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JCI at a Glance References Selected Projects Feasibility Assessment of Sediment Removal and Remediation of the Palić and Ludaš Lakes
Feasibility Assessment of Sediment Removal and Remediation of the Palić and Ludaš Lakes PDF Print E-mail

palic_01Client:
City of Subotica
Project Coordinator:
Mile Božić, M.S.C.E.
Project Team:
Goran Nikolić, B.S.C.E.; Željka Rudić, B.S. in Agriculture; and Dragiša Stević, B.S. in Agriculture

The Palić and Ludaš are shallow Pannonian lakes in northeastern Bačka, near the City of Subotica. They have been given special status as part of the region’s natural and cultural heritage:

  1. The Lake Ludaš is a Category 1 Special Nature Preserve (surface area 846 ha),
  2. The Lake Palić is a Category 3 Nature Park (surface area 713 ha).

The Lake Palić is divided into four sectors (water depth 1-2 m). The most important sector is Sector IV because there are many tourist attractions and facilities along the lakeshore.

Both lakes experience from advanced eutrophication. Their water quality is threatened by discharges of untreated household and industrial wastewater originating from the City of Subotica. Despite an environmental remediation project carried out in the Lake Palić in the 1970s, inadequately treated effluent released from the local wastewater treatment plant (WWTP) is devastating lake water quality and has already resulted in instances of fish kills and bathing bans. As a result, the Lake Palić and Lake Ludaš Revitalization Study was initiated with the following objectives:

  • To assess the nature and extent of sediment pollution;
  • To propose the best clean-up solution;
  • To define a sediment disposal method and location;
  • To propose the best sediment remediation method.

palic_01

 

Figure 1: Map of Lake Palić and Lake Ludaš area

The project titled Feasibility Assessment of Sediment Removal and Remediation of The Palić and Ludaš Lakes included collection, compilation and critical review of available technical documentation and detailed site inspections, which indicates that supplemental investigations is needed to design the clean-up and remediation of polluted sediments (baseline surveys, physical and chemical analyses of water and sediment, and the like).

The design of the technical solutions was based on the following key parameters:

  • Large sediment volume (1.9 million m3 in the Lake Palić and more than 2.6 million m3 in the Lake Ludaš), within a bed layer whose thickness varies from 0.3 to 1.5 m;
  • High organic load and high concentrations of total phosphorus and nitrogen in the sediments;
  • Lake sediments do not exhibit high concentrations of heavy metals (they generally comply with levels approved by international institutions); and
  • To maintain water quality in Lake Palić during the summer months, Sector IV requires 20,000 m3 of fresh water per day.

Lake eutrophication will be addressed in three stages:

I    Clean-up and remediation of the Lake Palić and the Lake Ludaš sediments;
II    Provision of water to refresh the lakes and maintain required water levels; and
III    Monitoring and management of water and sediment, to ensure sustainability of the lakes.

Three clean-up and remediation options were studied and for each the fundamental premise was to maximize utilization of the lakes’ self-purification potential (gradual transformation of organic substances to an acceptable level). For this reason, there are two preconditions for implementation of the clean-up and remediation project:

  • Completion of construction and efficient management of the WWTP; and
  • Collection and treatment of wastewater originating from diffuse sources of pollution.

The large volumes of deposited sediments require hydraulic removal; the sediments will be used to rehabilitate eroded lakeshores and lakeside depressions, and to construct wetlands and islands in certain sectors of the lakes.


palic_03Figure 2:  Constructed wetlands and islands in Sector III of Lake Palić

The proposed Option 1 includes rehabilitation of the relief channel, whose function will be to refresh lake’s water with fresh water delivered via the Tisa-Palić subsystem.

In case that water and sediment quality monitoring shows that the aquatic ecosystem can further reduce the organic load from the WWTP to an acceptable level for sustainable management of Sector IV, the water need not be evacuated via the relief canal but discharged into Sector IV. This would help establish a water balance in the Lake Palić and Lake Ludaš, and the Tisa-Palić subsystem would serve as a backup. Still, the relief channel, pumping station and ancillaries should be kept in good working conditions to respond to any environmental accidents.

In view of the sediment volume, the clean-up and remediation project will take several years. During this period, pilot projects should be undertaken to verify the efficiency of the proposed solutions for constructed wetlands and islands.

 
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