基于GIS的平面二维水质模型构建及其对广域平原河网水系数值模拟的适用性分析

Construction of two-dimensional water quality model based on GIS and its applicability of wide-area plain river system

为探究大范围平原河网地区众多圩区“大包围”背景下河网水质对内外源污染负荷及初级生产的时空响应分异特征,阐明不同泵闸调控模式对河网水质的改善效果,基于泛滥解析模型和水生态模型构建了苏州市吴江区广域范围的平面二维水动力-水质模型.同时,基于平面GIS地图,将吴江全域切分为2562×2487个(20 m×20 m)作为计算对象的网格来表达吴江区域范围内所有河网与湖荡的空间分布,并通过将平面二维排列数据转换为一维排列的空间网格信息来实现对水动力与水质的数值模拟.通过验证得到基于对水深及流速模拟的水位及流量值与实测值的吻合程度较高,闸泵排水对于整个区域水量的影响较大.通过分析2019年7月的模拟值与实测值之间的差异,比较不同模拟情境下的模型拟合程度,得到在闸泵调控模式未启动且不考虑生产消费项的情境下,外河水系模拟值与实测值最为接近;在闸泵启动所有内河与外河联通情境下,干流模拟情况好于支流;引入生产消费项后,整体模拟值有增大趋势,表明模拟结果对来自内河的藻类生产有实时响应,但闸泵开启调控的情境下,河网水系的水质呈现改善趋势,表明水体流动的稀释效果超过了河流水体中来自于浮游藻类内部生产的贡献.各项模拟结果均可实现GIS的可视化.基于对不同模拟值结果的统计学分析,模型的精确性与适配性得到了验证,可为今后的模型改进和应用效率提升提供数据支持.

This study examines the spatiotemporal characteristics of river network water quality,internal and external pollution loads,and primary production under the"large encirclement"conditions.Using a flood analysis model and a water ecological model,a plane two-dimensional hydrodynamic-water quality model was constructed to clarify the effect of different pump gate regulation modes on the water quality of the river network.Simultaneously,based on the planar GIS map,the entire Wujiang region(2562 m×2487 m)is divided into(20 m×20 m)grids as calculation objects to reflect the spatial distribution of all river networks and lakes in the Wujiang area.Numerical simulation of hydrodynamic water and water quality is well to the measured value,and the pump's drainage has a large impact on the amount of water in the entire region,based on the verification.Analyzing the discrepancy between the simulated and measured values in July 2019,the external river system's simulation value is close to the observed value;the simulation scenario is better than the tributaries.The overall value of the simulation shows a real-time response to algal production in the Inland River.However,under the situation of the pump opening and regulation,the water quality of the river network water system shows an improvement trend,indicating that the dilution effect of the water flow exceeds the contribution from the internal production of planktonic algae in the river water body.All the simulation results can achieve the visualization of GIS.The accuracy and flexibility of the model are validated based on statistical analysis of the results of different simulated values,which gives data support for future model improvement and application efficiency enhancement.