2.2 Hydrological Processes

Hydrological is a fancy way of saying hydrosphere.

The hydrosphere is all about flows and storages of water.
The hydrosphere plays a pivotal role in the accretion cycle on Coastal Sand Dunes.
It is mainly through The flow of water in the hydrosphere through rivers, currents, waves, and rain that helps in the depositing and removal of sediment in the accretion cycle. In other words it is the key mechanism in erosion (movement and depositing of weathered material).

For the Stockton Coastal Sand Dune System much of the sediment that is the source of its sand is from the Hunter River.Much of the sediment that flows in the river comes from runoff from the surrounding areas.
Furthermore, there is a close relationship to the atmosphere as the climate determines the amount of sediment the river delivers to the coastal area. This is called the climate sediment yield. The more rain in the mountains at the source of the river the more the river flows and discharges sediment at the end.
The Hunter River is the fifth largest river in NSW and it has high climate sediment yield. This has been exacerbated by human activities such as land clearing in the Upper Hunter region.

The image below shows the sediment discharging out of the Hunter River and moving towards Stockton Bight, where the sand particles will be weathered and eroded into finer particles.

The next important hydrological flow that assists the transporting of sediment in the accretion cycle, especially ones sourced off coastlines, is longshore drift
The importance of longshore drift lies in its role as a transporter of sediment. Sediment that is produced or deposited in one part of the coastal system, is transported to other locations by the ebb (flow back) and swash (flow on) of waves.
On the East Coast of Australia, sand particles move northward along the beach. It zig zags up the beach with the ebb and swash of the waves. This allows dunes and other sediment-based landforms to develop in areas some distance from the source of coastal sediments. The figure below highlights the process.
Queensland's Fraser Island, a vastisland made entirely of sand, demonstrates this point. Some of the sand that makes up the island and its huge Coastal Dune System comes from sandstone deposits found in the Sydney region. Longshore drift and ocean currents have transported the sand northwards along Australia's eastern coastline.
Click on this link to see an animation of longshore drift http://oceanica.cofc.edu/an%20educator%27sl%20guide%20to%20folly%20beach/guide/driftanimation.htm
Please note that the animation and image below go the opposite direction to Stockton. Stockton's longshore Drift is Northwards (up the beach)

Long shore drift

Waves are another hydrological flow that play a crucial role in the accretion cycle.
The movement of water via waves can either deposit sand onto a beach and be constructive or they can remove sand off and away and be destructive.
http://geography-site.co.uk/pages/physical/coastal/waves.html follow this link to see the different types of waves.

Rainfall is another hydrological flow that helps in the development of Coastal Sand Dunes. While rainfall infiltrates sand dunes with relative ease, heavy downpours can produce runoff, which erodes the sandy surface exposing it to the wind.
Another important change caused by rainfall is the development of dune lakes. These lakes form in low-lying areas (swales) of the dune system.
In times of heavy rainfall, surface runoff accumulates in a swale, which is a trough or shallow depression between the crests of coastal dunes. Eventually the sand becomes saturated and the water table rises. With the return of warmer weather, the swale dries out and the water table retreats. By this time, however, much of the protective vegetation has drowned and the sand is now left exposed. This causes a migrating dune to form and begin moving away from the now dry lake.