Effect of Drought Crisis on Salinity Level of Bangkok Water Supply

Transcription

1 Effect of Drought Crisis on Salinity Level of Bangkok Water Supply Auttapol Kordach 1,*, Aungkhoon Bunya 2, Chantira Khanboon 2, Sathapana Charoenchai 2, Sauwalak Sangphitak 2, and Nisapas Wongpat 3 1 Water Supply Section Water, Surveillance Division, Water Quality Department, Metropolitan Waterworks Authority, Bangkok, Thailand 2 East Bank Water Resources Section, Surveillance Division, Water Quality Department, Metropolitan Waterworks Authority, Bangkok, Thailand 3 Water Quality Department, Metropolitan Waterworks Authority, Bangkok, Thailand Abstract. Drought crisis has well-documented effects on every organism in the world. During , Thailand has also been catastrophic affected. Dam water levels in Chao Phraya basin were at minimum in 50 years. The consequences on raw water resources examined. Metropolitan Waterworks Authority (MWA), Thailand is responsible for providing and producing water supply in Bangkok, Nonthaburi, and Samutprakan provinces. The impacts on water quality and water production were investigated especially, the rise of salinity in tap water from sea level intrusion in the most past 100 years. However, conventional water treatment process of MWA water supply did not eliminate salt from production system. The forecasted impacts on tap water quality and quantity of supplied water were discussed. To solve this problem, MWA has developed countermeasures such as the improvement of monitoring and predicting the salinity situations in order to prevent problems immediately. Moreover, MWA coordinated with Department of Royal Irrigation to increase the drainage of salt water, to manage raw water pumping system in order to reduce salinity of raw water before entering into canal, and to reduce capacity of water supply production of facilities affected by salt water while increasing that of the ones with no effects. Additionally, MWA notified people and major users of water in advance in case that water supply would have higher level of salinity than monitoring standard through Line application and MWA s Website. These measures were able to reduce effects from the highest sea level in As of 27 th May 2016, the salinity level of raw water at raw water pumping station has been reduced from 0.87 gram/litres to 0.45 gram/litres accounting for percent reduction. This result has eased the concerns and has resumed confidence of users toward quality of water supply even in crisis situations. Keywords: salinity, drought crisis, tap water, water supply * Corresponding author: Auttapol.k@mwa.co.th

2 1 Introduction Metropolitans Waterworks Authority (MWA), State Enterprise, has major responsible for providing tap water to people in Bangkok Metropolitan Region of Thailand; Bangkok, Nonthaburi, and Samut Prakarn provinces. Our customers are about 10 million. Eighteen branches included 3,195-kilometer square are our responsible areas. Water Treatment Plants (WTP) are composed of Bangkhen, Mahasawat, Samsen, and Thonburi Water Treatment Plants. Total production capacity is approximately 5.9 million cubic meters per day. The two MWA raw water sources are Chao Phraya River and Maklong Dam. However, the primary raw water source of MWA is Chao Praya River, which more than 75 percent of a raw water source is used for tap water production.[1] Bangkhen, Samsen, and Thonburi WTPs apply Chao Phraya River for raw water source, which transmitted to MWA raw water intake at Samlae Pumping Station located in Pathum Thani province (above Bangkok), as shown in Figure 1. Fig. 1. Map of MWA raw water sources and Water Treatment Plants Chao Phraya River is an essential river of Thailand, combinating from four rivers: Ping, Wang, Yom, and Nan Rivers. These rivers originate from the north region of Thailand flown from north to south and are converged in the central of country at Nakhon Sawan province. Chao Phraya River, which is 372 kilometers long, flows to Gulf of Thailand. Climate change, growth of population and communities, agricultural and industrial expansion in Chao Phraya Basin lead to be high water consumption and result in continuous high water pollution. Lower section of the Chao Phraya River before flowing to Gulf of Thailand has an effect particularly on salinity problem. The Samlae Pumping Station located in the middle section of Chao Phraya River (RKM , RKM: km th from the river mouths), is far from Gulf of Thailand about 96 kilometers (RKM 96) to prevent saltwater intrusion impacted on water supply production process. Water quality is classified in River Classification Class 3, which is medium clean used for consumption but passing through ordinary treatment processes and for agriculture.[2]

3 Water volumes and flow rates are related to Bhumibol, Sirikit, and Chao Phraya Dams. During , Thailand faced with drought, rainfall volumes decreased over country, caused by Ei Nino Phenomenal.[3] Moreover, in 2014, precipitation volumes over Bhumibol and Sirikit Dams were the latest in 10 years led to be the smallest water volumes in 50 years. Consequently, during dry season, there was not adequate water volumes for agriculture and prevention saltwater intrusion resulting in the most past 100 years sea level intrusion at Chao Phraya River.[4] Therefore, public sectors had to countermeasure to appropriate water management and provide enough water volume for pushing saltwater back to prevent saltwater intrusion, which affected the tap water production. One of the measures for solving the problems was reducing water volume for agriculture during dry season, shutting water gates at branch canals to complete water drainage for fully prevent saltwater intrusion. The main drawbacks of MWA are unchangeable raw water resources and conventional water treatment technology, which do not remove salinity from raw water sources. Therefore, in drought crisis, MWA must have countermeasures and alleviate the salinity problem both in raw water and tap water. Water quality monitoring and reducing salinity in raw water have been created. Monitoring salinity value in raw water at Samlae Raw Water Pumping Station must be less than 0.25 mg/l so that tap water quality complies with World Health Organization (WHO) guidelines for drinking water quality, which determined chloride lower than 250 mg/l.[5] The main objective of this paper is to find out the appropriate salinity management affected in tap water quality during drought crisis. Although we do not change raw water sources and conventional water treatment technology tap water quality has to comply with WHO guidelines for drinking value. 2 Methodology 2.1 Raw water salinity monitoring MWA determined salinity raw water monitoring level was less than 0.25 g/l or conductivity was less than 500 μs/cm. at Samlae Raw Water Pumping Station. Online monitoring and field sampling were used for forecasting salinity to warning WTPs. Monitoring and remote measuring point; Monitoring and remote measuring points were installed belong raw water intake of MWA along the Chao Phraya River; Samlae Pumping Station (RKM 96), Wat Makham (RKM 91), Pak Kred (RKM 71), Phra Nangklao Bridge (RKM 66), and Siriraj hospital (RKM 50), as shown in Figure 2. In case of salinity raw water level trend increased and impacted on tap water production, we warned related agencies to close up monitoring and prepare for salinity situation. Moreover, emergency salinity plan was immediately used when the salinity level at Samlae Raw Water Pumping Station was higher than monitoring level. Field monitoring salinity; Field monitoring salinity plan is proceeded in drought season during November and July every year. However, we assessed the online salinity monitoring data for increase frequency field monitor sampling in upward salinity trend. Furthermore, salt wedge estuary map, as shown in Figure 3, was created for pointing seawater intrusion. Forecasting seawater intrusion; Online raw water quality monitoring data, field water quality data, and Tide Tables Thai Waters Chao Phraya River-Gulf of Thailand and Andaman Sea [6] were integrated to forecast seawater intrusion. This forecasting would predict the maximum salinity and duration of tidal bore. The example of Tide Tables Thai Waters was shown in Figure 4. The salinity forecasting predicted the seawater intrusion to MWA raw water intake for 24-hour notice advance.

4 Fig. 2. Map of raw water quality Station for salinity monitoring in Chao Phraya River Fig. 3. The example of seawater estuary which penetrates above Samlae Raw Water Pumping Station Fig. 4. Chart of tide-water level in Chao Phraya River on May, 2016

5 2.2 Pumping management of raw water source One of the methods to reduce the effect of salinity was by decreasing pumping rate or pausing pumping during high tide, high salinity level in raw water. On the other hand, pumping rate increased in low tide period. However, with the limitation of raw water reservoir, the pumping was not able to pause more than two hours as it might break or collapse embankment. 2.3 Cooperation with Royal Irrigation Department Besides, the two measures above, Royal Irrigation Department also took action to increase drainage to accelerate seawater back in Chao Phraya River until normal situation recovered. The flow rate, which had no effect on WTP process, should be more than 100 m 3 /s at Bangsai District (RMK 114).[7] 3 Findings and disscussion Integrating of online water quality monitoring data and field water quality data were created. The chart of salinity level in raw water and tap water were shown in Figure 5-7. The finding revealed that in 2014, the salinity problem occurred from January to March and the hightest salinity was at 1.81 g/l. It was the highest salinity level of MWA raw water source in 100 years. This was probably because the unprecedented event at that time. The seawater intrusion also was a severe situtation as it was our first time event and preparation plan for salinity management was not established. Moreover, in Figure 6, the results reported that during the period from June 2015 to August 2015 the salinity complication happened and the highest salinity was at 1.09 g/l. The experience of salinity management contributed to be better management than previous crisis. As shown in Figure 7, the chart indicated that the salinity problem in 2016 occurred in February to June and the highest salinity value was at 0.87 g/l. Fig. 5. Salinity level of raw water and tap water in 2014 In 2014, the salinity problem was the most severe salinity problem resulting from the first year of Ei Nino effect in Thailand, less water storage, and much planting than agricultural plans. Therefore, there was insufficient amount of water to push seawater back.

6 It took about four days to drain water to reach MWA raw water intake. However, raw water pumping management also reduced salinity level reach 19.89%. In 2015, the percentage of reducing salinity level was less than those in This might result from less rainfall and consequently water storage in dams was less than those storage in However, the situation was less severe than in 2014 probably because the government established national center for prevent the salinity problem by integrating disciplinary departments and informing Chao Phraya Basin farmers refrained from planting during dry season to maintain water for washing the saline water back to the sea. Furthermore, in 2016, the results indicated that the percentage of decreasing salinity in raw water was the highest number, as shown in Figure 7. This was probable because it had an experience in salinity management and the government restricted Chao Phraya Basin farmers planting during dry season and shut off water gates along the Chao Phraya River. However, the number of the affected seawater intrusion day in 2016 was longer time than the other years. It may cause by the drainage did not enough to push all salinity back out to sea. The seawater was still under raw water intake and would be intruded when high tided. Fig. 6. Salinity level of raw water and tap water in 2015 Over all results reported in Figure 8, the results exhibited that the countermeasures decreased the salinity level of raw water in 2014 to 2016 were at the percentage of 19.89, 15.60, and 47.15, respectively. In Figure 9, the chart showed that when the salinity in Chao Phraya River was high level, a number of working pumps were decreased and immediately increased the salinity down resulting in the reduction of tap water salinity value. Besides, the period of the affected seawater intrusion day was 65, 48, and 88 days. The maximum, minimum, average of tap water salinity, and conductivity were shown in Figure 10. It pointed that tap water salinity during were the range of , , and g/l., respectively. In addition, the results exhibited that similary, conductivity and salinity were in the same trend.

7 Fig. 7. Salinity level of raw water and tap water in 2016 Although MWA had various measures to solve the salinity problem tap water had still out of WHO Guideline level in some time. Announcement tap water quality situation played an important role in solving the salinity problem. The only high salinity time occurred some time of a day because of the impact of high tide. Therefore, people were informed that tap water might change water taste periodically and asked them to preserve water in the period of tap water quality complied with WHO guideline drinking water quality value. The people might access the tap water quality data on the website; Fig. 8. The comparison chart of the highest salinity in raw water and tap water as well as a period of salinity problem 4 Conclusions and recommendation The salinity management which has an effect on tap water quality needs to be integrated with disciplinary organizations for problem solving. The unchangeable main raw water

8 sources and conventional water treatment technology are limitation of MWA. Therefore, the preventive measures and alleviation the problem are created. The cooperation with Royal Irrigation Department contributes to increase drainage to wash the saline water back to the sea. The government policy is one of the main factors to relieve the problem by prohibiting the planting during drought season. In addition, salinity fluctuation depends on the tide of sea level led to MWA raw water pumping management, which is decreased by more than 10% off the tap water salinity level. Notifying customers about the tap water salinity situation plays a role in maintaining low salinity water in their storage tanks. They can access the real-time tap water quality online on the website. Fig. 9. Chart of the relation of Chao Phraya water level, conductivity, and a number of working pumps Fig. 10. Chart of tap water salinity level and conductivity during 2014 to 2016 MWA has examined schemes for long term solution such as finding other raw water sources, raising raw water intake, and improving water treatment technology are examples. However, MWA has the West (Maeklong Dam) and the East (Chao Phraya River) raw

9 water sources, as shown in Figure 1. The diversion water from the West source does not impact on salinity is used for raw water source during seawater intrusion. The tunnel diversion will be built to connect between the West and the East raw water sources. It contributes to reduce salinity in raw water source. In case of upper raw water intake, this is a benefit for preventing the salinity intrusion reach raw water intake. Furthermore, desalination technology will relieve the salinity problem in the future. 5 Acknowledgement The authors acknowledge Metropolitan Waterworks Authority of Thailand for financial support of the project and permission to publish these results. We also thank to Water Resources and Environment Department for raw water quality online data. A special thanks to Asst. Prof. Dr. Bhakaporn Kuljirundhorn for helpful proof reading. Also, we would like to acknowledge the Director of Water Quality Department for their valued suggestion and supporting. 6 References 1. Metropolitan Waterworks Authority (MWA), Thailand: Annual Report 2016 Metropolitan Waterworks Authority. (accessed May, ) 2. Wijarn, S., Pimon, W., Vuttichai, K., and Akaluk, Y., (2000) Water quality situation in the Chao Phraya delta. Proceedings of the international conference: The Chao Phraya Delta: Historical development, dynamics and challenges of Thailand's rice bowl, p Interisk Asia (2016)., Interrisk Thai Flood Report: Drought Report, Thailand 2016., 18_16_005_Drought_ pdf 4. Hydro and Agro Informatics Institute (2017)., Drought Situation Record in 2014/2016., (in Thai) (accessed May, 2017) 5. World Health Organization (WHO) 2011., Guidelines for Drinking Water Quality, 4rd ed, Genev 6. Hydrographic Department Royal Thai Navy (2016)., Tide Tables Thai Waters Maw Nam Chaophraya-Gulf of Thailand-Andaman Sea 2016, p (in Thai) 7. East Bank Water Resources Section (2014)., Water Quality Department, Metropolitan Waterworks Authority, Thailand,: Overcome Salintiy Crisis in 2014., (in Thai) (accessed February, 2016)