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14. “Developing into a Water-Efficient City”

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[February 8, 2016] Fukuoka Growth 2015-2016 GlobalCityStatus リレーコラム View this post in pdf pdficon_small (968KB, Japanese)

Column 14. Developing into a Water-Efficient City

(by Teruaki INOUE, Deputy Director General)
Although lacking any major rivers within its administrative area, Fukuoka City has grown into a city with a population of more than 1.50 million. Let’s consider why that has been possible from a basic infrastructure (water) perspective.
During the latter part of January, various areas of Kyushu faced a series of problems such as suspension of water services because of a cold snap. Thirty-eight years earlier in 1978, Fukuoka City was forced to implement water use restrictions that continued for 287 days. At that time, the population of Fukuoka City was 1.05 million, and its system could supply 478,000 m3 of water daily, which was obtained from the Egawa Dam, four other dams within the city’s administrative area, and rivers, but extremely little rainfall (70% of a typical year) had a major impact on the lives of residents of not only Fukuoka City but also surrounding cities.
In order to resolve this precarious situation, the General Plan for Measures Related to Water Use in a Water-efficient Fukuoka was created in 1979, and fundamental measures to resolve the problem were launched. Up until the present, the city has implemented numerous measures, which have been based on the idea of a stable supply of water and water-efficient urban development.
First of all, dams were constructed on and water obtained from the Tatara River and Naka River systems within the city’s administrative area, and the long-awaited aqueduct from the Chikugo River, the largest river in Kyushu, was completed in 1983. The benefits from this were shared throughout the city by the Fukuoka District Waterworks Agency. For Fukuoka City, if one includes the increased volume from the Egawa Dam and Oyama Dam (competed in 2013), 32% of the city’s current capacity, 777,700 m3, comes from the Chikugo River system. This was possible precisely because of the understanding and cooperation of various parties, including local governments and residents of the watershed.
At the same time, efforts have been launched to employ new technologies, such as using a seawater desalination plant (MAMIZU PIA) that was completed in 2005 and makes a stable supply of water possible regardless of the weather.
On the other hand, progress has been made in creating a water-efficient city through cooperation with residents, and this has involved greater awareness of water conservation among residents, the spread of water-efficient faucets and other equipment, and the use of recycled water (a first for Japan), and for FY2013, Fukuoka’s water demand was 400,000 m3 per day, giving it the lowest per capita water demand among major cities in Japan. Incidentally, Fukuoka City was hit by a heat wave in the summer of FY2013, and the monthly average temperature was 30°C, the highest in Japan, and there were seventeen consecutive days that the daytime high temperature was 35°C or more, a historically long streak, but even so, the water use volume was the lowest among major Japanese cities.
Furthermore, by installing a water supply coordination system (water management center) to provide a fair and smooth supply of water to all areas of the city and investigating water leaks, the city is working to not only make the most effective use of water as possible but also maintain water quality and safety .
Between 1994 and 1995, water restrictions were implemented 295 days on account of unusual little rainfall, less than the previous time, and for the total period, rainfall was only 60% that of the previous time. In 2005, there was another period of little rainfall, the third smallest recorded amount, but water restrictions were not implemented. This is probably because of water resource development (expansion from those within the watershed to those outside the watershed and the use of sea water), the water supply coordination system, and above all the cooperation of residents.
The water level at the eight related dams is more than 90% on account of the large amount of rainfall since last year, but there have still been years when restrictions have been placed on the amount of water that can be taken from these reservoirs on account of the recent high volatility in the weather.
The Gokayama Dam, which will be the largest dam in the prefecture with an effective storage capacity of 39.70 million m3 is being constructed upstream from the Minamihata Dam on the Naka River system, is expected to come into use in 2018. The dam is unique in that part of its capacity is allocated for drought countermeasures, and of the overall 16.60 million m3, 13.10 million m3 is for Fukuoka City, and will serve as water in the case a once-in-a-decade of more severe drought. It will probably be necessary to continue to develop a water-efficient city as a reassuring backstop for future crisis.
Waterworks are indispensable lifelines, and efforts to secure water resources and get communities to work together to conserve water on account of the harsh local water resource environment are probably some of the reasons that Fukuoka City continues to grow.

14. 節水型都市への発展
~都市の成長に不可欠な水資源確保の経緯~

✔福岡市は大きな河川を持たず水資源に乏しい
✔過去には度重なる給水制限が市民生活の脅威に
✔「節水型都市づくり」を進め、一人当たり給水量は大都市最少に!
テキスト:副理事長 猪上 照明
福岡市は市域内に大きな河川を持たないにもかかわらず、150万を超える人口を有する都市に成長しました。なぜ可能だったのか、水という基本的なインフラの面から考えてみます。

昭和53年渇水 給水を受ける市民(写真:福岡市水道局提供)

昭和53年渇水 給水を受ける市民(写真:福岡市水道局提供)

1月下旬、九州各地は寒波の影響による断水等が相次ぎましたが、今から38年前、昭和53年、福岡市は287日にも及ぶ給水制限に追い込まれました。当時の人口105万人、施設能力日量47.8万立方メートルを江川ダムと都市圏内の4ダム、河川からの取水で賄っていたのですが、平年の7割という異常少雨の結果、福岡市のみならず福岡都市圏含めて市民生活などに甚大な影響をもたらしました。

そういった危うい基盤の解消に向けて、昭和54年に「福岡市節水型水利用等に関する措置要綱」を制定し抜本的な対策を図り、今日まで、より「安定的な水の供給」と「節水型都市づくり」を基本に様々な施策に取り組んできています。

まずは都市圏内の多々良水系や那珂川水系のダム建設や取水を進めるとともに、待ち望んだ九州一の河川筑後川からの導水が昭和58年完成しました。その恩恵は福岡地区水道企業団を通して都市圏に及んでいますが、福岡市でみると江川ダムと平成25年の大山ダム供用による増量分を含めて、現在の施設能力日量77.77万立方メートルの実に32%を筑後川水系に負っていることになります。まさに流域の住民や自治体などの理解と協力があってこそのものです。

併せて、気象条件に左右されず安定給水が可能な海水淡水化施設(まみずピア) が平成17年に完成するなど、新しい技術の活用にも乗り出しています。

fggcs2015_14_data01一方、市民の高い節水意識と節水じゃ口等機器の普及、日本初の再生水利用などにより、市民と一体になった「節水型都市づくり」が進み、平成25年度の配水量は日量約40万立方メートル、1人当たり配水量は大都市で一番少なく(図1)なっています。ちなみに、平成25年度の夏は、福岡市は猛暑に見舞われ、月間平均気温が全国最高の30度、連続猛暑日も17日間を記録した年でしたが、それでも水の使用量は大都市最少でした。



fggcs2015_14_data02また、市内全域に公平で円滑な給水を図るための配水調整システム(水管理センター) の設置や漏水調査により、水の有効利用を極限まで図ると同時に、水質維持や安全な配水にも努めています(図2)。

平成6年から平成7年にかけては前回を上回る異常少雨で、295日の給水制限でしたが、延べ時間では前回の6割、さらに平成17年は観測史上3番目の少雨でしたが、給水制限には至りませんでした。流域内から流域外、さらには海水からつくるという水資源開発、配水調整システム、そしてなにより市民の協力による「節水型都市づくり」によるものでしょう。

現在、関係の8ダムの貯水状況は昨年来の多雨傾向により、9割を超えています。しかしながら、近年は気候変動の波が大きく、取水制限が続いた年もあります。

建設中の五ケ山ダム(平成28年1月撮影:福岡市水道局提供)

建設中の五ケ山ダム(平成28年1月撮影:福岡市水道局提供)

五ケ山ダム完成予想イメージ図

五ケ山ダム完成予想イメージ図


そこで、那珂川水系南畑ダム上流に、有効貯水容量3,970万立方メートルと県内最大となる五ヶ山ダムが平成30年度供用開始予定で建設中です。このダムは渇水対策容量を持つことが特長で、全体で1,660万立方メートル、福岡市分1,310万立方メートルを有し、10年に1回を超える規模の異常渇水時に対応するものです。ストッパーの出現は心強い限りですが、引き続き「節水型都市づくり」も必要でしょう。

生活インフラとしての欠かせない水道ですが、地域を取り巻く厳しい水資源環境を踏まえ、水源確保や地域が一体となった節水への取組を進めてきたことが、福岡市が今なお成長を続ける要因の一つになっていると考えています。

【参考】fggcs2015_14_data03水道水のおいしさ向上度(残留塩素濃度目標達成率)は高い水準を維持している。(図3

Image is for illustration purposes only. (The page top image uses “expected completion image of Gokayama Dam”)
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