Water Journal : Water Journal December 2012
operations technical features 76 DECEMBER 2012 water However, the strength of the tsunami was much greater than these pipes could resist. Before the earthquake, the total length of the water distribution network in the city was about 230 kilometres. Approximately 164km remained after the earthquake and tsunami devastated the city. Near the coastline, the water distribution network was completely destroyed and much of it entirely disappeared. The tsunami was so powerful that it moved roads under which many of the water supply pipes were buried. Figure 5 shows an example of the destruction of a road by the tsunami. Deterioration of Raw Water Quality The water quality at the wells relied on by the three largest DWTPs deteriorated dramatically after the earthquake. Table 2 shows the partial results of the water quality analysis of a sample taken on 11 April at Sukezukuri DWTP. The chloride ion (Cl-) concentration level greatly exceeded the level specified by the Japanese national drinking water standard of 200mg/L. Similar results were also found from samples taken at other shallow wells in the city, such as at Isatomae DWTP. As it was suspected the deterioration of water quality was caused by the intrusion of tsunami water (seawater) into the ground, the groundwater was continuously pumped out to remediate it. However, water quality improvement was slow, and the chloride ion concentration even increased after rainfall. It was not until September, five months after the tsunami, that the water quality of the wells improved and stabilised at treatable levels. Water Supply Rescue Effort Shortly after the earthquake, tons of bottled water arrived in the city as emergency relief supplies from all over Japan and abroad. Neighbouring cities helped transport water by water carrier trucks. However, there was a clear shortage of water available for citizens. The water supply rescue effort was a collaborative effort by the city, other Japanese cities, the national government and private companies. Besides Veolia Water, a number of local companies also provided support. Table 3 summarises the main activities concerning water infrastructure recovery. To coordinate everyone’s rescue efforts, the water supply recovery team was set up and meetings were held regularly. As shown in Table 3, 99% recovery of the water supply was not achieved until early August 2011. Of all the cities devastated by the Great East Japan Earthquake, the water supply of Minamisanriku City was among the slowest to recover. This was because the raw water quality of the wells that the city almost entirely relied on did not improve quickly, while in other cities groundwater quality improved much faster or they had alternative sources of water. Another factor that made the recovery difficult was that the office of the water bureau was swept away by the tsunami. While all the staff and contractors survived the devastation, many lost family members and about 70% of all staff and contractors lost their homes. Electricity and telephones stopped working for a number of days after the earthquake and Table 3. Summary of the water supply recovery work (summarised from the city’s press announcements). 2011 Events related to water supply March On 11 March, the Great East Japan Earthquake hits the city and disrupts the water supply. Tons of bottled water arrive as emergency relief supplies. Water supply mainly relies on transported water from the neighbouring city (about one hour’s drive each way) by water carrier trucks by the national self-defence force and cities around the nation. April Veolia Water sets up two Aquaforce 5000 units (temporary treatment plants) and provides about 80m3/day of non-potable water. May The city starts sending non-potable water to limited areas (water with high chloride ion concentration exceeding drinking water standards). The city decides to drill new wells with high raw water quality and starts building temporary pipelines to connect with existing pump stations. Veolia Water adds a microfiltration membrane treatment process to one Aquaforce 5000 unit and starts providing about 40m3/day of potable water. June Local Japanese company constructs and starts operating a small membrane facility, bringing the water recovery rate to about 7%. Out of 2,100 households that need water, about 1,600 households (about 75% of total) receive non-potable water with high chloride ion concentration. Veolia Water decides to deploy desalination units at Isatomae DWTP to remove chloride ion from the treated water. July With the new wells and temporary pipelines, the city starts supplying potable water to Shizugawa and Iriya areas (about one-third of the city’s population). August With the improvement of the raw water quality, the new wells, and the desalination units, potable water goes to about 99% of the population. September Typhoon destroys the temporary pipelines causing water disruption to about 340 households. Figure 5. A road destroyed by the tsunami.
Water Journal February 2013
Water Journal November 2012-1