THE ENVIRONMENT
interglacial periods, such as at the present time, the global sea level rose to its present level and higher, and marine sediments were deposited.
A description of the onshore and offshore geology of Hong Kong can be found in a series of 15 geological maps published at a scale of 1:20 000 and six memoirs produced by the Hong Kong Geological Survey, a part of the Geotechnical Engineering Office.
Hydrography and Oceanography
Hong Kong's waters are characterised by the interaction of oceanic and estuarine water masses which vary in relative effect throughout the year. The variable freshwater discharge from the Pearl River has a marked influence on Hong Kong
waters.
During the summer, an oceanic flow from the south-west to the north-east brings. the warm, high-salinity water of the Hainan Current into Hong Kong waters. This interacts with fresh water from the Pearl River and divides Hong Kong into three distinct zones. In the west, where the fresh water influence is greatest, the environment is estuarine and the water is brackish. In the east, the water is mainly oceanic with relatively minor dilution from rainfall and runoff from streams. The limits of the central transitional zone vary depending upon the relative influence of Pearl River water and marine currents.
During the winter dry season, the Kuroshio oceanic current brings warm water of high salinity from the Pacific through the Luzon Strait. The fresh water discharge of the Pearl River is much lower than in the summer and salinity is more uniform across Hong Kong. The coastal Taiwan current also brings cold water from the north-east down the South China coast affecting inshore waters.
The normal tidal range in Hong Kong waters is between one and two metres, depending on the relative influence of the moon and sun. The tidal pattern is complex due to the relative effects of the diurnal and semi-diurnal components. The basic pattern during flood tides is for oceanic water to flow north into Mirs Bay and west through Lei Yue Mun into Victoria Harbour and through Kap Shui Mun and the Ma Wan Channel. This flow is reversed during the ebb tide. Maximum tidal currents generally range from 0.5 to 1.5 knots, peaking at up to five knots in narrow channels.
Meteorological Services
Hong Kong Observatory
The Hong Kong Observatory was established in 1883, mainly to provide scientific information for the safe navigation of ships. Since then, it has evolved in line with community needs providing services in and studies on weather forecasting, hydrometeorology, climatology, physical oceanography, aviation and marine meteorology, and radiation monitoring and assessment. The Observatory also operates the official time standard for Hong Kong, provides basic astronomical information and maintains a seismological monitoring network.
The Central Forecasting Office at the Observatory's headquarters is responsible for issuing weather forecasts and warnings of hazardous weather. Marine weather forecasts cover the South China Sea and the East China Sea. Forecasts and advice are
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