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Anthropogenic interventions and hydrological-risk phenomena in the fluvial-maritime delta of the Danube (Romania)
Ocean & Coastal Management 102 (2014) 123e130
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Ocean & Coastal Management journal homepage: www.elsevier.com/locate/ocecoaman
Anthropogenic interventions and hydrological-risk phenomena in the fluvial-maritime delta of the Danube (Romania) Gheorghe Romanescu a, b, *, Cristian Constantin Stoleriu a, b a b
Alexandru Ioan Cuza University of Iasi, Faculty of Geography and Geology, Department of Geography, Bd. Carol I 20A, 700505 Iasi, Romania Alexandru Ioan Cuza University of Iasi, ARHEOINVEST e Interdisciplinary Platform, Laboratory of Geoarchaeology, Bd. Carol I, 20A, 700505 Iasi, Romania
a r t i c l e i n f o
a b s t r a c t
Article history: Available online
The Danube Delta represents the most important wetland of Europe and the manifestation area of periodical spring-summer floods. The hydrotechnical works executed in the Danube Delta between 1950 and 1990 were meant to protect the localities against floods and to facilitate the fluvial transport. For rapid access to the locality of Caraorman (for the exploitation of quartziferous sand) and to the Rosu touristic complex, the CrisaneCaraorman channel was oversized (12 km long, 60e70 m wide, with a maximum depth of 4e6 m). The access mouth of the channel in the Sulina arm and the outlets towards the Black Sea of the deltaic lacustrine complex were poorly designed. The aggradation of the channel determined the increase in the solid discharged carried by the water and the accentuation of the alluvia accumulated in lakes. To facilitate the transit of the fluvial waters towards the Black Sea, a weir was built at the mouth of Lake Rosulet (1.20 m r MNS). Unfortunately, the weir is too high, and the water level within the lacustrine complex increases alarmingly during floods. This is why the locality of Caraorman e situated 25 km away from the Black Sea e becomes flooded. That is, there is an increase in the phreatic level (the localities of Sulina and St. George are also affected but not to the same extent). The topographic and bathymetric measurements and the precise positioning of the targeted critical points (GPS) served as the methods for investigating the deltaic area affected by flooding. The causes of the backwater floods were identified, and the measures of an adequate management plan were set out. To eliminate this impediment, alterations to the hydrotechnical works must be made as follows: reducing the height of the existing weir and building two other weirs with lower crests; dredging the secondary channels and the lacustrine cuvettes; and using shallow-draft ships. The lack of funds and the apathy of the habilitated institutions delays the implementation of the necessary measures. © 2014 Elsevier Ltd. All rights reserved.
1. Introduction The rectification of the Danubian arms and the construction of channels in the Danube Delta have a long tradition. The first significant hydrotechnical works were executed by the European Commission, instituted in 1856 by the Peace Treaty of Paris. The works enabled the navigation of deep shallow-draft ships on the old Sulina arm, channelled a distance of 62 km (of the initial 83-km length) (Panin and Overmars, 2012; Romanescu, 2013a, 2013b). The practice of extensive agriculture and the exploitation of local resources determined the implementation of a land
* Corresponding author. Alexandru Ioan Cuza University of Iasi, Faculty of Geography and Geology, Department of Geography, Bd. Carol I 20A, 700505 Iasi, Romania. Tel.: þ40 744774652; fax: þ40 232 201481. E-mail address: [email protected] (G. Romanescu). http://dx.doi.org/10.1016/j.ocecoaman.2014.09.007 0964-5691/© 2014 Elsevier Ltd. All rights reserved.
management plan by damming and channel building in the period 1900e1940. Most channels connected the main fluvial arms (Chilia, Sulina and St. George) to the great lacustrine complexes. Thus, the waters within the delta were renewed, and the floods could be mitigated by taking over the water excess. When the water level in the branches was low, a reversed transit was ensured, meaning flow from the inside towards the main hydrographical arteries. Unfortunately, many channels were poorly designed. They are straight and very shallow. This has led to the clogging of the lacustrine cuvettes and to blocking of the access paths. The period of the large, exclusively anthropic channels is now outdated. Currently, the preferred solutions are the old secondary arms, which meander and comprise aquatic vegetation capable of stopping a portion of the transited alluvia (Giosan et al., 1999; Romanescu and Cojocaru, 2010; Tiron et al., 2009).
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Fig. 1. Geographic location of the Danube Delta and of the Caraorman-Rosu maritime sector (left). Location of the CrisaneCaraorman channel compared to the main landforms (left) and the mathematical coordinates (right).
The fluvial transport in the Danube Delta d from the arms towards the lacustrine complexes and between the main lacustrine cuvettes d is usually ensured by small-sized vessels (crops, peoples). Tourism and the exploitation of natural resources have led to the construction of large channels, as follows: Dunavat, Dranov, Mustaca, Lipovenilor, Mila 35, Pardina, Dovnica, and Sontea, among others. Most of the world deltas have gone through the same process. The single most important economic and technical issue for the Danube Delta is flood risk. The reduced altitude (mean of 0.52 m; 13 m maximum) and the temperate-continental climate of transition characteristic to the entire hydrographical basin e where heavy rains are numerous e has led to fluctuating discharges (Gastescu et al., 1985; Grigoras, 2012). In this case, frequent floods occur on the Danube and implicitly in the delta. The most affected areas are the localities developed along the arms. Those of the fluvio-maritime levees are affected by the floods provoked by the increase in the water level and by the emergence of infiltrating waters in the phreatic level of coarse sands (Caraorman, Letea, C.A. Rosetti, etc.). Floods are frequent in all deltas of the world, but the risk phenomenon is specific to populated areas. Considering the great scientific and economic interest represented by deltaic regions e mostly the mouths of the great rivers e there is an abundance of studies examining this subject. These studies are both national and international (Apel et al., 2009; Cech and Cech, 2013; Cencini et al., 1988; Chen and Zong, 1999; Choudhury et al., 2004; Cummings et al., 2012; Frihy, 1996; Marchand et al., 2011; Mierla nchezand Romanescu, 2012; Palanques and Guillen, 1998; Sa Arcilla et al., 1996). The present study aimed to identify the causes of the backwater floods impacting the village of Caraorman, and to elaborate a series
of measures for eliminating or mitigating them. The identification of the causes involved high-precision topographic and bathymetric methods. The new data was corroborated with the previously available scientific information. The main objective was to elaborated a program of measures for eliminating the backwater floods affecting the settlements from the Danube Delta, and for refreshing the lacustrine waters by creating a proper link between the deltaic area and the sea. 2. Regional settings The Danube Delta occupies the south-eastern part of Romania, and it unfolds in the territory of two countries: Romania and, partially, Ukraine (Fig. 1). The surface area of the Danube Delta is 5600 km2; it is the only delta in the world that has been declared a Reservation of the Biosphere (in 1992) (Romanescu, 2010; Romanescu and Bounegru, 2009). In the case of the GangeeBrahmaputra common delta, only the Sunderban area was included (since 2001) into the UNESCO World Heritage List. The area studied here concerns the maritime delta between the arms of Sulina (to the north), St. George (to the south), the fluvio-maritime levee of Caraorman (to the west) and the littoral of the Black Sea (to the east). The locality of Caraorman is situated in the central-eastern sector of the fluvio-maritime levee of Caraorman. To facilitate the access to the area, an old secondary arm was channelled. The channel was oversized because, in the communist period, there was an attempt to industrially exploit the quartziferous sand. This is why a precinct was created to install an industrial harbour. The exploited sand was supposed to be transported via the CrisaneCaraorman channel with exiting to the Sulina
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channel. The CrisaneCaraorman channel also facilitated access to Lake Rosu, where one of the most important summer resorts was developed. 3. Methodology The field measurements were taken by using the LEICA TCR 1201 Total Station. Alongside the LEICA GPS 1200, it is part of the SYSTEM 1200 LEICA. The Topographic Directorate of Tulcea provided the coordinates of the survey markers. Forty station points were emphasised and marked in the field by wooden stakes, in various areas of firm ground or swamps, for an optimal covering of the entire surface. After finalising the measurements, the data were processed in AutoCAD. At the same time, a high-quality GPS was used to exactly delimit the analysed perimeter. The data of the topographic surveys were represented using Stereographic 70 Projection. The limits of the channels and of the lakes were delimited based on the topographic measurements and on the GPS. For the bathymetric measurements, the Valeport Midas Surveyor (Bathy-500DF Dual Frequency Hydrographic Echo Sounder) was used. The resolution of this echo sounder is 1 cm/1 cm, and it includes a GPS. To process the bathymetric data and to generate the thematic maps, the TNTMips v.7.2 and ArcGis v.9.3 software products were used. This enabled the elaboration of the numerical field model and its graphic transposition for various uses. In this case, over 250 000 points were indexed, and approximately 200 000 points were interpolated within graphs. These are innovative graphic representations of the lacustrine cuvettes in mathematical modelling. The longitudinal routes for channels were pinpointed on three alignments: centre, side left and side right. For a higher bathymetric precision, 100 transects were measured on the entire alignment of the CrisaneCaraorman channel. For each confluence, transects were measured downstream and upstream from the mouth of the secondary channel. Special attention was paid to the outlet areas of the channels linking the main lakes. In this case, the alluvial cones were outlined. The cartographic materials used are part of the collection owned by the “Alexandru Ioan Cuza” University of Iasi, through the annex of the Geoarchaeology Laboratory: orthophotoplans and satellite images. After finishing the measurements, the data was processed with the AutoCAD software suite (Autodesk, San Rafael, CA, USA). Concurrently, a GPS was used to establish the exact surface area of the RosuePuiu lacustrine complex. The research stages are summarised according to a simplified plan (Fig. 2).
Fig. 2. The breakdown of the research stages.
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4. Results The Administration of the Danube Delta Biosphere Reservation has improvement of the water regime in the deltaic depressions and in the network of channels as one of its goals (Coops et al., 2008; Navodaru et al., 2001). The target is to protect the water quality and the deltaic ecosystems. Most hydrotechnical works constructed in the past few years have had the purpose of improving the repartition of liquid and solid discharges on the main arms and of protecting against floods. The RosuePuiu lacustrine complex was naturally supplied through the secondary branches and the brooks. The first channel built in the period 1930e1940 was Litcov, supplied by the St. George arm. It drained and supplied the depression areas of Carasuhat, Rusca and Gorgova. After transiting the delta over a significant length of it, on the ancient location of a secondary arm, it finally discharged filtered, suspension-free water. For this reason, the RosuePuiu lacustrine complex was well outlined, and the degree of clogging ranged within reasonable limits. Enclosing the access mouth of the Litcov channel e when the works for the development of the CrisaneCaraorman channel began e led to its organic clogging and to the reduction of the water flows towards the RosuePuiu complex. The CrisaneCaraorman channel e 12 km long, 60e70 m wide, comprising maximum depths of 4e6 m e was finalised in 1981. After the construction of this artery, the clogging degree of the lakes within the RosuePuiu complex has increased, but the circulation of vessels towards the locality of Caraorman was facilitated. Most of the channels within the area in question were built after 1960: Litcov-Imputita, Vatafu-Imputita, Tataru and Sondei. The Potcoava channel, which connects the lakes Puiu and Rosu, was built in the period 1952e1960, whereas the BusurcaeImputita channel was constructed in 1941e1951, with a connection to the Sulina arm. The CrisaneCaraorman channel starts from the Sulina arm, and it is directed towards the RosuePuiu lacustrine complex. A secondary artery is oriented towards the locality of Caraorman. The connection with the Sulina arm is ensured upstream. An island emerged at the mouth of the channel. This is why the channel now has two mouths: the first, with an upstream opening, frontally with the direction of the current and the second, with a downstream opening, in the direction of the current. The mouth of the CrisaneCaraorman channel records maximum depths of 4 m in the upstream channel and 3 m in the downstream channel. The left bank of the channel (eastwards) is more abrupt, with slopes exceeding 45 (Fig. 3A, B). Upstream from the fluvio-maritime levee of Caraorman, the channel divides into two arteries: a southern one, which ends at the level of the Caraorman locality and an eastern one, which continues towards the RosuePuiu lacustrine complex. The maximum depth within the bifurcation sector is 6 m. The CrisaneCaraorman channel records depths of 4 m. The right bank has slopes measuring more than 35 , whereas the left bank comprises slopes exceeding 45 (Fig. 3CeE). The secondary artery oriented towards the village of Caraorman has a 10-m maximum depth, recorded at the level of the port. Actually, this is the deepest point of all the internal sectors of the Danube Delta. The main channel maintains depths of 6 m. The southern bank has slopes measuring more than 45 (Fig. 3F, G). Depths of over 4 m are recorded in the bifurcation sectors. The mouth of the Vatafu-Imputita channel has a maximum depth of 10 m, whereas the main channel has a maximum depth of 6 m (Fig. 3H, I). At the entry to Lake Puiu, the depths measure 4 m. The alluvia carried by the water determine an asymmetrical alluviation, with
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Fig. 3. The connection of the CrisaneCaraorman channel with the Sulina arm as the central axis of the Danube in the delta: A) bathymetry; B) submerged slopes; The bifurcation area of the CrisaneCaraorman channel: C) bathymetry; D) submerged slopes; E) 3D image; The harbour precinct of Caraorman: F) bathymetry; G) submerged slopes; Sector of confluence with a secondary arm (the Vatafu-Imputita brook): H) bathymetry; I) submerged slopes.
maximum intensity in the southern sector. In this area, the depths measure 1e2 m. On the right bank of the channel, at the outlet, slopes of over 45 are present (Fig. 4A, B). The high amount of alluvia determined the partial alluviation of certain lacustrine cuvettes. In this case, the small-sized lakes were affected. For this water body, the channel has reduced widths and depths down to 2 m. The longitudinal levees penetrate deep in the lake. The slopes are even on both sides (Fig. 4C, D). At the exit from Lake Puiu, the maximum depths measure 8 m. In Lake Rosu, the depth of the channel is maintained at 5e6 m (Fig. 4E, F). The slopes are even on both banks of the channel. Lake Rosu presents a similar situation to the one in Lake Puiu. The RosuePuiu lacustrine complex has a surface area of 42,300 ha. In the years 1980e1990, it has suffered significant anthropogenic interventions. The CrisaneCaraorman channel and the Sulina-St. George littoral sector are in a direct relation, and they influence each other. To eliminate the inconveniences caused by the increase in the lake water levels during the floods, the following hydrotechnical works were constructed: -a protective dam in the littoral area (along the Tataru channel), 2 m high, to prevent the emergence of breaches, created by spontaneous and uncontrolled runoffs (points favouring the development of erosion at the level of the Imputita and Sondei mouths); -a weir in the littoral dam, with a 1.20 m crest level compared with the level of the Black Sea and with a width of the tailboard of 200 m; -a channel bordering the littoral dam, oriented towards the delta, to take over the discharging role of the small and medium
streams towards the Sulina and St. George arms (Tataru channel). The old project also included the plan of recalibrating the access mouth of the Crisan channel. Unfortunately, it was not finalised. 5. Discussion The hydrotechnical works executed in the Danube Delta have focused mostly on improving the water circulation of the arms and in the lacustrine complexes and, at the same time, on protecting the human settlements against floods. Concerning the studied area, the village of Caraorman is affected because it often is flooded by the high waters coming from the Sulina arm, as well as by the backwater from the RosuePuiu lacustrine complex (after the construction of the Sulina-St. George dam). Secondarily, similar phenomena are the causes for flooding of the localities of Sulina and St. George (Giosan et al., 1999; Romanescu, 2013a). The cone-shaped mouth of the CrisaneCaraorman channel led to the emergence of a circular current, which created an island in the middle. This is why the mouth has two openings of the Sulina arm. The main current unfolds on the upstream mouth. In this channel, the waters oriented towards the Sulina arm-the CrisaneCaraorman channel run off. The downstream mouth is available for the runoff of the waters oriented towards the CrisaneCaraorman channel and the Sulina arm, in the summer, when the Danube levels are low (Fig. 3A, B). The high slopes on the eastern bank are the result of the current with an NWeSE direction, but reversed current also has manifested in the summer only along this bank.
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Fig. 4. Entry of the CrisaneCaraorman channel in Lake Puiu: A) bathymetry; B) submerged slopes; Image of the alluvial cone and the accelerated clogging of a lacustrine cuvette at the entry to Lake Puiu: C) bathymetry; D) submerged slopes; The connection channel between Lake Puiu and Lake Rosu: E) bathymetry; F) submerged slopes.
The channel was ramified for economic reasons: to facilitate the transport of the quartziferous sand from the Caraorman fluviomaritime levee and to transport the merchandise from and to the village of Caraorman (Fig. 3CeE). For this reason, the channel was enlarged and deepened. The transit is possible for barges and medium-sized sailing ships. The great depth in the southern sector of the roadstead (10 m) is also due to the fluvial current that strikes this bank directly. The current e with an NeS direction, towards the village of Caraorman e engages a significant amount of water that infiltrates in the sandy deposits, and, when the water is high, it floods the village (Fig. 3F, G). The greater depths of the right bank indicate that the river waters (the Sulina arm) enter and move e most of the time e on this alignment. The waters from the RosuePuiu lacustrine complex can also move in the right bank, The greater depths of the rightbank Vatafu-Imputita channel mouth indicates creation by the NWeSE current (from the Sulina arm) (Fig. 3H, I). The high clogging within the lacustrine complexes of the Danube Delta is due to the Danubian alluvia transport. The high level of solid discharge causes serious clogging problems at the entry of the main lacustrine cuvettes. The total amount of alluvia transported by the Danube has fluctuated over time, and it has displayed a descending trend (Table 1). The drastic decrease of the past few years is due to the construction of the Iron Gates I (a dam), which stops over 30 million tons of alluvia every year. The direction of the channel mouths and of the brooks, as well as their size, directly influences the penetration of alluvia in the inner sectors of the delta (Romanescu, 2010; Tiron et al., 2009). At the entry of Lake Puiu, an asymmetrical alluvial cone (lacustrine delta) emerged, with maximum development of the right side. The asymmetry is determined by the dominance of the
Table 1 Evolution of the solid discharge transported by the Danube and its distribution among the main arms (Gastescu et al., 1985; Giosan et al., 1999; Romanescu, 2013b; Tiron et al., 2009). Danube and the main arms
Chilia St. George Sulina Danube
Year 1894 Million t
1958 Million t
2000 Million t
56.2 17.8 7.0 81.0
48.4 16.5 5.5 70.4
15.0 5.0 2.0 22.0
NeE winds, which push the alluvia-loaded waters southwards. The clogging is accelerated by the existence of winds, just as in the case of flocculation in seawaters (Fig. 4AeF). The small-sized lakes crossed by the CrisaneCaraorman channel display a high degree of clogging. In this case, the longitudinal levees cross the entire lacustrine cuvette, and the aquatic vegetation is luxuriant. The morphological characteristics of the channel are a consequence of the local factors: the fluvial current, the geological constitution of the substratum, the vegetation, and the winds, among other factors. The construction of the CrisaneCaraorman channel led to easier circulation of the vessels between the main localities of the delta and to refreshing of the waters within the RosuePuiu lacustrine complex. Unfortunately, the hydrotechnical works of the past have failed to consider other local particularities. The significant width and depth of the channel, as well as its linearity have led to a massive alluvia loading and to an acceleration of the clogging in case of the big lakes. The construction of the dam
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on the littoral alignment (with NeS direction) and by partially eliminating the deltaic water towards the Black Sea determined the emergence of a backwater manifesting up to the village of Caraorman. This is why the groundwater rises up to the sandy substratum and most dwellings have been affected by the spring floods. The phenomenon is also accentuated by the fact that, during the floods, a high amount of water from the Sulina arm enters through the wide mouth of the channel and directly towards the upstream sector. The lack of channel meandering facilitates the flood waters acquiring high velocity, which thus directs them towards the harbour basin of the sandy fluvio-maritime levee of Caraorman. In this case, the high-speed waters of the CrisaneCaraorman channel amplify the backwater from the RosuePuiu lacustrine complex. The littoral area between the mouths of Sulina and St. George is influenced by fluvial waters (from the west) and by maritime waters (from the east). In this case, the mouths of the main mouths (Sulina and St. George) feature secondary deltas, whereas the intermediary sectors are continually withdrawing. At the level of the RosuePuiu lacustrine complex, at the mouths of the Imputita secondary arm and of the Sondei channel, the highest littoral erosion rate of the entire delta has been recorded: 10e15 m/year (Romanescu, 2013a, 2013b). The fact that the CrisaneCaraorman channel was not calibrated and that the Litcov channel was desilted and reopened determined the emergence of tributary discharges in the RosuePuiu depression. To allow the ships with a shaft exceeding 60 cm e loaded with tourists, who visited the Rosu touristic complex e on the channel, dredging works were executed, to ensure optimal navigation. This has led to an aggradation of levels and to an increase of the water stationing in the depression. The alluvia inflow has maintained high levels. The reduction of discharges and pressures on the dams within the RosuePuiu lacustrine complex has been possible through the breaches made in the dam on the Sulina-St. George littoral (Fig. 5). The derivation of the channel that reaches the north of the Caraorman village was built to facilitate the transport of passengers and merchandise from and to the village and to ensure the transport of the quartziferous sand, which is used in the glassware
industry. The anti-communist revolution of December 1989 resulted in a ceasing of exploitation of the sand. Currently, the local sand-exploitation-related construction is only a ruin. The plan was for tugboats and large barges to be allowed in the channel. The sandy deposit within the fluvio-maritime levee of Caraorman had an insignificant amount of quartz, as the new political regime, post1989, stopped the work in the area. The basins resulting from stripping and from sand exploitation could have endangered the existence of the Caraorman forest, which has been declared a strictly protected area and has high scientific value. Between the protective dam in the eastern part of the Caraorman fluvio-maritime levee and the village with the same name, there is a zone with low altitudes, where the water from infiltrations and rains gathers. The infiltrations are favoured by the coarse granulometry of the sands and by the low altitude (0e1 m). In this case, the piezometric level of the phreatic is 0e2 m deep (Romanescu and Cojocaru, 2010). Caraorman village is flooded because of the rise in groundwater. Calibrating the access mouth of the CrisaneCaraorman channel (closing the upstream mouth and calibrating the downstream mouth) would lead to large discharge limitations. The CrisaneCaraorman channel produces negative effects on the deltaic world: the channel acts like an absorbing cone for the Danubian flow. As a consequence, the inner levels within the RosuePuiu lacustrine complex and within the channels sometimes exceed the initial level of the Danubian arms by 40e75 cm (because of the pressure exerted by the river waters). The high discharge is responsible for significant alluvia loading, which thus clogs the lakes (Puiu, Puiulet, Rosu, and Rosulet) and the mouths of the channels. The waters loaded with alluvia contribute to the decrease in water quality because of increased turbidity; the channel facilitates the absorption of ice floes and discharges from the Sulina arm during the winter (in this case, the banks are destroyed and the luxuriant vegetation that blocks the access ways and even the weirs is disrupted). The channel has brought essential alterations to the deltaic landscape, and it has led to the disappearance of valuable fish species in favour of others. As it was built 30 km away from the Sulina arm, upstream, it is a threat to the town of Sulina because the
Fig. 5. The maritime area between the Sulina arm, the Caraorman fluvio-maritime levee, the Black Sea and the St. George arm.
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flow that penetrates the lacustrine complex cannot discharge into the river or into the Black Sea in time. The high level of the water softens the protection dams within the area of the town of Sulina. The pressure caused by the difference in level has a tendency to break the protection dams. The floods occurring in the locality of Caraorman and in the RosuePuiu lacustrine complex have both natural and anthropic causes: the amplification of heavy rains in the context of the global climatic changes and the high levels of Danube waters, resulting from the marine storms from EeNE and from the “high sea” effect, with values of 2.2 m. In addition, among the causes, it is worth noting certain hydrotechnical works lacking impact studies, constructed after 1965, and the resizing of the natural access mouths of the channels to facilitate industrial reed harvesting, fishing, etc. The effect of these changes is the faulty balancing of the excess discharge, which has penetrated the inner delta from the Danubian arms. The natural entries of the access channels towards the lakes has acted upon the inner level within the lacustrine complex on the principle of absorption/siphon, conditioned by the runoff speed of the Danube towards the sea. The modifications brought to the channel mouths by dredging have a cone effect; they take over the excess discharges imposed by the river runoff speed (the water level within the lacustrine complex is imposed by the direct pressure of the Danubian arms). In this case, the channels no longer act reversibly, with water discharging from the main arms (Sulina, St. George) towards the lacustrine complex and vice versa, from the complex towards the Danubian arms. To eliminate the water excess within the RosuePuiu lacustrine complex, a weir was constructed on the existing dam between the localities of Sulina and St. George (Lake Rosulet). This weir e at the level 1.20 m r MNS e starts working at a Danubian discharge of 11 000 m3/s. At a Danubian discharge of 16 000 m3/s, a discharge of 81 m3/s at the level of 1.50 m may be transited. There are two variants that would supplement the transit during high waters: building a weir at the 0.60 m level (r MNS) and with a width of 200 m and building another weir at the 0.80 m level (r MNS) and with a width of 250 m. The two additional weirs could be built at the crossroads of the Imputita channel with the Sulina-St. George dam, at the level of Lake Rosu. In this case, the backwater and flooding of the locality of Caraorman can be avoided. Because the current weir is undersized, the waters can move on to the Tataru channel and thus potentially flood two localities (Sulina and St. George). At the same time, other actions can also be performed such as the calibration of the CrisaneCaraorman channel by totally closing the upstream mouth (320 m) and by partially closing the downstream one (180 m), providing an opening of approximately 20 linear meters for the transit of water and ships. Other actions include supplementing the water discharging capacity by building a new weir (a continuation of the existing one), with a length of 180 linear meters at the level 0.60 m r MNS). Construction of works for the improvement of environmental conditions in the areas of natural reproduction of the autochthonous fish (earth-works to reshape and dig channels and brooks) and desilting the upstreamdownstream areas of lakes RosuePuiu can also be performed (Fig. 5). The Sulina Local Council proposed the construction of a channel to ensure a direct connection (to go around the Busurca channel) for leisure and fishing vessels between the town of Sulina and the RosuePuiu lacustrine complex. This project involves the execution of the following works: an 830-m long channel, flanked by two adjacent dams sized at the protection level of the agricultural precinct; a basin for small vessels (2000 m2); a landing stage; and an embankment, among others. At the same time, a simple sluice e with flat, dismountable gates and a total opening of 4e5 m, placed on the Imputita-downstream brook e will be constructed at the
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crossroads with the dam that connects the localities of Sulina and St. George. The Tataru channel was dug before 1989 to ensure the material necessary for the construction of the dam meant to ensure the electrical supply line. The dam separates the RosuePuiu lacustrine complex from the Black Sea. The channel that resulted from dredging took over the role of discharging channel for the flows towards the arms of Sulina and St. George. The current weir is aggradated. This is why the weir cannot ensure the elimination of the excess water in time during flooding. The weir can also be blocked with large pieces of aquatic vegetation carried during high waters. It is very difficult, and even sometimes impossible, to break them. At the same time, the water evacuation channels within the RosuePuiu lacustrine complex need active and permanent maintenance, implemented via annual dredging works, to ensure a proper depth and ensure they are capable of eliminating excess water. The construction of a draining network in the village of Caraorman will solve the issue related to the water from rain and infiltration. The water will be collected in the draining channels up to the lift station and eliminated in the harbour basin. The reduction of the additional discharges from the area of the fluviomaritime levee can also be accomplished through desiltation works for certain channels (the Caraorman channel downstream from the confluence with the Crisan channel; the Vatafu-Imputita channel; the Vatafu-Lumina channel; the Rosu-Tataru channel; the Erenciu-Puiu channel) or by dredging the large lacustrine cuvettes (Lake Rosu 25 000 m3; Lake Puiu 15 000 m3) (Fig. 5). The Sulina-St. George dam encloses the discharging channels for the flows that are naturally discharged into the Black Sea. The distance from the dam to the seashore ranges between 800 and 1300 m, over a length of 32 km (between the mouths of Sulina and St. George). The impact produced by the emergence of the backwater e after the elevation of the dam e is cumulative with the impact of the water from the CrisaneCaraorman channel. Thus, the following propositions are made: closing the Caraorman channel upstream (where an uncontrolled discharge penetrates); correcting the access mouth to the delta in case of the Busurca channel; constructing, on the path of the Sulina-St. George dam, several small-sized discharging bridges (small bridges do not allow the penetration of saltwater from the sea towards the inner delta during storms of standing waves, which are frequent in this area); resizing the dams that delimit the dammed precincts because they are sized at the flood level of 1970 (the levels of 2 m), but these levels are lower than the ones recorded for the years 2006 and 2010; and the inauguration of the drainage lift stations should all be performed. The works proposed have the following functions: repair (they improve the physical environment by reactivating the phenomena of self-cleaning and water quality improvement), preservation (they target a favourable water transit through the lacustrine complex and they determine a reduction of the alluvia and the maintenance of relatively higher levels compared to the situation before 1980), and protection (the localities of Caraorman, Sulina and St. George will no longer be at risk for floods). 6. Conclusions Most hydrotechnical works executed before 1989, in the communist period, were not based on impact studies because their main purposes were of an economic nature. Preserving the natural environment was a secondary issue, or it was simply ignored (Giosan et al., 2012; Lechner et al., 2014; Maselli and Trincardi, 2013; Stein et al., 2012). Thus, some deltaic surfaces were completely drained to be transformed into agricultural fields.
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Taking into account that the Danube Delta was declared a Reservation of the Biosphere, there is a special focus on the impact of economic activities on the environment. The development of tourism does not need to involve the construction of channels or dams that destabilise the ecologic balance. It can be performed using the proper methods, in agreement with the European standards in the field. Currently, there is no industry in the territory of the Danube Delta. The reduced altitudes in the Danube Delta and the existence of a rich network of arms, channels and lakes make the floods propagate over its entire surface. During the greatest floods, only some portions of the fluvio-maritime levees and of the pre-deltaic land (10%) are affected. The construction of the CrisaneCaraorman channel and of a dam on the sea littoral, along the Tataru channel resulted in the emergence of backwater and of floods in the village of Caraorman and, secondarily, in the arms of Sulina and St. George. In order to reduce the risk of floods in the localities of the RosuePuiu lacustrine complex, it is recommended that other hydrotechnical works be constructed or the old ones restored. We refer here to recalibrating the mouth of the CrisaneCaraorman channel by closing the northern derivation and under-sizing the old one; recalibrating the weir at the level of Lake Rosulet, by lowering the crest; building two other weirs at the level of the Imputita brook and of Lake Rosu; desilting the main channels and the lacustrine cuvettes of Rosu and Puiu; and creating a network of drainage channels around the locality of Caraorman and eliminating the excess water by pumping, among other actions. Acknowledgements We are thankful to the Geo-archaeology Laboratory within the Faculty of Geography and Geology, “Alexandru Ioan Cuza” University of Iasi, which provided the tools and carried out the processing of the data. The Ministry of Education and Research paid for the measurements and the publication through CNCS grant no. 0857, for the period 2011e2014, with Professor Bounegru Octavian, PhD, as a grant director. References Apel, H., Aronica, G.T., Kreibich, H., Thieken, A.H., 2009. Flood risk analysesdhow detailed do we need to be? Nat. Hazards 49 (1), 79e98. Cech, M., Cech, P., 2013. The role of floods in the lives of fish-eating birds: predators loss or benefit? Hydrobiologia 717 (1), 203e211. Cencini, C., Marchi, M., Torresani, S., Varani, L., 1988. The impact of tourism on Italian deltaic coastlands: four case studies. Ocean Coast. Manag. 11 (4e5), 353e374. Chen, X., Zong, Y., 1999. Major impacts of sea-level rise on agriculture in the Yangtze delta area around Shanghai. Appl. Geogr. 19 (1), 69e84. Choudhury, N.Y., Paul, A., Paul, B.K., 2004. Impact of control embankment on the flash flood in Bangladesh: a case study. Appl. Geogr. 24 (3), 241e258. Coops, H., Buijse, L.L., Buijse, A.D., Constantinescu, A., Covaliov, S., Hanganu, J., €ro €k, L., Ibelings, B.W., Menting, G., Navodaru, I., Oosterberg, W., Staras, M., To 2008. Trophic gradients in a large-river Delta: ecological structure determined
by connectivity gradients in the Danube Delta (Romania). River Res. Appl. 24, 698e709. Cummings, C.A., Todhunter, P.E., Rundquist, B.C., 2012. Using the Hazus-MH flood model to evaluate community relocation as a flood mitigation response to terminal lake flooding: the case of Minnewaukan, Nort Dakota, USA. Appl. Geogr. 32 (2), 889e895. Frihy, O.E., 1996. Some proposal for coastal management of the Nile delta coast. Ocean Coast. Manag. 30 (1), 43e59. Gastescu, P., Driga, B., Anghel, C., 1985. Caracteristicile morfohidrografice ale Deltei Dunarii ca rezultat al modificarilor naturale si antropice actuale. Hidrobiologia 18, 29e42. Giosan, L., Bokuniewicz, H., Panin, N., Postolache, I., 1999. Longshore sediment transport pattern along the Romanian Danube delta coast. J. Coast. Res. 15 (4), 859e871. Giosan, L., Coolen, M.J.L., Kaplan, J.O., Constantinescu, S., Filip, F., FilipovaMarinova, M., Kettner, A.J., Thom, N., 2012. Early Anthropogenic Transformation of the Danube e Black Sea System. Scxientific Reports 2(582). http://dx.doi.org/ 10.1038/srep00582. Grigoras, I., 2012. Using remote sensing to analyse hydro-morphological changes on Danube delta biosphere reserve coast line. Sci. Ann. Danube Delta Inst. 18, 319e324. Lechner, A., Keckeis, H., Lumesberger-Loisl, F., Zens, B., Krush, R., Tritthart, M., Glas, M., Schludermann, E., 2014. The Danube so colorful: a potpourri of plastic litter outnumbers fish larvae in Europe's second largest river. Environ. Pollut. 188, 177e181. http://dx.doi.org/10.1016/j.envpol.2014.02.006. Marchand, M., Sanchez-Arcilla, A., Ferreira, M., Gault, J., Jimenez, J.A., Markovic, M., Mulder, J., Rijn, L., Stanica, A., Sulisz, W., Sutherland, J., 2011. Concept and science for coastal erosion management e an introduction to the conscience framework. Ocean Coast. Manag. 54, 859e866. Maselli, V., Trincardi, F., 2013. Man Made Deltas. Scientific Reports 3(1926). http:// dx.doi.org/10.1038/srep01926. Mierla, M., Romanescu, G., 2012. Method to assess the extreme hydrological events in Danube fluvial Delta. Air Water Compon. Environ. 149e157. Navodaru, I., Staras, M., Cernisencu, I., 2001. The challenge of sustainable use of the Danube Delta Fisheries, Romania. Fish. Manag. Ecol. 8 (4e5), 323e332. Palanques, A., Guillen, J., 1998. Coastal changes in the Ebro delta: natural and human factors. J. Coast. Conserv. 4 (1), 17e26. Panin, N., Overmars, W., 2012. The Danube Delta evolution during the Holocene: reconstruction attempt using geomorphological and geological data, and some of the existing cartographic documents. Geo-Eco-Marina 18, 75e104. Romanescu, G., 2010. Morphology and dynamics of the Danube Delta littoral between the sulina and Sfantu Gheorghe river mouths (Romania). Pontica 43, 515e531. Romanescu, G., 2013a. Geoarchaeology of the ancient and medieval Danube Delta: modeling environmental and historical changes. A review. Quat. Int. 293, 231e244. Romanescu, G., 2013b. Alluvial transport processes and the impact of anthropogenic intervention on the Romanian littoral of the Danube delta. Ocean Coast. Manag. 73, 31e43. Romanescu, G., Bounegru, O., 2009. The dynamics of the north-western delta littoral of the Black Sea during historical periods (Danube delta). Pontica 42, 519e527. Romanescu, G., Cojocaru, I., 2010. Hydrogeological considerations on the western sector of the Danube Delta e a case study for the Caraorman and Saraturile fluvial-marine levees (with similarities for the Letea levee). Environ. Eng. Manag. J. 9 (6), 795e806. nchez-Arcilla, A., Jime nez, J.A., Stive, M.J.F., Iban ~ ez, C., Pratt, N., Day, J.W., Sa Capobianco, M., 1996. Impacts of sea-level rise on the Ebro Delta: a first approach. Ocean Coast. Manag. 30 (2e3), 197e216. Stein, H., Griebler, C., Berkhoff, S., Matzke, D., Fuchs, A., Hahn, H.J., 2012. Stygoregions e a Promising Approach to a Bioregional Classification of Groundwater System. Scientific Reports 2(673). http://dx.doi.org/10.1038/srep00673. Tiron, L.J., Coz, J., Provansal, M., Panin, N., Raccasi, G., Dramais, G., Dussouillez, P., 2009. Flow and sediment processes in a cutoff meander of the Danube Delta during episodic flooding. Geomorphology 106 (3e4), 186e197.
Contents lists available at ScienceDirect
Ocean & Coastal Management journal homepage: www.elsevier.com/locate/ocecoaman
Anthropogenic interventions and hydrological-risk phenomena in the fluvial-maritime delta of the Danube (Romania) Gheorghe Romanescu a, b, *, Cristian Constantin Stoleriu a, b a b
Alexandru Ioan Cuza University of Iasi, Faculty of Geography and Geology, Department of Geography, Bd. Carol I 20A, 700505 Iasi, Romania Alexandru Ioan Cuza University of Iasi, ARHEOINVEST e Interdisciplinary Platform, Laboratory of Geoarchaeology, Bd. Carol I, 20A, 700505 Iasi, Romania
a r t i c l e i n f o
a b s t r a c t
Article history: Available online
The Danube Delta represents the most important wetland of Europe and the manifestation area of periodical spring-summer floods. The hydrotechnical works executed in the Danube Delta between 1950 and 1990 were meant to protect the localities against floods and to facilitate the fluvial transport. For rapid access to the locality of Caraorman (for the exploitation of quartziferous sand) and to the Rosu touristic complex, the CrisaneCaraorman channel was oversized (12 km long, 60e70 m wide, with a maximum depth of 4e6 m). The access mouth of the channel in the Sulina arm and the outlets towards the Black Sea of the deltaic lacustrine complex were poorly designed. The aggradation of the channel determined the increase in the solid discharged carried by the water and the accentuation of the alluvia accumulated in lakes. To facilitate the transit of the fluvial waters towards the Black Sea, a weir was built at the mouth of Lake Rosulet (1.20 m r MNS). Unfortunately, the weir is too high, and the water level within the lacustrine complex increases alarmingly during floods. This is why the locality of Caraorman e situated 25 km away from the Black Sea e becomes flooded. That is, there is an increase in the phreatic level (the localities of Sulina and St. George are also affected but not to the same extent). The topographic and bathymetric measurements and the precise positioning of the targeted critical points (GPS) served as the methods for investigating the deltaic area affected by flooding. The causes of the backwater floods were identified, and the measures of an adequate management plan were set out. To eliminate this impediment, alterations to the hydrotechnical works must be made as follows: reducing the height of the existing weir and building two other weirs with lower crests; dredging the secondary channels and the lacustrine cuvettes; and using shallow-draft ships. The lack of funds and the apathy of the habilitated institutions delays the implementation of the necessary measures. © 2014 Elsevier Ltd. All rights reserved.
1. Introduction The rectification of the Danubian arms and the construction of channels in the Danube Delta have a long tradition. The first significant hydrotechnical works were executed by the European Commission, instituted in 1856 by the Peace Treaty of Paris. The works enabled the navigation of deep shallow-draft ships on the old Sulina arm, channelled a distance of 62 km (of the initial 83-km length) (Panin and Overmars, 2012; Romanescu, 2013a, 2013b). The practice of extensive agriculture and the exploitation of local resources determined the implementation of a land
* Corresponding author. Alexandru Ioan Cuza University of Iasi, Faculty of Geography and Geology, Department of Geography, Bd. Carol I 20A, 700505 Iasi, Romania. Tel.: þ40 744774652; fax: þ40 232 201481. E-mail address: [email protected] (G. Romanescu). http://dx.doi.org/10.1016/j.ocecoaman.2014.09.007 0964-5691/© 2014 Elsevier Ltd. All rights reserved.
management plan by damming and channel building in the period 1900e1940. Most channels connected the main fluvial arms (Chilia, Sulina and St. George) to the great lacustrine complexes. Thus, the waters within the delta were renewed, and the floods could be mitigated by taking over the water excess. When the water level in the branches was low, a reversed transit was ensured, meaning flow from the inside towards the main hydrographical arteries. Unfortunately, many channels were poorly designed. They are straight and very shallow. This has led to the clogging of the lacustrine cuvettes and to blocking of the access paths. The period of the large, exclusively anthropic channels is now outdated. Currently, the preferred solutions are the old secondary arms, which meander and comprise aquatic vegetation capable of stopping a portion of the transited alluvia (Giosan et al., 1999; Romanescu and Cojocaru, 2010; Tiron et al., 2009).
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Fig. 1. Geographic location of the Danube Delta and of the Caraorman-Rosu maritime sector (left). Location of the CrisaneCaraorman channel compared to the main landforms (left) and the mathematical coordinates (right).
The fluvial transport in the Danube Delta d from the arms towards the lacustrine complexes and between the main lacustrine cuvettes d is usually ensured by small-sized vessels (crops, peoples). Tourism and the exploitation of natural resources have led to the construction of large channels, as follows: Dunavat, Dranov, Mustaca, Lipovenilor, Mila 35, Pardina, Dovnica, and Sontea, among others. Most of the world deltas have gone through the same process. The single most important economic and technical issue for the Danube Delta is flood risk. The reduced altitude (mean of 0.52 m; 13 m maximum) and the temperate-continental climate of transition characteristic to the entire hydrographical basin e where heavy rains are numerous e has led to fluctuating discharges (Gastescu et al., 1985; Grigoras, 2012). In this case, frequent floods occur on the Danube and implicitly in the delta. The most affected areas are the localities developed along the arms. Those of the fluvio-maritime levees are affected by the floods provoked by the increase in the water level and by the emergence of infiltrating waters in the phreatic level of coarse sands (Caraorman, Letea, C.A. Rosetti, etc.). Floods are frequent in all deltas of the world, but the risk phenomenon is specific to populated areas. Considering the great scientific and economic interest represented by deltaic regions e mostly the mouths of the great rivers e there is an abundance of studies examining this subject. These studies are both national and international (Apel et al., 2009; Cech and Cech, 2013; Cencini et al., 1988; Chen and Zong, 1999; Choudhury et al., 2004; Cummings et al., 2012; Frihy, 1996; Marchand et al., 2011; Mierla nchezand Romanescu, 2012; Palanques and Guillen, 1998; Sa Arcilla et al., 1996). The present study aimed to identify the causes of the backwater floods impacting the village of Caraorman, and to elaborate a series
of measures for eliminating or mitigating them. The identification of the causes involved high-precision topographic and bathymetric methods. The new data was corroborated with the previously available scientific information. The main objective was to elaborated a program of measures for eliminating the backwater floods affecting the settlements from the Danube Delta, and for refreshing the lacustrine waters by creating a proper link between the deltaic area and the sea. 2. Regional settings The Danube Delta occupies the south-eastern part of Romania, and it unfolds in the territory of two countries: Romania and, partially, Ukraine (Fig. 1). The surface area of the Danube Delta is 5600 km2; it is the only delta in the world that has been declared a Reservation of the Biosphere (in 1992) (Romanescu, 2010; Romanescu and Bounegru, 2009). In the case of the GangeeBrahmaputra common delta, only the Sunderban area was included (since 2001) into the UNESCO World Heritage List. The area studied here concerns the maritime delta between the arms of Sulina (to the north), St. George (to the south), the fluvio-maritime levee of Caraorman (to the west) and the littoral of the Black Sea (to the east). The locality of Caraorman is situated in the central-eastern sector of the fluvio-maritime levee of Caraorman. To facilitate the access to the area, an old secondary arm was channelled. The channel was oversized because, in the communist period, there was an attempt to industrially exploit the quartziferous sand. This is why a precinct was created to install an industrial harbour. The exploited sand was supposed to be transported via the CrisaneCaraorman channel with exiting to the Sulina
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channel. The CrisaneCaraorman channel also facilitated access to Lake Rosu, where one of the most important summer resorts was developed. 3. Methodology The field measurements were taken by using the LEICA TCR 1201 Total Station. Alongside the LEICA GPS 1200, it is part of the SYSTEM 1200 LEICA. The Topographic Directorate of Tulcea provided the coordinates of the survey markers. Forty station points were emphasised and marked in the field by wooden stakes, in various areas of firm ground or swamps, for an optimal covering of the entire surface. After finalising the measurements, the data were processed in AutoCAD. At the same time, a high-quality GPS was used to exactly delimit the analysed perimeter. The data of the topographic surveys were represented using Stereographic 70 Projection. The limits of the channels and of the lakes were delimited based on the topographic measurements and on the GPS. For the bathymetric measurements, the Valeport Midas Surveyor (Bathy-500DF Dual Frequency Hydrographic Echo Sounder) was used. The resolution of this echo sounder is 1 cm/1 cm, and it includes a GPS. To process the bathymetric data and to generate the thematic maps, the TNTMips v.7.2 and ArcGis v.9.3 software products were used. This enabled the elaboration of the numerical field model and its graphic transposition for various uses. In this case, over 250 000 points were indexed, and approximately 200 000 points were interpolated within graphs. These are innovative graphic representations of the lacustrine cuvettes in mathematical modelling. The longitudinal routes for channels were pinpointed on three alignments: centre, side left and side right. For a higher bathymetric precision, 100 transects were measured on the entire alignment of the CrisaneCaraorman channel. For each confluence, transects were measured downstream and upstream from the mouth of the secondary channel. Special attention was paid to the outlet areas of the channels linking the main lakes. In this case, the alluvial cones were outlined. The cartographic materials used are part of the collection owned by the “Alexandru Ioan Cuza” University of Iasi, through the annex of the Geoarchaeology Laboratory: orthophotoplans and satellite images. After finishing the measurements, the data was processed with the AutoCAD software suite (Autodesk, San Rafael, CA, USA). Concurrently, a GPS was used to establish the exact surface area of the RosuePuiu lacustrine complex. The research stages are summarised according to a simplified plan (Fig. 2).
Fig. 2. The breakdown of the research stages.
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4. Results The Administration of the Danube Delta Biosphere Reservation has improvement of the water regime in the deltaic depressions and in the network of channels as one of its goals (Coops et al., 2008; Navodaru et al., 2001). The target is to protect the water quality and the deltaic ecosystems. Most hydrotechnical works constructed in the past few years have had the purpose of improving the repartition of liquid and solid discharges on the main arms and of protecting against floods. The RosuePuiu lacustrine complex was naturally supplied through the secondary branches and the brooks. The first channel built in the period 1930e1940 was Litcov, supplied by the St. George arm. It drained and supplied the depression areas of Carasuhat, Rusca and Gorgova. After transiting the delta over a significant length of it, on the ancient location of a secondary arm, it finally discharged filtered, suspension-free water. For this reason, the RosuePuiu lacustrine complex was well outlined, and the degree of clogging ranged within reasonable limits. Enclosing the access mouth of the Litcov channel e when the works for the development of the CrisaneCaraorman channel began e led to its organic clogging and to the reduction of the water flows towards the RosuePuiu complex. The CrisaneCaraorman channel e 12 km long, 60e70 m wide, comprising maximum depths of 4e6 m e was finalised in 1981. After the construction of this artery, the clogging degree of the lakes within the RosuePuiu complex has increased, but the circulation of vessels towards the locality of Caraorman was facilitated. Most of the channels within the area in question were built after 1960: Litcov-Imputita, Vatafu-Imputita, Tataru and Sondei. The Potcoava channel, which connects the lakes Puiu and Rosu, was built in the period 1952e1960, whereas the BusurcaeImputita channel was constructed in 1941e1951, with a connection to the Sulina arm. The CrisaneCaraorman channel starts from the Sulina arm, and it is directed towards the RosuePuiu lacustrine complex. A secondary artery is oriented towards the locality of Caraorman. The connection with the Sulina arm is ensured upstream. An island emerged at the mouth of the channel. This is why the channel now has two mouths: the first, with an upstream opening, frontally with the direction of the current and the second, with a downstream opening, in the direction of the current. The mouth of the CrisaneCaraorman channel records maximum depths of 4 m in the upstream channel and 3 m in the downstream channel. The left bank of the channel (eastwards) is more abrupt, with slopes exceeding 45 (Fig. 3A, B). Upstream from the fluvio-maritime levee of Caraorman, the channel divides into two arteries: a southern one, which ends at the level of the Caraorman locality and an eastern one, which continues towards the RosuePuiu lacustrine complex. The maximum depth within the bifurcation sector is 6 m. The CrisaneCaraorman channel records depths of 4 m. The right bank has slopes measuring more than 35 , whereas the left bank comprises slopes exceeding 45 (Fig. 3CeE). The secondary artery oriented towards the village of Caraorman has a 10-m maximum depth, recorded at the level of the port. Actually, this is the deepest point of all the internal sectors of the Danube Delta. The main channel maintains depths of 6 m. The southern bank has slopes measuring more than 45 (Fig. 3F, G). Depths of over 4 m are recorded in the bifurcation sectors. The mouth of the Vatafu-Imputita channel has a maximum depth of 10 m, whereas the main channel has a maximum depth of 6 m (Fig. 3H, I). At the entry to Lake Puiu, the depths measure 4 m. The alluvia carried by the water determine an asymmetrical alluviation, with
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Fig. 3. The connection of the CrisaneCaraorman channel with the Sulina arm as the central axis of the Danube in the delta: A) bathymetry; B) submerged slopes; The bifurcation area of the CrisaneCaraorman channel: C) bathymetry; D) submerged slopes; E) 3D image; The harbour precinct of Caraorman: F) bathymetry; G) submerged slopes; Sector of confluence with a secondary arm (the Vatafu-Imputita brook): H) bathymetry; I) submerged slopes.
maximum intensity in the southern sector. In this area, the depths measure 1e2 m. On the right bank of the channel, at the outlet, slopes of over 45 are present (Fig. 4A, B). The high amount of alluvia determined the partial alluviation of certain lacustrine cuvettes. In this case, the small-sized lakes were affected. For this water body, the channel has reduced widths and depths down to 2 m. The longitudinal levees penetrate deep in the lake. The slopes are even on both sides (Fig. 4C, D). At the exit from Lake Puiu, the maximum depths measure 8 m. In Lake Rosu, the depth of the channel is maintained at 5e6 m (Fig. 4E, F). The slopes are even on both banks of the channel. Lake Rosu presents a similar situation to the one in Lake Puiu. The RosuePuiu lacustrine complex has a surface area of 42,300 ha. In the years 1980e1990, it has suffered significant anthropogenic interventions. The CrisaneCaraorman channel and the Sulina-St. George littoral sector are in a direct relation, and they influence each other. To eliminate the inconveniences caused by the increase in the lake water levels during the floods, the following hydrotechnical works were constructed: -a protective dam in the littoral area (along the Tataru channel), 2 m high, to prevent the emergence of breaches, created by spontaneous and uncontrolled runoffs (points favouring the development of erosion at the level of the Imputita and Sondei mouths); -a weir in the littoral dam, with a 1.20 m crest level compared with the level of the Black Sea and with a width of the tailboard of 200 m; -a channel bordering the littoral dam, oriented towards the delta, to take over the discharging role of the small and medium
streams towards the Sulina and St. George arms (Tataru channel). The old project also included the plan of recalibrating the access mouth of the Crisan channel. Unfortunately, it was not finalised. 5. Discussion The hydrotechnical works executed in the Danube Delta have focused mostly on improving the water circulation of the arms and in the lacustrine complexes and, at the same time, on protecting the human settlements against floods. Concerning the studied area, the village of Caraorman is affected because it often is flooded by the high waters coming from the Sulina arm, as well as by the backwater from the RosuePuiu lacustrine complex (after the construction of the Sulina-St. George dam). Secondarily, similar phenomena are the causes for flooding of the localities of Sulina and St. George (Giosan et al., 1999; Romanescu, 2013a). The cone-shaped mouth of the CrisaneCaraorman channel led to the emergence of a circular current, which created an island in the middle. This is why the mouth has two openings of the Sulina arm. The main current unfolds on the upstream mouth. In this channel, the waters oriented towards the Sulina arm-the CrisaneCaraorman channel run off. The downstream mouth is available for the runoff of the waters oriented towards the CrisaneCaraorman channel and the Sulina arm, in the summer, when the Danube levels are low (Fig. 3A, B). The high slopes on the eastern bank are the result of the current with an NWeSE direction, but reversed current also has manifested in the summer only along this bank.
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Fig. 4. Entry of the CrisaneCaraorman channel in Lake Puiu: A) bathymetry; B) submerged slopes; Image of the alluvial cone and the accelerated clogging of a lacustrine cuvette at the entry to Lake Puiu: C) bathymetry; D) submerged slopes; The connection channel between Lake Puiu and Lake Rosu: E) bathymetry; F) submerged slopes.
The channel was ramified for economic reasons: to facilitate the transport of the quartziferous sand from the Caraorman fluviomaritime levee and to transport the merchandise from and to the village of Caraorman (Fig. 3CeE). For this reason, the channel was enlarged and deepened. The transit is possible for barges and medium-sized sailing ships. The great depth in the southern sector of the roadstead (10 m) is also due to the fluvial current that strikes this bank directly. The current e with an NeS direction, towards the village of Caraorman e engages a significant amount of water that infiltrates in the sandy deposits, and, when the water is high, it floods the village (Fig. 3F, G). The greater depths of the right bank indicate that the river waters (the Sulina arm) enter and move e most of the time e on this alignment. The waters from the RosuePuiu lacustrine complex can also move in the right bank, The greater depths of the rightbank Vatafu-Imputita channel mouth indicates creation by the NWeSE current (from the Sulina arm) (Fig. 3H, I). The high clogging within the lacustrine complexes of the Danube Delta is due to the Danubian alluvia transport. The high level of solid discharge causes serious clogging problems at the entry of the main lacustrine cuvettes. The total amount of alluvia transported by the Danube has fluctuated over time, and it has displayed a descending trend (Table 1). The drastic decrease of the past few years is due to the construction of the Iron Gates I (a dam), which stops over 30 million tons of alluvia every year. The direction of the channel mouths and of the brooks, as well as their size, directly influences the penetration of alluvia in the inner sectors of the delta (Romanescu, 2010; Tiron et al., 2009). At the entry of Lake Puiu, an asymmetrical alluvial cone (lacustrine delta) emerged, with maximum development of the right side. The asymmetry is determined by the dominance of the
Table 1 Evolution of the solid discharge transported by the Danube and its distribution among the main arms (Gastescu et al., 1985; Giosan et al., 1999; Romanescu, 2013b; Tiron et al., 2009). Danube and the main arms
Chilia St. George Sulina Danube
Year 1894 Million t
1958 Million t
2000 Million t
56.2 17.8 7.0 81.0
48.4 16.5 5.5 70.4
15.0 5.0 2.0 22.0
NeE winds, which push the alluvia-loaded waters southwards. The clogging is accelerated by the existence of winds, just as in the case of flocculation in seawaters (Fig. 4AeF). The small-sized lakes crossed by the CrisaneCaraorman channel display a high degree of clogging. In this case, the longitudinal levees cross the entire lacustrine cuvette, and the aquatic vegetation is luxuriant. The morphological characteristics of the channel are a consequence of the local factors: the fluvial current, the geological constitution of the substratum, the vegetation, and the winds, among other factors. The construction of the CrisaneCaraorman channel led to easier circulation of the vessels between the main localities of the delta and to refreshing of the waters within the RosuePuiu lacustrine complex. Unfortunately, the hydrotechnical works of the past have failed to consider other local particularities. The significant width and depth of the channel, as well as its linearity have led to a massive alluvia loading and to an acceleration of the clogging in case of the big lakes. The construction of the dam
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on the littoral alignment (with NeS direction) and by partially eliminating the deltaic water towards the Black Sea determined the emergence of a backwater manifesting up to the village of Caraorman. This is why the groundwater rises up to the sandy substratum and most dwellings have been affected by the spring floods. The phenomenon is also accentuated by the fact that, during the floods, a high amount of water from the Sulina arm enters through the wide mouth of the channel and directly towards the upstream sector. The lack of channel meandering facilitates the flood waters acquiring high velocity, which thus directs them towards the harbour basin of the sandy fluvio-maritime levee of Caraorman. In this case, the high-speed waters of the CrisaneCaraorman channel amplify the backwater from the RosuePuiu lacustrine complex. The littoral area between the mouths of Sulina and St. George is influenced by fluvial waters (from the west) and by maritime waters (from the east). In this case, the mouths of the main mouths (Sulina and St. George) feature secondary deltas, whereas the intermediary sectors are continually withdrawing. At the level of the RosuePuiu lacustrine complex, at the mouths of the Imputita secondary arm and of the Sondei channel, the highest littoral erosion rate of the entire delta has been recorded: 10e15 m/year (Romanescu, 2013a, 2013b). The fact that the CrisaneCaraorman channel was not calibrated and that the Litcov channel was desilted and reopened determined the emergence of tributary discharges in the RosuePuiu depression. To allow the ships with a shaft exceeding 60 cm e loaded with tourists, who visited the Rosu touristic complex e on the channel, dredging works were executed, to ensure optimal navigation. This has led to an aggradation of levels and to an increase of the water stationing in the depression. The alluvia inflow has maintained high levels. The reduction of discharges and pressures on the dams within the RosuePuiu lacustrine complex has been possible through the breaches made in the dam on the Sulina-St. George littoral (Fig. 5). The derivation of the channel that reaches the north of the Caraorman village was built to facilitate the transport of passengers and merchandise from and to the village and to ensure the transport of the quartziferous sand, which is used in the glassware
industry. The anti-communist revolution of December 1989 resulted in a ceasing of exploitation of the sand. Currently, the local sand-exploitation-related construction is only a ruin. The plan was for tugboats and large barges to be allowed in the channel. The sandy deposit within the fluvio-maritime levee of Caraorman had an insignificant amount of quartz, as the new political regime, post1989, stopped the work in the area. The basins resulting from stripping and from sand exploitation could have endangered the existence of the Caraorman forest, which has been declared a strictly protected area and has high scientific value. Between the protective dam in the eastern part of the Caraorman fluvio-maritime levee and the village with the same name, there is a zone with low altitudes, where the water from infiltrations and rains gathers. The infiltrations are favoured by the coarse granulometry of the sands and by the low altitude (0e1 m). In this case, the piezometric level of the phreatic is 0e2 m deep (Romanescu and Cojocaru, 2010). Caraorman village is flooded because of the rise in groundwater. Calibrating the access mouth of the CrisaneCaraorman channel (closing the upstream mouth and calibrating the downstream mouth) would lead to large discharge limitations. The CrisaneCaraorman channel produces negative effects on the deltaic world: the channel acts like an absorbing cone for the Danubian flow. As a consequence, the inner levels within the RosuePuiu lacustrine complex and within the channels sometimes exceed the initial level of the Danubian arms by 40e75 cm (because of the pressure exerted by the river waters). The high discharge is responsible for significant alluvia loading, which thus clogs the lakes (Puiu, Puiulet, Rosu, and Rosulet) and the mouths of the channels. The waters loaded with alluvia contribute to the decrease in water quality because of increased turbidity; the channel facilitates the absorption of ice floes and discharges from the Sulina arm during the winter (in this case, the banks are destroyed and the luxuriant vegetation that blocks the access ways and even the weirs is disrupted). The channel has brought essential alterations to the deltaic landscape, and it has led to the disappearance of valuable fish species in favour of others. As it was built 30 km away from the Sulina arm, upstream, it is a threat to the town of Sulina because the
Fig. 5. The maritime area between the Sulina arm, the Caraorman fluvio-maritime levee, the Black Sea and the St. George arm.
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flow that penetrates the lacustrine complex cannot discharge into the river or into the Black Sea in time. The high level of the water softens the protection dams within the area of the town of Sulina. The pressure caused by the difference in level has a tendency to break the protection dams. The floods occurring in the locality of Caraorman and in the RosuePuiu lacustrine complex have both natural and anthropic causes: the amplification of heavy rains in the context of the global climatic changes and the high levels of Danube waters, resulting from the marine storms from EeNE and from the “high sea” effect, with values of 2.2 m. In addition, among the causes, it is worth noting certain hydrotechnical works lacking impact studies, constructed after 1965, and the resizing of the natural access mouths of the channels to facilitate industrial reed harvesting, fishing, etc. The effect of these changes is the faulty balancing of the excess discharge, which has penetrated the inner delta from the Danubian arms. The natural entries of the access channels towards the lakes has acted upon the inner level within the lacustrine complex on the principle of absorption/siphon, conditioned by the runoff speed of the Danube towards the sea. The modifications brought to the channel mouths by dredging have a cone effect; they take over the excess discharges imposed by the river runoff speed (the water level within the lacustrine complex is imposed by the direct pressure of the Danubian arms). In this case, the channels no longer act reversibly, with water discharging from the main arms (Sulina, St. George) towards the lacustrine complex and vice versa, from the complex towards the Danubian arms. To eliminate the water excess within the RosuePuiu lacustrine complex, a weir was constructed on the existing dam between the localities of Sulina and St. George (Lake Rosulet). This weir e at the level 1.20 m r MNS e starts working at a Danubian discharge of 11 000 m3/s. At a Danubian discharge of 16 000 m3/s, a discharge of 81 m3/s at the level of 1.50 m may be transited. There are two variants that would supplement the transit during high waters: building a weir at the 0.60 m level (r MNS) and with a width of 200 m and building another weir at the 0.80 m level (r MNS) and with a width of 250 m. The two additional weirs could be built at the crossroads of the Imputita channel with the Sulina-St. George dam, at the level of Lake Rosu. In this case, the backwater and flooding of the locality of Caraorman can be avoided. Because the current weir is undersized, the waters can move on to the Tataru channel and thus potentially flood two localities (Sulina and St. George). At the same time, other actions can also be performed such as the calibration of the CrisaneCaraorman channel by totally closing the upstream mouth (320 m) and by partially closing the downstream one (180 m), providing an opening of approximately 20 linear meters for the transit of water and ships. Other actions include supplementing the water discharging capacity by building a new weir (a continuation of the existing one), with a length of 180 linear meters at the level 0.60 m r MNS). Construction of works for the improvement of environmental conditions in the areas of natural reproduction of the autochthonous fish (earth-works to reshape and dig channels and brooks) and desilting the upstreamdownstream areas of lakes RosuePuiu can also be performed (Fig. 5). The Sulina Local Council proposed the construction of a channel to ensure a direct connection (to go around the Busurca channel) for leisure and fishing vessels between the town of Sulina and the RosuePuiu lacustrine complex. This project involves the execution of the following works: an 830-m long channel, flanked by two adjacent dams sized at the protection level of the agricultural precinct; a basin for small vessels (2000 m2); a landing stage; and an embankment, among others. At the same time, a simple sluice e with flat, dismountable gates and a total opening of 4e5 m, placed on the Imputita-downstream brook e will be constructed at the
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crossroads with the dam that connects the localities of Sulina and St. George. The Tataru channel was dug before 1989 to ensure the material necessary for the construction of the dam meant to ensure the electrical supply line. The dam separates the RosuePuiu lacustrine complex from the Black Sea. The channel that resulted from dredging took over the role of discharging channel for the flows towards the arms of Sulina and St. George. The current weir is aggradated. This is why the weir cannot ensure the elimination of the excess water in time during flooding. The weir can also be blocked with large pieces of aquatic vegetation carried during high waters. It is very difficult, and even sometimes impossible, to break them. At the same time, the water evacuation channels within the RosuePuiu lacustrine complex need active and permanent maintenance, implemented via annual dredging works, to ensure a proper depth and ensure they are capable of eliminating excess water. The construction of a draining network in the village of Caraorman will solve the issue related to the water from rain and infiltration. The water will be collected in the draining channels up to the lift station and eliminated in the harbour basin. The reduction of the additional discharges from the area of the fluviomaritime levee can also be accomplished through desiltation works for certain channels (the Caraorman channel downstream from the confluence with the Crisan channel; the Vatafu-Imputita channel; the Vatafu-Lumina channel; the Rosu-Tataru channel; the Erenciu-Puiu channel) or by dredging the large lacustrine cuvettes (Lake Rosu 25 000 m3; Lake Puiu 15 000 m3) (Fig. 5). The Sulina-St. George dam encloses the discharging channels for the flows that are naturally discharged into the Black Sea. The distance from the dam to the seashore ranges between 800 and 1300 m, over a length of 32 km (between the mouths of Sulina and St. George). The impact produced by the emergence of the backwater e after the elevation of the dam e is cumulative with the impact of the water from the CrisaneCaraorman channel. Thus, the following propositions are made: closing the Caraorman channel upstream (where an uncontrolled discharge penetrates); correcting the access mouth to the delta in case of the Busurca channel; constructing, on the path of the Sulina-St. George dam, several small-sized discharging bridges (small bridges do not allow the penetration of saltwater from the sea towards the inner delta during storms of standing waves, which are frequent in this area); resizing the dams that delimit the dammed precincts because they are sized at the flood level of 1970 (the levels of 2 m), but these levels are lower than the ones recorded for the years 2006 and 2010; and the inauguration of the drainage lift stations should all be performed. The works proposed have the following functions: repair (they improve the physical environment by reactivating the phenomena of self-cleaning and water quality improvement), preservation (they target a favourable water transit through the lacustrine complex and they determine a reduction of the alluvia and the maintenance of relatively higher levels compared to the situation before 1980), and protection (the localities of Caraorman, Sulina and St. George will no longer be at risk for floods). 6. Conclusions Most hydrotechnical works executed before 1989, in the communist period, were not based on impact studies because their main purposes were of an economic nature. Preserving the natural environment was a secondary issue, or it was simply ignored (Giosan et al., 2012; Lechner et al., 2014; Maselli and Trincardi, 2013; Stein et al., 2012). Thus, some deltaic surfaces were completely drained to be transformed into agricultural fields.
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Taking into account that the Danube Delta was declared a Reservation of the Biosphere, there is a special focus on the impact of economic activities on the environment. The development of tourism does not need to involve the construction of channels or dams that destabilise the ecologic balance. It can be performed using the proper methods, in agreement with the European standards in the field. Currently, there is no industry in the territory of the Danube Delta. The reduced altitudes in the Danube Delta and the existence of a rich network of arms, channels and lakes make the floods propagate over its entire surface. During the greatest floods, only some portions of the fluvio-maritime levees and of the pre-deltaic land (10%) are affected. The construction of the CrisaneCaraorman channel and of a dam on the sea littoral, along the Tataru channel resulted in the emergence of backwater and of floods in the village of Caraorman and, secondarily, in the arms of Sulina and St. George. In order to reduce the risk of floods in the localities of the RosuePuiu lacustrine complex, it is recommended that other hydrotechnical works be constructed or the old ones restored. We refer here to recalibrating the mouth of the CrisaneCaraorman channel by closing the northern derivation and under-sizing the old one; recalibrating the weir at the level of Lake Rosulet, by lowering the crest; building two other weirs at the level of the Imputita brook and of Lake Rosu; desilting the main channels and the lacustrine cuvettes of Rosu and Puiu; and creating a network of drainage channels around the locality of Caraorman and eliminating the excess water by pumping, among other actions. Acknowledgements We are thankful to the Geo-archaeology Laboratory within the Faculty of Geography and Geology, “Alexandru Ioan Cuza” University of Iasi, which provided the tools and carried out the processing of the data. The Ministry of Education and Research paid for the measurements and the publication through CNCS grant no. 0857, for the period 2011e2014, with Professor Bounegru Octavian, PhD, as a grant director. References Apel, H., Aronica, G.T., Kreibich, H., Thieken, A.H., 2009. Flood risk analysesdhow detailed do we need to be? Nat. Hazards 49 (1), 79e98. Cech, M., Cech, P., 2013. The role of floods in the lives of fish-eating birds: predators loss or benefit? Hydrobiologia 717 (1), 203e211. Cencini, C., Marchi, M., Torresani, S., Varani, L., 1988. The impact of tourism on Italian deltaic coastlands: four case studies. Ocean Coast. Manag. 11 (4e5), 353e374. Chen, X., Zong, Y., 1999. Major impacts of sea-level rise on agriculture in the Yangtze delta area around Shanghai. Appl. Geogr. 19 (1), 69e84. Choudhury, N.Y., Paul, A., Paul, B.K., 2004. Impact of control embankment on the flash flood in Bangladesh: a case study. Appl. Geogr. 24 (3), 241e258. Coops, H., Buijse, L.L., Buijse, A.D., Constantinescu, A., Covaliov, S., Hanganu, J., €ro €k, L., Ibelings, B.W., Menting, G., Navodaru, I., Oosterberg, W., Staras, M., To 2008. Trophic gradients in a large-river Delta: ecological structure determined
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