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International Journal of Marine Science 2013, Vol.3, No.32, 253-257
http://ijms.sophiapublisher.com
256
Figure 3 The rapid sea level changing impact on rivers mouth
deformation in the study area
Haraz and Gorganroud are very important rivers and
have special significance. The Rivers of the Caspian
Sea southern coasts were classified to two orders:
Meandering and braided Rivers (Khoshravan, 2001).
Field survey result determined that braided rivers
usually have short trait and their mouth were covering
with coarse fluvial sediments in the western part of
Mazandaran and Gilan morphological zones. And
meandering rivers at the near beach zone have long
traits and they discharge fine sediments (sand, silt and
clay) to coastal zone in the central region of Gilan and
Mazandaran morphological zones. The Iranian Rivers
which enter to Caspian Sea have watershed basin with
135,000 km square and annually they charge
40,000,000 tons sediments to the Caspian Sea.
Hydrology data evaluation associated to rivers shows
that during many recent decades, with human activity
developed as dam making caused that the amount of
sediments of rivers decreased about 10 to 40 percent
(Khoshravan, 2001). Also hydrodynamic of Caspian
Sea in the study area has no stable situation seasonally
and it varied along the southern coasts of the Caspian
Sea (Khoshravan, 2007). So this region of the Caspian
sea from hydrodynamic effect to beach zone have
been classified to dissipative, reflective and transition
beach (Khoshravan, 2007). Also sediments of study
area were breakdown to three type regime (coarse
gravel, sand and very fine grain of clay) (Khoshravan,
2000). It is interesting that the beach zone sediments
were following from nearshore morphodynamic and
variety of rivers. As at the high slope shore, usually
coarse grain of sediments was deposited and reversely
at the low steepness beach, fine sediments have been
dominated.
4 Conclusions
As conclusion there is real direct relationship between
beach steepness and sediment size distribution. The
comparing of sedimentary parameters data of selected
stations show different result from natural condition of
sediments point of view. And with apply sediments
sorting, d50, mean, skewness, kurtosis as indicator the
estuaries of the southern coasts of Caspian Sea have
been order to:
Well sorted coarse grain sediments (Nashtaroud River)
Bad sorted coarse grain sediments (Shafaroud and
Lisar Rivers)
Well sorted fine to medium sand (Sorkhroud, Neka
and larim Rivers)
Bad sorted very fine sand and clay sediments
(Gorganroud and Sefidroud Rivers).
The hydrodynamic and Hydraulic energy level is
different between above classified estuaries. As in
Nashtaroud and Sorkhroud waves and currents have
been well developed and river effect is low to
sediment distribution and here is wave dominated
region. At the other hand in the Gorganroud and
Sefidroud territory sediments of rivers cover all part of
beach zone and there are active deltaic sedimentary
deposition. So these areas are called to River
dominated region. Hydrodynamic impact is very low
degree around them. Of course the Lisar and
Shafaroud Rivers are following as same statement. As
the field monitoring and satellite image analysis
results show that erosion processes associated to sea
have caused estuaries shape deformation like:
declination, tighten, widen, barred and inflation of the
mouth of rivers. And at the other hand in accretion
coastal zone with high hydraulic energy, other type of
morphodynamic formation like Delta and sand bar
have been created (Dan and Janr, 2011). In the
transition beach zone the estuary shape could be
change differently with common effect of rivers and
sea forces. Usually at this place sand spits were
originated by double impact of river and sea (Dan and
Janr, 2011). Finally on the basis of morphodynamic
index, the estuaries of southern coasts of the Caspian
Sea have been breakdown to three types as following
mentioned:
Erosion estuaries (Nashtaroud River)
Accretion estuary (Gorganroud, Sefidroud, Shafaroud
and lisar Rivers)