This chapter describes the onshore Quaternary (Holocene and Pleistocene)
superficial deposits and the historical development of land reclamation, which
has modified the coast line of Hong Kong. The offshore Quaternary deposits are
not dealt with in this interactive geological memoir.
The total area of Hong Kong is 2 755 km2.
This comprises 1 104 km2of land area, which
represents about 40% of the total area, while the remaining
1 651 km2, some 60% of the total area, is
covered by sea. About 14% of the onshore area is covered
by Quaternary deposits greater than 2 m thick (Figure
11.1). These deposits are up to 50 m thick, but
generally they form thin veneers, and are referred to
as 'superficial deposits' on the fifteen 1:20 000-scale
geological maps and in the six memoirs produced by the
Hong Kong Geological Survey (HKGS). The deposits are
unlithified and were formed by a variety of processes
in a wide range of environments. Almost 6% (67.4 km2)
of the current land area is reclaimed land (Figure
11.2). The earliest reclamation dates back to the
mid-1800s.
A lithostratigraphy has been proposed that encompasses all superficial deposits,
regardless of whether they occur onshore or offshore. Wherever possible,
the terminology used previously for offshore superficial deposits has been adapted
to include onshore equivalents. Thus, the Pleistocene Chek Lap Kok Formation is
extended onshore to embrace both alluvium and colluvium of Pleistocene age.
The Fanling Formation includes all onshore Holocene alluvium and colluvium. Holocene beach,
intertidal and estuarine deposits, however, are included within the offshore Hang Hau Formation.
Several regional studies have produced maps that depict the broad distribution of
Quaternary superficial deposits over the onshore areas of Hong Kong. Most notably,
Allen and Stephens (1971) recognized, and mapped photogeologically, three classes
of these deposits: alluvium, colluvium and, in littoral environments, marine sediments.
Bennett (1984)
carried out a review of published sources of information on the stratigraphy
of the onshore superficial deposits. He concluded that they could be divided into two broad
categories: fluvial deposits, which included alluvium and beach deposits, and mass wasting
deposits (colluvium), which included debris flow and talus deposits. These two categories
were adopted by the Hong Kong Geological Survey during the 1:20 000-scale geological mapping
of the whole of Hong Kong.
Prior to the publication of The Quaternary Geology of Hong Kong
(Fyfe et al., 2000),
only a limited attempt had been made to erect a formal lithostratigraphy
for the onshore Quaternary sequence in Hong Kong. The principal exception to this was the description
of two Pleistocene alluvial formations, the Wong Kong Shan Formation and the Shan Ha Tsuen Formation,
by
Lai (1997,
1998)
in the New Territories. With respect to chronostratigraphy, onshore Pleistocene
deposits of various types have been differentiated from similar deposits of Holocene age on some,
but not all, of the 1:20 000 geological maps of Hong Kong produced by the Hong Kong Geological Survey.
Otherwise, the onshore Quaternary deposits have generally been described, and their distributions mapped,
in terms of depositional processes and environments of deposition. This approach has been in contrast to
that adopted for offshore Quaternary deposits, for which a robust lithostratigraphy has been developed,
based on extensive seismic reflection and borehole data.
To redress the imbalance in treatment of the onshore
and offshore Quaternary stratigraphy,
Fyfe et al., (2000)
presented a comprehensive lithostratigraphy that encompasses
all Quaternary deposits. The proposed stratigraphy (Table
11.1,
Figure 11.3) is essentially an extension of the
existing offshore stratigraphy with the addition of
one new formation, the Holocene Fanling Formation. In
addition, the two alluvial 'formations' previously described
by
Lai (1997,
1998) are incorporated
in the lithostratigraphy, but as members within the
Chek Lap Kok Formation: the Wong Kong Shan Member and
the Shan Ha Tsuen Member.
The earliest reclamations were on tidal flats in the New Territories,
in particular at Sha Tau Kok, Nam Chung, Luk Keng, Shuen
Wan and Yuen Long (Guilford,
1997). These were carried out primarily to
create new agricultural land. Following the land auctions
of 1841, small urban reclamation began around Victoria
Harbour and formal waterfront reclamation commenced
in 1851. By 1886, an 8 km long strip had been formed
between Kennedy Town and North Point and areas of the
West Kowloon waterfront had been extended. Further phases
of reclamation occurred in the 1890s, the early 1900s,
the 1920s and the 1950s
(Guilford, 1988). By
1967, a total area of 1050 hectares had been reclaimed
(Figure
11.13).
Early reclamations were, in general, confined to relatively
narrow coastal strips in shallow water. More extensive
reclamation into deeper water began in the 1970s. By
1991 a further 3 050 hectares had been completed, most
of which was in deeper water. Between 1991 and 1995,
large reclamations were constructed in connection with
the new airport and related infrastructure projects.
Up to 1995 a total of 6 000 hectares of land had been
reclaimed (Figure
11.13 and 11.14).
Up to 2005, a total of 6 739 hectares of land, or approximately
6 % of the onshore area of Hong Kong, had been reclaimed
(Figure
11.2).
Initially the small, localized reclamations were completed using urban waste and spoil from nearby excavations. As urban development expanded on to the Kowloon peninsula during the 1900s, extensive hillside cutting was carried out to create building platforms. This produced a supply of fill material, mainly of residual weathered granitic rocks, that was used to reclaim onshore valleys and extend coastal sites. This material was also used for stabilisation work (Henry & Grace, 1948), construction of earth dams (Ruxton, 1957), and for mortar and aggregate (Redmond, 1936). Early reclamations were formed mainly by end-tipping directly onto the underlying marine deposits. In some instances, this practice led to displacements of the soft sediments and to the creation of mud-waves beneath the fill. Early reclamation also adopted balanced cutting and filling, creating additional development platforms on the borrow areas (Guilford, 1997). As Kowloon became more urbanized, fill had to be sought from farther afield, and land sources, usually in the New Territories, were identified.
Granular fill material from the seabed was first used to develop Kai Tak airfield (838903 820747 s-49). Kai Tak opened in 1924, but was extended in 1929 and 1931 partly using hydraulic fill from Victoria Harbour (Guilford, 1997). In the 1940s, the Causeway Bay Typhoon Shelter and Victoria Park reclamations (837572 816079 s-50) were both constructed using sand from Victoria Harbour off Hung Hom Bay
(Guilford, 1988).
Offshore fill was used in increasing quantities during the 1950s (Table
11.3). Between 1956 and 1959, Kai Tak runway was
realigned and extended seawards using 0.5 million cubic
metres (Mm3) of granular seabed material,
mostly obtained from Victoria Harbour
(Henry et al., 1961).
Subsequent major projects using marine sources of fill
included the construction of the Plover Cove Reservoir
main dam (842763
835942 s-51), and Tuen Mun New Town (814295
826300 s-52).
With the restricted availability of onshore fill sources,
the expanding scale and capital cost of proposed reclamations,
and the new generation of ocean-going trailing suction
hopper dredgers (Plate
11.16), offshore sources of sand became increasingly
attractive for both economic and environmental reasons.
Two major reclamation projects, the construction of
Container Terminal 6 and the Tin Shui Wai New Town,
were turning points in the history of seabed sand use
in Hong Kong. Container Terminal 6 at Kwai Chung was
completed using about 8.6 Mm3 of seabed sand
dredged from the area to the southwest of Tsing Yi
(Wragge-Morley, 1988).
Tin Shui Wai, a 400 hectare new town development site,
was created using 24 Mm3 of reclamation fill
obtained from off Black Point (Dutton,
1987). Since then, all major reclamations
in Hong Kong have used suction-dredged offshore sand
(Table
11.3). The largest reclamations are the Chek Lap
Kok airport platform, north of Lantau Island, the West
Kowloon Reclamation (834714
818874 s-53) (Plate
11.17), and the Penny's Bay in Lantau Island. Other
important developments include Tung Chung New Town (811823
816755 s-55), Chek Lap Kok Airport and related
infrastructure (809645
818288 s-56), Central and Wan Chai (835154
815636 s-57), Hung Hom Bay (836396
817936 s-58), and Tseung Kwan O (844768
819328 s-59).
