Erosion Problems in the eastern Black Sea region

Kos’yan R.D.
P.P. Shirshov Institute of Oceanology (Southern Branch)
Russian Academy of Sciences
Russia

Extended Abstract

Depending on local conditions, waves and wave flows either erode the original rocks in the coastal zone, thus moving the coast landwards, or build up it by means of sediment accumulation along the shore. This results in a stable outline and profile of the coast, manifesting a mobile equilibrium between the key factors.

However, the processes of the bottom profile and the evolution of a stable coastline cannot be researched in isolation, since the whole operation depends very much on human economic activities.

Among the mechanisms of anthropogenous transformation of physical processes in the Black Sea coast zone we can single out the following: influence of hydrotechnical constructions upon the coastal processes: the influence of mining for minerals on ecosystems of the coastal zone and on the coast; the consequences of the river run-off regulations.

On the Black Sea coast the most important negative factors are the transformations of the coastal processes which result in changes of the features of the cross profile and the shore outline evolution, such transformation being carried out by means of hydraulic constructions (of varying economic importance) erected in a different direction to the shoreline (longitudinal constructions - mooring and baffle walls, quays, slope shoring and breakwaters; cross ones - port moles, piers, groins).

Both submerged and above-surface breakwaters and other similar constructions redistribute sediments along the shore artificially, i.e., they distort the sediment balance. If they have triggered off a local beach erosion, then the sediment deficit on that section of the coastal zone will not be more than 10-20 percent from the value of longitudinal sediment discharge. This could be compensated naturally quite quickly, if the original structure were to be removed. Anomalous zones of accumulation constitute a much more serious danger to coastal stability. Constructions with parallel port jetties have a long both direct and indirect influence upon the evolution of large coastal sections (1-2 or 5-10 km long, and even more).

Latitudinal constructions on the Black Sea coast are represented by different types of constructions, including crib retaining walls, groynes and barrier flows. Their principal purpose is to accumulate beach sediment by means of an artificial breaking of longitudinal sediment transport. The length of a zone of a coastal transformation by latitudinal constructions depends on the dimensions of the longitudinal sediment flows.

In order to estimate technological impact son the coast one should take into consideration the ratio between the length of engineering constructions (jetties, groynes, walls etc.) and the total length of the coast. This coefficient has the largest value on the Caucasian Black Sea coast. For example, between Tuapse and Adler the groynes, walls and breakwaters are longer than the length of the shore line.

As can be seen from the above-mentioned facts, coastal and marine hydrotechnical erections can exert influence mechanically upon the sediment dynamics and the coast relief. As a result of serious disturbances of the structure of the moving water masses, the development of the whole coastal zone has changed.

The Black Sea eastern coast is composed of the Upper Cretaceous and Lower Tertiary aged flysch strata. Its typical feature is the proportional alternation of soft, easily destructible argillaceous rocks and dense sandstone, well resistant to wave erosion. Cliff height varies up to 100 meters. The type of the coast evolution can be described as abrasion-denudation. The wave erosion cuts the cliff base and denudation erodes its surface.

Until the end of the 19th century coastal processes occurred without human intervention. At that time the average beach width reached 46 meters, sufficient to suppress waves. The coast was then at a stage of stable dynamic balance, when amounts of incoming detrital material was approximately equal to the abraded gravel amounts.

Active economic development of the Black Sea East coastal zone started at the beginning of the 20th century. In those days pebbles taken from beaches were used in building construction, in rail and road construction. Such large-scale consumption of pebbles from the beaches and river banks caused a sharp increase in sea shore abrasion and washout rate, and led to an increase in the number of landslides. This required a certain development and implementation of coast protection programs. First coast protection structures, such as sea walls made of a rubblework or a concrete, were built in 1914 – 1916 to protect the railroad between Adler and Tuapse.

For a long time coastal protection works were being carried out as a means of eliminating local erosion spots, and were thus not satisfactory for the growing needs of civil and resort construction. The first Master Plan for coast protection was developed in 1961. The scheme was based on the construction of rigid systems for coast protection. In practice it was pursuing the task of protection of local parts of the shore within settlements and communication areas. The incomplete and partial implementation of this plan was so inefficient that ten years later (1971) it became necessary to develop a new Master Plan. By that time the coastal shore protective activities had increased both due to increase of the length of protected areas, and due to applications for a greater number of constructions. Similar to the previous system, the coast protection was planned for town areas, resorts and ports. And therefore the Master Plans reflected purely bureaucratic approach to the problem’s solution. There was no due coordination between users and managerial structures. In a number of cases the constructions of industrial facilities and major communications were designed without consideration of appropriate compensatory actions to preserve the environment and to protect sea coasts against destruction. Such actions do not comply with the requirements of complex approach to the coastal zone as an integrated natural system and that resulted in very serious economic and environmental damage.

Wide usage of concrete has not resulted in the stabilization of the shore. It may sound paradoxical, but those parts of the coast that were under such “protection” for longer times ended up in the worst situation. The inefficiency of this purely technical approach began to be especially obvious, when the costs of repair work started to exceed the cost of coast protection units.

The main technical solutions on coast protection structures for creation of artificial beaches were borrowed from the experience of construction of coast protection structures (bunas, breakwaters and sea walls) at Caucasian and Crimean coasts of the Black Sea. The areas of application of bunas and breakwaters are formally divided by the steepness of the underwater slope, which is 0.03. But such divisions did not have and still do not have physical bases and are not underpinned by hydro- and lithodynamic studies of the surf zone. Types of structures and their layout in the coast protection complexes are assigned subjectively.

By the time of development of the Master Plan, the coast protective construction on the shore between Adler and Tuapse had been in progress for 58 years. This therefore served as a sort of training ground for different methods of protection for steep shores with gravel beaches. This experience was generalized in appropriate regulatory documents. It was acknowledged that during the development of coast protective measures, beaches constitute the best possible way to protect the coast against waves impact. In all cases it is necessary to avoid a downstream washing out of adjacent parts of the coast.

These requirements were poorly observed and that led to very serious damage to the coasts.

A sea wall built by Rail Road Ministry in the late 70s to protect the second railroad part may serve as an example of coast protection with negative effect. According to the monitoring results (1914 – 1967) on the long section of this coast there was a stable gravel beach with average width of 35m. Under natural conditions the alongshore stream was feeding the beach with gravel thus providing stability to it. In result of abrupt cutoff of rivers sediments, the gravel feeding went down and at the time there was a bad deficit of material in the area. Consequently, the beach’s width reduced from 35 to 10 – 15 meters and in front of the sea wall (area about 2 km long) it completely disappeared in the early 80s.

An attempt to protect Imeretia lowlands with bunas of traditional design can also be considered as a negative effect example. These structures had caused such intensive downstream washout that they had to be fully disassembled.

Summarizing the analysis of coastal protective activities executed on the East coast of the Black Sea, we may conclude the following:

  1. For a long period of time the coast protective activity was concentrated on elimination of localized zones of washout, without consideration of lithodynamic system in which the protected area is located, that led to disturbance of sediments flows, and, consequently, to the acceleration of abrasion on the related parts of the shore.
  2. Wide usage of enforced concrete did not stabilize the coast. It might sound paradoxical, but those parts of the shore, which had been protected for the longest period of time, turned out to be in the worst shape. Inconsistency of purely technical approach began to be especially evident, when repair works costs started to exceed the cost of the facilities under protection.
  3. The main technical solutions regarding coast protection constructions for the creation of artificial beaches, accepted in the Plan, have been borrowed from the experience of coast protection (construction of bunas, breakwaters and wave walls) at Caucasus and Crimean shores of the Black Sea. Application of bunas and breakwaters is formally divided by the steepness of the underwater slope equal to 0.03. However, this division did not and does not have any physical grounds and is not confirmed by materials of study of surf zone’s hydro- and lithodynamics. Types of constructions and their composition in the coastal protective complexes were assigned subjectively.
  4. The USSR Government’s Decree, prohibiting the extraction of alluvium, undoubtedly has helped to improve the beaches condition over the last twenty years. The deficit of alluvium in the rivers live beds was eliminated. Nevertheless, it will take more time to reinstate the full balance in the “river – sea coastal zone” system. Of course, only if we do not repeat the previous sad mistakes.
  5. The absence of guaranteed sources of non-metallic materials and regulatory base for design and civil construction did not allow the development of coastal protection with the help of free artificial gravel beach. So, the available experience is limited by several examples and it requires very thorough investigation, particularly for creation of appropriate regulatory basis.
  6. Considering the Master Plans as initial stage of design, we need to mention, that available materials of studies can be used for justification of modern coast protective measures, especially with regard to the expediency of enforced concrete constructions, etc. Accumulated experience quite evidently votes for flexible systems of coast enforcement and artificial beaches in conjunction with sediment preserving rockfills (berm-type noncontinuous breakwaters, wave-dissipating rockfills, etc.).
  7. In the previous Master Plans the coast protection measures were considered as a part of engineering preparation of the territory. Not enough attention was paid to preservation or improvement of seaside landscape. In the minds of old-time designers the coastal zone was not considered as an environment for human living and recreation. Accordingly, the regulatory basis for protection of natural landscapes was not developed. The coast protective measures in the frame of Master Plans has had both positive and negative effects. These bore in mind the principle of seacoasts protection with help of beaches. However, because of a general deficit in the sediments, the free beaches of large length were difficult to create. It was necessary to build sediment-retaining constructions like bunas, on the landslide sections – underwater breakwaters. Thus, the beaches in the coast protective complexes had a primary role, and the constructions a secondary one. It is obvious that the positive effect of such a coast protection complex is the construction of wave-dissipating beach with width no less than twenty five – thirty meters in the Tuapse – Psou part of the coast.

In conclusion it needs to be noted that the seacoasts protection does not support standard solutions. Each part of the shore needs to be creatively approached and its hydrodynamic, lithodynamic, geological, geomorphological and other peculiarities must be thoroughly studied for each particular situation. It takes a complex scientific approach, which takes into consideration not only local features, but also the reaction of whole lithodynamic system within limits of which the coast protective activity is planned, also bearing in mind calculated hydrodynamic parameters (waves, sea level, etc.).

Engineering solutions shall be preceded by forecasting estimations of shores’ development under natural conditions and after the completion of coast protection measures. This, in its turn, requires the organization of special studies in the field, and wide usage of mathematical, computer and hydraulic modeling during design stage. Any studies and forecasts should be based on solid foundation of regional knowledge of nature and dynamics of seacoasts. In addition, a thorough analysis of successful worldwide experience of coast protection is required.

It must be especially emphasized that the implementation of any programmed actions on the protection of seacoasts presumes the creation of the appropriate industrial bases, in particular, highly productive beach-forming materials quarries, on-shore and off-shore transportation means, specialized machinery, etc. Unless these purely technical matters are solved even a perfect programme will not be successful.

Attempts to use standard solutions and schemes suggested by obsolete regulatory documents may lead to the results we see now at large in certain parts of the Black Sea East coast.