永定河北京段生态需水量研究

Study on Environmental Flow in Beijing Section of Yongding River

永定河北京段是人工重建河道,人工重建河道的生态需水量估算是河道修复研究中的重要课题。永定河北京段生态需水主要包括生态基流,人工重建河道的河湖蒸散发和渗漏量以及河滨带植被的生态补水量等。根据研究河段的不同要求,本文概化了天然河道,设计了人工河道断面形状和河床特征,较为清晰地划分了消耗性生态需水和非消耗性生态需水的范畴。在确定各种生态需水目标前提下,计算不同河段的消耗性生态需水和非消耗性生态需水量。结果显示,北京市最低到最优生态的目标下,永定河山峡段和平原河段的生态基流需水量为0.79~4.75×10~8 m^3;平原城市段和平原郊野段的河湖和河滨带植被用水0.28~0.92×10~8 m^3,其中河湖蒸发渗漏用水0.34~0.59×10~8 m^3,河滨带植被用水0.33×10~8 m^3。研究显示,人工河道的生态基流与河道断面、河道粗糙度、纵坡比及河道防渗关系密切。为满足生态修复目标,在水量受到限制的情况下,可以通过调整人工河道的断面、粗糙度、水力坡度和河道渗透性来达到相应的生态需水量。

The Beijing section of Yongding River is an artificial rebuilt river. The environment flow study is of great significance on ecology and environment rebuilt in a polluted watershed and river course. The principle of environment flow in an artificial river is studied in this paper. First of all,the ecological goal theory and specific ecological objectives are studied for different purposes. This paper indicates that environmental flow in an artificial rebuilt river includes ecological base flow,water evaporation and infiltration in the artificial river and lakes,and water demand of the riverside plants. In this research,the natural river course is abstracted and generalized based on specific requirements of different sections of natural river course and artificial river bed; the artificial river cross-section is designed subsequently. Furthermore,this paper has divided the content of consumptive and non-consumptive environmental flow. Based on the ecological targets decided,research result of the consumptive and non-consumptive environmental flow is calculated in the case study as follows： 1） the ecological base flow of the gorges section and the plain section is 0.79~4.75×10~8 m^3 under the basis of the lowest to best target; normally the main course flow is included only in the low objective and some tributary environment flow could be also included in the higher objective; 2） the consumptive water demand of the urban plain section and rural plain section is 2.81~9.17×10~7 m^3 under different ecological targets,among which the water demand for evaporation and infiltration of the artificial river and lake is 3.40~5.87×10~7 m^3; the water demand for riverside plant is 3.30×10~7 m^3 for different ecological targets. The research indicates that the environmental flow of the artificial rebuilt river is related to the transect of the river,the roughness of the river course,the ratio of longitudinal slope,and the seepage prevention works in the course. In the case of water limitation,the above factors could be adjusted to regulate environmental flow for proper ecological targets.