RATIONAL APPROACH TO THE SOLUTION OF THE … Papers... · production of peak quantities of domestic wastes. Population increase and a higher standard of liv-ing in the coastal zones,

INTRODUCTIONMost of the world population lives in coastalareas, particularly in large coastal cities, whichhave been quickly growing over the past severaldecades (Olsen, 1993). It is assumed that in thefuture the coastal area will be exposed to an evengreater population pressure, development and

changes in national economies (UN, 1992). Thewidespread coastal population growth, the exten-sion of urban wastewater discharge networks andthe higher standard of living have considerablyincreased the amount of sewage discharged intothe sea. The situation has been aggravated by thecontinuously growing tourist population and the

Global Nest: the Int. J. Vol 3, No 2, pp 117-130, 2001Copyright© 2001 GLOBAL NEST

Printed in Greece. All rights reserved

RATIONAL APPROACH TO THE SOLUTION OF THE PROBLEM OF WASTEWATERS MANAGEMENT-THE KAS¡ TELA BAY CASE

1 University of SplitFaculty of Civil Engineering

Matice Hrvatske 1521000 Split, Croatia

2 Institute of Oceanography and FisheriesP.O. Box 500

21000 Split, Croatia

*to whom all correspondence should be addressede-mail: [email protected]

tel: + 385-21-303 356; 21-399 073fax: +385-21- 65 177

ABSTRACTUncontrolled disposal of urban and industrial wastewaters into the sea led to the fact that in mid eight-ies the Ka�tela Bay, near the city of Split, Republic of Croatia, became one of the largest and most wide-ly known pollution �hot-spot� areas of the Mediterranean region. The pollution of the Bay caused �redtide� and mass mortality of marine organisms. Numerous conflicts arose, and the quality of life wasreduced due to the changed quality of the sea. Local communities recognized the problem, and the long-term solution of wastewater management has been developed. This solution envisages the collection ofall domestic wastewaters at two points in the area, and, after treatment at an appropriate level, their dis-charge via long submarine outfalls into a less sensitive marine environment. For the implementation ofthe first phase of the long-term solution, a project �Eco Ka�tela Bay� has been launched. The project isfinanced from local and governmental sources, as well as loans of the World Bank and the EuropeanBank for Reconstruction and Development. The present paper describes the area, environmental con-ditions, and the approach applied in the long-term solution of waste waters management.

KEYWORDS: sewage; sewerage system; marine disposal; ecological approach; Ka�tela Bay.

J. MARGETA1,*A. BARIC2

Received: 14/06/01Accepted: 08/11/01

margeta.qxd 1/2/2002 4:29 Page 117

production of peak quantities of domestic wastes.Population increase and a higher standard of liv-ing in the coastal zones, as expected, have beenaccompanied by the extension and diversificationof industries. More new substances have beenintroduced in industrial processes and products,and new uses found for the existing materials.Most of these changes are reflected in the indus-trial wastes, and represent an additional dimen-sion of the problem of pollution of the receivingmarine environment.Serious concern about the state of pollution ofthe coastal sea and negative impacts on bothecosystems and human society, mainly as a resultof waste discharges originated from sourceslocated on land (UNEP/WHO, 1996a), led to ageneral attitude that the marine environmentshould be protected from land based activitiesand sources of pollution (UNEP, 1995). For thispurpose various criteria and guidelines have beenprepared, such as the Guidelines for Treatment ofEffluent prior to Discharge into the MediterraneanSea (UNEP/WHO, 1996b), and Guidelines forSubmarine Outfall Structures for MediterraneanSmall and Medium-size Coastal Communities(UNEP/WHO, 1996c).

DESCRIPTION OF THE STUDY AREAThe wider area of the Ka�tela Bay, covering themunicipalities of Split, Solin, Ka�tela and Trogir,is the largest one on the Croatian coast (Figure 1).

It represents an economic and territorial entitywith the city of Split as the dominant center. Thecity of Split is the second largest city of Croatiaand the administrative center of the County ofSplit-Dalmatia.The total population of the narrow coastal strip,limited by the seashore and mountain slopes, andcovering approximately 14,500 hectares, hastripled over the past half a century, with 280,000inhabitants in the year 1991, while the estimatedpopulation for the year 2015 is 355,000. The fastpopulation growth was accompanied by the devel-opment of industry, traffic and trade.The climate of the area is of the Mediterraneantype, characterized by dry summers and wet win-ters. Average annual air temperature is 16 °C. Thelong-term annual average rainfall is 837.2 mm.The area of the Ka�tela Bay is known as one ofthe most polluted areas of the eastern coast ofthe Adriatic. The environmental pollution is aconsequence of fast industrialization and urban-ization without development of appropriateurban infrastructure, in particular of a waste-water collection and disposal system. Increasedamounts of both urban and industrial waste-waters are disposed untreated in the coastal searesulting in numerous ecological problems andconflicts, as well as in the reduction of quality ofliving. The main conflicts are between industryand tourism, industry and housing, and wastewater discharge and tourism.

118 MARGETA and BARIC

Figure 1. The study area


Characteristics of the Kas¡ tela Bay and the Brac¡and Split ChannelsTwo distinctive water bodies encompass the areaof concern: the semi-enclosed Ka�tela Bay andthe Braè and Split Channels. Despite their inter-connection they represent different sea basins interms of ecological characteristics and impactsfrom land-based sources.

The Ka�tela BayThe Ka�tela Bay is the largest bay of the centralpart of the Croatian coast. The total surface areaof the Bay is 61 km2 and the average depth is 23m, resulting in a total volume of 1.4 km3. The nar-row coastal belt of the Bay is densely populatedand has a number of various industrial plants.By its origin the Ka�tela Bay is a synclinal foldwhich was transgraded and submerged inPleistocene. The Bay displays different bathymet-ric and morphometric properties, and two sepa-rate parts can be clearly distinguished: the deepereastern and the shallower western ones. Thefreshwater inflow is, in addition to rainfall, by thenumerous submarine springs and small karsticriver, Jadro, (yearly average flow is 10 m3 s-1). Thefresh water inflow has a strong seasonal fluctua-tion.The Bay exchanges the water masses with theadjacent Braè Channel through the entrancebetween the Marjan peninsula and the island ofCiovo. The water renewal period of the entire Bayis about one month, while of its eastern part it isabout 15 days (Zore-Armanda, 1979). Since thevolume of the entire Bay is four times greaterthan the volume of its eastern part, the rate of thewater exchange between the eastern part and therest of the Bay is relatively low. As a result, theeastern part of the Bay is poorly aerated, particu-larly in the hot period of year.Vertical temperature distribution indicates thepresence of a thermocline in the water columnfrom April to October at a depth of 10-25 m(Buljan and Zore-Armanda, 1996). The freshwater entering into Bay has very limited influenceon the salinity variance in the Bay (Zore-Armanda, 1980). The annual mean salinity valuesin the surface and bottom layer are 34.43 � and37.27 �, respectively.Based on the primary production, the Ka�tela Bayis naturally a moderate productive basin (Pucher-Petkovic and Zore Armanda, 1973.). For the peri-

od 1962-1967 the primary production in the Baywas estimated at 150 gC m-2 y-1. Due to wastes dis-charge, the primary production in the Bay in theperiod 1982-1986 increased to 325 gC m-2 y-1

(Baric et al., 1992). In the summer of 1980 the first�red tide�, i. e. an extreme bloom of the dinofla-gellate species, Gonyaulax polyedra, occurred inthe Bay causing mass mortality of marine organ-isms in the eastern part due to reduced oxygenconcentration in the water column (Marasovicand Vukadin, 1982). In the past years the �redtide� has become quite common, not only in theeastern part, but also practically throughout theBay. Moreover, a significant change in the phyto-plankton community structure occurred due toeutrophication (Marasovic and Pucher-Petkovic,1991). A typical diatom type has gradually beentransformed into a community of dinoflagellates.An increase of dinoflagellate proportion isaccompanied by a respective increase of primaryproduction. Moreover, new species, such asAlexandrium minutum have been introduced.Research over the last thirty years indicated thatthe structure of the benthic flora of the Bay haschanged. Of particular interest is the introductionof new species known as nitrophilic species (Spanand Antolic, 1997). Their introduction is favouredby the eutrophic conditions.Eutrophication in the Ka�tela Bay is considerable(Baric et al., 1992). The present nutrient concen-trations are in the range as follows: nitrate 0.2-1.0mmol m-3; nitrate 0.0-0.8 mmol m-3; ammonia 0.5-1.3 mol m-3; phosphate 0.09-0.20 mmol m-3; sili-cate 0.1-4.0 mmol m-3. The ratio of nitrogen tophosphorous concentrations in the Bay has beenreduced to the value of 23, indicating phospho-rous introduction by the wastewater having N/Pratio of 6 (Baric et al., 1992). The concentration ofdissolved oxygen has increased in the euphoticlayer (annual average 5.8 ml dm-3) and decreasedin the bottom layer (annual average 5.1 ml dm-3)(Baric et al., 1992). Such a divergent behavior oftwo layers with respect to dissolved oxygen con-centrations indicates a long-term trend of intensi-fied phytoplankton photosynthetic activity in theeuphotic layer, followed by an increase in themineralization of organic matter in the bottomlayers. Long-term transparency measurements bythe Sechi disc confirm the increase of eutrophica-tion in the Bay with strong negative impacts onthe ecosystem.

119RATIONAL APPROACH TO THE SOLUTION OF THE PROBLEM OF WASTEWATERS MANAGEMENT


The Bay is contaminated by heavy metals, partic-ularly mercury. Mercury was released into theBay from a chlor-alkaly plant for about 40 years,until 1990. The estimated total amount of mer-cury discharged into the Bay is 200 t (Odzak et al.,1999). The recent data show that the mercurylevel in mussels Mytilus galloprovincialis, taken inthe vicinity of the plant, are higher than at otherstations in the Bay, but still bellow the maximumpermitted level (Odzak et al., in press). Tracemetals concentration in surface sediments showscontamination of the entire Bay by lead (25-45 mgPb kg-1), and of a limited part by cadmium (0.8 mgCd kg-1) (Bogner et al., 1998; Ujevic et al., 1998;Ujevic et al., 2000). In any case, harvesting ofshellfish from the Bay has been prohibited due tomicrobial contamination.Concentration of faecal indicators in the surfacelayer is higher than the permissible limits forbathing and recreational waters almost over theentire Bay (Krstulovic and Solic, 1991). As a con-sequence, the most attractive beaches of the areaare not safe for recreational use, resulting in greatlosses for tourism.

The Braè and Split ChannelsThe Braè Channel is located between the main-land and the island of Braè. The Channel is nar-rowest, 5 km, along the central part of the islandof Braè, and widest at the western end, 13 km.The greatest depth of 78 m is in the south-easternpart and 68 in the western part of the channel.The Braè Channel extends westwards to the SplitChannel located between the islands of Solta,Ciovo and Veli Drvenik. The volumes of watermasses of the Braè and Split Channels are 16 and12 km3, respectively.The Braè and Split Channels represent a uniformbasin mainly exchanging water masses with theadjacent sea through three main passages. Theexchange of water masses through the Split strait,between the islands of Braè and Solta and theKa�tela Bay is negligible. The average time ofwater mass renewal has been estimated at 2.25months (Margeta and Baric, 1996).The hydrologic system of the Braè and SplitChannels is complex and variable. The area of theBraè and Split Channels is relatively abundant infresh water. Estimated average yearly fresh waterinflow is 2,510.78 million m3. The largest sourceof fresh water is the Cetina River (average flow

55.22 m3 s-1). The main feature of the fresh waterinflow is its high fluctuation depending on precip-itation in the hinterland.Temperature and salinity data show that theentire area is horizontally homogeneous through-out most of the year. Salinity ranges mainly from37� to 38�. The temperature varies dependingon the season, and ranges from 10 to 16.5 °C atthe bottom, and from 10 to 25 °C at the surface.In the period from April to October a thermo-cline is formed at the depth of 10 to 20 m below awell mixed surface layer. The sea transparencyranges from 12 to 23 m (Tudor et al., 1990; Tudoret al., 1991). The impact of fresh water is limitedto an area in the vicinity of inflows and extendsdepending on the intensity and direction of localwind and current flows.Concentrations of ammonia (annual ranges 0.14-3.10 mmol m-3), nitrates (annual ranges 0.00-1.80mmol m-3), ortho-phosphates (annual ranges0.000-0.156 mmol m-3) and ortho-silicate (0.14-6.88 mol m-3) in the Braè Channel are relativelylow and show uniform distribution consideringboth the depth and the year seasons, indicatingthe oligotrophic condition of the channels interms of nutrient concentrations (Baric et al.,1998). Oxygen saturation varies seasonally in anarrow range: 95-110 % and 85-100 % in the sur-face and bottom layers, respectively (Baric et al.,1998).A long-term study of the phytoplankton in theChannels shows that the phytoplankton com-munity is rather undisturbed (Marasovic,unpublished data) without any sign of eutroph-ication. Concentration of Chlorophyll a variesbetween 0.09 and 2.49 mg m-3, with maximalvalues in March and minimal at the end ofSeptember (Baric et al., 1998). However, stud-ies of phyto-benthic communities indicatedchanges in the vicinity of the sewage outlets ofurban waste waters. A total number of specieshas been reduced, while Chlorophite speciespercentage has increased at the expense ofRhodophyta species which are sensitive to thecontamination by urban wastewater (Span andAntolic, 1997).Microbial pollution is only recorded in the coastalarea in the vicinity of the towns of Split andStobrec due to discharge of untreated urbanwaste water via numerous outlets. Data on tracemetals concentrations in the surface sediments



show no contamination of the area (Bogner et al.,1998; Ujevic et al., 1998).

Existing sewerage systems in the areaThe greatest part of the existing sewerage systemswas built in the urban area of Split where approx-imately 70% of the population is served by publicsewerage. In terms of surface area, only 55% ofthe urban area is covered by the sewerage system.The total length of the sewerage system is approx-imately 200 km. In the areas of the towns of Solin,Ka�tela and Trogir public sewer systems are lessdeveloped. They cover only a part of the townnuclei, and only approximately 25% of the popu-lation is served by the sewerage system. The totallength of the Solin sewerage system is 13 km, andthe length of the systems of the towns of Ka�telaand Trogir are 31 and 16 km, respectively.Buildings not served by the public sewerage sys-tems have individual, mostly permeable septictanks.The public sewers in each of the towns consist ofnumerous small subsystems; each of them con-sists of a gravity sewer collecting waste and rainwaters, and a coastal outlet discharging into thecoastal sea. Industries, such as food and bever-ages processing plants, including a large brewery,a winery and a slaughter house, metal and chem-ical processing, discharge their wastewatersdirectly (without pretreatment) into to the com-munal sewerage system, or directly into the sea.Because of this, there are several large and morethan several hundred small outlets in the area.Obviously, there is no wastewater treatment inthe area.

Quantity and quality of wastewater and sourcesof the sea pollutionThe quantity of the urban and industrial waste-waters of the entire area has been estimated at49,000,000 m3 y-1 (Margeta and Baric, 1996), ofwhich industrial wastewaters account for approxi-mately 5%. About 60% of that quantity is dis-charged into the eastern part of the Ka�tela Bay,while the remaining part is discharged into theBraè and Split Channels. The Ka�tela Bay hasbeen used as a recipient of the urban wastewatersince late sixties when the town of Split expendedonto the Bay�s watershed. The brewery and foodand beverages processing plants, discharging intothe Bay wastewater rich by organic matter, wereconstructed in that period, as well. The shipyardand metal processing industry have been dis-charging their waste- and storm waters, as well assome materials, into the Bay sea over the past 80years. Apart from direct and indirect dischargesof the wastewaters, the sea receives large quanti-ties of wastes from various diffuse sources: (i)deposits from the atmosphere; (ii) runoff fromurban areas; (iii) runoff from agricultural areas;(iv) runoff from the watershed area; (v) rivers, asshown for the Bay in Figure 2. The yearly load ofthe Ka�tela Bay by organic matter, expressed asBOD5, suspended solids, and inorganic phospho-rus and nitrogen is shown in Table 1 (Baric et al.,1998).As shown in Table 1, the largest portion of organ-ic matter is discharged with domestic and indus-trial wastewaters, while the largest portion of sus-pended solids is arriving with storm waters andfrom the atmosphere. However, the highest con-


Table 1. Estimated load of the Ka�tela Bay by organic matter, expressed as BOD5, suspended matter, and

inorganic phosphorus and nitrogen from different sources (Baric et al., 1998)

SOURCE BOD5

(t y-1)Suspended Solids

(t y-1)Pinorganic

(t y-1)Ninorganic

(t y-1)

Domestic wastewater 2,226 2,431 14.1 64.8Industrial wastewater 1,562 954 3.1 14.4Storm water 984 4,920 � �Air deposit � � 1.2 9.6Underground water 205 89 � �Surface runoff 27 87 6.1 16.0Rivers 388 1,419 6.5 55.2

TOTAL 5,392 9,900 31.0 160.0


tribution of inorganic nitrogen and phosphorus isfrom domestic waste water and rivers.

STRATEGIC APPROACH TO THE PROTECTION OF THE KASTELA BAY AND THE BRAC¡ AND SPLIT CHANNELS AGAINST POLLUTION FROMLAND-BASED SOURCES AND ACTIVITIESIn order to analyze the problem, a number ofstudies and projects have been launched. Themost comprehensive study was the national pro-ject �Environmental Management of the Ka�telaBay�. The general objectives of the project, to beachieved by the application of scientific methods,were to:� identify the causes of the present situation and

trends;� assess their impacts and significance, and

� identify development alternatives for sustain-able development.

The specific project objectives were as follows:� to define the sensitivity, vulnerability and (lim-

ited) carrying capacity of the naturalresources;

� to introduce standard procedures and parame-ters into the process of management of natur-al resources;

� to apply, within the project scientific frame-work, an integrated approach and principlesof sustainable development.

The project was structured in three basic compo-nents:� Models and Modelling;� Environment and Ecosystem;� Socio-Economic-Spatial Systems;


Figure 2. General hydrological scheme of the Ka�tela Bay


resulting in an integrated Synthesis. The majorresults of the individual project components wereas follows:Methods and Modelling: This sub-project was con-ceived and implemented as support for the othertwo sub-projects. Methods were defined, relatedto database, environment/development scenario,land-use (physical) management, and evaluationof ecosystems by multicrioterional analysis. Anumber of Decision Support Systems, of a sec-toral or issue-specific nature was designed andapplied.Environment and Ecosystems: This sub-projectwas implemented through research modulesrelated to soil, land, air, freshwater, and marineecosystems. Each module was elaborated indetail, the sectoral results to be integrated withinthe scenarios and development options.Socio-Economic-Spatial System: The sub-projectfocused on the state, dynamics and trends ofdevelopment within the given environmentalframework, elaborated by the second sub-project.A simulation model was developed and applied.Furthermore, applying the participatory princi-ple, a survey on social and development aspira-tions was carried out among citizens, the resultssystematized, analyzed and used. Finally, interre-lations among the economic potential and theenvironmental capacity were studied.Among the specific results of the project, itshould be mentioned that the project implemen-tation and its results confirmed in practice theneed for, and benefits from the application of ascientific approach, application of the methodol-ogy and tools of integrated coastal management,and of the principles of sustainable development,when dealing with complex environment/develop-ment problems, in this case of the Ka�tela Bayarea. The project widely contributed to the risingof awareness of the general public and authoritiesregarding the state of the environment and theneed for a sustainable development. Its Socio-Economic-Spatial component provided a conceptfor pollution mitigation and reduction and for afuture sustainable development, based on:� establishment of a system of infrastructure

aiming at sustainable and efficient liquid andsolid wastes management;

� reduction of other sources of pollution byestablishment of appropriate treatment facili-ties;

� recovery and rational utilization of naturaland man-made resources;

� proposals for restructuring of the economy byadopting clean technologies, by applying eco-nomic instruments such as urban rent, andimplementing an environmentally sound sys-tem of land use and urban development.

Studies and projects implemented in the 1986-93period, in addition to their individual achieve-ments, resulted in a well-founded understandingof concepts and strategies to be applied:a) the causes of deterioration of the socio-eco-

nomic context and the state of the environ-ment, the resulting impacts and their signifi-cance, indicated the need for the adoption andgradual implementation of comprehensive,long-term multi-phase remedial and sustain-able development program, to be formulatedaccording to priorities and existing conditionsfor its implementation,

b) the strategy of the program should be basedon an active development concept combinedwith appropriate remedial actions,

c) the socio-economic studies and the environ-ment/development scenario prepared indicat-ed the need for a radical change of the hither-to development concept, implying a change ofstrategy of the national and coastal economydue to the new political context of the inde-pendent Republic of Croatia, and structuralchanges during the transition period, applyingan integrated approach to coastal develop-ment, oriented towards Europe, theMediterranean region and the world, based onmarket economy and principles of sustainabledevelopment,

d) the conceptual approach to the programshould be based on the principles of: (i) sus-tainable development; (ii) integrated coastaland marine areas management; and (iii) mar-ket economy, and

e) as urgent priorities to be included in the long-term program, the design and construction ofthe urban wastewater collection, treatmentand disposal system were identified.

The protection of the coastal sea is obviously oneof the most important prerequisites for the sus-tainable development of the area, also recognizedby the local community. It includes the integratedland use management (soil, fresh waters, sea andair) (Margeta, 1997). As mentioned above, the



main sources of the sea pollution are wastewaters,domestic and industrial. Therefore the priority isgiven to the management of all kinds of waste-waters. In order to achieve the long-term protec-tion of the Ka�tela Bay and the Braè and SplitChannels against urban and industrial wastewaters the following strategic approach wasapplied:The Ka�tela Bay is considered as an ecologicallysensitive and socio-economically important area,and for its protection it is necessary to:� eliminate from the Bay all outlets and outfalls

discharging untreated and/or partially treatedmunicipal wastewaters, as well as the leakagefrom permeable septic tanks;

� eliminate from the Bay all outlets discharginguntreated and/or partially treated industrialwastewaters;

� establish a permanent monitoring program ofthe coastal water.

The Braè and Split Channels, considered as lessecologically sensitive areas, are selected as arecipient of all urban and industrial wastewatersof the area. The selection was done taking intoaccount their relatively high volume and depth,intensive dynamics of water masses, and presentbiological and ecological conditions which havenot, so far, been affected by the waste water dis-charge.The wastewater discharge should be performedunder the following general and specific condi-tions:

a. General conditions1. Construction of appropriate municipal sewer-

age system(s) for the collection, treatment anddisposal of the entire amount of urban andindustrial wastewaters of the region.

2. Wastewater disposal via long submarine out-falls ensuring appropriate initial and sec-ondary dilution, and sanitary protection of a300 m wide coastal sea belt.

3. Use of natural capacities of the marine envi-ronment for wastes treatment and applicationof a minimal level of urban wastewater treat-ment. The final level of waste treatmentshould be determined on the basis of monitor-ing results. The applied level of waste treat-ment should ensure that negative impacts areavoided.

4. Pre-treatment of industrial wastewaters prior

to their discharge into the municipal seweragesystem(s) in order to remove substances thatcan be detrimental to:� the operation of a biological treatment

plant� the usage of the sludge produced at the

treatment plant� marine ecosystems.

5. Elimination of all existing uncontrolledcoastal outlets in the area.

b. Specific conditions1. Studies for the sitting and design of the subma-

rine outfallsA detailed study of hydrodynamic, physicaland biological characteristics of areas pro-posed for the location of submarine outfallshave been performed in order to get appropri-ate information for the sitting of diffuser andthe construction of outfalls.

2. Baseline studySince the final treatment level will be deter-mined upon the results of systematic monitor-ing, before the construction of the seweragesystem(s) a baseline study of physical, chemi-cal and biological characteristics of the Bayand Channels have been performed. Thisstudy will be used as a reference for the com-parison with the monitoring data in theprocess of assessing the impacts of wastes dis-charge on the marine environment.

3. Design and construction of sewerage systemsIn order to ensure the collection, efficienttreatment and disposal of all wastewaters, andto avoid negative impacts, the best availableknowledge, materials and technology havebeen suggested for use in the design and con-struction of the systems. The micro-location ofdiffusers should be determined on the basis ofa detailed study of hydrodynamic, physical,chemical and biological characteristics ofpotential micro-locations.

4. Efficient management and maintenance of thesewerage systemsEstablishment of efficient management andmaintenance of the sewerage systems is thekey element of the effective protection of theenvironment. Efficient organisation and expe-rienced, well trained and adequately paid staffare prerequisites for ensuring permanent andproper functioning of the sewerage systems.



5. Public participationThe public (general public, NGOs, scientificcommunity, etc.) should be the main promot-er of protection measures, as well as proof-reader of all activities, already undertaken orplanned, for the protection of the environ-ment. Therefore, it is necessary to involve thepublic in the development of the project at theearliest possible stage.

6. Monitoring and informationFeedback information on the environment isnecessary for appropriate management of thesewerage system(s). Therefore, the monitor-ing of marine environment, as well as of efflu-ent quality should be and partly have beenestablished. In addition, an appropriate infor-mation system to inform the general public,the scientific community and other interestedparties about all achievements and plannedactivities should be developed.

7. Computer-based Decision Support System forCoastal Water Resources ManagementA computer-based Decision Support System(DSS) would transform the monitoring datatogether with other relevant information intoa form understandable to decision makers,enabling them to undertake environmentallysound decisions regarding the wastewatersmanagement. This tool is important in deci-sion making related to the protection of theenvironment, particularly in this case when thefinal treatment level will be achieved by a step-by-step approach using feed-back informationon the environment.

Long-term objectivesThe following long-term objectives should beachieved by the fulfilment of the above listed con-ditions:

a. Sanitary quality of the coastal seaThe coastal sea belt, 300 m wide in the entirearea, should be sanitary clean and safe forbathing and recreation in all weather condi-tions. It means that at many locations in thecoastal area the sanitary quality of the seashould be improved.

b. Aesthetic value of the sea waterThe aesthetic value of the sea water in thecoastal belt should be unaffected by the dis-

charged wastewaters which implies theimprovement of the water quality at mostlocations, which are presently under theimpact of small outlets. Only a slight increaseof turbidity may be expected in the wider zoneof the channels near the diffuser(s) location.

c. Benthic communitiesDisturbed benthic communities in the coastalregion should be recovered, particularly in theentire Ka�tela Bay, but the communities in thevicinity of the submarine diffusers will be com-pletely destroyed.

d. EutrophicationThe discharge of urban waste would increasethe eutrophication in the Channels, resultingin the increase of primary productivity andphytoplankton biomass, as well as slightchanges in the structure of phytoplanktoncommunity, but the �red tide�, oxygen deple-tion in the bottom layer (except in the vicinityof the diffuser) and other accompanying phe-nomena should be avoided. At the same time,a gradual improvement is expected in the Bay.

CONCEPTUAL SOLUTION OF THE SEWERAGESYSTEM The long-term solution of the sewerage system,developed on the basis of a detailed analysis ofecological, technical and economic parameters,envisages the construction of two sewerage sys-tems, one for the Split-Solin area (Margeta 1990)and a another one for the Ka�tela-Trogir area(Margeta, 1992) (Figure 3). Each system has aseparate sewage system, normally consisting oftwo pipelines, one carrying wastewater and othersurface water. Each sewerage system consists of adrain system and pump stations, a central waste-water treatment plant, and a corresponding sub-marine outfall. The Split and Solin wastewaterswould be treated at the central plant �Stupe� anddischarged into the Braè Channel in front of thetown of Stobrec. The wastewaters of the Ka�telaand Trogir area would be collected and treated atthe treatment plant located in the central-south-ern part of the island of Ciovo and dischargedinto the Split Channel in the front of the village ofMavarscica.The development of each sewerage system hasbeen planned so as to be executed in several phas-



es. The system segments constructed graduallywill function in an adequate manner and form asatisfactory technical-technological unit in com-pliance with the legal and other constrains,including EU Directives (91/271/EEC), at thesame time being one of the construction phases ofthe integrated sewerage system. The first phase ofboth systems consists of the construction of a pri-mary wastewater treatment plant and main col-lectors together with accompanying pump sta-tions. The second and further phases envisage theconstruction of secondary sewers and connectors,and, if necessary (based on the results of the mon-itoring program), the secondary or higher-level ofwastewater treatment. The gradual approach toimplementation would enable optimal sea protec-tion considering the negative impacts and theeconomic potential of the region. At the momentit is impossible to define a precise time-table ofthe project development since the implementa-tion depends on a number of political, socio-eco-nomic and ecological factors that will change withtime. Namely, we must not forget that this is acountry that has only recently come out of war,and is in transition from communist to capitalistsocial system, as well as in the process ofapproaching the EU. Such a situation hinderssafe planning as it is impossible to predict theintensity of population growth, industrial devel-opment, or the dynamics of construction of thedrain system, and especially of secondary drains.Thus, the step-by-step approach is the only reli-able and efficient approach to problem solution.

The adopted plan anticipates the construction ofeach new step in accordance with:� the results of the previous step;� newly acquired data and information;� new local, national and international require-ments and needs;� newly developed technologies;� economic possibilities;� organizational and other capacities of localcommunities and organizations.The aforementioned approach can be achievedthrough the application of the proposed integrat-ed approach using an adequate DSS.The hydraulic load of the waste water treatmentplants of �Stupe� and �Ciovo� at the end of thefirst phase is presented in Table 2. A long subma-rine outfall (3,230 m long and 1,400 mm in diam-eter), with a 400 m long diffuser at the sea depthof 42 m is envisaged in the first phase at the treat-ment plant of �Stupe�. If a biological treatment isapplied in later phases, the outfall may be shorter(930 m) and of a smaller diameter (1,340 mm).With a length of 400 m the diffuser will end at thesea depth of 32 m. At the treatment plant of�Ciovo� the primary treatment requires a subma-rine outfall 2,400 m long and 900 mm in diameter.With a length of 400 m the diffuser would end atthe sea depth of 52 m. The same outfall would beused in case of a secondary treatment. Theplanned step-by-step construction of the waste-water treatment plant and submarine outfallenable the simple adaptation to future needs andrequirements in order to comply with the increase


Table 2. Hydraulic load of the wastewater treatment plants of �Stupe� and �Ciovo� at the end of the first

phase

Qaver- summer Qaver Qrain

m3 day-1 161,568.0 � �m3 h-1 7,732.0 8,352.0 15,804.0m3 s-1 1.87 2.32 4.39

m3 day-1 35,888.0 � �m3 h-1 1,494.0 2,340.0 3,087.0m3 s-1 0.415 0.650 0.864

�Stupe� treatment plant

�Ciovo� treatment plant



Figure 3.

Concept of a long-term

solution of the sewerage system

in the Ka�tela

Bay area


of wastewater quantity, as well as sustainabledevelopment criteria.Industrial wastewaters treatment is envisaged intwo ways: (i) by treatment at the central waste-water treatment plant; and (ii) locally, by treat-ment at own treatment plant. Namely, all indus-trial wastewaters, before being discharged intothe sewerage, must meet trade effluent dischargestandards, except for BOD5. All industries inca-pable of meeting this standard must treat theirwastewaters prior to discharging into the publicsewerage system.

�ECO KAS¡TELA BAY� INVESTMENT PROJECTIn order to implement the mentioned adoptedconceptual solution for the management ofwastewaters in the area, a project entitled �ECOKA�TELA BAY� has been developed. The firstphase of project is worth about 140,000,000 US$,while total cost is much higher. The project envis-ages the construction of the main elements of thesewerage systems in order to divert the waste-waters from the Ka�tela Bay into the Braè andSplit Channels. In the western part of area, thesystem includes a main collector with accompany-ing pumps along the northern coast of the Ka�telaBay, a treatment plant, a tunnel through theCiovo Island, and a submarine outfall in the SplitChannel. In the eastern part of the area (towns ofSolin and Split) the system consists of a main col-lector with accompanying pumps in the easternpart of the Ka�tela Bay, a hydrotechnical tunnel,a treatment plant, and a submarine outfall in theBraè Channel. The realization of the seweragesystems would be the first step towards the pro-tection of the Ka�tela Bay. These selected struc-tures ensure that each sewer system can functionas a separate and complete technological systemwhich secures environmental protection and highstandards for the users of these systems. This sys-tem also ensures the use of the coastal sea inaccordance with the legislation and developmentplans.The project has a number of components, each ofwhich will produce some favourable environmen-tal effects. Those are:� Wastewater treatment plant �Stupe� and the

belonging submarine outfall: It is certain thatthis will be the component to have the greatestmerit in preventing further pollution of theKa�tela Bay, as well as in eliminating the pol-

lution of the coastal strip of the town of Split.All the wastewaters of the towns of Split andSolin, hitherto discharged into the Ka�telaBay, will now be treated and discharged intothe Braè Channel through a long submarineoutfall.

� Split-Solin sewerage system extension andimprovements: The work on the extension andimprovement of the Split-Solin sewerage sys-tem will include the interception of all waste-waters now discharged into the Ka�tela Bayfrom this area, and their collection in the�Stupe� wastewater treatment plant, whichwill prevent further pollution of the Bay. Also,the wastewaters from the part of Split hithertodischarged locally into the Braè Channel willbe intercepted and collected at the �Stupe�plant.

� Wastewater treatment plant �Ciovo� and thebelonging submarine outfall: This componentwill contribute greatly to the prevention of fur-ther local pollution of the Ka�tela Bay fromthe Ka�tela area, as well as of the Trogir Bayform the Trogir area. All the wastewaters ofthe towns of Ka�tela and Trogir, hitherto dis-charged into the Ka�tela and Trogir Bays, willnow be treated and discharged into the SplitChannel through a long submarine outfall.

� Ka�tela-Trogir sewerage system extension andimprovements: The work on the extension andimprovement of the Ka�tela-Trogir seweragesystem will include the interception of allwastewaters now discharged into the Ka�telaand Trogir Bays from these areas, and theircollection at the �Ciovo� wastewater treat-ment plant, which will prevent further pollu-tion of the Bays.

In addition to the waste water management, theproject contains another component dealing withthe freshwater supply of the western part of thearea. It plays a double role. Besides the improve-ment of the freshwater supply in the western partof the area, lacking fresh water, particularly in thesummer season, it will enable further economicdevelopment, as well as increase the water con-sumption, ensuring necessary funds to pay backthe international loans. The project is implement-ed by a newly formed agency �Eco- Ka�tela bay�,established by the local administrations includedin the project, the Croatian Water Authorities,and the local water and sewerage company.



CONCLUSIONThe long-term solution of waste water manage-ment can be implemented step-by-step applyingthe build-on approach. Initially, the primary levelof waste water treatment will be implemented and,if necessary, it will be upgraded, depending on theimpacts of waste water discharge on the marineenvironment and development of the seweragesystem and quantity of wastewater collected to thetreatment plant. Such approach would require an

intensive monitoring program, but would ensurethe maximal and safe use of the marine environ-ment for the additional wastewater treatment. Itwould secure a rational use of limited financialresources and protect the marine environment.Implementation of the project would have signifi-cant beneficial impacts on the social and econom-ic conditions in the area by resolving the existingconflicts and enabling the development of tourismand other economic activities.


REFERENCESBaric, A. (1998), Results of the sea investigation for the design of the submarine outfall Split-Stobrec (In

Croatian), Institute of Oceanography and Fishery, and Croatian Hydrographic Institute, Split, pp 198.Baric, A., Gacic, M., Grbec, B., Margeta, J., Milos, B., Onofri, I. and Veldic, V. (1996), Implications of Expected

Climatic Changes for the Ka�tela Bay, Region of Croatia, In: Climatic Change and the Mediterranean,Volume 2, (Edts) L. Jeftic, S. Keckes and J.C.Pernetta, Arnold, London, 143-249.

Baric, A., Marasovic, I. and Gacic, M. (1992), Eutrophication phenomenon with special reference to the Ka�telaBay, Chemistry and Ecology, 6, 51-68.

Bogner, D., Juracic, M., Odzak, N. and Baric, A. (1998), Trace metals in fine grained sediments of the Ka�telaBay, Adriatic Sea, Water Science and Technology, 38, 169-175.

Buljan, M. and Zore-Armanda (1996), Hydrographic data on the Adriatic Sea collected in the period from 1952-1964, Acta Adriatica, 12, pp 438.

Krstulovic, N. and Solic, M. (1991), Spatial distribution of faecal pollution in the Ka�tela Bay under differentmeteorological conditions, Acta Adriatica, 32, 827-835.

Marasovic, I. and Pucher-Petkovic, T. (1991), Eutrophication impact on the species composition in a natural phy-toplankton community, Acta Adriatica, 32, 719-730.

Marasovic, I. and Vukadin, I. (1982), �Red tide� in the Vranjic basin (Ka�tela Bay), Biljeske -Notes, Institute ofOceanography and Fisheries, Split, 48, 7.

Margeta, J. (1990), Preliminary Design of Sewerage system Split-Solin (In Croatian), Faculty of Civil Engineering,University of Split, Croatia.

Margeta, J. (1992), Preliminary Design of Sewerage system Ka�tela-Trogir (In Croatian), Faculty of CivilEngineering, University of Split, Croatia.

Margeta, J. (1997), Integrated Approach to Development, Management and Use of Water Resources, PriorityAction Program, Regional Activity Centre, Split.

Margeta, J. and Baric, A. (1996), Environmental Impact Assessment Study of Sewerage System Split/Solin andKa�tela /Trogir, World Bank, Washington, D.C.

Odzak, N., Zvonaric, T., Erak, M., Raspor, B. and Baric, A. (1999), Biomonitoring of Mercury in the Ka�tela Bay,Book of Abstracts, 5th International Conference �Mercury as a Global Pollutant�, Rio de Janeiro, May23-29, 239.

Odzak et al. (in press), Biomonitoring of mercury in the Ka�tela Bay using transplanted mussels, Sci. Tot. Env.Olsen, S.B. (1993), A Learning Approach to the Management of Coastal Ecosystems: Lessons from High and Low

Income Nations, Document presented at the Conference �World Coast�, The Hague, November 2-6.Pucher-Petkovic, T. and Zore-Armanda (1973), Essai d�evolution et pronostic de la production en fonction des

facteurs du milieu dans l�Adriatique, Acta Adriatica, 15, 3-39.Span, A. and Antolic, B. (1997), Composition, distribution, and condition of the benthic flora in the Split area (in

Croatian), In: Thousand years of the first recording of fisheries in Croats, Croatian Academy of Scienceand Arts, Zagreb, 493-513.

Tudor, M. et al. (1990), Oceanographic investigation of the Braè and Split Channels for the Integrated EcologicalProject Split-Solin- Ka�tela-Trogir, Institute of Oceanography and Fishery, Split.

Tudor, M. et al. (1991), Oceanographic investigation of the Braè and Split Channels for the Integrated EcologicalProject Split-Solin- Ka�tela-Trogir, Institute of Oceanography and Fishery, Split.


Ujevic, I., Baric, A. and Odzak, N. (2000), A Trace Metal accumulation in different grain size fraction of sedimentfrom a semi-closed bay heavily contaminated by urban and industrial wastewater, Water ResourcesResearch, 34, 3055-3061.

Ujevic, I., Bogner, D., Zvonaric, T. and Baric, A. (1998), Trace metal distribution in coastal sediment from theAdriatic Sea, Fresenius Environmental Bulletin, 7, 701-708.

UN (1992), Report of the United Nations Conference on Environment and Development. Rio De Janeiro, June3-14. A/Conf.151/26 (Vol. I)

UNEP (1995), Global Program of Action for the Protection of the Marine Environment from Land-BasedActivities, UNEP(OCA)/LBA/IG.2/7.

UNEP/WHO (1996a), Guidelines for authorization for the discharge of liquid wastes into the Mediterranean Sea,MAP Technical Reports Series, No. 107, Athens.

UNEP/WHO (1996b), Guidelines for treatment effluent prior to discharge into the Mediterranean Sea, MAPTechnical Reports Series, No. 111, Athens.

UNEP/WHO (1996c), Guidelines for submarine outfall structures for Mediterranean small and medium-sizedcoastal communities, MAP Technical Reports Series, No. 112, Athens.

Zore-Armanda, M. (1979), Water renewal in the basins along the eastern Adriatic Coast, Acta Adriatica, 19, 73-80.Zore-Armanda, M. (1980), Some dynamic and hydrographic properties of the Ka�tela bay, Acta Adriatica, 21, 55-74.



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