SOIL CONSERVATION SERVICE OF NEW SOUTH WALES

RECONNAISSANCE URBAN CAPABILITY SURVEY

RURRAJONG HEIGHTS

OCC-;.‘4420A

Prepared for

HAWKESBURY SHIRE COUNCIL

June, 1985

Report compiled by:

D. JOHNSTON, Soil Conservationist, Sydney

G. A. CHAPMAN, Soil Conservationist, Sydney

K.J. DAVEY, Trainee Soil Conservationist, Sydney

No material may be extracted from this report for publication without the permission of the Comnissioner,

Soil Conservation Service of N.S.W.

Page

INTRODUCTION •

CONTENTS

PHYSICAL FEATURES .. • • 90 410 3

Climate . .. • .. • .. 3 Landform .. . .. 3 Geology and Soils . .. . .. .. 3

URBAN CAPABILITY • • • • 7

Class B-e .. • • . . .. • • 9 Class B-e(d) • • . • • • • • • .. • • 9 Class C-se • • • • • • . • • • • • • 10 Class C-se(d) . • • • • .. • • • • • • 10 Class D-f • • • • . . • • .. 11 Class D-s .. . • • .. • • .. • • 14 Class D-se(d) . • • .. .. • • .. 14 Class D-sm • • .. • • .. • • • • • • 15 Class E-s .. • • • • • • .. .. .. .. 15 Class E-sm .. • • • • • . .. .. • • 16

RECOMMENDATIONS • • • • . . • . . . .. . . • • 17

REFERENCES • • • • . • . . . . . • • • • 18

APPENDICES

Appendix I - Northcote Code and Representative Description for each Soil Unit ▪ 19

Appendix II - Summary of Soil Characteristics • 23

Appendix III - Summary of Laboratory Data • 24

Appendix IV - Interpretation of Analytical Data 25

FIGURES

Locality Diagram • 00 00 00 00 2

INTRODUCTION

A reconnaissance urban capability survey of approximately 245 hectares of land at Kurrajong Heights was carried out by the Soil Conservation Service of N.S.W. at the request of the Rawkesbury Shire Council. The survey area is generally bounded by Bells Line of Road, Burralow Road, Warks Hill Road, and a power transmission line which runs north west-south east and adjoins Little Wheeny Creek.

This study has been undertaken to assist Council to evaluate the environmental impact of possible future urban subdivision. It is presented in three main parts:

• inventory of physical resources

• urban capability, and

• recommendations

The inventory of physical resources includes landform (i.e. terrain and slope gradients), drainage and soils. Is is based upon aerial photograph interpretation supplemented by field reconnaissance. Salient soil properties have been identified by hand augering and laboratory testing.

A reconnaissance urban capability survey has been undertaken. The accompanying map has been compiled at a scale of 1:4000. Capability assessments identify the limitations of the use of the land as a result of the interactions between the physical land characteristics and a specific land use. This assessment will assist council in the planning and management of the Kurrajong Heights area for urban land uses.

This survey is intended to form a basis upon which other planning considerations can be imposed to assist wise land use allocation. It is important that information is not extracted from maps at a scale larger than the scale of the original maps.

The map and written report is not a substitute for specific engi-neering and design investigations which may be required to more accurately define constraints in the location and design of roads, individual buildings, etc. They provide a basis onto which other planning considerations may be imposed to derive urban development plans.

The soil conservation recommendations outline appropriate soil erosion control and prevention measures necessary to maintain land surface stability under urban land use. To ensure effective implementation of the recommendations, continued consultation with officers of the Soil Conservation Service is desirable during any proposed development phases.

""N. Bells

Kurrajong

STUDY AREA

Heights

I.

4 of

T 1.0r/Kurrajong

0

oa Richmond

bothur to Sydney

LOCALITY DIAGRAM

URBAN CAPABILITY STUDY

KURRAJONG HEIGHTS

SCALE 1:250000

M. N.

3.

PHYSICAL FEATURES

CLIMATE

The Kurrajong Heights area falls within Rainfall Zone 5 of New South Wales as described by Edwards (1979). Within this zone rainfall varies from an average of 100-120 mm/month from January to March, to an average of 4m/month from July to September.

Of particular significance is the pronounced storm activity during the summer months and the high likelihood of water runoff during the winter months.

The area experiences mild to cold winters and mild summers.

LANDFORM

Rolling to gently undulating topography is characteristic of the study area. Relief is highly variable and ranges from 60m to 160m.

The majority of the area comprises sideslopes which have slope gradients between 10 and 30 per cent. These sideslopes are dissected by incised drainage lines of similar slope gradients, which generally flow in an easterly direction. To the south they drain into Little Wheeny Creek whereas to the north they drain into Little Island Creek.

Other significant landform features of the survey area include ridges and hillcrests with slope gradients between 0 and 10 per cent. These are scattered throughout, but particularly adjacent to the western boundary. In the northern and southern corners of the study area the sideslopes are extremely steep, with slope gradients in excess of 30 per cent.

GEOLOGY AND SOILS

The geology of the survey area is principally Wianamatta Shales, however there are also significant areas of Hawkesbury Sandstone.

Wianamatta Shales occupy the central section of the survey area. They consist of claystones and siltstones with occasional bands of laminates and mudstones.

Hawkesbury Sandstone is mostly found in the southern and northern sections of the study area. It consists of fine and coarse-grained sandstones which occur as benched, rock outcrops. Siltstone and mudstone lenses may be present.

The Kurrajong Heights survey area is located near the top of the 0 Lapstone Monocline. The rock strata dip at angles between 5 and

300, with strike directions between 70° and 120°. These factors greatly increase the mass movement hazard on relatively steep, easterly sideslopes. This hazard is most pronounced where shales overlie sandstone.

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Soil profiles were described at 62 sites and classified at several other sites using the Northcote (1979) classification system. Appendix I outlines the Northcote code and includes representative description for each Soil Unit. Appendix II is a summary of soil characteristics. Appendix III provides a summary of laboratory data.

Seven principal soil units have been identified within the survey area.

Unit A : Siliceous Sands

These shallow, sandy soils are restricted to areas of outcropping Hawkesbury Sandstone, especially on steep sideslopes greater than 20 per cent gradient. However, they occur to a lesser extent in drainage lines and footslopes of terrain developed on Hawkesbury Sandstone.

The topsoils are loose, incoherent, greyish yellow-brown sands to brownish black sandy barns. They are acidic (pH 4.5 to 5.5), highly erodible and often water repellant. Average depth of the topsoil is less than 0.3m. They abruptly overlie sandstone bedrock or subsoils. When sub-soils are present they consist of yellowish brown clayey sands, fine sandy clay barns or sandy clays. They are aci-dic (pH 5.0) and are generally composed of weathered sandstone rock fragments.

This unit has limitations to urban development which include high inherent erodibility, shallow soil depths (less than 0.5m), and an extreme erosion hazard. In addi-tion, up to 50% of the land surface may be covered by rock outcrops and up to 90% of the subsoil volume may be occupied by weathered sandstone rock fragments. In the drainage lines, inundation is the most serious limitation to urban development.

Unit B: Yellow Earths

The yellow earths are restricted to the ridges and upper sideslopes of Hawkesbury Sandstone terrain, often in asso-ciation with rock outcrop.

The topsoils are loose, incoherent, brownish black to yellow brown sands to sandy barns. They are acidic (pH 4.5 to 5.5), highly erodible, generally shallow (less than 0.5m), often water repellant, and very well drained.

The subsoils vary from yellow, light sandy clay loans to sandy clay barns. They are acidic (pH 5.0 to 5.5) earthy, porous, massive and hardsetting (if exposed). The subsoils are very highly erodible as they have large amounts of fine sand and silt. At depth, there may be a transition to a bright yellow brown sandy clay. Fragments of ironstone or sandstone rock are often present in the subsoils. They can extend to 1.3m in depth and are generally well drained.

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The yellow earths associated with areas of sandstone rock outcrop are often highly erodible and consist of very shallow topsoils. In some areas the topsoil is no longer present and the subsoil is exposed.

The principal limitations to urban development of the yellow earths are their very high erodibility, their shallow depth (less than 0.5m), areas of rock outcrop, and a very high erosion hazard.

Unit C : Brown Duplex Soils

The brown duplex soils are confined to twa small mudstone lenses located on steep sideslopes in the south-eastern corner of the survey area.

The topsoils are hardsetting, weakly structured brown barns to reddish brown clay barns. They extend to a depth of approximately 30 cm and are highly erodible. They often contain mudstone rock fragments.

The subsoils are moderately structured yellow orange to bright brown light clays. They are highly erodible, slightly to moderately dispersible and are moderately well drained. Depth ranges between 0.5 and 1.0 m and they con-tain significant amounts of mudstone rock fragments.

The main limitations to urban development of the brown duplex soils are their high erodibility and moderate ero-sion hazard.

Unit D : Deep Red Duplex Soils

These soils occur on sideslopes that are probably asso-ciated with iron-rich strata within the Wiannamatta Shales. They are found in a band between Dabbage Place and Pine Dale Place.

The topsoils are friable, moderately structured brownish black barns. They are acidic (pH 5.5), moderately ero-dible, well drained and extend to a depth of approximately 0.3 m.

The deep, acidic (pH 4.5) subsoils are reddish brown, highly structured, subplastic light clays. They are moderately to highly erodible, slightly dispersible and moderately well drained. They have a low to moderate shrink-swell potential, ard this needs to be taken into account when designing and constructing buildings, roads and pavements. Subsoil depths are generally greater than 1.8 m, and the deep subsoils are susceptible to mass move-ment.

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The main limitations to urban development of One deep red duplex soils are their moderate to high erodibility, the low to moderate shrink-swell potential of the subsoils, susceptibility to mass movement and high erosion hazard.

Unit E : Deep Dark Structured Loams

These soils are confined to the lower drainage lines of the Wianamatta Shale terrain.

Both topsoils and subsoils are friable, moderately struc-tured black to dark brown clay barns. They become more strongly structured and lighter coloured with increasing depth. These soils are highly erodible as they contain a large proportion of fine sand and silt. Soil depths range from 0.8 m to more than 2.0 m.

The principal limitations to urban development of the deep dark structured barns are inundation and their very high erosion hazard.

Unit F : Yellow Duplex Soils

The yellow duplex soils are the most widespread soils of the survey area. They occur on the sideslopes of Wianamatta Shale terrain.

The thin upper topsoil (Al) horizons consist of friable, brownish black bosoms. These abruptly overlie acidic, hard-setting, weakly structured, dark yellowish brown to dull yellow-orange lower topsoil (A2) horizons. The topsoils are moderately erodible, moderately well drained and extend to 0.3 to 0.8 cm in depth.

The subsoils are moderately well structured yellowish brown medium clays. They are moderately erodible and slightly to moderately dispersible. The deep subsoils occasionally contain red and orange mottles which grade into a light coloured (pallid) zone. Soil depths are generally 0.9 m but range from 0.7 m to 1.7 m. The stoniness of the sub-soil increases with depth. Subsoil drainage is moderate where the subsoils overlie shale bedrock, but is impeded in those small areas which have mudstone or greywacke strata. They have a low to moderate shrink-swell potential and this needs to be taken into account when designing and constructing buildings, roads and pavements.

The major limitations to urban development of the yellow duplex soils are their moderate to high erodibility, moderate to slow internal drainage, the low to moderate shrink-swell potential of the subsoils and the high to extreme soil erosion hazard.

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Unit G : Shallow Structured Loams

The shallow structured barns occur on steep sideslopes on the upper catchments of the Wiannamatta Shale terrain.

The topsoils are hardsetting, dark brown, weakly to modera-tely structured clay barns. They have a moderate to high erodibility. They are very stony soils and the proportion of deeply weathered shale rock fragments greatly increases with depth. The topsoils are generally less than 0.5 m in depth, and overlie shale bedrock.

The major limitations to urban development of the shallow structured barns are their shallow soil depth, moderate to high erodibility and high to extreme erosion hazard.

URBAN CAPABILITY

The urban land capability classification system used by the Soil Conservation Service is based upon an assessment of the interac-tion between landform, soils and surface drainage characteristics and the influence of these physical features on the use of the land for urban development. An outline of the system is pre-sented by Hannam and Hicks (1980).

Four of the five primary urban capability classes are iden- tified on the attached map and are defined as follows:

Class B - Areas with minor to moderate physical limitations to urban development. These limitations may influence design requirements on development to ensure a stable Land surface is maintained both during and after development.

Class C - Areas with moderate physical limitations to urban development. These limitations can be overcome by careful design and by adoption of site management conditions to ensure the maintenance of a stable land surface.

Class D - Areas with severe physical limitations to urban development which will be difficult to overcome, requiring detailed site investigation and engineering design.

Class E - Areas where no form of urban development is recommended because of very severe physical limitations to such development that are very difficult to overcome.

Within some primary classes, a number of classes are defined on the basis of the dominant physical limitations which will restrict development potential. Letter subscripts have been used to define these physical limitations as follows:

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- shallow soil e - erodibility - flooding

m - mass movement S - slope

The combination of two or more subscripts indicates physical features of equal significance which may interact to affect capa-bility. Where a letter is placed in brackets, it is considered to be of lesser importance among the several limitations that are listed for a particular class.

The classification provides an assessment of the_maximum accep-table degree of surface disturbance associated with urban deve-lopment. Three types of urban development are recognized:

(i) Extensive building complexes refer to the development of commercial centres such as offices or shopping malls, which require large scale clearing and levelling for broad areas of floor space and parking bays.

(ii) Residential development infers a level of construction which provides roads, drainage and services to cater for housing allotments in the order of 600 square metres or larger.

(iii) The development of reeerves, on the other hand, may require shaping and modification of the ground surface and vegeta-tive improvement, but no building, and minimal roadway construction are envisaged.

The capability indicated for each class refers to the most inten-sive urban use which each area will tolerate without the occurrence of serious erosion and sedimentation in the short term and possible instability and drainage problems in the long term. In assessing this capability, no account is taken of development costs, social implications, aesthetics, or other factors relating to ecology and the environment.

Using the capability map for planning at the conceptual level will take account of soil and landform limitations, while being generally consistent with the preservation of an aesthetically pleasing landscape and the minimization of long term repair and maintenance costs.

_Reference is made in the following text to various sections of the Soil Conservation Service "Urban Erosion and Sediment Control" Handbook (Quilty et at, 1978). These sections provide detailed guidance on relevant sediment and erosion control and stormwater management measures which may be adopted in the Kurrajong Heights area as development proceeds.

The following urban capability classes have been depicted on the attached map.

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Class B-e : Minor to moderate physical limitations - soil constraints - suitable for residential development/extensive building complexes.

This class comprises ridges, hillcrests and upper sideslo-pes with slope gradients up to 10 per cent on the yellow duplex soils of soil unit F.

The yellow duplex soils exhibit moderate or occasionally poor subsoil drainage. Subsoil drainage should be care-fully considered with regard to the on-site disposal of effluent. Any effluent which collects and moves laterally through the subsoil will either enter local drainage lines or rise to the surface in lower slope positions.

In addition, the subsoils have a low to moderate shrink-swell potential, and this potential needs to be taken into account when designing and constructing buildings, roads and pavements.

The erosion hazard associated with soils in this class is moderate to very high, and careful management of these soils during construction will be required to prevent ero-sion. Uncontrolled development of Class B-e land will lead to sheet and rill erosion, minor gullying, erosion of cut and fill batters and sedimentation of local drainage lines.

Surface disturbance should be minimized and sequentially confined to small areas. A good vegetative cover needs to be maintained as bare soil surfaces will rapidly erode, causing sedimentation of lower slopes and drainage lines.

This class is suitable for residential development. However, only those areas with slope gradients of 5 per cent or below, are suitable for extensive building complexes. Soil conservation measures defined in Sections 2, 5.3, 5.6 and 6 in guilty et al (1978) should be applied to development of Class B-e.

Class B-e(d): Minor to moderate physical limitations - soil constraints - suitable for residential development/extensive building complexes.

This class consists of ridges and upper sideslopes with slope gradients up to 10 per cent associated with the yellow earths of soil unit B. It contains significant areas of shallow soils and rock outcrops.

Shallow highly erodible soils and rock outcrops limit road-way and building construction and the installation of reti-culated services. Shallow soils also result in impeded soil drainage and effective drainage measures are required' in the design and installation of roads, pavements and building foundations to prevent problems such as rising damp in buildings and undermining of pavements.

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The potential for on-site effluent absorption is limited by shallow soils since they lack the capacity to store large quantities of effluent. Seepage onto lower slopes will occur, with the possibility of effluent emerging onto lower topographic areas and in drainage lines. The installation of an effective effluent disposal system should, therefore, be a primary consideration prior to development of the shallow soil areas.

This class is suitable for residential development, but only those areas with slope gradients of 5 per cent or below are suitable for extensive building complexes. Soil conservation measures defined in Sections 2, 4.5 and 5.3 in Quilty et al (1978) should be applied in developing Class B-e(d).

Class C -se : Moderate physical limitations - slope and soil constraints - suitable for residential development.

This class occurs on sideslopes with slope gradients bet-ween 10 to 20 per cent on the yellow duplex soils of soil unit F. It also occurs on a small sideslope area of the red duplex soils of soil unit D with slope gradients bet-ween 10 and 15 per cent. This class is very similar to Class B-e, but the steeper slope gradients increase the erosion hazard.

The moderate to poor subsoil drainage of the yellow duplex soils limits on-site disposal of effluent and increases the risk of effluent emergence on lower areas and in drainage lines. The subsoils of both the yellow duplex soils and the deep red duplex soils exhibit a low to moderate shrink-swell potential. This may affect design of buildings, roads and pavements.

To minimize erosion, building construction techniques which minimize ground disturbance are recommended. A good groundcover of vegetation should be maintained to prevent erosion of bare soil surfaces. Road batters and embank-ments should be formed to stable grades and protected by vegetative measures.

This class is suitable for residential development. However, soil conservation measures as described in Quilty et at (1978), Sections 2, 4.5, 5.3 5.6 and 6 should be applied in the development of this class.

Class C-se(d) : Moderate physical limitations - slope and soil constraints - suitable for residential development

This class comprises sideslopes with slope gradients bet-ween 10 and 20 per cent on the yellow earths of soil unit

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B. The class occurs on the same soils as for Class B-e(d), but the slope gradients are steeper and so the erosion hazard is increased.

Substantial areas of shallow soils and rock outcrops occur on this class. Shallow soils generally have impeded soil drainage and lack drainage capacity for on-site effluent disposal, roadway and building construction and reticulated services. These limitations are fully outlined in paragraphs 2 and 3 of the description for Class B-e(d).

Particular attention should be paid to the high erosion hazard associated with the steep slope gradients of this class. Disturbance of these soils will create a serious risk of erosion and subsequent sedimentation of lower slope areas and drainage lines. Erosion and sediment control techniques must be used during the development phase of construction.

This class is suitable for residential development. Soil Conservation Service guidelines described in Sections 2, 4.5, 5.3 and 6 of Quilty et ca (1978) should be applied in the development of this class.

Class D-f : Severe physical limitations - flooding and soil constraints - suitable for drainage reserves.

This class includes the natural drainage lines and asso-ciated drainage plains of the study area. In the central and northern sections of the study area this class occurs on the deep dark structured loans of soil unit E, where” in the southern section this class is found in the sili-ceous soils of soil unit A. Sideslope gradients are highly variable and range from 10 per cent to over 30 per cent. The steepest slope gradients are found in the southern sec-tion of the study area.

Lard in this class is subject to periodic inundation, and should be retained as part of an open, natural drainage system to cater for the control and disposal of runoff from the survey area.

In the event of more intense forms of development within the catchment areas of any of the drainage courses, signi-ficant hydrological changes will occur leading to possible instability of the natural channels. These changes involve an increase in runoff volume, increase in peak discharge, erosion of channel banks, sedimentation and flooding of low-lying areas.

12.

Increases in the volume of sediment will reduce the capa-city of streams in their lower reaches, block culverts and increase the cost of drainage system maintenance. These factors result in the need for careful planning and design to minimize damage from bank erosion, bed scour and sedi-mentation of lower reaches. Measures and techniques which can be used to minimize these problems include the following:

Development of grassed drainage reserves.

Installation of stormwater retarding basins and sedi-ment basins.

Development of Drainage Reserves

The benefits of grassed reserves include:

1. lower velocities of flow and increased channel storage, which result in a longer time of con-centration and lower flood peaks downstream;

green belts can be developed along the reserves, pro-viding an attractive break in subdivision. These may be used for recreation and incorporate cycle or pedestrian paths;

grassed reserves encourage filtration and/or settle-ment of pollutants such as sediment and oils, etc., washed from urban areas. By comparison, these would flow freely through stormwater pipes or lined chan-nels.

Urban development should not encroach onto the drainage reserves so that they can provide for unimpeded flood flows.

To develop the reserves, existing drainage lines should be shaped into broad, shallow, parabolic waterways. These should be of sufficient width to carry flows at a velocity not exceeding two metres per second. Flows of greater velocity require structural lining to prevent scour of vegetated channels.

After their formation, the reserves should be stabilized with suitable waterway vegetation. A heavy dressing of fertilizer should be applied at the time of sowing, and follow up applications of fertilizer may be necessary. Turf may be laid to protect local critical areas, such as culvert inlets, where scour occurs.

Stabilisation will be assisted if a surface binding agent such as jute mesh and bitumen, straw and bitumen, or another suitable chemical or organic mulch is applied at

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sowing. This will impart a temporary surface stability until vegetation is established. It is a particularly desirable measure where reserves are developed after sub-division work has commenced. If possible, however, the drainage reserves should be formed and stabilized before any major development occurs in their catchments.

Continuous trickle flows should pass through small underground pipes beneath the reserves, or through half-round pipes or lined inverts along the centre of the reser-ves. Without this provision these flows will erode the reserve floors while rushes, sedges, blackberries and other species will proliferate along, trickle paths. _

Where roadways cross drainage reserves, floodways or culverts should be provided, and these should be stabilized to withstand high flows. Rock grouting, hay and wire netting, jute mesh and bitumen, or structural energy dissi-pators may be required below culvert outlets to alleviate potential erosion problems.

A detailed discussion on formation of drainage reserves and revegetation techniques are described in Sections 3.1 and 6 of Quilty et at (1978).

Installation of Sediment Basins and Stormwater Retarding Basins

Retarding basins are storages designed to impound runoff and regulate its flow through a pipe outlet. Their effect is to reduce peak discharges by increasing the time of con-centration of runoff. These structures should have provi-sion for flows greater than their flood storage capacity in the form of an emergency spillway. Stringent design and construction controls are essential, as failure of these structures could have serious consequences, including flash-flooding of areas below them.

A variety of measures can be adopted to delay the flow of stormwater from an area and to reduce flow peaks below that area (Section 3.2 of Quilty, et at, 1978). The desirabi-lity of locating sediment basins on drainage reserves within the site must be highlighted.

Retarding basins can function as temporary sediment basins. Their installation prior to any other site construction activity allows de-watering without sediment loss. When development is completed, sediment should be removed and either stockpiled or spread in a safe location where it will not be subsequently erode. The basins can then con-tinue to function as stormwater retarding basins.

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Class D-s : Severe physical limitations - slope constraints - suitable for strategic resi-dential development/reserves.

This class includes steep sideslopes with slope gradients generally between 20 and 30 per cent. It occurs on the siliceous sands, yellow earths, brown duplex soils and yellow duplex soils of soil units A, B, C and F, respec-tively.

The combination of variable steep slope gradients and high to extreme soil erodibility and very high erosion hazard imposes severe restrictions on the development of these areas, expecially with regard to the installation of building foundations and services.

Without proper control of stormwater runoff, considerable soil movement downslope would be associated with large scale disturbance. of this class. It is recommended that if any building development is permitted on this land, that it be subject to prior geotechnical survey and strict engi-neering controls.

There may be an opportunity, however, for a low density form of residential development, by strategically locating houses within this class or on adjacent classes with fewer limitations, and using the majority of the area containing the steeper slopes for backyards or open space. A good tree and ground cover will help maintain stability. To prevent potential severe soil erosion and sedimentation problems, care should be taken to avoid placing any struc-tural works close to the boundary of this class with steeper land of classes E-s and E-sm.

The use of this class as reserves for passive recreation would impose few soil erosion or instability problems, pro-vided good vegetation cover is maintained and site drainage is effectively controlled. Soil conservation measures outlined in Sections 2, 4.5, 5.3 and 6 of Quilty et at (1978) apply to Class D-s.

Class D-se(d): Severe physical limitations - slope and soil constraints - suitable for strategic residential development/reserves.

Land in this class comprises sideslopes with slope gra-dients between 15 and 25 per cent on the shallow structured loams of soil unit G. The class has very severe limita-tions to development because of the combination of moderate to very high soil erodibility, very high to extreme erosion hazard, steep slope gradients and the often unstable nature of the deep weathered rocky subsoil materials.

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The shallow, rocky soils generally have impeded drainage. They lack drainage capacity for on-site effluent disposal, roadway and building construction and reticulated services. It is recommended that if any building development and drainage works are permitted in this class, that they be subject to prior geotechnical survey and engineering controls.

Land use activities involving minimal disturbance, such as passive recreation or use as backyards or open space, are preferred. The use of this class as reserves for passive recreation should reduce potential instability problems, provided good vegetative cover is maintained and site drainage is effectively controlled.

Soil conservation measures outlined in Sections 2, 4.5, 5.3 and 6 in Quilty et al (1978) provide further guidelines applicable to-the development of this class.

Class D-sm : Severe physical limitations - slope and mass movement constraints - suitable for strategic residential development/reserves.

This class consists of sideslopes with natural slope gra-dients generally between 15 and 20 per cent. It occurs only on the deep red duplex soils of soil unit D.

Physical limitations to development include a potential for mass movement (based on soil depth, slope and high clay content), high erosion hazard and the low to moderate shrink-swell potential of the subsoils.

For further details concerning problems associated with land subject to mass movement refer to Section 5.5 in Quilty et at (1978).

Land use activities involving minimal disturbance such as passive recreation or use as background space are pre-ferred. The use of this class as reserves for passive recreation should reduce potential instability problems, provided good vegetative cover is maintained and site drainage controlled. It is recommended that if any building development is permitted on this class, that it be subject to prior geotechnical survey and engineering controls.

Further guidelines to the development of this class are described by Quilty et at (1978) (Sections 2, 4.5, 5.3, 5.5 and 6).

Class E-s : Very severe physical limitations - slope constraints - not recommended for development.

This class comprises very steep sideslopes with slope gra-dients of 30 per cent or greater. It occurs on the sill-

16.

ceous sands and yellow earths of soil units A and B.

Any disturbance of land in this class will lead to soil erosion and instability (e.g. rock fall). This will not only affect this class, but will also endanger development works and drainage areas on adjacent or downslope land (particularly classes D-f and D-s).

As a result of the very high to extreme erosion hazard, development of this class is, therefore, not recommended. It should be retained in its present condition, maintaining a good vegetative cover to stabilize it against erosion.

Class E-sm : Very severe physical limitations - slope and mass movement constraints - not recom-mended for development.

Land in this class consists of steep sideslopes with slope gradients generally above 20 per cent. It is associated with the deep duplex soils, yellow duplex soils and shallow structured loamy soils of soil units D, F and G, respec-tively.

This class delineates the steep headwater areas of drainage lines and other slope segments which receive substantial volumes of run-on from upslope lands. However, it also includes steep slope segments, generally above 20 per cent, located on deep subsoils.

Land in class E-sm is potentially highly susceptible to mass movement.

Development of this class requiring any form of disturbance is not recommended. It should be retained in its present condition, with a good vegetative cover.

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RECOMMENDATIONS

It is recommended that :

• Extensive building complexes should be confined to Classes B-e and B-e(d) which have slope gradients below 5 per cent.

• Residential development should be confined to Classes B-e, B-e(d), C-se and C-se(d). Any development implemented should be consistent with the physical capability and ero-sion potential of these classes. Consideration should also be given to the provision of an effective effluent disposal system if pollution is to be avoided on low-lying areas, drainage lines and ultimately the Hawkesbury River.

• Class D-f land should be developed as drainage reserves. Runoff from adjacent urban sites may be directed onto this land once the drainage reserves are fully stabilized.

The existing sub-catchment layout and natural drainage net-work should be considered in the planning and design of the area. It is recommended that a.detailed hydrological study be undertaken prior to any development.

• Classes D-s, D-se(d) and D-sm should be subject to further detailed site investigation and geotechnical assessment, prior to any development.

• Classes E-s and E-sm should be excluded from any form of development or disturbance.

• Erosion and sediment control techniques outlined in the Service's "Urban Erosion and Sediment Control" Handbook (Quilty et a/, 1978) should be adopted as part of urban design and with any ensuing development or disturbance.

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REFERENCES

EDWARDS, K. (1979) Rainfall in New South Wales, with special reference to soil conservation. Soil Conservation Service of N.S.W. Technical Handbook No. 3. Soil Conservation Service of N.S.W., Sydney.

HANNAM, I.D. & HICKS, R.W. (1980) Soil Conservation and Urban Land Use Planning. J. Soil Cons. N.S.W., 36(3), 134-145.

NORTHCOTE, K.H. (1979) A Factual Rey for the Recognition of Australian Soils. Rellim Technical Publications, Adelaide.

QUILTY, J.A., HUNT, J.S. and HICKS, R.W. (1978) Urban Erosion and Sediment Control. Soil Conservation Service of N.S.W. Technical Handbook No. 2. Soil Conservation Service of N.S.W., Sydney.

APPENDIX I

NORTHCOTE CODE AND REPRESENTATIVE DESCRIPTION FOR EACH SOIL UNIT

NORTHCOTE CODE SOIL DESCRIPTION SOIL Lower UNIT Average

Dominant Sub-dominant Present Horizon Depth (cm) Colour Texture Structure pH Notes

(A) Shallow Uc1.23 Uc1.22 Uc5.21 10YR2/1 Sand to Apedal, 4.5 Overlies bed- Sandy Gn2.21 A 50 10YR4/3 sandy single to rock, earthy soils loam grained 5.5 sands or

lithosols. This unit is an erodible sandy wash.

(B) Yellow Gn2.21 Gn2.84 Uc5.23 Al 10 - 30 10YR4/2 Sand 5.8 This unit is a Earths Gn2.24 Uc5.21 10YR2/2 erodible sandy

Um1.2 wash. Um5.52

A2 40 10YR4/3 Sandy loam Apedal, 5.6 'Highly erodibl, to loamy massive sand

B 70 - 130 10YR4/6 Light Apedal, 5.4 Highly erodibli 10YR6/4 sandy clay massive

loam to sandy clay loam

APPENDIX I (continued)

NORTHCOTE CODE ADD REPRESENTATIVE DESCRIPTION FOR EACH SOIL UNIT

NORTHCOTE CODE SOIL DESCRIPTION SOIL Lower UNIT Average

Dominant Sub-dominant Present Horizon Depth (cm) Colour Texture

Structure pH Notes

(C) Brown

Db3.11 Db1.11 Gn2.2 30 5YR3/2 Loam to Hardset- 5.1 Cultivated Duplex Dy2.21 10YR3/2 clay loam ting, Soils weakly

pedal

45 - 60 10YR7/8 Light Moder- 5.1 10YR5/8 clay ately

pedal

100 10YR5/8 Light Moder- 4.6 clay ately

pedal

(D) Red Duple Dr4.11 Dr2.11 A 30 10YR2/3 Loam Friable, 5.4 Fertile Soils 10YR3/2 hardset- erodible

ting, topsoil moder-ately pedal

150+ 5YR2/4 Light to Highly 5.4 Deep plastic 5YR4/6 medium pedal subsoil subject

clay to mass movement (sub-plastic)

APPENDIX I (continued)

NORTHCOTE CODE AND REPRESENTATIVE DESCRIPTION FOR EACH SOIL UNIT

NORTHODTE CODE SOIL DESCRIPTION SOIL Lower UNIT Average

Dominant Sub-dominant Present Horizon Depth (cm) Colour Texture Structure pH Notes

(E) Deep, dark Um6.23 Um6.21 A 80 10YR2/1 Clay Moder- 5.7 Subject to structured 10YR3/3 loam ately inundation. loans pedal

200 + 10YR4/4 Clay Moder- 5.6 10YR4/6 loam ately

pedal

(F) Yellow Dy2.11 Dy3.11 Db2.11 Al 10 10YR2/2 Loam Friable 5.1 A horizons are Duplex Dy3.21 fertile and Soils A2 30 - 80 10YR3/4 Clay Moder- 5.0 easily eroded.

10YR7/3 loam ately pedal

B to 170 10YR5/8 Light Moder- 5.0 Subsoil hard to 10YR6/8 clay ately to revegetate.

strongly May be deeply pedal weathered.

Occas- Strongly 5.0 ional pedal mottles

APPENDIX I (continued)

NORTHCOTE CODE AND REPRESENTATIVE DESCRIPTION FOR EACH SOIL UNIT

NORTHCOTE CODE SOIL DESCRIPTION SOIL Lower UNIT Average

Dominant Sub-dominant Present Horizon Depth (cm) Colour Texture Structure pH Notes

(G) Shallow Um6.21 Dy2.11 A 30 10YR2/2 Clay Hardset- 5.0 Deeply weatheredStructure loam ting, stony subsoil. Loams we

pedal

AC Highly erodible soil

23.

APPENDIX II

SUMMARY OF SOIL CHARACTERISTICS

Soil Unit Soil and Linear Depth Erosion

Dominant Soil Erodibility Shrinkage (cm) Permeability Hazard

(A) Shallow Sandy High Very low <50 Very high Extreme Soils

(B) Yellow Earths Very high Low 30-130 High Very high

(C) Brown Duplex High Low 50-100 Moderate Moderate Soils

(D) Red Duplex Moderate to Low to >150 Moderate High Soils high moderate

(E) Deep, Dark High Low 80->200 Low to Very high

Structured moderate Loams

(F) Yellow Duplex Moderate to Low to 70-170 Moderate to Moderate Soils high moderate low to very

high

(G) Shallow Moderate to Low to <30 High to High to Structured very high moderate moderate extreme Loams

PPIPBADIX III

SUMNPRY OF LAEORMORY DATA

SOIL UNIT: A Sub- Sub- Sub- Deep

-1;) ,Izon Topsoil Subsoil Topsoil soil Topsoil Soil Topsoil Soil Topsoil Subsoil Topsoil Subsoil Subsoil Topsoil

A B AI B A B A B B C A A2 A1 A2 B A1 A2

1 Average Sarrp le

Depth (cm) 30 30 20 25 55 2 15 6 20 40 30 70 10 30 90 20

OL, OH,

U.S.C.S. Code SM, SP - SM SP M_-CL SL, CL OL CL CL OL CH CL-OL Pi MI, M_ OL CL, CH CL, CH OH

Clay (%) 8 14 3 27 35 22 30 47 27 59.5 34 37 36.5 32 57.5 30-73 40

Si It (%) 2 4 0 7 7 21 27 19 12.5 17 28 25 21.5 22 23 21-26 16

lline Sand (%) 13 21 15 33 31 30 19 20 41 21 28 34 28 33 15 9-15 29

Coarse Sand (%) 77 61 82 33 27 27 24 1 9.5 3 10 4 14 12 5.5 44-19 15

Liquid Limit 17 19 NA 31 29 48 47 44 43.5 52.5 48 47 51.8 50 50 39-55 54

Plasticity Non Non Non 9 8 10 7 19 8.5 12 11 9 9.5 17 19 7-12 10

Index Plastic Plastic Plastic

Li near 1 1 0 3 7 5 6 8 6 13 8 10 6 6 10 6-11 8

Stir inkage

5 4g gregate Test 5 3 5 5 5 5 5 5 5 5 5 5 5 5 5 5

Dispersion 32 23 89 12 32 23 8 43 15 33.5 12 12 11.3 12 33 11-30 10

°or-cent-age '

rii 5.0 5.2 5.8 5.6 5.4 5.1 5.1 4.6 5.4 5.4 5.7 5.6 5.1 5.1 4.8 4.6-5.1 5.2

25.

APPENDIX IV

INTERPRETATION OF ANALYTICAL DATA

UNIFIED SOIL CLASSIFICATION SYSTEM (U.S.C.S.)

The U.S.C.S. is a classification system which has been correlated with certain engineering properties of soils such as optimum moisture content, permeability, compressibility and shear strength.

A full description of the classes is as follows:

GW Well graded gravels, gravel-sand mixtures, little or no fines.

GP Poorly graded gravels, gravel-sand mixtures, little or no fines.

GM Silty gravels, poorly graded gravel-sand-silt mix- tures.

GC Clayey gravels, poorly graded gravel-sand-clay mix- tures.

SW Well graded sands, gravelly sands, little or no fines.

SP Poorly graded sands, gravelly sands, little or no fines.

SM Silty sands, poorly graded sand-silt mixtures.

SC Clayey sands, poorly graded sand-clay mixtures.

ML Inorganic silts and very fine sands, rock flour, ' silty or clayey fine sands with slight plasticity.

CL Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays.

OL Organic silts and organic silt-clays of low plasti- city.

MH Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts.

CH Inorganic clays of high plasticity, fat clays.

OH Organic clays of medium to high plasticity.

Pt Peat and other highly organic soils.

26.

ATTERBERG LIMITS

Atterberg Limits are based on the concept that a fine grained soil can exist in any of three states depending on its water con-tent. Thus, on the addition of water, a soil may proceed from the solid state through to the plastic and finally liquid states. The water contents at the boundaries between adjacent states are termed the plastic limit and the liquid limit. Water content is expressed as a percentage of the oven dry weight of soil.

Liquid Limit (LL)

The liquid limit of a soil is_ the moisture content at which the soil passes from the plastic to the liquid state.

Liquid Limit: Low - less than 45 Medium - 45 - 55 High -55-75 Very high - greater than 75

Plasticity Index (PI)

The plasticity index of a soil is the, numerical difference between the plastic and the liquid limits. Toughness and dry strength are proportional to the plasticity index.

Plasticity Index: Low - less than 25 Medium - 25 - 35 High -35-45 Very high - more than 45

LINEAR SHRINKAGE

The linear shrinkage is the decrease in one dimension of a soil sample when oven dried from the moisture content at the liquid limit, expressed as a percentage of the original dimension.

Low - less than 12% Moderate - 12 - 17% High - 17 - 21% Very high - more than 21% ) Expansive Soils

27.

EMERSON AGGREGATE TEST

This is a measure of soil dispersibility or soil structural sta-bility.

The following general levels of dispersibility are assigned (Classes 2 and 3 are subdivided on the basis of degree of disper-sion under test - the subclasses are enclosed by brackets):

Dispersibility Emerson Aggregate Classes

Very high 1 and 2 (3) High 2 (2) and 2 (1) Moderate 3 (4) and 3 (3) Slight 3 (2), 3 (1) and 5 Negligible/Aggregated 6

DISPERSION PERCENTAGE

The Dispersion Percentage is a measure of the degree of disper-sion of a soil. Qualitative values are:

Negligible/Aggregated - < 6% Slight - 6 - 30% Moderate - 30 - 45% High - 45 - 65% Very high - 65 - 100%

Full descriptions of these tests are available from the Soil Conservation Service.

LEGEND

Degree of Maio!

limitations

Capability Class

limitation

Minor to moderate Soil constraints . . Residenbal/E BC • I B-e I

Minor to moderate 2 . Soil constraints . ResidentiaVEB C 0. . . I B-e Id)

Moderate Slope and soil constraints

Residential C-se

Moderate Slope and soil. constraints

. Residential C-se(d)

Severe Flooding and . . soil constraints

. Drainage Reserve D-f

Severe Slope constraints. Strategic ResidentieV . . I 0-s I

Reserve

Severe Slope and soil . constraints

. Strategic ResidentieV . Reserve

0-said)

Severe Slope and mass . . movement constraints

. Strategic ResidentiaV. Reserve

I 0- sm

Very severe Slope constraints . . Not recommended for development

I E-s

Very severe Slope and mass . . movement constraints

. Not recommended for development

E-sm

*Extensive Building Complexes

s.0

SOIL CONSERVATION SERVICE OF maw

URBAN CAPABILITY STUDY

KURRAJONG HEIGHTS

RECONNAISSANCE URBAN CAPABILITY

SCALE loniale“

Cu SCI: 18174/C

BoU

C.41