Summary:
Within the framework of this research we attempted the physic-geographical
study of the area determined by the drainage basin of Asopos River at Voiotia,
the area of which is 721.06 km2 and runs through the boundaries of Prefectures
of Voiotia and Attica, its sources are on Kithaironas Mountain and falls in the
Euboean Gulf. It is mostly covered by limestone, marl and Quaternary alluvial
deposits. The permeable substrate favours infiltration and percolation of the
greatest part of precipitation volumes, which combined with the low level of
rainfall, lead to bigger quantities of water runoff during the biggest part of
the year, with the exception of influxes of industrial waste. The two
aforementioned characteristics, as well as the small topographic slopes result
to small amounts of sediment yield. Indeed, its hydrological situation seems to
get worse in the course of time, as it is apparent a decrease in rainfall with
simultaneous reduction of the surface runoff and sediment yield, a fact that
would lead to further aggravation of the area with pollution load and would
endanger the coastal areas of the delta.
The determination of surface runoff was achieved on the one hand through the
calculation of several parameters of the water balance and on the other hand
through software freely available by U.S. Geological Survey (USGS) and which is
extensively described by McCabe and Markstrom (2007). The mean annual runoff
corresponding to evapotranspiration coefficient 50% of the atmospheric
precipitate is equal to 75,68 106 m3 (1st approach) while the one corresponding
to soil moisture 175 mm (2nd approach) is equal to 74,27 106 m3.
The lack of sediment yield measurements led to the need to evaluate the
parameter through empirical relations, on the basis of which the risen load is
estimated about 28-93 tones/km2 and its total load is not over 100 tones/km2.
Finally, the estimation of future levels of surface runoff and sediment yield
of Asopos at Voiotia was based on simulations of monthly rainfall and
temperature levels according to the regional climate model RAMCO-2 (KNMI) from
the European Project ENSEMBLES and are related to near future 2021-2050 and
distant future 2071-2100 in relation to the reference period 1961-1990. Thus it
is determined that the surface runoff is expected to be reduced by 18,35% in
near future (2021-2050) and by 45,15% in distant future (2071-2100), while the
sediment yield is expected to be reduced by 2,4 % in near future and by 15,7 %
in distant future
Keywords:
Viotikos Asopos, Water balance, Thornthwaite model, Sediment yield, Climate models
