Berkeley Vale

When a Flood Comes

When Tuggerah Lakes floods, the rivers and streams carry vast amounts of water to the estuary over a relatively short time. The lakes and surrounding floodplains fill with water from the streamflows, stormwater and rain. As floodwaters rise, the water flowing out of the lake at each low tide becomes faster and more powerful. It washes away sand at the beach berm and makes the channel wider.

The floodwater can continue to flow out of the lakes for several days. For it to drain away more quickly, the ocean's water level must be lower than the lake's. Otherwise, the water stays where it is. Weather conditions during the flood also influence how soon the draining away can happen. For example, when a flood coincides with a coastal storm, an east coast low or a king tide, the water can flow back into the lake during low tide, and the floodwater recedes more slowly.

Large waves and storm surges move the sand offshore, but it is mostly retained in the coastal sediment compartment not far from the lakes' entrance. Even though it seems counter-intuitive, the sand offers welcomed protection from coastal storms and coastal erosion, which can both be severe at times.

Once the floodwaters recede, the channel slowly fills in and closes over again within months, depending on the follow-up rainfall. During this time, the entrance berm grows from the northern shoreline in a southerly direction, eventually reaching the rock shelf again. This process can slowly constrict the tidal exchange between the lake and the ocean, bringing it back to normal conditions.

During a series of storms that savaged the coast in February 2020, the Central Coast area received around 440mm of rain over just four days. This amount of water is the equivalent of 500 Olympic swimming pools being poured into the Tuggerah Lakes catchment alone, and would typically equal the Australian rainfall average for nearly 12 months. These storms caused the water surface to rise from 80km2 to around 100km2 again, increasing the lakes’ water level from 0.25 mAHD to 1.67 mAHD. The floodwater took a long time to drain away and was affected by the oceanic conditions.

Flood Peak 2020

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