How might high tide worsen existing flood situations?

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High Tide Can Exacerbate Flooding Through Drainage Obstruction and Increased Water Levels

The phenomenon of high tide, particularly when it coincides with periods of heavy rainfall, possesses the potential to significantly worsen existing flood situations. This is primarily due to the elevated sea levels during high tide which can impede the natural drainage of rainwater from inland areas into the sea. In coastal regions, drainage systems are designed to facilitate the outflow of water, and when the sea level is already raised by high tide, this outflow becomes restricted or even reversed, causing water to back up. Furthermore, during severe weather events, the combination of high tide and potential storm surges can lead to a substantial increase in coastal water levels, overwhelming natural and man-made defenses and pushing water further inland.
Elevated Sea Levels Hinder Coastal Drainage

During high tide, the sea level naturally rises, reaching its peak typically twice a day. This elevated sea level directly impacts the efficiency of coastal drainage systems. Rivers and canals that normally discharge into the sea will find their outflow channel significantly constricted. If heavy rainfall occurs simultaneously, the water accumulated inland cannot be effectively released, leading to a rise in water levels in rivers, streams, and low-lying areas. The Kedah Civil Defence Force (APM) has identified 18 specific locations across five districts in Kedah that are at risk of increased flooding should this confluence of high tide and rain occur between October 7th and October 9th.
Backflow and Water Accumulation in Coastal Areas

When the sea level during high tide is sufficiently high, it can create a backflow effect, pushing seawater into river mouths and drainage channels that are typically filled with freshwater. This prevents the outgoing flow of rainwater and can cause water to accumulate rapidly in coastal communities. For instance, areas like Kuala Kedah Jetty and Seberang Kota Fishermen’s Jetty in Kota Setar, and Kampung Kuala Raga in Yan, are listed as being at risk, underscoring the vulnerability of communities situated near the coast to these tidal influences.
Potential for Storm Surges Amplifying the Impact

While the provided information focuses on high tide and rainfall, it is worth noting that severe weather conditions can also bring about storm surges. A storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tide. If a storm surge were to occur during an already high tide, the combined effect could be catastrophic, leading to unprecedented inundation levels. The APM's preparedness, with 900 personnel on standby, highlights the seriousness with which such potential events are viewed, even if current forecasts suggest favourable weather.

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How might high tide worsen existing flood situations?

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