基于OTIS模型的巢湖十五里河源头段参数灵敏性分析

OTIS Model-Based Parameter Sensitivity Analysis for Headwater Stream in the Shiwulihe River,Chaohu Lake Basin

为探究城市地区渠道化源头河段水环境模型参数灵敏性,以巢湖流域十五里河源头段为对象,选择氯化钠(NaCl)为保守型示踪剂,采用瞬时投加方式,开展现场示踪试验.在此基础上,利用OTIS模型(小河流水体溶质迁移扩散模型)模拟溶质(示踪剂)输移扩散规律,并以均方误差(RMSE)为目标函数,就±10%和±20%等参数多种变幅情景,采用扰动分析方法对A(河道过水断面面积)、As(暂态存储区断面面积)、α(交换系数)及D(扩散系数)等参数开展局部灵敏性分析.结果表明:在十五里河源头段溶质迁移特征模拟方面,OTIS模型具有很好的适用性;尽管不同河段各参数的灵敏性排序存在一定的变化性,但总体趋势较为明显,表现为A>α>As>D,这与欧美国家空间尺度相近的一些小河流水体基本相同;由于α和As的灵敏性超过D,表明在渠道化的城市小河流源头段,考虑暂态存储对于溶质输移扩散的影响十分必要.研究结果进一步验证了扰动分析方法对于OTIS模型参数灵敏性分析的有效性.

Stream hydrodynamic properties, in particular transient storage, are potential regulators of solute uptake. Little work has been done to assess parameter sensitivity of transient storage modeling over multiple spatial scales in headwater streams. The objective of the present study is to investigate characteristics of parameter sensitivity of water environmental models in the channeled headwater stream in urban areas. The headwater stream of Shiwuli River in Hefei City, Chaohu Lake Basin, was chosen as the study object. A slug field tracer experiment, in which NaC1 was used as a conservative tracer, was conducted in the stream reach over combinations of four consecutive sub-reaches （63, 82, 120 and 92 m below injection point）. OTIS （one-dimensional transport with inflow and storage） model was used for the simulation of solute transport by view of the OTIS model code and OTIS-P optimization procedure. Each simulated stream solute concentration breakthrough curve （BTC） accurately fit to the observations. Perturbation, in which the root mean square error （RMSE） was taken as the objective function, was employed to analyze the sensitivity of the following parameters： main channel cross-sectional area A, storage zone cross-sectional area A,, storage zone exchange coefficient α and dispersion coefficient D, with a variation of ±10% and ± 20%. Results showed that the OTIS model was useful for characterizing the in-stream solute transport in the headwater of Shiwuli River. Although there was some variability in the degree of parameter sensitivity among the later three consecutive sub-reaches, a total remarkable regularity was found in the headwater stream, namely A 〉 α 〉 As 〉 D, which formed the same regular pattern as many other streams with the similar spatial scale in European and American countries. Due to the sensitivities of a and AI being higher than that of D, the effects of transient storage on solute transport should be taken into consideration in the channeled headwater stream in urban area. In general, the results further testified to the effectiveness of perturbation method utilized above on sensitivity analysis of parameters in OTIS model.