D. E. N. GOGOASE ET AL.
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ern distributary of Danube Delta, St. George, for flood
events having return periods between 20 and 1000 years.
For this purpose, a 2D hydraulic model was set up with
the help of CCHE-2D finite difference code (University
of Mississippi, USA). In this context, the objectives of
present study are: 1) to extend the sparsely available
measured values of hydrodynamic parameters over the
entire study reach for discharge values in the (800-1600)
m3/s range; 2) to draw the flood maps and compare them
with corresponding satellite images [4]; 3) to analyze the
flooding behavior of St. George village and assess the
risk factors under various scenarios such as: river flood
events, sea level raise or sea storms (which lead to high
waves and raised sea level at the downstream boundary
of the study reach). The findings are helpful for local
authorities in order to inform th e population and take the
appropriate defense measures in the future.
2. Site and Data
The Danube Delta is located in the north-western part of
the Black Sea, between 44˚25’N and 45˚30’N and be-
tween 28˚45’E and 29˚46’E. The Romanian delta plain
covers an area of about 5,800 km2 (including water)
(Figure 1). It has three distributaries (main branches),
named from N to S: Kilia, Sulina and St. George. Delta
apex is known as Ceatal Izmail.
About 20% of the Danube delta represents areas with
negative relief (i.e. with an average level below the
Black Sea-Sulina gauging system), about 54.5% of the
Danube delta plain consists of areas having altitudes be-
tween 0 and 1 m above the sea-level and 18% with alti-
tudes between 1 and 2 m. The reed plot swamp vegeta-
tion is predominant and it covers about 78% of the total
area, while the salting vegetatio n covers about 6% of the
total area. These two factors: flat terrain and compact
vegetation (generally up to few meters in height) makes
it almost impossible for the topographic surveys to be
performed, and erroneous for the remote sensing topog-
raphic data acquisition (such as LIDAR, [5]).
Average multiannual (1960-2006) river flow near the
Danube apex (Isaccea gauging station) is 6638 m3/s with
a maximum value of 16500 m3/s (registered in April
2006) and a minimum value of 1970 m3/s (registered in
September 2003). The monthly multiannual average sea
level has the same trend as the corresponding Danube
flow, with amplitudes of 14 cm between high levels in
spring and low levels in autumn [6].
Predominant winds are from the N and NE, and the
most frequent induced wind waves recorded are from NE
corresponding to the prevailing wind direction [7]. The
mean maximum heights of wind induced sea waves in
front of the Danube Delta reached even 7.0 m. The storm
Figure 1. Map of the Romanian Danube Delta with the
three main distributaries (from N to S): Kilia (Romania-
Ukraine border), Sulina and St. George.
surges from N, NE, E and SE directions calls water level
rises of 1.2-1.5 m. Therefor e, water level at the mouth of
the three distributaries has important variations, its aver-
age annual amplitude being of about 0.70–0.80 m. The
Black Sea tide has small amplitudes of only 7 ÷ 11 cm
[6].
In such conditions, flooding events in the Danube
Delta occur when the water flow at the apex exceeds
10,000 m3/s [8] and/or when waves from the sea are high.
Most recent historic event (having a return period of ap-
proximately 200 years) took place in spring 2006. This
paper focuses on St. George distributary, which is the
most meandered (local meandering coefficient = 2.35)
and conveys approximately 20-25% of the total Danube
discharge. Top width varies between 150m and 600m,
whereas the depth varies between 3 and 27 m beneath
water level corresponding to the low flow regime. At its
mouth, a secondary delta with conic entangled branches
has been form ed.
A study site was chosen at the mouth of this distribu-
tary. Its length is 4.3 km, minimum top width of 200 m
in front of the St. George port and maximum top width
of 600 m at km 1.5 from the mouth (Figure 2). Maxi-
mum depth along the study reach is of about 15 m (cor-
responding to an approximate average multiannual flow)
near the port.
At km 8 from distributary mouth there is a gauging
station (where flow is measured), and at km 4.3, in the St.
George port, there is a level gauge (where water surface
elevations are systematically recorded and flow data is
obtained only through correlation). The flow hydrographs
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