向家坝水库水温时空特征及其成因分析

水温是水环境评价的重要因子之一,其对水生态系统中的物理、化学和生物过程起着重要作用。为了分析向家坝水库运行期内的水温分布特征及其成因,本文建立CE-QUAL-W2立面二维水温模型,并基于2014年野外原位监测水温数据对模型可靠性进行了验证,应用其对水温分布进行数值模拟。研究发现向家坝水库水温存在季节性垂向分层,4~6月中上层水体(水深0~60 m)受入流水温和气温回升影响迅速升温,表底温差达10℃,垂向分层加剧;7、8月水库泄洪加快了库区水体交换,底层水温迅速升高,中间等温层水体厚度增加,表底温差减小在2℃内,9月以后表底温差进一步缩小,垂向水温分层逐渐消失。通过分析发现:气象要素、入流水温、电站取水口高程、泄洪方式成为影响向家坝水温分布的主要因素。入流水温的变化只影响水库水温波动范围,对其垂向分层结构影响较低;表层水温受气象条件影响显著;取水口高程和泄洪方式决定了水温的垂向结构。

TEMPORAL AND SPATIAL CHARACTERISTICS OF WATER TEMPERATURE IN XIANGJIABA RESERVOIR

Water temperature is one of the most important factors in the evaluation of water environment,which plays an important role in the physical,chemical and biological processes.In order to analyze the water temperature distribution in the Xiangjiaba Reservoir,the longitudinal/vertical two-dimensional water temperature model with CE-QUAL-W2 was constructed.The water temperature structure in the Xiangjiaba Reservoir was simulated by the model with the monitoring data.The results showed that seasonal stratification was present in the Xiangjiaba Reservoir,the upper middle water (60 m above) was heated quickly by the warming-up inflow water and the air temperature from April to June,followed by increasing temperature difference between surface and bottom water.The temperature difference reached 10℃ at the end of June,and the vertical stratification became more severe.As the flood discharge in July and August increased,the bottom temperature in the Xiangjiaba Reservoir rose rapidly and the middle isothermal layer increased as well,and the water temperature difference between the surface and the bottom decreased to 2℃.The main factors affecting the temperature distribution in the Xiangjiaba reservoir included inflow water temperature,meteorological,intake elevation and discharging patterns,which affected the whole aptitude,the surface water temperature and vertical temperature stratification structure,respectively.