第1个回答 2010-09-24
Urbanization on water environment and the comprehensive improvement of water environment
Abstract: city of major impact on water environment were included in two areas: urban precipitation, urban construction of the rainwater runoff and water quality. In order to achieve comprehensive improvement of water environment, need to improve the water environment from the construction of infrastructure, and reasonable measures to control rainwater runoff, sewage and rainwater to carry out resource utilization, and give full play the role of water information, and strengthen environmental management regulations and policies of water so taken into account. And briefly introduced the Shanghai Suzhou Creek Rehabilitation Project Overview 1.
Keywords: City of Water Environment Comprehensive Treatment
1 Introduction
In urban development, urban infrastructure facilities, mass transportation system, developed to increase trade and industrial production, to stimulate the concentration of population change in the city's land use, such as the removal of trees, or leveling , the construction of houses, streets, river training and the construction and improvement of drainage networks, etc., resulting in natural fields, forests, rivers disappear, and a large number of pollution. One must preserve and restore urban ecosystems, the establishment of new material and energy flow system to ensure balance. The development of urbanization and degree of direct and indirect impact on water environment in urban areas, the resulting urban storm and flood control and water pollution control. Building and improving water environment governance infrastructure and scientific management, will create a modern city with a good living environment, guarantee the necessary conditions for sustainable development. To this end, on the comprehensive improvement of urban water environment.
2 Urbanization on Flood Runoff
2.1 City of precipitation
Growing size of cities, to a certain degree, changed the local climate conditions in urban areas, has further affected the city's rainfall conditions. In urban construction, change it on the surface radiation balance changes, changes in aerodynamic roughness affected the air campaign. Industrial and civil heating, cooling and motor vehicles increased by the heat in the atmosphere, and the burning of the vapor with a variety of chemical substances into the atmosphere. Buildings can cause mechanical turbulence, the city as a heat source also leads to thermal turbulence. Therefore the urban construction of air movement can produce a considerable effect. In general, strong winds weaken and the breeze in the urban areas could be strengthened, the city and its suburbs when compared with small or without wind. The city over the formation of condensation nuclei, thermal turbulence and mechanical turbulence can affect the local cloudiness and rainfall [1] .
1984-1988, the Shanghai hydrological station in Shanghai urban districts (not including Baoshan, Minhang District) 149 km 2 within the set of 13 points and the original distribution of rainfall in the suburban counties 55 rainfall stations parallel observation of urbanization on Shanghai area extent and scope of rain. The study conclusion [2] : (1) the rainfall is greater than the urban outskirts of rainfall, average rainfall is 6%; (2) under the city and its suburbs wind precipitation intensity than large ; (3) The clear trend of spatial and temporal distribution of precipitation, precipitation in the urban area decreases as the center to outside; (4) different order of magnitude of urbanization on precipitation occurrence frequency of rain days has an impact: City of rain days after the storm will increase, due to heavy rain, heavy rain, the effects of urbanization is relatively weak, when rainfall levels reached after the storm, no further increase in the urban rain day.
2.2 city construction
With urbanization, trees, crops, lawns, and gradually reduce the area, industrial park, commercial and residential area on the rise. Urbanization is also a considerable part of the basin (such as small rivers, lakes and wetlands) as replaced by impervious surface, reducing the water space. As the amount of impervious surface infiltration close to zero, so that runoff increases, making water much faster convergence, thus accelerating the timing of peak emergence. Infiltration area decreases, the corresponding decrease of groundwater recharge, stream base flow in dry season will be reduced accordingly.
Drainage System, such as the placing of road ditches, dense water pipe network and flood discharge trench so, increase the hydraulic efficiency of convergence. The city was the natural river straightening, dredging and remediation to increase the river channel flow, resulting in increased runoff and peak flow.
Example, Emei Mountain, Chengdu, Sichuan Emei Boryeong Quarter experimental stations in small watershed runoff rainwater observation point, the catchment area of 1.43 km 2 . 1964, the process of urbanization on storm runoff impact here, and now the whole drainage area of impervious area has reached more than 25%. Increased peak flow, peak emergence time in advance of urbanization on storm runoff characteristics.
In addition, the majority of the urban form in the plains or the mountains along the Yangtze River (river) cross. Along the (river) in the city, the urban ground level below the river (River) in the flood, it will be the threat of river flood; the city along the river, except by the river flood threats, but also by the threat of flash floods; in foot of the mountain slopes or the factories and towns mainly by the threat of mountain torrents.
Increased rainwater runoff, may make existing drainage ditches, drains, culverts, rivers, etc. over the water capacity was inadequate, resulting in downstream flooding in the city, causing traffic disruption, underpasses flooded, houses and property damage and losses.
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