城镇化人为扰动下垫面类型影响水源涵养功能的评价

Evaluation on impact of artificial disturbed underlying surfaces on water retention function during urbanization process

城镇化引起的各种人为扰动地貌单元的水源涵养功能较原地貌明显降低是造成城市水土流失的主要原因,在降雨和排水管网设计能力一定条件下,也是加剧城市内涝的主要原因。该文采用野外调查、室内物理分析及AHP(analytic hierarchy process)层次分析综合评价法,系统地分析了各种人为地貌单元的物质组成和持水性能变化并综合评价了其对原地貌水源涵养功能的影响特征。结果表明:1)各种扰动地貌单元>2 mm土体颗粒质量分数在45%以上,原地貌<2 mm土壤颗粒质量分数在92%以上;扰动地貌不均匀系数和曲率系数分别在11.05~41.30和0.32~3.15之间变化,其中不均匀系数较原地貌减小了4.51%~80.27%;各种扰动地貌单元土壤容重为施工便道(1.74 g/cm3)>边坡绿化带(1.54 g/cm3)>1 a弃渣堆积体(1.48 g/cm3)>2 a弃渣堆积体(1.34 g/cm3)>3 a弃渣堆积体(1.31 g/cm3),比坡耕地依次增加33.85%、18.46%、13.85%、3.08%和0.77%;扰动地貌的土壤总孔隙度、土壤田间持水量和饱和含水量则表现出相反趋势。2)人为扰动地貌单元土壤入渗性能总体小于原地貌单元,而原地貌土壤稳定入渗率则在2.83~6.22 mm/min之间变化;当项目区林地转化为新弃渣堆积体时对降雨和城市洪水动态调节功能影响最大,转化为施工便道时影响最小;人为扰动地貌单元土壤水库总库容、兴利库容和滞洪库容总体低于原地貌,当项目区草地转化为施工便道时对土壤持水能力及调蓄地表径流能力危害最大。3)各种扰动地貌单元水源涵养能力明显小于原地貌单元,以施工便道(0.421)最差,林地最好(0.651);在城镇化过程中应重视城镇水面、林草地的空间分布及占地面积,对短期松散堆积体也最好进行临时绿化措施。4)加强对扰动地貌物质组成、大孔隙结构和降雨-径流-入渗连续性定位研究,同时关注各扰动地貌在不同压实条件下土壤水库蓄水性能对项目区雨洪过程线和排水系统的影响。研究结果可为城市水土保持生态服务功能恢复、城市绿化带建设和洪水内涝缓解提供科学依据。

Great decrease in water retention function of various artificial disturbed landform units （DLU） caused by urbanization activities, when compared with original landform units （OLU）, is the main reason and factor that not only cause urban water and soil loss but also aggravate urban waterlogging under the certain rainfall and special designed drainage network capability. Field investigations, physical laboratory analyses and analytic hierarchy process composite method were performed comprehensively to analyze the impacts of various DLUs on water retention function of OLU. Results indicated that： 1） 〉2mm particle content for various DLU was over 45%, and 〈2 mm particle content of OLU was more than 92%; natural repose angle of soil-sock mixture （34°-38°） in DLU were all higher than OLU; uniformity coefficient and curvature coefficient changed between 11.05-41.30 and 0.32-3.15, in which uniformity coefficient decreased by 4.51%-80.27% than OLU. 2） The soil bulk density of various DLU showed the order as construction road （CR, 1.74 g/cm^3） 〉slope greening belt （SGB, 1.54 g/cm^3） 〉 1 year disturbed soil accumulation （DSA1, 1.48g/cm^3） 〉 2 year disturbed soil accumulation （DSA2, 1.34 g/cm^3） 〉3 year disturbed soil accumulation （DSA3, 1.31 g/cm^3）, which increased by 33.85%, 18.46%, 13.85%, 3.08%, 0.77%, respectively, compared with sloping land; and the soil total porosity, field capacity and saturated water content presented the contrary trends. 3） Soil infiltration capacity of various DLU were lower than that of OLU, the soil stable infiltration rate presenting the order as DSA3 （2.89 mm/min） 〉 SGB （2.65 mm/min） 〉 DSA2 （1.89 mm/min） 〉 DSA1 （1.64 mm/min） 〉 CR （0.45 mm/min）, at same time, the soil stable infiltration rate of OLU ranged between 2.83 and 6.22 mm/min; the conversion from forest to new-DSA had greatest impact on regulating function for rainfall and urban flood, while conversion to CR was the lowest. 4） The soil total reservoir storage, usable storage and flood control storage in various DLU were lower than that in OLU, soil total reservoir storage showing the order as DSA3 〉 DSA2 〉 DSA1 〉 SGB 〉 CR, which presented decreases of 1.08%, 2.27%, 5.63%, 15.41% and 21.96%, respectively, compared with sloping land （453.70 t/hm2）; the conversion process from grass to CR caused the greatest damage to storing water and regulating the overland flow. 5） The water retention functions in DLU were all obviously weaker than that in OLU, and CR was weakest （0.421） while NF was strongest （0.651）, the water retention function was influenced by factors such as soil depth, particle-size distribution, soil porosity, soil organic matter content, soil bulk density, and soil permeability, so more attentions should be paid to urban surface water, forest and grassland occupied area and its spatial distribution, short-term disturbed soil accumulation should also be conducted by temporary greening measures at the same time during urbanization process. These results could provide scientific basis for the function recovering of urban soil and water conservation ecological services, which also help for constructing urban green belts and alleviating flood waterlogging during the urbanization construction process.