Layman's Guide to Landslide Prevention in Hong Kong PDF

LAYMAN’S GUIDE TO LANDSCAPE TREATMENT OF SLOPES Geotechnical Engineering Office Civil Engineering and Development Department © The Government of the Hong Kong Special Administrative Region First published, July 2002 Second edition, July 2008 Third edition, July 2012 Prepared by: Geotechnica...

LAYMAN’S GUIDE TO LANDSCAPE TREATMENT OF SLOPES Geotechnical Engineering Office Civil Engineering and Development Department © The Government of the Hong Kong Special Administrative Region First published, July 2002 Second edition, July 2008 Third edition, July 2012 Prepared by: Geotechnical Engineering Office, Civil Engineering and Development Department, Civil Engineering and Development Building, 101 Princess Margaret Road, Homantin, Kowloon, Hong Kong. Designed by Edwin Eddie Tommy Advertising Limited Foreword This Layman’s Guide is intended for the use of the general public. It provides information and general guidance on landscape treatment for slope works and natural terrain landslide mitigation measures. It is Government’s policy to make slopes in Hong Kong look as natural as possible. We are striving to improve the quality of our living environment through active planting, preservation of trees and other vegetations, together with proper maintenance. With this commitment and effort, we believe that we can achieve the overall aim of creating a greener, more harmonious and ecologically sustainable slope environment. The first edition of this document was published in 2002. There had since been continuous development in slope engineering and landscaping techniques, which led to the issue of GEO Publication No. 1/2011 “Technical Guidelines on Landscape Treatment for Slopes” by the Geotechnical Engineering Office. We have therefore taken the opportunity to update this Layman's Guide in order to promulgate the latest best practice. We trust that this document will continue to serve the purpose of helping and encouraging private slope owners to provide appropriate landscape treatment to their slopes when planning maintenance, upgrading and new developments. For more detailed guidance, readers may refer to GEO Publication No. 1/2011. Y C Chan Head, Geotechnical Engineering Office July 2012 1  Contents 1 Foreword 2 Contents 3 Why bother with landscape treatment for slopes? 7 What are the landscape design objectives? 12 Tips for landscaping slopes 23 Examples of landscape treatment 26 Typical maintenance of landscape works 26 Are landscape works costly? 27 Seven things to remember 28 Assistance 29 Relevant publications 2  Why bother with landscape treatment for slopes? Enhance Property Improve Value Appearance Contribute to Create a Greener Local Ecology Environment Achieve Sustainability 3  Landscaped man-made slope Before After Fat Kwong Street, Homantin 4 Landscaped retaining wall Before After South Lantau Road, Lantau Island 5  Landscaped natural terrain landslide mitigation measures Before After Artist’s impression of the mitigation measures upon maturing of landscaping plants Yu Tung Road, Tung Chung 6  What are the landscape design objectives? 1. Minimise impacts on the natural environment Minimise the extent of engineering works and retain as much existing vegetations as practicable 2. Fit in with surrounding landscape/natural topography The slope topography and composition should be designed to match the surrounding landform and landscape 7  3. Create a greener environment Vegetation is aesthetically pleasing and environmentally friendly 4. Contribute to environmental sustainability and local ecology Native tree species provide natural habitats for wild life to thrive, and they can spread naturally. Planting them improves the local ecology 8 5. Achieve a natural appearance Solutions using natural materials (e.g. rock and vegetation) are visually preferable to artificial materials 6. Mitigate visual impact Where artificial or built elements are used, efforts should be made to blend these elements into their surroundings 9  7. Aesthetically pleasing The landscape design of features should conform to the principles of good aesthetic design Unity and coherence Planting at the toe and above a retaining wall successfully creates a unified appearance to the whole slope Proportion and scale Buttresses with masonry facing suitably sized and dispositioned to create a sense of proportion 10  Pattern and texture Rhythm and complexity Various techniques used in a Ribbed finish and plain concrete co-ordinated manner, resulting create a scene with both rhythm in a composition having both and complexity pattern and texture Colo u r Colours of random patterned Small-sized surface blocks masonry complement the mingled with vegetation reduce surroundings the reflectivity of a hard surface 11  Tips for landscaping slopes Preserve existing trees Providing tree protection zone and/or protective wrapping around tree trunks during construction Planting masonry strips above and b growth o wall to promote ro elow f wall tree ot s Combined tr ll to retain existing trees ee rings Localised wa 12  Examples of tree preservation Existing wall trees are retained after upgrading works using soil nails Use of soil nails to stabilise an existing Soil nail heads are concealed masonry wall allows attractive “wall trees” behind blocks in the wall face to remain undisturbed 13  Select the planting goal (plant the right vegetation at the right place) Slope s in ru areas ral or urb fringe an areas conn – ected natur to al veg etatio n Ecological Planting Integration with the surrounding natural vegetation Slopes in parks/ gardens o r other visually se nsitive areas t a l P lantinngce amen Orn sis on a pleasingappeara Slopes in urban Empha areas isolated Amen ity Pla from natural Basic nting landsc vegetation en hance a pe ment Note: Consult a landscape architect on the selection of the planting goal as necessary 14  Examples of different planting goals Ecological Planting Improve visual appearance and enhance ecological value by planting native species Amenity Planting Basic landscape enhancement by planting a mixture of exotic and native species on slopes that are isolated from the natural vegetation Ornamental Planting Emphasis on a pleasing appearance by planting of flowering shrubs and trees 15  Create planting opportunities Non-biodegradable 90˚ erosion control mat and, if necessary Groundcover wire mesh and trailing plants Hard surfacing >55˚ Biodegradable or with planter holes non-biodegradable for groundcover erosion control mat and climbers Grass and 45˚-55˚ to suit site conditions groundcover Grass, Retaining wall with groundcover 35˚-45˚ decorative designed facing Climbers and climbers Grass, groundcover, climbers and small Shrubs trees Climbers ≤35˚ Tree Shrubs Shrubs and groundcover Biodegradable erosion control mat θ Planter for slopes over 15˚ Slope Gradient ( θ ) Possible Planting on Slope Face* Grass hydroseeding with pit planting of trees, θ ≤ 15˚ shrubs, groundcover and climbers Grass hydroseeding with pit planting of small trees 15˚ < θ ≤ 35˚ (up to about 3 m height when mature), shrubs, groundcover and climbers Grass hydroseeding with pit planting of shrubs, 35˚ < θ ≤ 45˚ groundcover and climbers Grass hydroseeding with groundcover and 45˚ < θ ≤ 55˚ climbers in root tube planters θ > 55˚ Planter holes through hard surface cover for planting of groundcover and climbers Source: Figure 2.15 and Table 2.2 of GEO Publication No. 1/2011 16 Note: (*) Recommendations are not mandatory and consult a landscape architect as necessary Examples of creating planting opportunities Climbers and screen planting at the toe Terracing of a retaining wall for planting Toe and berm planters 17  Species commonly planted in Hong Kong Use of native species is encouraged Climbe rs Ficus pumila (Creeping Fig) Parthenocissus dalzielii (Diverse-leaved Creeper) 18  Species commonly planted in Hong Kong Use of native species is encouraged Ground cover Dicranopteris pedata (Dichotomy Forked Fern) Blechnum orientale (Oriental Blechnum) 19  Species commonly planted in Hong Kong Use of native species is encouraged Shrubs Melastoma sanguineum (Blood-red Melastoma) Rhaphiolepis indica Ardisia crenata (Hong Kong Hawthorn) (Hilo Holly) 20  Species commonly planted in Hong Kong Use of native species is encouraged Small T rees Melicope pteleifolia (Thin Evodia) Polyspora axillaris (Hong Kong Gordonia) 21  Landscape the engineering elements and slope furniture Landscape the engineering elements Use of grillage system to retain existing vege tation t of climbers Establishmen wall on retaining Landscape the slope furniture Stairways blended in with the surroundings to minimise visual impact 22 Examples of landscape treatment 1. Land softwsocape rks Ecological planting to achieve a sustainable environment Well maintained trees and ornamental shrubs on a slope Provide ferns and other shade tolerant species under tree cover 23  Examples of landscape treatment 2. Land hardwsocape rks Decorative designs on a retaining wall, enhanced by trees and shrubs in a toe planter Masonry facing, common landscape hardwork for slopes Apply masonry-like finish to a hard surface Subdue grey colour paint applied to concrete rock slope preventive measures 24  Examples of landscape treatment 3. Hybr landsicda treatme pe nt Climbers forming a green curtain to screen the concrete buttresses Openings on slope to allow planting to green the hard surface Climbers on a retaining wall with palm trees and decorative shrubs in front 25  Typical maintenance of landscape works Landscape softworks: inspecting trees and plants trimming vegetation as necessary replacing vegetation where necessary spraying against pests removing invasive species Landscape hardworks: repairing damage to surface finishes Are landscape works costly? Landscape works are generally not costly. Advice on the cost of the landscape works should be obtained from a landscape architect. 26  1 2 adv ice Slo 3 e k Se a abo pe Sa from scape d lan itect ve a fety arch ll Reta vege in existin wher tation g 4 e po ssib le 5 More us pl a oppo n t e Creat ing rtunit ies 7 of nativ e species e Pr 6 Choose hard ma oper of inte wo land nanc rks sca e pin surface g materials that minimise visual impact T hings n r Seveemembe to R 27  Assistance More guidance can be found in GEO Publication No. 1/2011 “Technical Guidelines on Landscape Treatment for Slopes” which is available from: Publications Sales Unit Information Services Department http://www.bookstore.gov.hk Tel. No.: (852) 2537 1910 or from the following website: http://www.cedd.gov.hk/eng/publications/ For more information on slope related matters, please contact Community Advisory Unit Geotechnical Engineering Office Civil Engineering and Development Department Tel. No.: (852) 2760 5800 Other relevant websites: Civil Engineering and Development Department http://www.cedd.gov.hk Greening and Landscape Office of Development Bureau http://www.greening.gov.hk Hong Kong Slope Safety http://hkss.cedd.gov.hk The Hong Kong Institute of Landscape Architects http://www.hkila.com 28 Relevant publications 29 July 2012