The Flow of Water Through Catchments
What is a catchment?
A catchment, sometimes called a drainage basin, is the source area for runoff flowing to a particular point. The soils, geology, water and vegetation within a catchment are all interrelated; actions in one part of the catchment can affect other parts of the catchment. There is very little human activity that does not effect on the catchment in some way. Catchments form convenient management units. The State is made up of a series of catchments, and each river or lake catchment can be further divided into smaller sub-catchments.
Where is the Georges River Catchment located?
The Georges River catchment covers approximately 960 square kilometres and about 800,000 people live in the catchment. The Georges River rises south of Appin near Campbelltown and flows downstream for 96 kilometres to enter Botany Bay at Sans Souci. A substantial part of the catchment is bushland contained in Heathcote National Park, the Holsworthy Army Base and on private and Crown land.
The upper catchment includes the upper reaches of the Woronora River and Dam and the Upper Georges River, O'Hares Creek and Prospect Reservoir. The lower catchment includes the urban areas of Campbelltown, Liverpool, Bankstown, Sutherland, Kogarah, Kurnell, Botany and areas around Botany Bay
A catchment, sometimes called a drainage basin, is the source area for runoff flowing to a particular point. The soils, geology, water and vegetation within a catchment are all interrelated; actions in one part of the catchment can affect other parts of the catchment. There is very little human activity that does not effect on the catchment in some way. Catchments form convenient management units. The State is made up of a series of catchments, and each river or lake catchment can be further divided into smaller sub-catchments.
Where is the Georges River Catchment located?
The Georges River catchment covers approximately 960 square kilometres and about 800,000 people live in the catchment. The Georges River rises south of Appin near Campbelltown and flows downstream for 96 kilometres to enter Botany Bay at Sans Souci. A substantial part of the catchment is bushland contained in Heathcote National Park, the Holsworthy Army Base and on private and Crown land.
The upper catchment includes the upper reaches of the Woronora River and Dam and the Upper Georges River, O'Hares Creek and Prospect Reservoir. The lower catchment includes the urban areas of Campbelltown, Liverpool, Bankstown, Sutherland, Kogarah, Kurnell, Botany and areas around Botany Bay
| georges_river_-_introduction.doc |
FACTORS INFLUENCING WATER FLOWS
Vegetation
Vegetation absorbs water from soil to use in plant growth. Vegetation greatly reduces runoff. The less the vegetation, the more abundant and rapid the runoff will be. A close plant cover will modify the violent affects of heavy rains. Vegetation growing in and on river channels may be regarded as a surface roughness which can slow the flow of a river (this is particularly important in times of flood).
Vegetation serves a number of purposes along rivers and water ways. On river banks vegetation holds the sand and soil together. The roots of the vegetation hold clumps of soil together, while the actual plant reduces the effect of moving water on the top of the soil. This means that rivers can remain clear.
In coastal areas, where rivers meet the ocean, mangroves commonly grow. Mangroves are trees which have very long roots and which will grow in salty water. These mangrove forests provide the perfect breeding ground for fish and crustaceans. The health of wetlands can determine the number and types of fish which survive in river systems and oceans.
Vegetation also grows under the water. Plants like seagrasses are a hiding spot for young, small fish. These plants enable fish to grow to a larger size, before they move out into open water.
Vegetation like seagrass and mangroves, and the soils they grow in, filter the water. This natural cleaning process ensures that the water is the most suitable for organisms to function in.
Climate
Climate has a direct impact on a the way a river flows. At times of heavy rainfall a river will have a greater volume of flow (more water flowing). During hot weather evaporation of water increases. This reduces the volume of flow (less water flowing). Extended dry periods also impact negatively on water flow. Australia has a range of climate zones, impacting on the amount of rainfall receives, temperatures, etc. A number of conditions impact the climate in Australia such as El-Nino and La-Nina and the Indian Ocean Dipole.
Soil/Rock structure/ Ground covering
The ground surface surrounding a river/lake/ocean will affect how much water will enter it as run-off and ground water. Together ith vegetation the ground cover type influences the amount of water that will infiltrate or run-off. Some soils or rock structures are highly permeable (they absorb water) and have large water-holding capacity e.g. coarse-grained sandstones and porous limestones. These rocks/soils can even out the ground-water discharge during dry seasons. Other ground surfaces such as cement pathways/driveways and tarred roads greatly increase the amount of run-off because no water is able to infiltrate. This increased run-off generally known as stormwater enters drains and is directed to nearby creeks and rivers.
Landform shape and slope
Slope greatly affects the amount of run-off which will occur and thus how much water will enter a river. Generally, the steeper the slope, the more run-off. Flat areas (especially where marshes and lakes occur) tend to accumulate water and slow down the flow of water.
Catchments which are bordered by or contain high, steep landforms are more likely to have a greater volume of water due to the occurrence of orographic rainfall (cool air travels across the land and warms up, it hits the mountains and rises causing rain to fall).
The size of the catchment can also influence the volume of water flow. Small drainage basins (catchments) show great increase of flow after rainfall, while large catchments are more able to absorb the effects of precipitation.
Processes in catchments:
Vegetation
Vegetation absorbs water from soil to use in plant growth. Vegetation greatly reduces runoff. The less the vegetation, the more abundant and rapid the runoff will be. A close plant cover will modify the violent affects of heavy rains. Vegetation growing in and on river channels may be regarded as a surface roughness which can slow the flow of a river (this is particularly important in times of flood).
Vegetation serves a number of purposes along rivers and water ways. On river banks vegetation holds the sand and soil together. The roots of the vegetation hold clumps of soil together, while the actual plant reduces the effect of moving water on the top of the soil. This means that rivers can remain clear.
In coastal areas, where rivers meet the ocean, mangroves commonly grow. Mangroves are trees which have very long roots and which will grow in salty water. These mangrove forests provide the perfect breeding ground for fish and crustaceans. The health of wetlands can determine the number and types of fish which survive in river systems and oceans.
Vegetation also grows under the water. Plants like seagrasses are a hiding spot for young, small fish. These plants enable fish to grow to a larger size, before they move out into open water.
Vegetation like seagrass and mangroves, and the soils they grow in, filter the water. This natural cleaning process ensures that the water is the most suitable for organisms to function in.
Climate
Climate has a direct impact on a the way a river flows. At times of heavy rainfall a river will have a greater volume of flow (more water flowing). During hot weather evaporation of water increases. This reduces the volume of flow (less water flowing). Extended dry periods also impact negatively on water flow. Australia has a range of climate zones, impacting on the amount of rainfall receives, temperatures, etc. A number of conditions impact the climate in Australia such as El-Nino and La-Nina and the Indian Ocean Dipole.
Soil/Rock structure/ Ground covering
The ground surface surrounding a river/lake/ocean will affect how much water will enter it as run-off and ground water. Together ith vegetation the ground cover type influences the amount of water that will infiltrate or run-off. Some soils or rock structures are highly permeable (they absorb water) and have large water-holding capacity e.g. coarse-grained sandstones and porous limestones. These rocks/soils can even out the ground-water discharge during dry seasons. Other ground surfaces such as cement pathways/driveways and tarred roads greatly increase the amount of run-off because no water is able to infiltrate. This increased run-off generally known as stormwater enters drains and is directed to nearby creeks and rivers.
Landform shape and slope
Slope greatly affects the amount of run-off which will occur and thus how much water will enter a river. Generally, the steeper the slope, the more run-off. Flat areas (especially where marshes and lakes occur) tend to accumulate water and slow down the flow of water.
Catchments which are bordered by or contain high, steep landforms are more likely to have a greater volume of water due to the occurrence of orographic rainfall (cool air travels across the land and warms up, it hits the mountains and rises causing rain to fall).
The size of the catchment can also influence the volume of water flow. Small drainage basins (catchments) show great increase of flow after rainfall, while large catchments are more able to absorb the effects of precipitation.
Processes in catchments:
|
Braiding: When a river is carrying a lot of sediment it will divide into a series of diverging and converging channels. The eyots are formed from deposited sediment.
Meanders: When a river flows at low gradients (gentle slopes) towards the middle and lower reaches of a river, repeated curves in the river channel will occur. Alternating pools and rifles develop. Sediment is deposited on the inside of the bend. Oxbow lakes: During floods, the river may cut across the narrow neck of land separating two meander loops. The abandoned section is the oxbow lake. Floodplain: broad flat areas adjacent to the river/channel. Natural levee: elevated ground which develops on either side of the main channel. |
|
|
|
|
| georges_river_-_factors_affecting_water_flows.doc |
