西南山区防洪水库泄洪过饱和总溶解气体预测及影响研究——以江家口水库为例

Prediction and Impact of Supersaturated Total Dissolved Gas in Flood Discharge of Flood Control Reservoirs in Southwest Mountain Areas:A Case Study in Jiangjiakou Reservoir

高坝泄洪会产生总溶解气体(Total Dissolved Gas,TDG)过饱和,将导致坝下鱼类患气泡病甚至死亡。然而,中国西南山区防洪水库泄洪期间过饱和TDG对鱼类影响尚不清楚,开展防洪水库泄洪过饱和TDG生成规律及其对坝下鱼类的影响研究具有重要的研究意义和理论价值。耦合纵向一维水动力模型、过饱和TDG生成模型、混合模型和纵向一维输移释放模型建立了高坝泄洪过饱和TDG影响评估框架。以西南山区防洪水库江家口水库为例,研究了采用表孔溢洪道宣泄2年一遇洪水、表孔溢洪道宣泄5年一遇洪水、底孔泄洪放空洞宣泄2年一遇洪水、底孔泄洪放空洞宣泄5年一遇洪水,4种泄洪情景过饱和TDG的生成和坝下输移释放特性,分析了过饱和TDG对坝下重点保护鱼类的影响。结果表明:4种情景产生的TDG饱和度分别为110.9%、115.4%、113.7%和119.9%;随着坝下TDG的输移耗散,除采用表孔溢洪道宣泄5年一遇洪水时坝址—坝下2.7 km河段和采用底孔泄洪放空洞宣泄5年一遇洪水时候坝址—通江汇口河段外,各情景各河段的TDG浓度均低于115%;所有泄洪情景均不会对鲢鱼产生不利影响;坝下河段水深均满足岩原鲤的补偿水深,在其利用补偿水深后,岩原鲤不会受到过饱和TDG的影响。研究成果可为高坝泄洪对坝下水生态影响的评估提供技术支撑,可帮助水库管理者制定定点修复的减缓措施。

The supersaturated total dissolved gas(TDG)can be generated by high dam flood discharge,which will cause the downstream fish to get gas bubble disease and even die.However,the impact of supersaturated TDG on fish during flood discharge in flood control reservoirs in mountainous areas of Southwest China remains unclear.It is of great research significance and theoretical value to study the formation law of supersaturated TDG during flood discharge of flood control reservoir and its influence on fish resources in the downstream water.This paper develops an impact assessment framework of supersaturated TDG during high dam flood discharge by coupling the longitudinal one-dimensional hydrodynamic model,the supersaturated TDG generation model,the hybrid model,and the longitudinal one-dimensional supersaturated TDG transportation and dissipation model.The framework is applied in Jiangjiakou Reservoir in southwest mountain areas,which is a typical high dam,to explore the TDG generation levels and the characteristics of supersaturated TDG transportation and dissipation under the dam under four typical flood discharge scenarios.The four scenarios are using the surface spillway to discharge the flood once in two years,using the surface spillway to discharge the flood once every five years,using the bottom outlet discharge cavity to discharge the flood once every two years,and using the bottom outlet discharge cavity to discharge the flood once every five years.Based on the results,this paper analyzes the impact of supersaturated TDG on the key protected fish downstream of the dam.The results show that the TDG saturations of the four scenarios are 110.9%,115.4%,113.7%,and 119.9%respectively.With the transportation and dissipation of TDG under the dam,the TDG concentration of each river section under each condition is lower than 115%,except the river reach between Jiangjiakou dam site and river section downstream of the dam with a distance of 2.7 km(the surface spillway to discharge the flood once in five years)and the river reach between dam site and Tongjiang river confluence(the bottom outlet discharge cavity to discharge the flood once every five years);②In all four flood discharge scenarios,supersaturated TDG will not have adverse effects on the silver carp;and③the hydrodynamics shows that the water depths of the river reaches downstream of dam meet the compensation water depth for Rock carp under all scenarios,and this species will not be affected by supersaturated TDG after using the compensation water depth.The research results provide technical support for the assessment of the impact of high dam flood discharge on the water ecology under the dam,which can help reservoir managers make mitigation measures for fixed-point restoration.