestos
River are presented. A nonlinear regression curve (4th degree polynomial curve; r2 equals 0.62)
between bed load transport rates and stream discharge, on the basis of 63 measurements, was
developed. In addition, a nonlinear regression curve (5th degree polynomial curve; r2 equals 0.95)
between suspended load transport rates and stream discharge, on the basis of 65 measurements,
was developed.
The relatively high r2 values indicate that both bed load transport rates and, especially, suspended
load transport rates can be predicted as a function of the stream discharge in the Nestos River.
However, the reliability of the regression equations would have been higher if more measured data
were available.

Investigation of open channel flows is very important for a wide range of applications, including restoration and enhancement of river aquatic systems. As a result, the scientific community has focused on providing further insights on the flow characteristics in vegetated channels. Vegetation may be submerged or emerged, rigid or flexible with high or low density. For rigid vegetation, the hydraulic behaviour of the channel is similar to the behaviour of a channel with macro-roughness which could be caused by the presence of geometrical elements (e.g. cylinders, cubes). For flexible vegetation, both the flexibility of the vegetation and the hydrodynamic of the flow contribute to the generation of several formations such as erect, gently swaying, and prone.
In this study, the characteristics of turbulent flow in an open channel were studied experimentally using Particle Image Velocimetry (PIV). This method assumes that the particles of a fluid faithfully follow the flow dynamics, hence the motion of these seeding particles are used to calculate velocity information of the flow. The experiments were conducted for both impermeable and permeable beds in a channel of 6.5m length, 7.5 cm width and 25 cm height. Two grass-like vegetation types of different height (2 and 6 cm) were used to represent permeable beds. These conditions are typical of flows encountered in sediment transport problems. Hydraulic characteristics such as distributions of velocities, turbulent intensities and Reynolds stress are investigated at a fine resolution using the PIV. Velocity is measured above the vegetation at different heights. Results show that velocity over the vegetation region is a function of the vegetation height and the total flow depth; velocity decreases as the vegetation height increases. In addition, we show that velocities above the vegetation region are much lower than velocities above an impermeable bed. This is due to the turbulent shear stresses and the existence of turbulence in the vegetation region, which reduce the mean velocity above the vegetation region. In addition, results show a region of zero velocity; between 3 and 6 cm and 1 and 2 cm for a 6 cm and 2 cm vegetation. This result shows that 50% of the vegetation behaves like an impermeable bed.

The occurrence of trihalomethanes (THMs) was studied in the drinking water samples from urban
water supply network of Karachi city that served more than 18 million people. Drinking water
samples were collected from 58 locations in summer (May-August) and winter (November-February)
seasons. The major constituent of THMs detected was chloroform in winter (92.34%) and summer
(93.07%), while the other THMs determined at lower concentrations. Summer and winter
concentrations of total THMs at places exceed the levels regulated by UEPA (80 μg l-1) and WHO
(100 μg l-1). GIS linked temporal variability in two seasons showed significantly higher median
concentration (2.5%-23.06%) of THMs compared to winter.

The potential regional future changes in seasonal (winter and summer) temperature and
precipitation are assessed for the greater area of Greece over the 21st century, under A2, A1B and
B2 future emission scenarios of IPCC. Totally twenty-two simulations from various regional climate
models (RCMs) were assessed; fourteen of them with a spatial grid resolution of 50km for the period
2071-2100 under A2 (9 simulations) and B2 (5 simulations) scenarios and eight of them with an
even finer resolution of 25km under A1B scenario for both 2021-2050 and 2071-2100 time periods.
The future changes in temperature and precipitation were calculated with respect to the control
period (1961-1990). All the models estimated warmer and dryer conditions over the study area. The
warming is more intense during the summer months, with the changes being larger in the continental
than in the marine area of Greece. In terms of precipitation, the simulations of the RCMs estimate a
decrease up to -60% (A2 scenario). Finally it is shown that the changes in the atmospheric
circulation over Europe play a key role in the changes of the future precipitation and temperature
characteristics over the domain of study in a consistent way for the different emission scenarios.