Hydrology In Stensovsko-zhebriyanski Plavni Practical Management, Danube Delta, Ukraine*
SOME PROPOSALS AND SUBSTANTIATION OF
HYDROLOGY IN STENSOVSKO-ZHEBRIYANSKI PLAVNI PRACTICAL MANAGEMENT, DANUBE DELTA, UKRAINE*
M.Ye. Zhmud
Danube Biosphere Reserve, Ukraine
The Danube Delta is the second largest delta in Europe. It is characterized by large areas of natural habitat and by very high biodiversity. The Delta lies in two countries: Romania and Ukraine. International Nature Protection Organizations and Governments of both countries are aware of the very important ecological value of this wetland. In the Ukrainian part the Danube Biosphere Reserve (DBR) occupying an area 46.402,9 ha was established in 1998. The Stensovsko-Zhebriyanski Plavni (SZP) with total area about 7.811 ha is the important part of the Reserve.
Before human activity in this area the SZP was a typical delta wetland. Now the whole area is completely surrounded with dikes and more or less artificial wetland. There are many ecological and economical problems in this area. Management of SZP has to serve two purposes that are difficult to combine. On one hand, it has to ensure long-term ecological sustainability of the ecosystem under consideration and make it as natural as possible, on the other it has to support economic potential of the area on high level (fishery, hunting, muskrat trapping, reed harvesting, frogs catching, grazing etc.). To combine the solution of the two mentioned tasks as much as possible became the responsibility of the DBR as the SZP is now under its jurisdiction.
All the parties concerned share practically the same opinion about SZP management during primary restoration of the degraded ecosystem. That was convincingly proved by many special meetings and discussions on different level (Odessa-Shevchenkovo, 1995; Kiev, 1997 and 1998; Vienna, 1998; Lelystad, 1998; Odessa, 1998 atc.). The essence of the opinion is the necessity to reduce the accumulated layer of alive and dead organic that occupy significant volume of the waterbody, destroy reed-stands, restore on the maximum possible area mosaic structure and waterflow. To achieve the
mentioned objectives within the foreseen future drying of reed-beds during summer-autumn period as much as possible will be needed.
At the stage of the consequent SZP management all the parties are interested at ensuring maximum waterflow through the wetland during floods in the Danube Delta (3-4 months in spring and early summer). However, the opinions of the main parties concerned about further management are different.
Nature conservation organizations would like to maintain the level regime in SZP as close to the natural as possible. In the understanding of WWF experts and staff members, for example, under the present conditions that should be ensured by maintaining maximum possible waterflow through all the hydrotechnical facilities as long a year as possible and, in the ideal case – all year round (J.C.J. van Wetten, 1998; oral presentations by some WWF staff members at the Steering Group Meeting on SZP Management). That would have lead to drying from time to time of significant wetland area in the years with medium and low water level.
The main users, on the contrary, would like to maintain high water level in the reed-beds as long as possible. To achieve that all the outer hydrotechnical facilities should be closed as soon as the water level in the Danube will start to decrease and the water will not enter the wetland – approximately in the end of June. High water level in SZP is necessary to maintain high economic potential of the wetland, as it is understood now (fish resources, games waterfowl in autumn, muskrat etc.).
In the present situation to find an option to satisfy everybody and form the basis for SZP management by the DBR it would be useful to overview the wetland’s natural evolution as a part of the Danube Delta, to determine its direction, trends and to outline the time-table for the future changes.
Before the secondary delta of the Kiliya arm of the Danube downstream of town Vilcovo started to form (about 350 years ago) there was probably was the most northern small arm of the river passing through the area now occupied by SZP. It probably was connected to the sea through a small breach in old Zhebriyanska Range near the root bank. There was a vast sandbar stretching to the south from its mouth. Some day it separated the Drevnedunaiski liman from the sea and in the last centuries restricted the primary Danube Delta.
Due to the closeness of the present SZP to the sea, shallowness of the mentioned river arm and insignificant height of the sandbar the influence of wind driven seawater to the area was significant. Under its influence, especially during the low water period in the second half of summer, the corresponding ecosystem of floodplain-estuarine type was formed.
As the secondary delta of Kilia Arm appeared and grew intensively during last fifty years a significant natural isolation of SZP from the sea began to show. The wetland is now connected to the sea not directly but through the freshwater bays Badyk and Soleny Kut. The rapid growth of Pereboynaya Kosa spit separating the wetland from the sea (see the recent satellite images) speeds up the process of the wetland isolation. To some extend the process is slowed down by dredging of the dying Belgorodski Arm of the Danube entering the mentioned bays.
Now salt water reaches the sluices of SZP only one-three times a year during several days – driven by exclusively strong and long wind.
In the long run it will be more and more difficult for marine water to reach SZP. After the full isolation of the bays Badyk and Soleny Kut that is likely to happen within nearest decades there will be no possibility for marine water to enter the reed-beds. That is the inevitable result of natural evolution of this part of the delta. As the result SZP will become a typical floodplain waterbody.
Similar processes are more intensive in the other deltaic zones that are more active (the central parts of the Kilia Arm secondary delta). The evolution of waterbodies from an open marine bay in the avandelta to the fully isolated from the sea and absolutely freshwater lake takes place within the lifetime of one generation. There is a lot of examples (see the map of Kilia Arm secondary delta, e.g., Lazarkin Kut Lake and other now isolated waterbodies in the area). It will never occur to anyone to restore the influence of sea (estuarine regime) to the Lazarkin Kut Lake. The same future waits for SZP in the nearest future.
Before the dike was built between SZP and the sea in the 40th for the purpose of road construction the wetland was connected to the sea through a wide but shallow strait. During low water period the strait was becoming more shallower and narrower which is absolutely natural. The next quite natural stage of connection between SZP and the sea development on condition of no anthropogenic changes should be first seasonal and then permanent cessation of direst connection between the waterbody and the bay. It is quite possible that this would have already happened by present time. That can be proved by the existing during the last decade’s trend of the watercourses of secondary significance in the Kilia Arm to die off quickly. So, the natural isolation of SZP from the sea is quite possible.
Thus, the SZP water system isolation from the sea on condition of no anthropogenic changes in that part of the delta would have been inevitable within the nearest decades; moreover, two natural barriers would have isolated it. That is why we can not understand why some WWF experts insist so much on estuarine regime restoration for SZP. Even at existing artificial slowing the processes down SZP will inevitably become a typical floodplain waterbody fully isolated from the sea. Artificial restoration of the connection between SZP and the sea does not agree with the general idea of WWF aimed at ensuring of maximum natural conditions, sustainability and long-term natural evolution of the protected and restored ecosystems. That is why we don’t consider it expedient to restore and maintain the estuarine conditions of the wetland for the purposes of long-term management.
Coming out of all mentioned above, if, as some WWF experts are insisting, the sluices on the artificially deepened canals that connect the reedbeds with the sea through the semi-isolated fresh bays will be opened during the low water period, the hydrology of SZP will be fare from the natural.
As it was pointed out above, before the anthropogenic transformation of the coastal SZP part there used to exist only a shallow breach but not the deep watercourses like the canals with sluices we have now. That is why open sluices in the low water period will lead to intensive draining of the reedbeds and unnatural yearly drying of a significant part of the wetland (especially during low water periods).
To our mind, the only way to make SZP hydrology as close as possible to the natural is the following. During the flood period it is expedient to keep all the facilities open as long as possible compensating for the restricted by dikes connection of the wetland with the river and the sea (but preventing the irrigation stations situated in the low places from waterlogging and keeping in mind the technical conditions of the dikes). That would ensure maximal possible flushing of the reedbeds under the present conditions.
When the Danube water level will start to get lower it will be necessary to install gates of a certain height on the outlet sluice (“Tupikovy”) and two inlet sluices (Nos. 4 and 5). The last should be close to the most probable height of the underwater bars to develop in those places in case of natural evolution of that part of the delta. Determination of precise gate height for each sluice is an issue of secondary importance in this analysis, so we are not going to dwell on it. It is clear that the bars in the watercourses existed and they were much higher than the lower point of the working aperture in the existing sluices. The proposed gates in the sluices will imitate the destroyed natural underwater bars in the hydrological systems Danube-SZP and SZP-sea. Their use will ensure much more natural hydrology of SZP than the existing deep canals with fully opened sluices.
The sluices arranged according to these proposals so as to be higher than the gates (natural bar) at any changes of water level in the hydrological system Danube-SZP-sea will automatically during the low water period let the water through in any direction freely, thus imitating the natural processes. That is very important for the practical management of hydrotechnical facilities. If the wind will drive the water from the side of the sea, doesn’t matter fresh or brackish, it will enter the SZP freely. If the water level in the river will rise to some reason higher than the gates, it will also automatically get into the wetland. If during the low water period more water will evaporate from the SZP surface than enter into the reed-beds, the shallowest places will get dry. The lower the water level will be in a particular year and the hotter the summer, the more area will get dry. That will make the hydrology of SZP as natural as possible with the entire attendant positive ecological processes (the presence of ecological gradients, mineralisation of organic matter, maintenance of mosaic structure of the wetland etc.) The natural seasonal fish migrations will become more possible. But for the security purposes there should be a technical possibility to fully close the reconstructed sluices in case of disastrous high wind-driven water from sea or other extreme situation. First of all that is necessary to prevent from possible waterlogging of the village of Primorskoye that already happened in early spring 1999.
The proposed and substantiated option of SZP hydrology management, to our mind, is a compromise and will be acceptable for the DBR having specific tasks to conserve natural complexes and ensure sustainable use of natural resources, for local nature users and local and international purely nature conservation organizations.
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* The analysis of the Danube Delta in the area of SZP natural evolution and the forecast of the most probable changes for the nearest future were to this or that extend reported by the author to all the WWF Steering Group Meetings on SZP and other formal and informal meetings dedicated to the area restoration. The proposed option of sluices arrangement and SZP hydrology management was presented for the firs time during the trilateral Dutch-Romanian-Ukrainian Workshop dedicated to SZP restoration organised by RIZA in summer 1998 (Lelystad).
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