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The tides they are a changin’

What happened to the Waglan tide gauge?

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横瀾島潮汐站現況如何?

By Paul Arkwright

It may not have escaped your notice, but the Waglan Island tide gauge on the Hong Kong Observatory's (HKO) weather page has been “under maintenance” for the last three years. So I decided to contact the HKO to find out what the problem was and how long it usually takes to repair a tide gauge. Fortunately, their reply was a lot swifter than the repair.

The tide gauge in question provides tidal measurements on Waglan Island at the Waglan Pier, a government pier maintained by Marine Department (MD). Unfortunately, the pier was severely damaged by Super Typhoon Mangkhut in September 2018 … and as the Observatory put it, “The tide station and related facilities were devastated during the strike.”

Fast forward almost three years, and on 2 August 2021, MD issued a Marine Works Notice detailing the reconstruction of the Pier at Waglan Island, which is scheduled to take another eight months, which takes us to March 2022. The notice details the reconstruction works at the Island at the following location (WGS 84 Datum) from (A) to (D) and the adjacent shoreline:

(A) 22° 10.934’ N 114° 18.126’ E (B) 22° 10.994’ N 114° 18.078’ E (C) 22° 11.066’ N 114° 18.179’ E (D) 22° 11.012’ N 114° 18.223’ E

根據香港天文台天網頁上的資訊,橫瀾島潮汐站在過去三年一直處於維修階段,所以我決定聯 繫香港天文台,想知道原因為何,以及是次維修工程需時多久。慶幸的是,他們給予回覆的速 度比維修要快得多。

該潮汐站位於橫瀾島橫瀾碼頭,負責測量潮汐,橫瀾碼頭是海事處轄下的政府碼頭。不幸的 是,該碼頭在2018年9月遭超級颱風「山竹」嚴重侵襲,對應天文台所說:「潮汐站和相關設 施在遭颱風吹襲期間被損壞。」

三年過去了,海事處終於在2021年8月2日發出海事工程公告,詳細說明橫瀾島碼頭的重建工 程。根據公告所說,重建工程預計需時8個月,即至2022年3月。該公告詳列以下橫瀾島區域 ((WGS84基準面)由 A 至 D 段及鄰近海岸線進行的重建工程:

Image courtesy of Marine Department

According to the MD notice, works will be carried out using one dumb lighter (aka barge) and one workboat, with one tugboat assisting. A working area of approximately 15 metres around the lighter will be established. Yellow marker buoys fitted with yellow flashing lights will be laid to mark the positions of the anchors extending from the lighter.

A silt curtain, extending from the sea surface to the seabed, will be established within the works area. The silt curtain is a large piece of netting used to contain mud and sediment. Yellow marker buoys fitted with yellow flashing lights will be laid to mark the extent of the silt curtain.

The hours of work will be from 0700 to 1900 hours, with no works carried out on Sundays and public holidays. Vessels employed for the works will stay in the works area outside the hours of work. Diving operations will also be carried out from time to time during the hours of work.

Vessels engaged in the operations will display signals as prescribed in international and local regulations. Vessels navigating in the vicinity should proceed with caution and keep clear of the works area at slow speed, bearing in mind that divers are working in the area.

Finally, after the pier’s reconstruction, a new set of tide gauges will be installed and resume the tidal measurement at Waglan Island.

根據海事處通知,工程將使用一艘躉船(非自航 駁船)、一艘工作艇和一艘拖輪。將在非自航駁 船周圍圈出一個約15米的作業區域。該區域將設 置黃色閃爍燈的浮標,以標示從非自航駁船到錨 的大概位置。

在作業區域內,將設置由海面延伸至海床的泥屏 障。泥屏障是一種用來容納淤泥和沉積物的大 網。該區域將設置黃色閃爍燈的浮標,以標示泥 屏障的範圍。

工作時間為上午七時至下午九時,星期日及公眾 假期休息。在非工作時間期間,負責工程的人員 所使用的船隻將停在作業區域內。工作人員在工 作時間內會不時進行潛水作業。

負責工程的船隻將展示國際通用和當地國際信號 旗。在附近航行的船隻應小心行事,並以慢速遠 離作業區域,同時應留意周圍是否有人員正在該 區域潛水作業。

最後,在碼頭重建工程完成後,當局會購置新的 氣象儀器,恢復橫瀾島的進行天氣監測工作。

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