Activity 3:
Hydrological Systems
Catchment functioning
A catchment is an area where water is collected by the natural landscape. The outside edge of a catchment is always the highest point. Gravity causes all rain and runoff in the catchment to run downhill where it naturally collects in creeks, rivers, lakes or oceans. This means that rain that falls outside the edge of one catchment will fall into a different catchment, before flowing into other creeks and rivers. (Water NSW). The upper estuary of the Sydney Harbour is fed water from the Parramatta and Lane Cove Rivers.
The catchment area draining to the Sydney Harbour is approximately 484 km2 which has been broken into 550 subcatchments. (Sydney Coastal Councils).
Water flows in catchments include surface flows – overland flow and within stream flow, as well as flows below the surface – ground water flow. The water that collects in a catchment often shows the effect of some or all of the activities and land uses that people are undertaking in that catchment. People need to remember that what someone does upstream will affect someone else downstream. With 47% of the harbour being residential, 18.5% roads and 14.04% parkland, water quality after rainfall can decline significantly from this run off. See 'Storm water and Water Quality in Sydney Harbour" infographic by Sydney Water below.
The main parts of a catchment are:
the watershed which is a boundary that separates one catchment and its flows from the neighbouring catchment;
the headwaters which are generally the more elevated parts of a catchment (usually hills or mountains and with most runoff collecting into many small but often steep sided channels that collect together and form a rapid flow quickly after rain);
the mid reaches of a catchment, where the stream begins to slow down and widen (typically it forms features such as meanders, levees and ox-bows or billabongs);
the lower reach of a catchment which is usually the delta where a stream enters an estuary (eg. Sydney Harbour) or the sea.
(Extract from: https://www.oceanwatch.org.au/wp-content/uploads/2021/02/2-What-is-a-catchment-2.pdf)
This map (left) shows the greater Sydney catchment (upper and lower estuary) highlighting the waterways impacted by urban development.
Source:
https://www.environment.nsw.gov.au/ieo/sydneyharbour/maplg.htm
Prepared by NSW EPA remote sensing/GIS Service
Source:
Development of the Sydney Harbour Catchment Model
By Hawkesbury Nepean Catchment Management Authority
SydneyHarbour-conceptual-model-FINAL20210526.pdf
Source: Sydney Harbour Catchment Model
Melting glaciers and sea levels
The Sydney Harbour is a "ria" or a drowned river valley. This is a special type of river estuary that has filled the valley with water overtime. 15-29 million years ago the Parramatta River eroded into bedrock forming steep-sided banks. 17 000 years ago during the Interglacial periods the sea level rose sharply and the valley way flooded. As a result there was the deposition of sediments in estuary.
Some 10,000 years ago, the valley that had formed began to fill with rising seawater unleashed from melting glaciers to shape Sydney Harbour. Watch the video (right) to see how the valley was flooded to create the Harbour that we see today.
Read more about the history of the harbour here:
https://dictionaryofsydney.org/entry/river_cycles_a_history_of_the_parramatta_river
https://www.visitsydneyaustralia.com.au/history-1-natural.html
Sydney Harbour Creation (no sound).mp4As our earth continues to warm, sea levels continue to rise as a result of thermal expansion and melting land ice. Global sea levels are expected to increase by 45 to 82 cm by 2090 for the high concentration scenario. Projected increases around Australia are very similar. Extreme high sea-level events will occur more frequently in future, increasing the risks of flooding and erosion in coastal areas. Between 1886 - 2022, NOAA has found a relative sea level increase of 0.8 mm/ year in the Sydney Harbour (Fort Denison). See graph below to show this increase. Overtime, this will impact the landforms and environments along the Sydney Harbour including Balls Head and Berry's Bay.
Read more here about climate change and sea level rise in Australia: https://coastadapt.com.au/climate-change-and-sea-level-rise-australian-region
Currents (EAC)
Ocean currents are the continuous, predictable, directional movement of seawater driven by gravity, wind (Coriolis Effect), and water density (National Geographic).
Ocean currents transport enormous amounts of heat around the world. This makes them one of the most important driving forces of climate. Because they respond extremely slowly to changes, the effects of global warming will gradually become noticeable but over a period of centuries. Climate changes associated with wind and sea ice could become recognisable more quickly. (World Ocean Review)
Read more here: https://worldoceanreview.com/en/wor-1/climate-system/great-ocean-currents/
There are five major ocean-wide currents (gyres)—the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres.
The East Australian Current is a large ocean current that sweeps warm (nutrient poor) water down the east coast of Australia. The water temperatures range from 12 -25 degrees Celsius. The EAC impacts the water temperature and nutrient levels in and around Sydney including the Sydney Habrour and Balls Head.
Explore the interactive map from Earthnullschool above. This map shows the ocean currents moving around the world's oceans using re
Source: https://earth.nullschool.net/#current/ocean/surface/currents/orthographic=-243.30,-3.56,762
Tides and Wave activity
The circulation of water in Sydney Harbour is dominated by the high and low tide cycle. Tidal flow is strongest near North Head and here, up to 6000 m3 can be discharged on an ebb tide. Harbour water is replenished by the tides on average between 0- 20 days. However, the topography/bathymetry of the harbour can result in retention of organisms or pollution. Current tide information is found in the link below.
Wave refraction refers to how waves bend around headlands and cause waves to break roughly parallel to the shoreline. The energy of the wave is therefore concentrated on headlands where erosion occurs. Lower energy waves continue to bays and beaches where deposition occurs. Both these processes impact the types of landform in the Sydney Harbour and Balls Head. During fieldwork you will create a field sketch of various landforms (such as Manns Point, Ballast Point, Balls Head Bay, Gore Cove and Snails Bay) which have been impacted by these processes.
Carbon Sink: Oceans
Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide. A carbon sink is a natural or artificial reservoir that absorbs and stores the atmosphere’s carbon with physical and biological mechanisms. Did you know that our oceans absors 25 percent of all carbon dioxide emissions? The ocean holds around 42 times more carbon than the atmosphere.
Oceans are an important carbon sink. The ocean absorbs carbon dioxide from the atmosphere wherever air meets water through movement, this carbon dissolves. Wind causes waves and turbulence, giving more opportunity for the water to absorb the carbon dioxide. Ocean plants take in the carbon dioxide and give off oxygen, just like land plants. Organic carbon in the form of dead plants, algae and animals is mostly eaten by other creatures. Most organisms in the ocean are so small (less than 1mm in size) they remain invisible, but as they die and sink, they transport carbon to the deep ocean.
Read more here about the importance of our oceans in fighting climate change: https://www.un.org/en/climatechange/science/climate-issues/ocean#:~:text=The%20ocean%20generates%2050%20percent,the%20impacts%20of%20climate%20change.
Assess the current tide at Waverton in Balls head. How do tides impact other cycles or processes at Balls Head and Berry's Bay?
(Think about atmospheric systems, geomorphic systems and ecological systems)