白石水库饮用水水源保护区划分合理性研究

Rationality evaluation of the delineation of drinking water source protection areas in the Baishi Reservoir

饮用水水源地水环境安全事关人民生命健康,是生态环保工作的重中之重。饮用水水源地保护区划分以类比经验法为主,无法反映保护区内水质指标的时空分布及达标情况。利用EFDC建立白石水库垂向平均的二维模型,模拟其水动力和水环境变化过程,对水库水龄、污染物迁移衰减规律进行分析,评价类比经验法划定的饮用水水源保护区的合理性。通过验证水位库容曲线,丰、平、枯3种典型年水位对应曲线的相对均方根误差均小于0.1,纳什系数均大于0.85,水质模拟曲线模拟趋势与实测数据一致,模型可靠。研究发现,在丰、平、枯3种典型年条件下坝前平均水龄分别为304.4,656.4和673.2 d,水库水力交换周期长;在丰、平、枯3种水动力条件及设计污染物边界条件下模拟污染物衰减过程,结果表明除丰水年取水口处氨氮超标外,其余条件下取水口水质均可达标;以116 m水位(库首)对应高程线以下全部水域为一级保护区的划分范围可以满足取水口水质要求,验证了上述策略在保护区划分上的合理性。

The safety of the water environment in drinking water source areas is of vital importance to the lives and health of people,and is the top priority of ecological protection work.Delineations of drinking water source areas are mainly based on the analogue-empirical method,which cannot reflect the spatial and temporal distributions,or the compliance of water quality indicators in protection areas.In the study,the Environmental Fluid Dynamics Code(EFDC)was used to establish a two-dimensional vertical average model of the Baishi Reservoir.Its hydrodynamic and water environment change processes were simulated.The water age,eutrophication,and law of pollutant migration and attenuation were then analyzed to evaluate the rationality of the drinking water source protection areas as delineated by the analogue-empirical method.Through the verification of water level and storage capacity curves,and the verification of three typical annual water-level corresponding curves,RRE<0.1 and CNSE>0.85.The simulation trend of the water quality simulation curve is consistent with the measured data,and the model is reliable.It is found that the average water ages in front of the dam are 304.4 d,656.4 d,and 673.2 d,under the three typical annual conditions of high flow year,median flow year,and low flow year,respectively.The reservoir has long hydraulic exchange periods and is prone to eutrophication.The attenuation process of pollutants is simulated under the above three hydrodynamic conditions and the boundary conditions of the designed pollutants.The results demonstrate that the water quality of the water inlet is generally up to the standard,although the ammonia nitrogen in the high flow year exceeds the standard in the water inlet.The simulation results also show that the delineations of all water areas below the 116 m water level as the firstgrade protection areas can meet the water quality requirements of the water intake.The delineation of drinking water source protection areas is therefore reasonable.