Danica Županski, M.Sc.Eng.Forestry,
Institute for the development of water resources “Jaroslav Černi”
Editors note: Presented at the Sixteenth International Conference “Danube – River of Cooperation” in 2005. Vidite: verzija ovog članka na srpskom.
Pancevo is a city with population of 80,000. It is located at the left bank of the Danube river, in south Banat province of Serbia. To the north of Pancevo there is a natural preserve area, Deliblatska Pescara, to the west Pancevo is bordered by the river Tamis, and to the south by the river Danube, and the city of Belgrade. On the Danube banks there are many industrial objects, such as NIS oil processing plant, HIP nitrogen processing plant, HIP petrochemical plant and a shipyard. The area between the Tamis and Danube rivers belongs to Gradska Suma (wooded area).
A very favorable geopolitical location of Pancevo, near Danube, developed infrastructure of roads and water irrigation channels, fertile soil, natural gas an oil resources, as well as the rich flora and fauna, they all represent a significant potential for development of commerce, nautical traffic, energy, food industry, tourism, and water sports.
In last ten years, however, it is noted an increase in floating debris in Danube and Tamis, which has a potential to endanger activities related to the use and regularization of water resources. This is a common situation in other rivers and lakes in Serbia. In addition to the environmental pollution, floating debris is responsible for disrupting the work of motors and machines in the river area, eventually causing significant financiall loss for the cost of repairs and cleaning. For example, the hydroelectric plants Bajina Bašta i Potpec have significant problems and reduced energy production due to floating debris.
Characteristics of floating debris
In the past, only bed loads (e.g., sand, rocks, mud) have been investigated. Appearance of floating debris was noted only recently. The floating debris consists of plastic bags, bottles and glasses, plastic packages, tires, dead branches and tree trunks, aluminum waste, carcasses, and other mud and organic waste materials (fig.1). In general literature, floating debris refers mostly to dead branches and tree trunks, so it appears that the mentioned content of floating debris is of local character.
Due to noticeable similarity between floating debris and municipal waste, it is likely that their source is similar, such as:
- non-sanitary landfills,
- parks and viewpoints near roads, river banks and channels,
- unprofessional behavior of individuals and organizations responsible for collection and transport of waste.
City of Pancevo has ten waste collection sites that are still in use. Some are located near irrigation channels, or by the rivers. Only in 2005 a closure of old waste collection sites and the use of a new sanitary landfill at Dolovo begun.
Many city dwellers commonly take their own trash and waste and dispose it by the road or by the river banks. Light-weighted waste is dispersed by the wind, water, precipitation, and even by animals (e.g., birds, rats, dogs). Often the travelers stop at a convenient location by the road to take a rest, or have a meal. Since there are no available rest areas, with tables, restrooms, and trash cans, the trash is freely disposed in the environment. In industrial plants, there are so-called temporary sites for disposal of waste and industrial materials. This means that there is no prepared space for storing industrial materials, and there is no organized transport of waste. If kept in open space, most of the waste and industrial materials are dispersed by precipitation. When waste reaches rivers and lakes, it floats on the water. After some time in water, part of the waste, entangled by plastic bags, descends to the bottom.
Accumulation of debris and forming of “islands” of waste
It was noted that the debris appears often after strong rains and floods. Large amount of water has a consequence of undermine of river banks and washing-out of waste downstream. In Danube and Tamis it is recorded a lot of individual waste, mostly plastic bottles. Floating debris can be transported from few to few-tens of kilometers downstream. In this process, part of the debris is collected around obstacles in the river, such as: small river islands, docked ships and boats, dams.
When the water levels are not changing much, the debris accumulates into floating “islands”. These islands (fig.2) can be strongly connected to the obstacle which helped it form (e.g., boat, river bank), or sometimes disconnect from the main body and dissolve into smaller pieces. Considerable amount of debris sinks under water, and is typically located at the depth of 0.5-15 m. Part of debris sinks to the bottom as well.
An investigation of the floating debris at the lake of HE Potpec, in 1999, indicated three categories of debris:
- floating debris consists of dead branches, leaves, plastic bottles and bags. Debris covers an area of 15 m by 20 m, and is at the depth of 05-075 m.
- suspended debris consists of smaller branches, plastic bottles, plastic bags. Debris is entangled with the organic-mud material.
- settled debris is located at the bottom, and is of 4.5-5 m height. It consists of tires, plastic packages, all entangled with plastic bags.
Since in Danube and Tamis there are similar kinds of debris as found in the lakes of HE Potpec and Bajina Basta, it appears that the mentioned classification of debris could be applied to rivers, streams, and channels.
Adverse effects of debris
There are multiple adverse effects of floating debris on the environment:
- pollution of air, soil, water
- interference and blocking of nautical traffic
- endangerment of water sports
- interference with normal operations of a dam on Tamis
- unpleasant visual impact.
In the waste disposed to waste collection sites, or to non-sanitary landfills, one can often find pathogen microorganisms, toxic materials, and other environmental pollutants. Some are water dissolvable, but most are transported by rivers, eventually causing pollution and health problems at distant locations downstream (water, air, soil contact, flora and fauna).
Normal nautical traffic on Danube and Tamis rivers requires rivers free of any debris that could cause adverse effects on transport of goods, people, building materials, fuels, and boats. Branches and nylons can be entangled in the boat engine, and cause various problems for traffic.
General climate conditions and vicinity of rivers are convenient for water sports on Tamis and Danube, especially in summer. Rowing in canoes and kayaks, recreational boating, fishing, swimming, are common activities for that region and traditional Pancevo sports. Existence of floating debris can adversely impact all these activities.
On the Tamis river there is a dam, near where Tamis flows into Danube, which consists of three gates. Basic function of this object is to regulate the water levels on Tamis, and to adjust the water level regime changes on Tamis and Danube. However, slow water flow near the dam caused accumulation of the regular river debris, as well as of the floating debris. The ultimate impact of this is an almost total blocking of the dam, and serious interference with the dam functionality.
Waste is a part of life, but it is known that due to unpleasant odor and visual impacts it can cause emotional and physical discomfort among people, eventually requiring laws and regulation of waste disposal. In developed countries there are strict penalties for unlawful waste and trash disposal. Clean rivers and banks are necessary for successful tourism.
Collection, transport and treatment of floating debris
Cleaning of floating debris from rivers and lakes is done by boats. For small amounts of debris, small boats and wood catchers are used. Debris is first collectd in the boath, an then taken to the shore, and transported to the landfill.
For large pieces and amounts of debris larger, specifically designed boats are used. There are two types of vessels, the cleaner of water areas, and the Trashcat. These boats are typically used for collection of tree waste in lakes and rivers in mountainous regions with logging industry, or for cutting and cleaning of aquatic plants in irrigation channels. The first cleaner of water areas used in Serbia dates to the beginning of 2005, at the lake Perucac (HE Bajina Basta).
The cleaner of water areas (fig.3) is a vessel with two diesel engines. Its load capacity is 2500 kg. The vessel is essentially a floating deck with hydraulic power, submerged in water. It requires one person to operate. After collecting, waste is transferred to two 4 m3 containers. It is possible to install additional equipment on the vessel, for surface cleaning up to 5 m in depth. In addition, the vessel can be used in tourism, by installing seating benches. Advantages of the cleaner are its movability and maneuverability in small areas, so it is also used in coves and other small areas of a river and lake.
The trashcat is a vessel with double-body design, equipped with a transferable system of vents on hydraulic power, and it requires one person to operate. The machine located on the front is designed to work under water up to the depth of 15 m. Large vertical wings are used to collect the waste in a cubical of 20 m3. The width of the vessel is 5 m.
After collection, the waste is deposited at the location on the shore, followed by:
- transfer into containers or trucks, transport to landfill
- waste classification into plastic, wood, glass, and other, and subsequent transport to recycling center or a landfill.
Waste classification is done manually, and this is the most difficult component of the process. Treatment of plastic waste is done by using a shredding machine for plastic, which considerably reduces the waste volume. A shredding machine for wood waste (branches, leaves, small trunks) is also used. Both mentioned machines are owned by Zelenilo-Beograd, and first time used for cleaning of the Danube quay and walking area 25 May, near the Kalemegdan fortress. Cleaning of aquatic plants was done at the Ada Ciganlija lake in Belgrade.
A visual examination of the rivers Danube and Tamis, from land and water during the year 2005, indicated that floating debris exists near Pancevo. Multiple locations with accumulated waste and “islands” of waste which require removal, are found on the river. These locations are in front of the shipyard Pancevo, and around docked ships. Overall water area of Danube and Tamis is covered by individual floating debris. The location most endangered by floating debris is at the dam on Tamis, which requires immediate attention since the object is practically inoperable.
It is recommended that an organized fundraising is needed, so that an appropriate plan can be designed and an action taken on this matter.
Studija: “Zastita akumulacija sa hidroenergetskom namenom od zasipanja recnim nanosom i unosenja povrsinskog nanosa”, Institut “Jaroslav Cerni” i Energoprojekt-Hidrinzenjering, 2003-2005, Interni materijal.
Studija: “Zastita zahvata vode od plivajuceg nanosa”, Energoprojekt –Hidroinzenjering, 2000, Interni materijal.
D.Zupanski, “Inventory of municipal solid landfills in Serbia”, Fifth international symposium and exibition on environmental contamination on central and eastern Europe, Praque, 2002.
Zbornik radova: Prekogranična saradnja opština na polju zivotne sredine-Sliv reke Drine, Bajina Basta, 2003.