The River Torrens is the most significant river of the Adelaide Plains and is said to be the major reason for the siting of the Adelaide township and city. It flows 85 kms from its source near Mount Pleasant across the Adelaide Plains, past the city centre and empties into Gulf Saint Vincent between Henley Beach South and West Beach. The upper stretches of the river and the reservoirs in its Watershed supply a significant part of the city's water supply, supplemented by pumping from the Murray River along the length of the Torrens.
It originates close to the eastern fault scarp of the Mount Lofty Ranges, near the Barossa town of Mount Pleasant, approximately 480 metres (1,575 ft)above sea level. It runs predominantly along faulted north-south ground structures, which were formed over 250 million years ago during the Paleozoic era then further dislocated during the Cretaceous and earliest Tertiary. There is a 400 metre subsidence along the Para Fault which also affects the rivers flow.
From its origin to Birdwood the river follows rolling, relatively level country before entering a hilly section that continues to Gumeracha. The river then follows sedimentary rock strata before entering a gorge after Cudlee Creek. It flows through the gorge to Athelstone, passing over the Eden Fault Zone of the Adelaide Hills face and associated escarpment. After the scarp it flows over sedimentary rocks of varying resistance to erosion, which has led to interspersed narrows and broad basins.[4] From the base of the Adelaide Hills to Adelaide's central business district it runs in a shallow valley with a terraced floor, then down the slope of its own alluvial fan. The structure of this fan shows that the river formerly entered Gulf St Vincent via the Port River. Over time the Torrens deposited sediment, choking its own outflow; becoming locked behind coastal sand dunes and forming the swampy areas of theCowandilla Plains and the reedbeds.
The Torrens is fed by numerous seasonal creeks, which are dry for most of the year. There are five main creeks that join from the south side as it crosses the Adelaide Plains east of Adelaide, and at least five more in its path through the Adelaide Hills] The plains tributaries, known as First to Fifth Creeks, with First being the closest to Adelaide's city-centre and the rest numbered consecutively eastward, were originally named Greenhill, Hallett, Todd, Anstey and Ormsley rivulets respectively. They flow vigorously in winter and spring but are otherwise dry, except for small flows in limited areas upstream.
The river's catchment area of approximately 500 km2 (193 sq mi) is the largest of any waterway within the Adelaide region.. A drainage basin or catchment may be defined as an area of land that collects water, which drains to the lowest point in the area which could be either a lake, a dam, or the sea. Rain falling on the land will make its way to this lowest point, via creeks, rivers and stormwater systems. As well as rivers, creeks, lakes and dams, a catchment also includes groundwater, stormwater, wastewater, and water-related infrastructure.
The extent to which this river changes from its origins near Mount Pleasant to the major river it has become by the time it reaches Adelaide city is remarkable.
LOGGING THIS EARTHCACHE In order to log this EarthCache you must visit the Listed co-ordinates to obtain the answers to the set questions. You will then need to email the answers to the questions to claim your find. Please do not post any answers to the questions in your log, as it will be deleted. There is no need to wait for a confirmation email to log your find. I will read each email to confirm your answers and will contact you if there is a problem. Please do not email photos, just upload them with your log. If an email is not received in a timely manner after logging your cache, the log will be deleted.
1.What form of geological phenomenon do you think may have caused the Torrens Creek to commence in this region?
2.Estimate the width of the Torrens Creek at the bridge crossing. How does this compare with the river’s width by the time it reaches Adelaide city at the point adjacent to the Adelaide Zoo?
3. Describe the countryside around the geozone. To the North (and upstream) what happens to the creek bed?