Integrated catchment management

Water plays a major role in land degradation processes. Replacing the efficient, deep-rooted, perennial native vegetation with shallow-rooted, annual crops interferes with the water cycle. More of the rainfall reaches the water table and more water runs off across the surface. In areas where large amounts of salt have been stored in the subsoil, rising water tables bring it to the surface and cause soil and stream salinity problems. These problems rarely occur in isolation; other land degradation problems, such as soil erosion, loss of soil structure and waterlogging often accompany it.

Increasingly, land degradation in our State is tackled on a 'whole catchment' basis, since the actions of a landholder high in the catchment will influence what happens further down the slope. Integrated catchment management is a planning and implementation process that allows for good coordination between management authorities and landholders.

What is a catchment?

A catchment is an area where the land drains to a common creek or river. A Catchment's size can vary from several hectares to thousands of square kilometres. The soils, climate, geology, and hydrology of a catchment affect its water balance. Only when people understand the structure of their catchment can effective land protection measures be planned.

The hydrology is especially important. Data is collected on rainfall and evaporation in the catchment. The amount of water running off the surface and the amount reaching the watertable (recharge) are measured. Groundwater levels are determined and monitored to check their rate of rise.

A salinity example

Let's look at one water balance problem and see what integrated catchment management can do to solve it. The basic cause of salinity is the extra water that escapes beyond the root zone of agricultural plants compared with the native vegetation. The amount is not large (4 to 11 per cent of annual rainfall) but over periods of time this can bring the water table close enough to the surface to cause salinity problems. The main aim of integrated catchment management is, therefore, to use as much of the rainfall where it falls as possible. This can be achieved in many ways:

• Trees and other deep-rooted plants can be planted on areas where a lot of water enters the soil to recharge the water table. Forage trees, such as Tagasaste ("Tags") and Acacia salignia (Golden wattle) can reduce recharge while producing valuable stock feed.
• High-water-using crops and perennial pastures (for example, lupins and dryland lucerne) can be planted to reduce the amount of water reaching the water table.


• Increased cropping, by leaving out the annual pasture phase, will allow less water to recharge because crops use more water than pasture. (Continuous cropping - wheat lupin rotations.)


• Ensuring that plants are properly fertilised will enable plants to use as much water as possible.


• Remnants of native vegetation should be maintained; trees are very efficient water pumps.


• Grade banks can be used to discharge water safely to creeks, reducing the risk of water erosion and waterlogging.

It is obvious then that every landholder in the catchment has a part to play in the whole catchment solution. What each does depends on the location in the catchment and local conditions. Hence, landholders need a 'blueprint' for organising and sharing catchment-based strategies. Land Conservation District Committees and catchment groups are groups of farmers with a common goal in the area of land degradation. These groups are the driving force in drawing up catchment plans (see also Landcare Groups - The community response).

How do groups make it work?

Below is a brief outline of the concepts that catchment groups need to consider when they plan their catchment management strategy.

The assessment of physical features:

• Draw up an inventory of the physical resources: geology, soil, drainage, native vegetation.
• Define land units. Land units are parcels of land that have like characteristics.


• What are the current landuses in the catchment?


• Define land use options for each land unit, based on land capability.


• Map land management units for each land use.

Development of land management strategies

• Define existing land degradation problems.
• Determine options for solutions and their practical methods for implementation.
• Suggest how land degradation practices can be avoided.