| The Gansu-section of the Bailong River is an important ecological barrier of the upper Yangtze River area.The intense neotectonic activity,frequent earthquakes,high and steep mountains,deeply-cut valleys,concentrated rainfalls and storms and fragile geo-and eco-environments make the area one of the most severely affected areas by geological hazards in China.The severe geological hazards and fragile ecological environments lead to intense contradiction between human activities and land resources in the process of urbanization,forming a salient constraint on the geological environment bearing capacity.The town centers of Zhouqu and Tanchang,lying in the mid-section of the Bailong River,are two typical representatives of valley-type towns that are severely affected by geological hazards and fragile ecological environment.Recently,the accelerated rate of urbanization has accentuated the regional environmental issues leading to remarkable restrictions on ecological security and socio-economic development.In this regard,the assessment of the bearing capacity of geological environment is crucial in guiding hazard prevention and mitigation and securing ecological safety.However,the research on bearing capacity of geological environment is still in its infancy and presents itself with two key issues requiring immediate attention.Firstly,how different sub-systems interact to influence the bearing capacity of geological environment and how to quantify the contribution of different environmental factors on geological environment capacity.Secondly,the existing assessments are empirically semi-quantified separate evaluations.These evaluations have no observational data to validate the assessment results and lead to considerable uncertainty restricting the practical applicability of the results.Therefore,it is pivotal to establish a comprehensive assessing system using the latest technologies to support the planning in urban hazard prevention and reduction.This research aims at solving these issues and national demands mentioned above by studying the two typical areas,i.e.,Zhouqu and Tanchang.Using both one-fold and comprehensive assessment of geological environment bearing capacity,as well as statistic models,remote sensing and GIS etc.,the research establishes a parametric system and model for assessing the bearing capacity of geological environment and provides a zonation map of geological environment bearing capacity of the two sites.Based on the results,targeted suggestions for urban geological environment prevention and subduction are proposed.The conclusions of the study are below:(1)In light of the fragile ecological environment and the frequent geological hazards,the key environmental factors restricting urban construction based on “short plate” theory were analyzed.Assessments on regional hazard risk and ecological capacity were made.The risk assessment was conducted based on an AHP-based susceptibility assessment of geological hazards in combination with the socio-economic statistical indexed vulnerability.The result suggests that areas of excellent,good,fair and poor level in Zhouqu accounted for 58.57%,30.66%,5.84% and 4.93% respectively,while areas of excellent,good,fair and poor level in Tanchang accounted for 5.00%,76.66%,17.74%,5.80% respectively.Areas of excellent bearing capacity were mainly distributed in the low-level river terraces and the mid-high mountain ranges along the Bailong River.Areas of good bearing capacity were distributed in the deposition area of debris flow valleys and landslide bodies.Areas of fair bearing capacity were distributed along the Bailong River banks that are affected by the debris flows.The poor bearing capacity areas were distributed in ribbon-shape along the high-population-density areas.These areas were most affected by the geological hazards.To quantify the supply-demand balance between ecological and social factors,an assessment on the ecological capacity and ecological footprints was conducted.The result suggested that the magnitude of bearing capacity decreases sequentially from agricultural land,residential and factory land,forest land,grass land to water land.Spatially,the unit-area bearing capacity decreases gradually from the west to the east of the Zhouqu county center.For the Tanchang county center,the unit-area bearing capacity increases gradually from the northwest to the southeast.The ecological bearing capacity demonstrates a strong relationship between human activity and agricultural lands which is the main space for human activity.Accordingly,the intensity of human activity also influences the local ecological condition.Therefore,a sustainable human-land coupling model can play a vital role in establishing a stable ecological bearing capacity in a given area.The results of the study provide the bases for a comprehensive assessment of ecological bearing capacity,in addition to providing the support and guidance necessary for parameter selection in assessment of geological hazard risk and ecological bearing capacity.(2)The parameters associated with geological,ecological and social environments were selected based on the results of the two assessments.A comprehensive parametric system and model for assessment of geological environment bearing capacity using the statistical models of AHP and FL in combination with urban development was established.In the end,a zonation map of the geological environment bearing capacity for the study areas was produced.The zonation map was further validated using the ground deformation data from InSAR images.Generally,the geological environment bearing capacity is classified into four levels: excellent,good,fair and poor.The proportions of these areas classified as excellent,good,fair and poor in Zhouqu and Tanchan are 5: 6: 10: 6 and 6: 18: 19: 14 respectively.Further analysis of the impact of different parameters on geological environment bearing capacity suggested that in Zhouqu area,the geological hazards bear the largest impact on geological environment bearing capacity(accounting for 0.2470),and lithology,geological structure,earthquakes and geomorphic units pose a sequentially decreasing impact on the bearing capacity,accounting for 0.1716,0.1217,0.0792 and 0.0546 respectively.Similarly,in Tanchang,geological hazards hold the largest control on geological environment bearing capacity accounting for 0.2669,and the percentages of lithology,geomorphic units,geological structure and population density are 0.2035,0.0753,0.0568 and 0.0539 respectively.The areas of low geological environment bearing capacity are located in areas with high hazard risks.It is suggested that urbanization-associated activities should avoid these areas.(3)According to the assessment results,suggestions for urban construction and hazard prevention and reduction were proposed including distinct strategies for hazard prevention and mitigation for areas with different zonation codes.These suggestions are expected to provide key strategic support for improving the efficiency of hazard mitigation,resource utilization,and sustainable development.Specifically,for areas classified as excellent,management strategy should focus on hazard prevention.For areas classified as good,measurement strategy should focus on ecological measurement.For areas classified as medium,strategy should focus on controlling land utilization in combination with ecological recovery measurements.Lastly.for the areas classified as poor,comprehensive methods should be adopted to prevent and mitigate hazards.Besides these,suggestions for urban planning for the aim of hazard prevention and mitigation were also proposed.This study contributed to improve the methods for assessment of the bearing capacity of geological environment,maximizing the accuracy,operability and reliability of the assessment results.This is expected to promote the innovation of assessing system and methodology.Besides,the conclusions of the study can provide scientific grounds for the prevention and reduction of geological hazards along with the construction guidelines of urban area for the two typical urban centers.The study provides reproducible and propagable measurement strategies for geological hazard monitoring and early warning,engineering management,ecological restoration,land utilization,and urgent management.Therefore,the study provides a demonstration for the assessment of geological environment bearing capacity.The replicable study is expected to be applied to the other areas of the Bailong River and to many similar urban centers of China. |
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