Eprapah Creek facts for kids
Eprapah Creek is a special stream located in Redland City, near Brisbane in South East Queensland, Australia. It's a sub-tropical creek, meaning it's found in a warm, humid area.
The creek starts on the north-eastern side of Mount Cotton. From there, it flows directly into Moreton Bay at Victoria Point. Eprapah Creek is about 12.6 kilometers (7.8 miles) long. Around 3.8 kilometers (2.4 miles) of it is an estuarine zone, where fresh water from the creek mixes with salty ocean water. In this part, the water is usually one to two meters (3 to 6 feet) deep in the middle. The creek is also about 20 to 30 meters (65 to 98 feet) wide. The tides here are "semi-diurnal," which means they rise and fall twice a day, with a change of about two meters (6 feet).
The area around the creek, called its catchment, covers about 39 square kilometers (15 square miles). The lower parts of this area are mostly urban, with lots of buildings. The upper parts are more rural or have country-style homes. Eprapah Creek is home to important conservation areas, like the Eprapah area. These places protect endangered animals such as koalas, swamp wallabies, and sea eagles.
Water Quality in Eprapah Creek
For over thirty years, the water quality and living things in Eprapah Creek have been carefully watched. Groups like the Redland City Council, the Environmental Protection Agency (EPA), and local community groups have all helped.
In 1998, the creek faced a big problem. It became very polluted because harmful chemicals were illegally dumped into it. Even though parts of the creek are protected as environmental parks, there are still some things that affect its natural system. For example, there are marinas and boat yards nearby. Also, a large sewage treatment plant releases water into the creek. Upstream, the creek has been impacted by big poultry farms, wineries, and land being cleared for development. More recently, new shopping centers and homes were built very close to the creek's estuary in 2003-2004.
How Water Mixes in the Creek
Between 2003 and 2007, scientists studied the estuarine part of Eprapah Creek. This part is a typical small coastal plain estuary. The goal was to understand how the water mixes and moves. They collected data for a long time, sometimes up to 50 hours straight.
These studies showed that the way water mixes changes depending on the tides. It also acts differently in the middle and upper parts of the estuary. The mixing in small estuaries like Eprapah Creek is not always the same as in larger ones. This means that what we learn from big estuaries can't always be used for small ones. For example, scientists used to think that mixing in an estuary stayed the same throughout the tidal cycle. But in small estuaries, this is not true. These differences show why it's important to keep studying small estuaries. We need to understand them better.
Like most small subtropical estuaries, Eprapah Creek gets a quick flush of fresh water after it rains. But during dry seasons, there's almost no water flow. A recent study looked at what happens after a rainstorm. The fresh water seemed to come mostly from rain running off nearby shopping centers, parking lots, and roads. In the estuary, this fresh water dominated the surface flows, even when the tide was coming in.
Scientists also saw strong layers of water, where fresh water sat on top of saltier water. However, the levels of oxygen and how cloudy the water was seemed quite even throughout the estuary. This was very different from what they saw during dry weather. The saltiness of the water showed how the fresh water spread out. The way the salt water moved upstream into the creek followed a simple model. This model helped explain how salt mixes in the creek, especially how density differences cause mixing in the upper estuary during wet weather.
