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Lalor Creek EarthCache

Hidden : 6/17/2016
Difficulty:
1.5 out of 5
Terrain:
2 out of 5

Size: Size:   other (other)

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Geocache Description:

Lalor Creek

lalor Creek is part of the Upper Parramatta River catchment that flows into the Parramatta River and then into Sydney Harbour. Lalor Creek catchment is an area of 750ha accomodating 5325 properties.

Creek Rehabilitation

Extensive bank rehabilitation has recently taken place to repair the heavily eroded bank and to remove weeds and plant native plants that originally grew in this area.


You can complete the cache questions in any order you like.


THE CREEK BEFORE RESTORATION



THE CREEK AFTER RESTORATION

Catchments, Creeks and Wetlands.

A catchment is a drainage area that supplies water to wetlands and waterways. Each catchment is separated by higher land such as hills or mountains that direct the water flow towards wetlands and waterways. Everyone lives in a catchment so we all impact on the water that enters wetlands and waterways. 

Wetlands can be constructed by humans or may form naturally, they are areas that are wet for a long enough period that plants and animals living in them are adapted to and depend on living in wet conditions for at least part of their life cycle. Wetlands protect water quality by trapping sediments and retaining excess nutrients and other pollutants such as heavy metals. These functions are especially important when a wetland is connected to groundwater or surface water sources (such as rivers and lakes) that are in turn used by humans for drinking, swimming, fishing, or other activities.
These same functions are also critical for the fish and other wildlife that inhabit these waters.
Sediments, nutrients, and toxic chemicals enter wetlands primarily by way of "runoff," a term used to describe the rain and stormwater that travels over land surfaces on its way to receiving waters. In urban areas, runoff washes over buildings and streets in industrial, commercial, and residential areas where it picks up pollutants and carries them to receiving waters, such as Lalor Creek.
In rural areas, agricultural and forest practices can affect runoff. Where the runoff drains a freshly-plowed field or clear-cut area, it may carry too much sediment. Runoff may carry pesticides and fertilisers if these have been applied to the land. Sediments, which are particles of soil, settle into the gravel of stream beds and disrupt or prevent fish from spawning, and can smother fish eggs. Other pollutants -- notably heavy metals -- are often attached to sediments and present the potential for further water contamination. Wetlands remove these pollutants by trapping the sediments and holding them. The slow velocity of water in wetlands allows the sediments to settle to the bottom where wetland plants hold the accumulated sediments in place.
Runoff waters often carry nutrients that can cause water quality problems. An example of such an occurrence is an "algae bloom." Besides the aesthetic problems associated with algae blooms (a green, smelly slime) they result in low levels of oxygen in the water. This oxygen depletion can result in the death of fish and other aquatic life. Some algae release toxins that can kill pets and livestock when bloom conditions occur. Wetlands protect surface waters from the problems of nutrient overload by removing the excess nutrients, some of which are taken up and used by wetland plants, and some of which are converted to less harmful chemical forms in the soil.
Toxic chemicals reach surface waters in the same way as nutrients, and can cause disease, death, or other problems upon exposure to plants and animals (including humans). In a function similar to nutrient removal, wetlands trap and bury these chemicals or may even convert some of them to less harmful forms. Scientists are continuing to study what happens to toxic chemicals when they enter wetlands, and they warn us that even if the toxins are buried, they are still potentially dangerous. Disruptions of the wetland soils could release the toxins back into the aquatic environment.

Grassed Swales.

A grassed swale is a graded and engineered landscape feature appearing as a linear, shallow, open channel with trapezoidal or parabolic shape. The swale is vegetated with flood tolerant, erosion resistant plants. The design of grassed swales promotes the conveyance of storm water at a slower, controlled rate and acts as a filter medium removing pollutants and allowing stormwater infiltration. When properly designed to accommodate a predetermined storm event volume, a grassed swale results in a significant improvement over the traditional drainage ditch in both slowing and cleaning of water. They slow runoff from fields, trapping and filtering sediment, nutrients, pesticides and other potential pollutants before they reach surface waters. They can also be planted around drainage tile inlets for the same purpose.

Erosion

The energy in a river causes erosion. Not all energy is available to erode or transport sediment, friction with the bed and banks and turbulence reduces energy. The faster the flow of water, the greater the turbulence. Water with a more turbulent flow can transport more sediment. The bed and banks can be eroded making it wider, deeper and longer. There are four main processes of erosion that occur in rivers. These are: 1. hydraulic action 2. abrasion / corrasion 3. attrition 4. corrosion

HYDRAULIC ACTION The pressure of water breaks away rock particles from the river bed and banks. The force of the water hits riverbanks, and then pushes water into cracks. Air becomes compressed, pressure increases and the riverbank may, in time collapse. Where velocity is high e.g. the outer bend of a meander, hydraulic action can remove material from the banks which may lead to undercutting and river bank collapse. Near waterfalls and rapids, the force may be strong enough to work on lines of weakness in joints and bedding planes until they are eroded. Rapids are areas along a river where the water flows faster and is more turbulent. This is usually because there is an increase in the gradient of the river channel or where a river flows over alternating soft and hard rocks.

ABRASION / CORRASION Sediment carried by a river scours the bed and banks. Where depressions exist in the channel floor the river can cause pebbles to spin around and turn hollows into potholes. Potholes are round / oval shaped holes in the bedrock of a river bed. As the holes get bigger, even bigger debris can become trapped in the pothole and this material further supports erosion.

ATTRITION Eroded rocks collide and break into smaller fragments. The edges of these rocks become smoother and more rounded. Attrition makes the particles of rock smaller. It does not erode the bed and bank. Pieces of river sediment become smaller and more rounded as they move downstream.

CORROSION / SOLUTION Carbon dioxide dissolves in the river to form a weak acid. This dissolves rock by chemical processes. This process is common where carbonate rocks such as limestone and chalk are evident in a channel. Transportation of material in a river begins when friction is overcome. Material that has been loosened by erosion may be then transported along the river. There are four main processes of transportation. These are: 1. suspension / suspended load 2. solution / solution load 3. saltation 4. traction

SUSPENSION is when material made up of very fine particles such as clay and silt is lifted as the result of turbulence and transported by the river. Faster-flowing, turbulent rivers carry more suspended material. This is why rivers appear muddy as they are approaching bankfull discharge and towards the mouth of the river (where velocity is greater as is the occurrence of finer sediment).

SOLUTION is when dissolved material is carried by a river. This often happens in areas where the geology is limestone and is dissolved by slightly acidic water.

SALTATION is when material such as pebbles and gravel that is too heavy to be carried in suspension is bounced along the river by the force of the water.

TRACTION is when large materials such as boulders are rolled and pushed along the river bed by the force of the river.

DEPOSITION is the process of eroded material being dropped. This happens when a river loses energy. A river can lose its energy when rainfall reduces, evaporation increases, friction close to river banks and shallow areas which leads to the speed of the river reducing and therefore the energy reduces, when a river has to slow down it reduces its speed (and ability to transport material) and when a river meets the sea.


Pollution

Many towns and factories are built near rivers so that they can use water from the river. Sometimes the water is not cleaned before it is put back into the river, this dirtying of water (also air and soil) is called pollution. Pollution can come in a variety of forms. Rubbish like crisp packets, newspapers and bags, oil, poisonous substances, cans, bottles and other solid objects. Pollution can also be human waste / excrement. The main offenders can be agriculture, factories and people in general. Pollution can kill water plants and animals and also carries diseases. When animals drink the water, they may get diseases which can kill them. Often people can also get these diseases by eating the infected animal (fish). The polluted rivers can also look unsightly when there is rubbish in them and polluted rivers generally smell bad.

Claiming a find

To claim a find please email your answers to me via the GC.com website,
(DO NOT POST YOUR ANSWERS IN YOUR LOG).

There is no need to wait for confirmation before logging, if there is a problem with your answers I will get back to you. To log this cache you need to do the following things:

At GZ there is a sign listing details of the rehabilitation of the creek. This isn’t really a task but a chance for you to appreciate the lengths the council went to to rehabilitate the creek. If you don’t want to read this make your way straight to waypoint 1 or 2. Only waypoints 1 and 2 are mandatory to log the cache but I have created others for you to do should you wish.

1) At this waypoint can you identify any of the measures the designers have put in place to reduce the amount of erosion on the creek bed and bank? do you think its working?

2) This waypoint is where storm water runoff enters the creek. Looking around you and in particular behind you away from the creek, what drainage feature has been put in and what has been planted in this system to prevent erosion? Why do you think this feature is so effective and how might it help with pollution?

Feel free to post pictures of your walk around the creek, please don't post any that give any of the answers away. Otherwise I hope you enjoy.

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