NUMERICAL MODEL (MIKE21) APPLICATIONS IN OUTFALL … · MWWD 2002 ozcan - mike21 applications from turkey.doc - 2 of 12 Use of numerical models in estimating nearshore wave parameters

2N D INTERNATIONAL CONFERENCE ON MARINE WASTE WATER DISCHARGES MWWD 2002 - I STANBUL SEPT. 16÷20

ozcan - mike21 applications from turkey.doc - 1 of 12

NUMERICAL MODEL (MIKE21) APPLICATIONS IN OUTFALL DESIGN :

CASE STUDIES FROM TURKEY

Merih Ozcan (1), Dr. K. Tunc Gokce (2)

KEYWORDS mike21, wave, hydrodynamics, effluent, heat, modeling

ABSTRACT As a consultant and design company working in marine engineering field, ARTI Proje has participated in several outfall projects and applied numerical models at different stages of the design studies. In an outfall design, numerical models can be utilized effectively in a wide spectrum; starting from wave prediction and pipe hydraulics to effluent transport. Though the reliable and high quality field data is always a matter of concern in a typical model study, latest professional models have variety of tools that make them applicable even when the field data is limited. In following sections below, examples from the completed modeling and design projects are presented. In these projects, MIKE21 was used extensively for wave, hydrodynamics and water quality modeling and it coupled with CORMIX in some cases to combine near field analysis with far field. THE MODELLING SOFTWARE MIKE21 The professional modeling package MIKE21 developed by DHI Water and Environment is one of the well-known numerical models which are currently available in the market. It is a 2-dimensional simulation package and includes many different models applicable to various coastal engineering problems involving wave dynamics, hydrodynamics, water quality and sediment transport analysis. Though it is a general purpose software, MIKE21 is particularly very useful in outfall design problems. Its wind-wave models can be used to estimate the wave height and direction along an outfall line, which is very important in cases with complex bathymetries, its hydrodynamic models can be used effectively to simulate the current field around an outfall and its water quality models can be directly coupled with hydrodynamic model to investigate advection-dispersion of pollutants, to simulate water quality parameters including DO or BOD, or to study the risk of eutrophication. WAVE MODELLING EXAMPLES Turkish coastline has quite irregular and jagged shape especially in Aegean and Western Meditteranean parts. This situation is also reflected into sea bottom topography as many bays of various sizes, offshore islands, headlands and peninsula type formations, which have significant effects on design wave parameters. While the determination of offshore wave parameters are generally straightforward with regard to application of the classical methods, the definition of nearshore wave characteristics around an outfall line usually requires more sophisticated techniques. When detailed analysis of nearshore wave transformation is ignored, the result is usually failure in addressing the major bathymetrical effects and in estimations of critical parameters like wave breaking and attack angles. (1) Technical Executive, ARTI Proje Ltd, Istanbul, Turkey, [email protected] (2) Managing Director, ARTI Proje Ltd, Istanbul, Turkey, [email protected]

mailto:[email protected]

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MWWD 2002


Use of numerical models in estimating nearshore wave parameters could be very helpful to the understanding the wave effects in the vicinity of outfall line, selection of design parameters and testing different wave conditions. MIKE21 NSW (nearshore wind-wave) model was used by ARTI Proje in some latest marine outfall design projects of Turkey. In most of them, model studies helped to investigate the effects of complex bathymetrical conditions in the project areas. In Figure 1, sample model test results are given from the study carried out for Kas Wastewater Discharge project. The project area was typical for Western Mediterranean coastline in its complex bathymetry where the offshore waves penetrate into the area around offshore islands and the outfall line is placed behind a peninsula where diffraction and refraction effects are considerable. Transformation studies were carried out for the offshore waves of 6.3 meters corresponding to 50 yrs. return period. Model calculations revealed that wave height is reduced up to 2.4 m. when they reach to outfall area.

Figure 1 : Model bathymetry and wave height-direction inside the model area Kas Wastewater Discharge Project



In Figure 2, a sample output from wave transformation study for Avsallar Wastewater Discharge project is given. In this project, the concern was not the complex bathymetry but the accurate determination of wave attack angle with the outfall pipe. The angle of wave attack near the shoreline was also critical, as the bottom material is sand and subject to seasonal erosion and accresion. Transformation of the design wave was modeled for several directions and attack angles ranging from 10o to 50o along the pipeline were observed.

Figure 2 : Model bathymetry and wave height-direction inside the model area Avsallar Wastewater Discharge Project

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In Figure 3, a similar output from the studies for Antalya Outfall project is given. Here, the offshore wave parameters and number of test to be carried out was defined by the designer and ARTI Proje only carried out the transformation model studies. It was required to determine the wave parameters along the outfall line for two different peak wave periods (10 and 11 sec) and for two different offshore wave directions.

Figure 3 : Wave height-direction inside the model area Antalya Wastewater Discharge Project

HYDRODYNAMIC MODELLING EXAMPLES It was observed in many outfall design projects in Turkey that usually an average current speed value is used in estimating effluent dilution and calculating transport rates. Selection of those average values are generally based on random past observations made on a global area and have defects in reflecting local conditions. Though detailed current measurements were included in some of the latest projects, they are usually inadequate in terms of monitoring duration and number of sampling locations. It is always a matter of concern to derive average and extreme values from those limited duration measurements. MIKE21 HD (hydrodynamic) model was used effectively by ARTI Proje in some recent projects in Turkey. In those studies, the limited period field measurements were mainly utilized for model calibration and verification purposes whereas the average seasonal and extreme conditions were estimated by conducting model tests. In Figure 4, sample model result from Kas Wastewater Discharge project is given. Here, the current patterns in the area were found to be of more unidirectional nature. The project scope included water level and current velocity measurements at 4 different locations around the discharge line for a total duration of 4 weeks. The collected data were mainly used in calibration of the HD model.



Figure 4 : Current field in the project area and at the vicinity of the outfall line Kas Wastewater Discharge Project

In a study carried out for a LNG Terminal’s heating water discharge and intake system in Iskenderun Bay, the model tests emphasized bi-directional flow patterns throughout a day and alternating seasonally due to tidal and wind effects (see Figure 5).

Figure 5 : Daily changes in current field Iskenderun LNG Terminal Project

MWWD 2002


In presented examples, the setup and calibration of the models employed simultaneous measurements of water level, current velocity and wind velocity. In Figure 6 below, a sample calibration plot from the cooling water investigation study of Izmir Natural Gas Power Plant is given. The figure shows that a good level of calibration was achieved indeed with the available field data which can provide better estimations for extreme and long term average values.

Figure 6 : Sample calibration plots for current velocity

Izmir Combined Cycling Natural Gas Power Plant

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WATER QUALITY MODELLING EXAMPLES In Turkey, far field dilution calculations and investigation of the effects of discharge on the water quality are carried out by analytical methods which gives an indication only on steady state conditions. In most of the cases, like wastewater discharges around highly touristic areas however, seasonal and extreme conditions has to be considered as required by legal regulations defined on the basis of extreme cases. In Figure 7, a sample output from water quality modeling study carried out for Kas Wastewater Discharge is presented. In the figure, instantaneous outputs from the simulation showing the extent of the BOD5 concentration can be seen. In places like Kas which has significant tourist attraction, it is particularly important to distinguish if a shoreline detachment of the plume occurs.

Figure 7 : Instantaneous concentrations of BOD5

Kas Wastewater Discharge Project

MWWD 2002


Another example for water quality modeling is given in Figure 8 for Gocek wastewater discharge investigations. Gocek is one of the specially protected areas of the country and has outstanding natural attractiveness. Under the project scope, several scenarios for discharge locations and rates were tested to evaluate the effects of the pollution imposed on the water quality. The field data collection campaign included oceanographical and water quality monitoring inside the bay for a total period of 1 year.



THERMAL MODELLING EXAMPLES ARTI Proje carried out several thermal modeling studies for power plants and LNG terminals. Cooling or heating water discharge-intake system design of these kind of structures usually requires detailed investigation of hydrodynamic conditions and thermal advection-dispersion. As correct location of intake structures with respect to discharge point carries great importance for efficiency of the system and for the reduction of operational costs, these type of studies usually include detailed field data collection campaigns. Environmental regulations in Turkey requires less than 1oC change in water temperature at surface around the discharge point. The surface area affected from the discharge is also required to be well defined. Numerical models play an important role in this regard, as steady state analytical calculations fail to address the temporal and spatial change in these parameters. In Figure 9 a sample output from the thermal modeling study carried out for Izmir Natural Gas Power Plant is given. The model results reported to the client included the simple graphs as shown to indicate the excessive temperature at the intake location as imposed by the discharge.

Figure 9 : Excess temperature distribution in the area Izmir Combined Cycling Natural Gas Power Plant

Excess Temperature at Intake

MWWD 2002


Another sample from Sugozu Thermal Power plant is presented in Figure 10. Here, outputs from the simulation indicate a daily change in the transport patterns, which is not possible to identify with more conventional techniques.

Figure 10 : Excess temperature distribution Sugozu Thermal Power Plant

In most of these projects, MIKE21 AD (advection-dispersion) model was coupled with CORMIX. The initial dilution and near field temperature gradient firstly calculated by CORMIX, then the results were transformed into MIKE21 AD for far-field modeling. CONCLUSIONS It can be said that numerical models are started to be employed in outfall design projects in Turkey only very lately. It is still not very common except for some major wastewater and power plant projects. The designs generally lack the detailed analysis of wave and current conditions. With use of numerical modeling, it could be quite possible to obtain more information on the oceanographical conditions of the design area even when the field data is limited. Latest professional numerical models offer engineers very useful tools to cope with the limited data both in calibration and verification stages. Of course, a reservation should be made for the necessity of experienced and capable engineers and experts in the design team.



ARTI PROJE LTD.

C o m p a n y P r o f i l e

ARTI Proje is a private company offering specialized engineering services mainly in marine, offshore, coastal, water resources and environmental engineering fields. Scope of services covers;

!" Project planning and management #" Feasibility and master planning studies #" Environmental impact studies

!" Basic and detailed design

#" Water intake and discharge structures #" Breakwaters, jetties, groins #" Underwater pipelines #" Offshore structures

!" Inspection and supervision

#" Construction supervision, #" Site inspection

!" Field survey and monitoring

#" Bathymetrical / topographical surveys #" Geotechnical surveys #" Oceanographical surveys #" Flow, water quality monitoring

!" Modeling

#" Wave modeling #" Hydrodynamic modeling #" Water Quality Modeling #" Shoreline change #" Erosion/sedimentation #" River outlet modeling

In previous years, ARTI has successfully participated in many projects in Turkey. In most of those projects, ARTI has utilized its up-to-date technology both in overall planning and design stages to produce optimal solutions. ARTI also has comprehensive experience with the international cooperation. Consulting and research activities are undertaken independently and jointly with institutes, companies and experts from Denmark, Norway, Sweden and UK. ARTI is exclusive representative of most of DHI Software. ARTI’s services in the field of underwater pipelines extend from the field data collection to pipeline hydraulics and environmental impact modeling. The experiences gained in completed wastewater outfall projects were successfully utilized in the design of cooling water systems of lately constructed power plants of the country.

MWWD 2002


NUMERICAL MODEL (MIKE21) APPLICATIONS IN OUTFALL … · MWWD 2002 ozcan - mike21 applications from turkey.doc - 2 of 12 Use of numerical models in estimating nearshore wave parameters

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