景观格局汇水单元法与城区水量水质模拟研究

Simulation method of water quantity and quality in urban built-up areas based on landscape pattern

景观多样性有助于提高城市韧性,但其可能带来的透水斑块破碎化和廊道连通度的改变,会影响城区非点源污染的产生输移特性。传统对非点源污染的定量评估忽略了汇水单元内部景观格局(形状、比例和空间配置)对物质输移的影响,是导致模拟精度偏低的主要原因。针对这一问题,本研究结合遥感影像和城市景观格局分布特征,构建了基于景观格局的汇水单元划分方法(景观格局法)。采用SWMM模型,以巢湖一级支流十五里河为对象展开研究,结果表明:(1)基于实测数据进行验证,采用景观格局法模拟各项指标(水量、COD、TP和NH 3-N)的纳什效率系数(NSE)均大于0.7,结果可靠;(2)与传统方法(泰森多边形划分汇水单元)相比,水量模拟精度(以NSE计)提高8%,水质模拟精度提高6%;(3)与泰森多边形法相比,景观格局法计算的入河总水量和污染总负荷较低,且污染物浓度峰值滞后;(4)景观格局法通过改变汇水单元之间的水力联系,模拟出污染物冲刷减弱,初期雨水冲刷效应降低,且随着重现期的加大,降低初期雨水冲刷强度的效果越明显,表明一定程度上景观类型多样化有助于缓解瞬时高强度污染影响。本研究构建的方法充分考虑了城市斑块内部的景观格局分布特征和水力联系,可为城区面源污染输出控制提供新的评估手段。

Landscape diversity helps to improve urban resilience,but the fragmentation of permeable patches and the change of corridor connectivity caused by landscape diversity will affect the generation and transport characteristics of non-point source pollution in urban areas.The traditional quantitative assessment of non-point source pollution neglects the influence of landscape pattern(shape,proportion and spatial configuration)on material transport in catchment unit,which is the main reason for the low simulation accuracy.To solve this problem,this study combined remote sensing image and urban landscape pattern distribution characteristics,and built a landscape pattern based catchment unit division method(landscape pattern method).SWMM model was used to study Shwuli River,a first-level tributaries of the Chaohu Lake.The results show that:(1)Based on the measured data,the NSE of each index(water volume,COD,TP and NH 3-N)simulated by landscape pattern method is greater than 0.7,and the results are reliable;(2)Compared with the traditional method(Tyson polygon division of catchment units),the precision of water quantity simulation(NSE)increased by 8%,and the precision of water quality simulation increased by 6%;(3)Compared with the Tyson polygon method,the landscape pattern method weakened the total water flow into the river and the total pollution load,and had a lagging effect on the peak pollutant concentration;(4)By changing the hydraulic connection between catchment units,the landscape pattern method weakened the pollutant scour process,thus reducing the initial rain scour effect.Moreover,with the increase of the recurrence period,the effect of reducing the initial rain scour intensity becomes more obvious,indicating that to a certain extent,the diversification of landscape types can help to alleviate the impact of instantaneous high-intensity pollution.The method constructed in this study fully considers the landscape pattern distribution characteristics and hydraulic linkages within urban patches,which can provide a new assessment method for urban non-point source pollution output control.