Paper Submitted for:

9th ICUD September 8-13, 2002, Portland, Oregon USA

Modelling the interaction between drainage system, wastewater treatment plant and

receiver water in Pattaya beach

Ole Mark*, Sutat Weesakul*, Nguyen Quang Hung* *Water Engineering & Management, Asian Inst. of Technology, PO Box 4, Klong Luang, Pathumthani 12120, Thailand Email: Mark@ait.ac.th, Sutat@ait.ac.th, Xeko@hotmail.com. Abstract People now not only need a higher standard of living but also a clean environment - not only for themselves but also to take care of the coming generations. Coastal areas are sensitive and often in the risk of degradation and at some locations around the world, the coastal areas are so polluted that it poses a health risk to swim in the water off the beach. Often the pollution originates from sewer outfalls discharging directly into the sea. Pattaya is one such example, which has moved too quickly from being a small fishing village to a big city with high level of tourism. Hence, due to the booming tourism and other economic activities, the environment of Pattaya beach has been damaged, especially the water quality at the beach. The degradation of water quality is caused by discharging of wastewater from hotels, resorts and industrial factories into coastal water. The quality of the coastal water at Pattaya beaches has been identified by the Pollution Control Department, during certain periods of the years, as not suitable for swimming. Even though the new wastewater treatment plant has been built and in operation since November 2000, the issue is still serious. Reports from Tourism Organization of Thailand have shown that the number of tourists is down day by day and the tourism industry at Pattaya has been deeply affected. One of the indicators of pollution, the coliform bacteria, is found in the coastal water of Na Klua and Pattaya beach had increased and spread rapidly. A dynamic pollution transport model for urban drainage, MOUSE TRAPTM, is used to simulate and describe the drainage system of Pattaya as well as the transportation of bacteria. The function of WWTP is examined based on its historical data. The water quality beach is treated by the two-dimensional hydrodynamic model: MIKE 21TM. Pattaya’s drainage system is analyzed to see if it has enough capacity to avoid flooding, e.g. by use of Real Time Control and hence reduce the spills to the sea. A animated maps show spreading of the pollution in time together with time series of the simulated bacteria counts after heavy rain. Different cases were analyzed, e.g. for high and low tides with different sources and sinks. Alternative operation strategies of WWTP were also evaluated to find the optimum operation strategy, which minimizes the impact on the receiving waters based on existing infrastructure.

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Background Water is a basic necessity for sustaining life and development of society. Proper management, protection and development of the water resources is a challenge imposed by population growth, increasing pressure on the water and land resources by competing usage, and degradation of scarce water resources in many parts of the World. Currently, the general concepts and elements of Integrated Water Resources Management (IWRM) have been established and IWRM projects are in progress around the World. Urban Water Management (UWM) is to be seen a subset of IWRM – albeit a very important one. Usually the scope and sphere of UWM becomes more local compared to those of IWRM and the urban waters are often managed at a local level. In the future it is foreseen that there will be a strong competition between cities and irrigation schemes for water. The irrigation schemes need the water to produce food for the increasing population while the growing cities need more drinking water. Hence, detailed knowledge about the water needs and management in cities will be a necessity. As the cities in the Asian region are growing rapidly, it is important that attention be paid to the role of the cities in IWRM. The infrastructure related to water in the cities consists of water supply networks, sewer systems, purification and wastewater treatment plants. Many of the cities are old and they have developed according to the varying historical needs and visions. Hence, the layout and design of the infrastructure has gradually developed into rather complex systems, which require tools that can handle such situations. An understanding of the physical system and its interaction with the environment is a prerequisite for effective planning and management of urban water resources. In this regard, computer models provide the opportunity for well-structured analyses of water availability, water demands and wastewater disposal and they offer a sound scientific framework for a coordinated management and planning. The Asian Institute of Technology (AIT) has for many years been working with these types of models and has recently started a comprehensive project comprising a variety of teaching, training and research activities in water resources including urban water resources. These projects are financially supported by the Danish International Development Assistance (DANIDA) and entail collaborations with other institutions in the region and with Danish institutions. Several of the projects under the AIT-DANIDA collaboration aim to show the benefit from applications of computer models to cities in South East Asia. The application presented in this paper highlights the applicability of models within coastal pollution at Pattaya, Thailand Introduction Many places in SE Asia, the seawater in the coastal zone plays the role of receiving water for pollution. The household sewage is channeled from the sewage in each home to the sewer system, into which some industrial wastewater also discharge. Rainwater enters the system through sewage pipes or the drains and gratings in the street. Then all of it discharge into seawater with a load of polluted materials. Evidently, the coastal tourism industry has greatly contributed to the deterioration of the environment. The increasing environmental can be attributed to a failure in coordinating environmental conservation measures and tourist development policies.

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There are many ways to manage and evaluate the water quality. In those cases, we can use monitoring network or apply the model, or integrate both of them to get successful results. But it is not possible to analyze the performance of the drainage system based on measured values only, especially with respect to amount of cost and time requirements for field measurement. The need of the cost-benefit solution lead to the comprehensive investigation of the Integrated Urban Drainage using the range of hydroinformatics tools, including simulation models. The application of the technological hydroinformatics line makes it possible to analyze and evaluate the different “if – then” scenarios within a short time. Validated mathematical models are becoming necessary simulation tools for ensuring compliance with increasingly strict environmental standards. Moreover, the results of modelling can help engineers and/or maintenance to set up the powerful system of monitoring by identifying of “key-points” in the system and the set of variables (indicators) which has to be monitored. Pattaya city in Thailand is one of the examples which move too quickly from a small fishing village to a big city with high potential of tourism. The environment of Pattaya beach especially water quality, has been damaged, so nobody is swimming on the beach due to combined sewer overflow (CSO). Although there were no sewage treatment plants in Pattaya in the 1970s, the sea water in the coastal area of Pattaya was not yet polluted primarily due to the small population and low number of visitors then. But from the 90’s, with unbalanced infrastructure development and the booming number of visitors, water quality has been down and become considerably polluted. The result of many water quality surveys revealed that the Coliform bacteria found in the coastal water of Na Klua and Pattaya beach have increased and spread rapidly. The highest number of Coliform bacteria found at the same sampling station along Pattaya beach increased from 6000 MPN/100ml in 1976 to 11,000MPN/100ml, 118,000 MPN/100ml and 240,000 MPN/100ml in 1978, 1984 and 1986 respectively. It should be noted that the recommended value by the Thai EPA for Coliform in sea water (bathing water) is set to be below 1000 MPN/100ml. For Pattaya beach, the interaction between the drainage system, the wastewater treatment plant and the receiving waters are described by the following models from the company DHI Water & Environment - MOUSE for drainage system, MIKE 21 for the dilution of water discharged and the sea water, and historical description of input and output water quality from Wastewater Treatment Plant. The scope of the present work is:

1. To come up with a systematic evaluation of the water quality condition in Pattaya beach,

2. To quantity the impact of the construction of the wastewater treatment plant, and 3. To provide analysis of alternative schemes to find the optimum operation of the

whole system.

The phases of the project consist of: • Data Collection • Build and calibrate the model for drainage system • Describe the WWTP on its historical data • Build up and calibrate the 2D model of the sea to simulate a dilution process.

The whole drainage system can be divided into three main parts: • Sewer system

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• Wastewater treatment plant • Receiver water

Each part is individually treated by different models and then linked together by Integrated Catchment Simulator (ICS). The MOUSETM and add-on MOUSE TRAPTM are selected to simulate the sewer system and the water quality in the sewer system. The WWTP is not considered important because of the limited time thus only described on historical data, the input and output records. For receiver water, MIKE 21TM is applied to simulate the dilution process of wastewater into receiver water and to evaluate the water quality of Pattaya beach.

Figure 1. Description of the whole urban drainage system

Figure 2. Pattaya’s location in Thailand.

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Description of the study area

Pattaya, ranked the second best traveling spot in Thailand, has the feature as coastal lowland area, beach and islets. Pattaya beach, especially, is the famous attractive beach in the country. Being influenced by monsoon in summer and winter, the weather is warm throughout the year. Pattaya is located about 150 km to the Southeast of Bangkok. The total area of the city is 208.1 km2, including land, water and island. It consists of Tambon Na Klua (Coral Island, Krok Island, and Sak Island), Tambon Nong Prue, part of Tambon Huai Yai and Tamban Nong Pa Lai, 154.66 km2 of water. It has 15 km long beach. The Pattaya catchment is divided into two main zones : Na Klua Zone and Pattaya Zone, Na Klua Zone has about 46 sub-catchments, and Pattaya Zone has 44 sub-catchments. In those sub-catchments, there are some catchments with a high density of tourism with different water consumption standards.

Figure 3. A view of Pattaya Beach As a result, the Public Work Department planned to improve the drainage system. They managed to install large pipes at Kasemsuwan road to solve flood problems in Central Pattaya and South Pattaya. At the same time, the Pattaya City has improved the weirs by expanding them to be 6 m wide. The new wastewater treatment plant has been built and in operation since November, 2000. The existing sewer system in Pattaya is a combined sewer system and serves 80% of the city area. The closed sewers are designed for a return period for 5 years and 10 years for open channels. The system has two pumping stations at the end of the pipe system and seven weirs discharging a mixture of sewage and rainwater directly onto the beach (see figure 4). I.e. the Pattaya beach is seriously polluted, primarily due to domestic wastewater discharging from illegal settlements on the shoreline, hotels and restaurants together with the CSO during heavy rain.

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Figure 4A. The beach at Pattaya.

Figure 4B. Combined sewer overflow onto the beach at Pattaya Modelling the hydraulic process and pollutant transport in the drainage system The description of the flow in the drainage system of Pattaya is based on the hydrological and the hydrodynamic MOUSETM model. These models have been setup based on the database from PCD (Pollution Control Department). The modelling of pollutant is carried out by using the advection-dispersion model, i.e. assuming the bacteria to act as an conservation pollutant. This assumption is fair as the concentration time in the Pattaya’s sewer system is rather short. It has been decided only to use the indicator Total Coliform in the advection-dispersion model because the objective is to check the bathing water quality in the Pattaya beaches. Two cases are analyzed: before and after the WWTP has been built. Before the WWTP was built, the wastewater was discharged directly into the sea from several discharge points along the beach. After building the WWTP, half of the wastewater was pumped back to WWTP and treated there before discharging into the sea. At present, the WWTP has a capacity of 65,000 m3/day and will be increased up to 137,500 mp3/day in next ten years.

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Dry weather flow would be drained through block pipes laid along the coast and pumped back to the WWTP then discharged to the small stream and finally runs to the sea. During rain storms when the rainfall exceeds 20 mm, the weirs will be opened to discharge a mixture of rain and wastewater to the sea.

Figure 5. The layout of the pipe network of in the model of the Pattaya sewers.

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The standard water consumption for inhabitants in Pattaya is 185 l/p/d and for tourists it is 290 l/p/d. For those sub-catchments with the presence of tourists, the number of tourists is about 20% of the local population. Based on these data it is calculated that the standard of water consumption for those catchments is 203 l/p/d.

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Figure 6. Water consumption in Pattaya – Source PCD – Thailand 1995 The rail fall data used at input to the hydrological part of the MOUSEMT model has an one year return period. The cure is developed based on data from the weather station in nearby Butchery.

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linked and ran but the result shows that for representative the common situation, one-year return period is more suitable to run.

To calibrate the model, there is few data to use, a rainfall event equal to 5 year return period was used.

Rainfall event - 19 October 1994

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Figure 8. Rainfall event 19, October 1994

(Source: Survey and detail design of drainage system and WWTP in Pattaya, Final Project – PCD Thailand 1995)

For water quality part, the box rainfall 20 mm was used to run, there are also some more different rainfall was used but if the rainfall is too small then the hydraulic part is not correct, if the rainfall is high, then the concentration of Total Coliform is reduced. From different results, the result of 20mm box rainfall shown it is applicable for both purpose hydraulic and water quality simulation, then it was selected to analyze the drainage system of Pattaya, to compare between two cases: before and after the WWTP was built.

Figure 9. Measured point used for calibration of MOUSE model

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Figure 10. Water level in point 1 - Observed and simulated

Figure 11. Water level in point 2 - Observed and simulated

Figure 12. Water level in point 3 - Observed and simulated

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Figure 13. An example of one longitudinal profile – Model runs with 5 year return period,

without WWTP

Figure 14. Total Coliform concentration fluctuatate due to discharge changing inside the pipe

when rainfall event happened The results of MOUSE TRAPTM are applied as input for the WWTP, which is considers to be a black box. Measured output from the WWTP is used input together with the CSO for MIKE 21TM model.

Modelling of the receiving water along the Pattaya beach The bathymetry file of the upper Gulf of Thailand was set up by digitizing the map of the Upper gulf of Thailand. The data was obtained from Pollution Control Department. Then

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Nested Grid Hydrodynamic Module was used to build model from the bathymetry of Gulf of Thailand and then extract results into the Pattaya zone to be boundary conditions.

Figure 15. The bathymetry of Pattaya cover an area 12x12 km with grid spacing 50x50 m.

The model is run for one month period, there are two simulations has been done so far, one in dry season (April) and the other in rainy season (July). Rainy season was selected with reason that in the rainy season, the situation is worse. The MIKE 21TM model has three boundary conditions: North boundary, West boundary and South boundary. The input boundaries transfer file from the model of the Upper gulf of Thailand. Depending on the time of simulation and the size of result file and the purpose of the run, on the relationship between grid size and the number of grid step, model was set up to run with the time of simulation is 3 days (72 hrs) and the time interval is 5 sec. Those both two cases have been done with the neap tide boundary condition. The boundary conditions of three cases are the same, each boundary condition is inputted by a series data file created by MIKE 21. To run Water Quality Model in MIKE 21 for Total Coliform, there are some coefficients were used, which were calibrated with some data from a previous project run by JICA project. The results show the changing of the concentration of Total Coliform before and after the WWTP was built. Thus, the positive impact of WWTP on improving water quality can be seen clearly. The water quality can be consider suitable for swimming (the concentration of Total coliform is under 1000 MNP on the nearby costal). On the figure 16 and 17, the color on the beach area show very clear view about the Total Coliform concentration after 3-day simulation.

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Figure 16. The result at the end of 3-day simulation in condition without WWTP

Figure 17. The result at the end of 3-day simulation in the condition with WWTP

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After the WWTP was built, the water quality of Pattaya beach was improved, the number of Total Coliform range from 500 to 3,000 MPN/100 ml, comparing to its range from 2,000 to 9,000 MPN/100 ml before the WWTP was built. The WWTP removed a big amount of bacteria, but after the rain, there are still some place where the concentration of Total Coliform still can not meet the standards for bathing water. The outlet from WWTP directs to Naklua River, therefore Naklua zone is still in dangerous condition. To improve the water quality in Pattaya beach, an analysis on long deep sea outfall was done, the result reveal a new solution that can be applied in reality.

Point 4

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Figure 14. Total Coliform result from after constructed WWTP and and deep sea outfall

analysis at point 4 in Pattaya beach Conclusion The paper describes the interaction between three parts of the sewer system. The target of the study is to understand the integrated relationship of those components: Drainage system, WWTP and receiver water (river and sea). It shows that in order to improve the bathing water quality, all the processes involved in CSO effects: sewer system states, WWTP response and, receiving water behavior must be taken into account. In this study, the accuracy of each models depend on different conditions. For MOUSE TRAPTM, they are: - The data collected to run models include pipe system area, and the operation of the system. For Pattaya, the number of tourists, the peak and non-peak time schedule are very important for the calibration and validation both hydrodynamics and water quality. - For MIKE21 the grid distance is the key, if a large grid spacing is selected then the accuracy will be low along the beach, but if the distance is small then it takes to long time to simulate the scenarios. The boundary conditions are very important, because controls and has strong effects on the dilution and dispersion process. The results from the models show that water quality of Pattaya beach has been improved since the WWTP came into operating, the water near the coast is now considered suitable for swimming - if is has been some time since the last heavy rain. But the flooding problems

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control should be paid more attention to. Further studies can be done with the analyzes of some different schemes to find the optimum operation of the drainage system e.g. pumps, weirs and WWTP.

The advantages of integrated model are:

- Increased understanding about the interaction between the sanitary system and the coastal water.

- A holistic approach to design and manage the full urban system - The tradition was to study and optimize with constant input, this new integrated study can

provide a series data file, so results can demonstrate the changing of the system during the simulation time.

- Integrated model does not required more work compared to optimize each system individually – but more difficult as it requires better planning and knowledge of all 3 systems only. To integrate all the modules in the system, understandings of the entire module are required.

For Pattaya more data should be collected, e.g. tracer in the sea and the sewers to determine dispersion coefficient. A model for the WWTP should be applied for completely interactive modelling Integrated modelling is applicable under Asian conditions and should be further explored: - Adapt to local specifications - Enhance applicability in reality

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