Case study 5.2 ACT Hydrogeological Landscape Framework project

Hydrogeological landscape (HGL) frameworks build on soil landscape mapping by using additional information on geology, lithology, slope, soil depth, vegetation and climate to identify functional units for management within the landscape. The HGL framework concept can be used to address a wide range of land management issues, such as soil degradation (eg sodicity, acidity, erosion); soil carbon; biodiversity; and vegetation, revegetation and wetland processes (eg for hanging swamps, bogs and fens).¹⁰

The HGL framework is used to divide the landscape into areas that have similar hydrological characteristics. The resulting HGL units integrate information on lithology, bedrock structure, regolith (including soils), landforms, climate (including rainfall, seasonality, evaporation) and vegetation.¹¹

The ACT Hydrogeological Landscape Framework project will map individual HGLs and the different management areas within them at the 1:25 000 scale. The project will also help to determine the capability of rural, urban and conserved lands for a range of land uses and management objectives. Mapping will help identify key problems in each HGL and management area, and the options available to address them within land-use capability.

The project will also include an urban salinity pilot study; soil erosion/stability, soil carbon and wetlands frameworks; a climate change scenario for each HGL; and spatial identification of optimal locations for establishing biodiverse tree plantings and carbon sequestration.

For the salinity pilot study, the HGL unit descriptions will define salinity management areas, including:

• descriptions of how salinity manifests itself in the landscape
• the amount of salt stored in the landscape and its mobility
• the relative hazards associated with salinity and their likelihood of occurrence
• descriptions of soil landscapes, land and soil capability, land use, land degradation and other properties (Table 5.2).

Recommendations about how best to manage and prioritise these landscapes are also included. In this study, 25 different HGLs have been defined, each with unique salinity situations that require tailored management solutions involving specific management actions.¹⁰

The HGL project is funded through the Australian Government Regional Natural Resource Management Planning for Climate Change Fund.

Table 5.2 Salinity impacts for each hydrogeological landscape in the ACT

HGL	Land salinity impact	Salt load impact	EC impact on water quality	Overall salinity hazard
Bimberi	Low	Low	Low	Very low
Boboyan	Low	Low	Low	Very low
Brindabella	Low	Low	Low	Very low
Bruce	Moderate	Low	Low	Moderate
Bullen Range	Low	Low	Low	Low
Clear Range	Low	Low	Low	Very low
Gungahlin	Low	Moderate	Moderate	Low
Hall	Low	Moderate	Moderate	Low
Hoskinstown	Moderate	Moderate	Moderate	Moderate
Jeir Hill	Low	Moderate	Moderate	Low
Kambah Pool	Low	Low	Low	Low
Kowen	Moderate	Low	Low	Low
Lanyon	Low	Low	Low	Low
Majura Road	High	Moderate	High	High
Murrumbidgee Gorge	Low	Low	Low	Very low
Namadgi	Low	Low	Low	Very low
Orroral	Low	Low	Low	Low
Paddys River	Low	Low	Low	Very low
Picadilly	Low	Low	Low	Very low
Reedy Creek	High	Moderate	High	High
Royalla	Moderate	Moderate	Moderate	Moderate
South Canberra	Low	Moderate	Low	Low
Sullivans Creek	Low	Moderate	Moderate	Low
Symonston	Low	Low	Low	Low
Uriarra Road	Moderate	Low	Moderate	High

EC = electrical conductivity; HGL = hydrological landscape
Source: Muller et al¹⁰

Majura Road hydrogeological landscape

An example of an area assessed as having a high risk of salinity is the Majura Road HGL. The following provides a summary of the type of information contained in the assessment and how this may be used in land management.

The Majura Road HGL extends from the Federal Highway in the north to Lake Burley Griffin in the south; it covers an area of 54 square kilometres and receives 550–750 millimetres of rain each year.

The Majura Road HGL is characterised by a catchment-based landscape on a broad valley bounded by steep hills and a major fault line. The area exhibits salinity via waterlogged patches and saline seeps with spike rush, which are seasonal. On the western flanks, there are saline springs in the upper slopes, as well as soils with severe salinity at a depth of 150 centimetres. There is a history of saline sites in the lower reaches of the unit, and salinity has remobilised recently at some sites following development. Monitoring bores and stream electrical conductivity sites indicate moderate salinity levels. Local developments, including the Majura Parkway, are affected by the local salinity and soil conditions.

The land use of the area is highly variable, and includes small areas of irrigated agriculture, grazing and cropping, Defence lands, airport infrastructure and reserve areas of native vegetation. There are important remnant grassland areas that act as biodiversity conservation areas in the lower landscape. Sand mining activities have previously occurred in the area.

Salinity is driven by interactions between water-use capacity of vegetation, physical soil properties and hydrogeological processes within the HGL.

The management focus for the Majura HGL is to recognise salinity impacts on infrastructure that will need to be planned for and taken into account during construction. Grazing management is a major factor in landscape stability, as the soils are very sodic and are easily subjected to erosion. A balance between multiple land-use and conservation issues needs to be struck in this unit to satisfy the wide range of competing interests.

Specific land management opportunities for this HGL are:

• existing remnant grasslands that can act as a seed bank resource
• planning frameworks into the immediate future.

Specific constraints for land management in this HGL include:

• acid sulfate and salinity impacts on infrastructure, particularly road construction and buildings
• total grazing pressure on government lands
• the airport envelope with regard to noise and height restrictions
• increased peri-urban development in competition with agricultural land.