5 Marco de Referencia para supuestos del Estudio
7.2 Sensibilidades al modelo
Risk classes of the susceptibility of land units to wind erosion, water erosion, flooding and inundation are presented in Tables 2, 3, 4 and 5. The risk classes listed in these tables were adapted from those developed for land capability by Overheu et.al. (1993).
Susceptibility ignores land use and land management factors. Inherent properties of the land unit such as slope, topsoil texture, surface mantle (including rock outcrop) and condition of the soil surface are considered.
Wind erosion risk (Wi)
Wind erosion risk is defined as the susceptibility of a parcel of land to erosion caused by wind. Wind erosion is a process in which soil is detached and transported by wind. Table 2 shows wind erosion risk classes.
Table 2. Classes of wind erosion risk
Risk class Likely situation
High Soils with loose or soft surfaces and light to medium topsoil textures exhibiting low moisture retention*.
Soils with <25% stony mantles or cryptogamic crusts.
Highly saline soils with soft or puffy surfaces. Moderate Soils with firm surfaces and light to medium
topsoil textures exhibiting moderate moisture retention.
Soils with 25-50% stony mantles or cryptogamic crusts.
Soils with common gravel or coarse rock fragments in the topsoil.
Low Soils with hardsetting surfaces and heavy topsoil textures exhibiting moderate or high moisture retention.
Soils with 50-90% stony mantles or
cryptogamic crusts.Soils with abundant gravel or coarse rock fragments
in the topsoil.
Nil Soils with seasonal, semi-permanent or permanent waterlogging for >3 months a year.
*Low moisture retention suggests the topsoil will remain moist for less than one week after rain. Moderate moisture retention suggests the topsoil will remain moist for one to three weeks after rain. High moisture retention suggests the topsoil will remain moist for more than three weeks after rain.
Water erosion risk (Wa)
Water erosion risk is defined as the susceptibility of a parcel of land to erosion caused by water. Water erosion is a process in which soil is detached from the land and
transported by the action of rainfall, run-off or seepage. Sheet, gully and rill erosion are the most common. Table 3 shows water erosion risk classes.
Table 3. Classes of water erosion risk
Risk class Likely situation
High Land surfaces without protective surface mantles or cryptogamic crusts that are subject to high flood risk.
Sloping land surfaces with light or medium textured topsoils with minimal (<25%) surface mantles or cryptogamic crusts.
Moderate Land surfaces without protective stony mantles or cryptogamic crusts that are subject to moderate flood risk.
Sloping land surfaces with some soil protection afforded by moderate (25-50%) surface mantles orcryptogamic crusts.
Low Land surfaces without protective stony mantles or cryptogamic crusts that are subject to low flood risk.
Level or sloping land surfaces with soil protection afforded by abundant (50-90%) stony mantles or cryptogamic crusts. Level plains with deep sand soils. Nil Surfaces not subject to any flood risk.
Land surfaces protected by very abundant (>90%) surface mantles, cryptogamic crusts or rock outcrop.
Surfaces in sink or accumulation zones (e.g. lakes, playas and claypans).
Flooding risk (Fl)
Flooding is the temporary covering of land by water from overflowing creeks or rivers and run-off from adjacent slopes or plains. The water erosion risk is directly proportional to the intensity and velocity of overland flow. Table 4 shows flooding risk classes.
Table 4. Classes of flooding risk
Risk class Likely situation
High Land surfaces covered in water due to sheet flow or catchment overflow at a frequency of at least once per year.
Moderate Land surfaces covered in water due to sheet flow or catchment drainage overflow at a frequency of one in two years, to one in five years.
Low Land surfaces covered in water due to sheet flow at a frequency of one in five years to one in twenty (or more) years.
Nil No flooding frequency.
Inundation risk (In)
Inundation is the temporary covering of land by water from overflowing creeks or rivers and run-off from adjacent slopes or plains, which involves very little movement, or ponding of water over the land surface. This in turn relates to the drainage qualities of the land surface and the soil type. Table 5 shows inundation risk classes.
Table 5. Classes of inundation risk
Risk class Likely situation
High Water is removed very slowly in relation to supply; soils are inundated for longer than several weeks with seasonal, semi-permanent or permanent waterlogging for over three months a year.
Moderate Water is removed only slowly in relation to supply. Soils are inundated for up to 12 hours or may be waterlogged for more than one day to several weeks.
Low Water is removed readily in relation to supply; soils are inundated for up to 3 hours or waterlogged for up to one day.
Nil Water is removed rapidly in relation to supply; soils are never inundated or waterlogged.
Summary
Table 6 summarises the risk factors for the main land types/units, soil types and site types within the survey area. The site types are listed in abbreviated code form. The site types are described in detail in the Site type ecology chapter.
Table 6. Risk assessment summary for land types/units, soil types and site types
Land types/units Main soil types Dominant site Risk factors**
type(s)* Wi Wa Fl In
Ranges, hills and low rises
Hills, ridges and Stony soil (203) HSPG L L N N
slopes Red shallow loam (522) HSPG L L N N
Low rises Red shallow sandy duplex (406) HSPG L L-M N N
Red shallow loam (522) HSPG L L N N
Calcareous shallow loam (521) HSPG L L N N
Shallow gravel (304) HSPG L L N N
Red shallow sand (423) PAGS, HSPG L L N N
Stony soil (203) HSPG, SAES L L N N
Plateaux and Stony soil (203) HSPG L L N N
breakaways Shallow gravel (304) PHSG L L N N
Tor fields and rock Stony soil (203) HSPG L L N N
outcrop Red shallow sand (423) HSPG L L N N
Upper and lower Red shallow loam (522) HSPG L L N N
footslopes, scree slopes Stony soil (203) HSPG L L N N
and alluvial fans Calcareous shallow loam (521) HSPG L-M L N N
Plains; calcrete, lateritic, stony and loamy
Calcrete plains and Calcareous shallow loam (521) CASG, CACS L L L L stony calcrete plains
Calcrete platforms Calcareous shallow loam (521) CASG, CACS L L L L Hardpan plains and Red-brown hardpan shallow loam (523) HPMS, PSMS L L L L stony hardpan plains
Lateritic stony plains Red-brown hardpan shallow loam (523) HPMS, PSMS L L N N
Red loamy earth (544) PSSG L L N N
Lateritic plains Red loamy earth (544) PSSG, PMSS L L L N
Red sandy earth (463) PSSG L L L N
Red deep sandy duplex (405) PHSG, PMSS L L-M L N
Shallow gravel (304) PSSG, LHAS L L L N
Gritty-surfaced plains Red shallow sand (423) PSSG, PHSG L L L N
Loamy plains Red loamy earth (544) PSSG, PHSG L L-M L-M L
Red sandy earth (463) PSSG, PHSG L L L N
Red deep sandy duplex (405) PHSG, PSSG L L-M L N
Stony plains Red shallow loams (522) PHSG, PSSG L L L-M L-M
Red loamy earth (544) PMSS, PHSG L L L L
Red/brown non-cracking clay (622) PHSG L L L L
Calcareous shallow loam (521) PHSG, CASG L L L L
Red shallow sand (423) PHSG, PSSG L L L L
Table 6. continued...
Land types/units Main soil types Dominant site Risk factors**
type(s)* Wi Wa Fl In
Sandplains and dunes
Sand sheets Red deep sand (445) SSSG, SHSG L-H L N N
Red sandy earth (463) SSSG, SHSG L L N N
Sand dunes Red deep sand (423) SSSG, SHSG M-H L N N
Calcareous deep sand (445) PSSG, CDSG M-H L N N
Sand banks Red deep sand (423) SSSG, SHSG L-M L N N
Red sandy earth (463) SSSG, SHSG L L N N
Sand sheets with Red deep sand (445) PHSG, SAES L L N N
ironstone gravel Red sandy earth (463) PHSG, SAES L L N N
Alluvial plains and drainage zones
Alluvial and stony Red deep sandy duplex (405) AHSG, ASSG L M-H M-H M-H
alluvial plains Red loamy earth (544) ASSG, AHSG L L-M L-M L
Red/brown non-cracking clay (622) ASSG L-H L-H L-H L-H
Red sandy earth (463) ASSG, PSSG L L L L
Red deep loamy duplex (506) AHSG, ASSG L-M L-H L-H L-H
Grey non-cracking clay (621) APBG L-M L M-H M-H
Grey deep loamy duplex (509) APBG L L M-H M-H
Drainage foci Self-mulching cracking clay (602) GMGW L L L L
Grey deep loamy duplex (509) DMES L L L-M L-M
Red loamy earth (544) GMUW L L L-M L-M
Claypans Red/brown non-cracking clay (622) APTG L L M-H M-H
Swamps Red/brown non-cracking clay (622) DEGW L L M-H M-H
Self-mulching cracking clay (602) DEGW L L L-M L-M
Grey deep loamy duplex (509) DMES L L M-H M-H
Floodplains Red/brown non-cracking clay (622) DEGW, APTG L M-H L-M L-M
Red loamy earth (544) APBG, APTG L M L-M L-M
Red deep loamy duplex (506) PCGS L M L-M L-H
Gilgai and stony Self-mulching cracking clay (602) ARPG, APTG L L-M L L
gilgai plains Red/brown non-cracking clay (622) APTG L L-M L-M L-M
Gilgai/clay mosaic Red/brown non-cracking clay (622) PHSG, AHSG L L L L plains
Groves Red loamy earth (544) DAHW, GMGW L L L L
Groves with gilgai Red/brown non-cracking clay (622) GMGW L L L L
Red deep loamy duplex (506) GMGW L L L L
Major drainage River bed soil (705) DEGW L H L-M L-M
channels
Minor drainage Red loamy earth (544) DAGW, DEGW L L-M L-M L-M