Prediction Of The Surface-environmental Changes In The Tianjin Binhai New Area And Its Surrounding Region In The Middle Of The 21st Century

Fellowing economic booming in both the Pearl River Delta and the Yangtze River Delta in the past couple of decades, now Tianjin Binhai New Area, TBNA, being integrated into the national strategic development, has been facing an unprecedented opportunity, which enbles the TBNA for the third economic booming pole in China in the coming years.Nevertheless, TBNA coastal lowland is expriencing sea-level rise which is even greater and faster than ever before. The surficial elevation of this area is relatively lower. The modern sedimentation rate, measured by ²¹⁰Pb and ¹³⁷Cs dating, is about a mm/yr level for the coastal lowland, which totally contributed vertical accretion of 0.0642m in the past half a century. This accumulation is infinitesimal if comparing with the rate of land subsidence. Because the latter is a cm/yr level in average. All the aspects have caused environmental deterioration in the area.Therefore, it has major significance for making prediction about the surfacice-environmental changes in the near future in order to avoid and/or minimize the deterioration mentioned above.Particularly, the author makes quantatitive forecast for the extreme-water-level disaster during storm surges, adding on both the ground subsiding and sea level rising, as an alarm bell to avoid unnecessary pitfalls (Song Meiyu et al., 2008).Prediction trend (T) of the surface-environmental changes in the middle of the 21st Century can use following expression: T=(A+B)-(C+D), among which A is elevation, B is thickness of modern accretion, C is subsidence while D is projections of sea level change in 2050.The author uses three categories of ground subsiding rates: 7.1mm/yr (before human impacts), 15mm/yr (well-controlling of the subsiding in the area after human activities) and 25mm/yr (average rate in the studying area), and three categories of sea level rise projection in 2050: 0.2m (the best estimate of IPCC), 0.3m (the lowerest estimate of the State Oceanogrphic Administration) and 0.6m (the highest estimate of the State Oceanogrphic Administration).With such scenarios, the author forecasts the surface-environmental variation of the coastal lowland as nine different trends. The results demonstrate, in general, that about half a coastal lowland in the TBNA will be sank below the msl (mean sea level) by 2050. In extreme case, the area beneath the msl will be even ettended more. For this reason, increased salinization and paludification (swamping process) will have harmful impacts on industry and agriculture, esp. for the ecological maintaining, ie. the harmonic and sustainable development. This is why ground subsidence control by minimizing of groundwater abstract must be very important.Moreover, this thesis forecasts the disaster driven by extreme high water. According to the available statistic data the existing 1-in-50-year extreme-water-level (ewl) is +4.092m in TBNA. Following the 0.2m increasing of the projected sea level rise, Bengal Bay, London and Hamburger and the other places in the world will have 0.5m extra high water in 2050. Using such a result, the author forecasts the local ewl will be increased to +4.792m (4.092m+ 0.2m+0.5m) in TBNA in 2050.If 0.3m increasing of the projected sea-level-rise exists, the ewl will be as high as +4.892m (4.092m+0.3m+0.5m) at least while the 0.6m increase of the projected sea level rise will increase the ewl to +5.192m (4.092m+0.6m+0.5m) at least.Nowadays the elevation of coastal levee is discordant. The lowest is in the Trade Free area where the elevation is only +2.332m which is barely 1m higher than the MHWST. Elevation in the Nanjiang District is ca. +2.732m which is also lower. The highest elevation is +4.632m located between the Nanjiang District and Tianjin Binhai Bath leisure centre. In the sector, where both the lowest as the highest levee as well locate, has the subsiding rate ca. 18.5mm/yr and it will be sunk for ca. 0.83m (0.0185m/yr×45yr from the starting year of 2007). Following this subsidence, the lowest coastal levee in the Trade Free area will be at +1.502m and adding vertical accretion of 0.0642m, finally the top of the levee here will be +1.5662m. If sea level rise is 0.2m, it calculates that the predicted ewl will be 3.2258m (4.792m-1.5662m) higher than the subsiding top of levee in 2050. The highest levee will be sunk to +3.8662m (4.632m+0.0642m-0.83m), and the predicted ewl will be 0.9258m higher than the subsiding top of levee in 2050.From the aforementioned descriptions, it can be seen that the elevation of whole coastal levee is low, even the highest sector-can not compete against the 1-in-50-year ewl. This scenario depicts an increasing threat of the strengthening storm spilling. This future will be deteriorated by a number of uncertain factors such as wave overlying (the average wave height is 0.6m in TBNA), the funnel effect (+1 cm/km) and the extreme sea level rise (0.3m or 0.6m, respectively), etc.