Beware of High Tide Floodin
JAKARTA, KOMPAS — Excessive rain is expected to continue until Jan. 26. Its coincident occurrence with the peak of the tidal cycle could cause high tide flooding in coastal areas.
Excessive rain is expected in most parts of the country until next week. The high intensity of rainfall, which coincided with the peak of the tidal cycle during the supermoon on Jan. 21, could cause extreme flooding and tidal flooding in coastal areas.
According to the latest weather forecast from the Meteorology, Climatology and Geophysics Agency (BMKG), extreme rainfall is expected to continue until Jan. 26, 2019. Earlier, the BMKG issued a warning on extreme weather through Jan. 22 that could develop into a hydrometeorological hazard.
The phenomenon occurs because of the Indian Ocean low pressure center that extends to the southern part of Java and several air currents meet in a convergence zone that extends from the waters west of Sumatra to Java and the Banda Sea.
From among the regions in Indonesia, Semarang currently has the highest potential for heavy rain. "Rainfall in the southern part of Semarang could reach above 150 millimeters per day and 80 millimeters per day in the northern part of Semarang," BMKG weather forecast head Agie Wandala Putra said in Jakarta on Monday (01/21/2019).
Aside from the northern coast of Java, Agie said that almost all parts of East Nusa Tenggara (NTT) and Sumbawa Island in West Nusa Tenggara (NTB) could experience high intensity of rainfall. The coasts of Central Kalimantan, South Kalimantan and Belitung could also experience extreme rain.
Agie said that coastal areas should be on high alert, especially following the supermoon phenomenon, a full moon that occurs when the Moon is at its closest point to Earth. Because of its proximity, the moon reflects more direct sunlight and has a stronger effect on the Earth’s tides.
The supermoon coinciding with heavy rains in coastal areas can exacerbate tidal flooding. BMKG marine meteorology Information head Eko Prasetya said that analysis on intensity of rainfall and the high potential for heavy rain indicated that a number of areas were highly vulnerable to tidal flooding.
He said that the highest astronomical tide (HAT) began two days ago. The most vulnerable areas on Java were located along the northern coast, especially areas vulnerable to tidal flooding due to land subsidence like Semarang.
Coastal areas beyond Java that had the potential for hazards from HAT were South Sulawesi and West Kalimantan. "In Pontianak, among the impacts of a high astronomical tide is tidal waters flowing tens of kilometers upriver and onto land. This could also occur in Makassar and Bali. Flooding could occur along riverbanks," said Eko.
Anticipation
Jakarta is relatively safe because heavy rain is predicted to follow the HAT. Nevertheless, the North Jakarta municipal administration is anticipating tidal flooding from the supermoon in several districts. One of its strategies is preparing sandbags in each district to stem tidal overflow.
"Officers will install sandbags on the beach in case the tidal overflow reaches a significant height," said North Jakarta Deputy Mayor Ali Maulana Hakim.
The district most vulnerable to tidal flooding is Penjaringan. Penjaringan district head M. Andri said that tidal flooding could affect the Muara Angke residential area, especially Blok Eceng of RW (community unit) 022 in Pluit.
Khalil, 51, a local resident, said the sea rose to 80 centimeters above land on Monday morning. By 11:00 a.m., it had fallen to 40 cm. "When the sea was still high, about 40 cm to 50 cm of water came into the house," he said. The local administration ran three mobile pumps at the Muara Angke sluicegate. Dede Yahya, who oversaw the pumps’ operation, said that a team from the Jakarta Water Resource Agency was on 24-hour standby to pump water from the Muara Angke Reservoir and into the Adem River.
Dede said that the Muara Angke area often experienced high tide events. This week had seen the water in the reservoir increasing, especially over the past three days. Based on Kompas’ observation on Monday evening, tidal waters had receded from the roads in Pluit, Penjaringan and Muara Angke.
Dede added that the Water Management Office was implementing anticipatory measures for tidal overflows, especially in Muara Angke, by building sandbag dikes. However, local residents stole sandbags and the dike had disappeared in two days.
Many houses in Muara Angke obstructed the drainage system. “During high tides, it frequently floods here,” he said.
During last year’s supermoon on Jan. 2-4, tidal flooding affected several regions in Indonesia, including Muara Angke, when the tide in North Jakarta reached a maximum height of around 90 cm. The maximum elevation of the tide on Jan. 22 is predicted to reach 85 cm.
BMKG Climate and Air Quality Information head Siswanto said the current supermoon was likely to have a smaller impact than the supermoons in February and March. The current supermoon was also expected to have a smaller impact than the supermoon on Jan. 2-4, 2018, which also conceded with a total lunar eclipse.
In addition to the potential HAT hazard, the BMKG also warned that high waves could reach 6 meters. BMKG public relations head Taufan Maulana said very high waves of 4-6 meters could potentially occur in the North Natuna Sea, the southern part of the Makassar Strait, the waters west of South Sulawesi and the waters from the Sabalana Islands to the Selayar Islands regency.
Waves 2.5-4 meters high were likely to occur in the coastal waters of western Aceh, in the Indian Ocean west of Sumatra, the waters west of Nias Island southward to Mentawai Islands regency, the waters around Enggano Island to the west Lampung, and the southern part of the Sunda Strait (AIK/JOG/PDS/E14/E20)