关键词: 经济效果, 防护体系, 兰新线玉门段

Abstract: The railway in northwestern China most go through desert area, thus it is necessary to establish railway's protecting system. Resulted from over asking for protecting effect, the protecting system was becoming extended and with more facilities in the initial stage, which has formed heavy burden. How to constitute economic and rational protecting system is urgent. Against this problem, the paper studies the protecting effect, plant's growth and investment of the Gobi protecting system at Yumen section of Lanzhou Xinjiang railway. The railway's protecting system at this section consists of several belts including isolation belt, bare belt, wind break belt and sand preventing belt. At the southern side of the railway where wind sand activity is violent, there are 3 lines of barrier with 1.5-2 m height and 30 m interval, 3 successive forests with 30 m width and 60 m interval from the far to the close by the railway. At the northern side of the railway, there is a band of high forest with 35 m width. The space between the railway and the adjacent forest belt is 50 m. By investigating into the protecting period, sand accumulation, annual cost per kilometer, effect of reducing wind speed and economic result of different measures, the effect coefficient, the ratios of reducing wind speed, the height and the breast diameter of the tree as well as the cost are obtained. The effect coefficients are 2.15 under "2 barrier +1 forest", 1.70 under "single barrier", 1.37 under "depression+barrier", 1.22 under "1 barrier +1 forest" and 0.66 under "1 barrier +2 forest", which suggests that the more forest belts are, the lower effect is. The ratios of reducing wind speed after the first arbor-shrub belt, the second and the third high forests are 46%, 58% and 64% respectively, and 48% at railway's shoulder. These, to some extent, prove that the main factors influencing wind speed are the forest belt structure and the growing situation, while the protecting effect has less relation to do with belt's width and number. The annual average increases of forest's height and breast diameter under belt's widths of 10 m, 20 m, 25 m, 30 m and 35 m are 0.66, 0.56; 0.44, 0.44; 0.36, 0.35; 0.33; 0.30; 0.28, 0.27 in order. The corresponding annual costs are 0.6, 0.8,1.0, 1,3 and 1.7 ten thousands RMB Yuan. The results show that, within a certain range, the belt's width is in inverse proportion to economic effect.

Key words: Economic effect, Protecting system, Yumen section of Lanzhou Xinjiang railway