Release the floodgates: why is the water brown and is it safe to swim?

The big swells are gone, but it’s not exactly safe to swim just yet.

As you all know ex-tropical cyclone Alfred brought some pretty wild weather to the Mid North Coast recently, including flooding of the region’s rivers and creeks.

Now, many of our waterways including the ocean are full of brown water.

You may be wondering, have the floodgates been released, what’s in the water, and is it safe to swim?

We asked Kempsey Shire Council for answers, using the Macleay River and South West Rocks, Crescent Head and Hat Head as our case studies, but we think those living across the Mid North Coast could learn a thing or two.

Looks like poo, but is it?

Let’s dive straight into the pressing question – is the brown water sewerage?

In short – well, we can’t be 100 percent sure if there is an overflow of sewerage post-flood now seeping into the ocean.

I asked council, is it safe to swim? A Kempsey Shire Council spokesperson said: “Pollution from stormwater and sewage overflows can cause higher levels of faecal contamination that makes water quality unsuitable for swimming.”

However the brown colour can also be the result of water scouring the banks and causing sediment to churn.

You can choose you’re own adventure.

Release the flood gates

Flood gates are used to control water flow during a flood event to reduce the impact.

According to Kempsey Shire Council, the Lower Macleay Flood Mitigation Scheme was built over a 20-year period following devastating flooding in the mid-20th century. 

Where are the flood gates?

The key structures are at Kinchela Creek and Belmore River. 

There are two types of gates here: flood gates (also known as crossover flood gates) and flood relief gates.

The crossover flood gates span across the waterways, while the relief gates are positioned to the side.

There are also outlets at Ryans Cut and Big Hill in Crescent Head.

When are they open and closed?

Under normal conditions, the gates remain open to allow tidal movements and aerate the waterways. 

Before a flood, council staff close both sets of gates to prevent water from flowing upstream.

Closing the floodgates keeps floodwaters within the Macleay River and directs water out to the ocean at South West Rocks, where the Macleay River ends.

If the river reaches the levee's height (in line with the roads) on Belmore River and Kinchela Creek, the relief gates are reopened. 

“This creates a controlled water release into the floodplain, aiming to lower flood levels and prevent overtopping the levee system at Belmore River, Kinchela Creek and surrounding communities, reducing the damage to roads, residences and other infrastructure,” a Kempsey Shire Council spokesperson said.

The water level in the broader floodplain determines whether the Ryans Cut and Big Hill ocean outlets at Crescent Head can be opened. These outlets rely on upstream water pressure from the floodplain to operate. 

Pilot channels are created to guide water to the ocean, gradually increasing the flow to allow all gates to release floodwater. However, if the floodplain lacks sufficient water, the ocean will close the gates and prevent waterflow.

Why is the water brown at South West Rocks?

The Macleay River at the Entrance is the main outlet where the majority of floodwater and rainfall flows out.

“The brown colour of the water is due to the speed of the water coming from the upper catchment,” the spokesperson said.

“The water scours banks and causes sediment or suspended solids to travel downstream that causes the water to appear brown. The status of the flood relief gates has a minor impact on the colour of the bay.”

Why is the water brown at Crescent Head?

The flood relief gates at  Belmore River were open on Sunday morning (March 9) with the ocean outlet at Ryans Cut opened that afternoon.

Once the relief gates are opened, the flood water moves through the floodplain. Ryans Cut ocean outlet is one pathway that allows floodwater from the floodplain/swamp to flow out to the ocean via Killick Creek/Connection Creek at Crescent Head.

Why is Hat Head’s water not brown?

Sitting in between South West Rocks and Crescent is Hat Head, where the beach appears to have clearer water.

The reason: the floodplain water may not yet have reached Korogoro Creek. It is possible  dirty water from Korogoro Creek will flow into the ocean at some stage – it all depends how deep water in the floodplains gets.

Is it safe to swim?

Poo aside, floodwater may still contain harmful contaminants and hazardous debris including bacteria, chemicals, logs, sharp objects and other hidden dangers in beaches, rivers, creeks and lakes.

“For your safety, it is recommended to avoid these bodies of water for at least 72 hours (or three days) after flood water dissipates, as contaminants are likely still present,” said the spokesperson.

Additional information about Kempsey Shire Council’s flood mitigation can be found at ksc.pub/flood-info. Find out more: Maintaining health during and after floods and storm