极端干旱下河口咸潮上溯对径流过程的响应(Ⅰ):特征与规律

Response to runoff variations of saltwater intrusion in an estuary (Ⅰ):characteristics and regularities

针对极端干旱下入海径流锐减导致的咸潮上溯加剧问题,从流量均值、变幅、高流量脉冲以及低流量特征等方面构建了反映入海径流变化过程特征的指标体系,分析了广东省东江河口的含氯度对入海径流过程变化的响应规律,讨论了极端持续干旱、水库压咸补淡水量不足的情况下流域层面多水源、精细化的压咸调控机制。结果表明:短时间内的高流量脉冲过程对压制咸潮具有明显的效果,在大潮期间当东江下游博罗站小时流量超过400 m^(3)/s时,河口含氯度显著下降并维持在较低水平。24 h内高脉冲流量次数达到4次以上或持续时间超过12 h,河口万江站的最大含氯度减小到250 mg/L以下,可达到生活饮用水水源的取水标准。此外,除了上游水库集中下泄的压咸流量外,水库-河口区间的降雨产流会增加入海流量,对抑制咸潮上溯有一定的增强作用。将上游水库的人工下泄与河口区间的自然产流相结合,充分利用多种水资源协同压咸,可为干旱情况下河口咸潮的高效调控提供技术突破方向。

An index system was established in this study to understand the responses to upstream runoff variations of saltwater intrusion in an estuary in the context of increasing saltwater intrusion caused by deceased runoff into the sea and extreme drought in the Dongjiang estuary, Guangdong Province, China. The impacts of runoff changes on the chlorine in estuarine water were analyzed by exploring the relationships between the proposed runoff indicators including flow mean value, amplitude of variation, high flow pulse and low flow duration etc. and the chlorine changes in the downstream estuary. Based on this, a basin-scale regulation method to suppress the saltwater intrusion during droughts when there is insufficient environmental flow released from upstream reservoirs for flushing out the chlorine out of the estuary to the sea. The results show that the high flow pulse played an important role in suppressing the saltwater intrusion during the drought. During the spring tide in the Dongjiang estuary, the chloride drops significantly and remains at a low level when the hourly flow rate of Boluo Station upstream the estuary exceeds 400 m^(3)/s. Moreover, when the number of high pulse flow reaches more than 4 times in 24 h or the duration of high pulse flow exceeds 12 h, the maximum chlorine of Wanjiang Station in the case area reduced to below 200 mg/L, which can meet the drinking water withdraw standard in China. It is also found in this study that, in addition to the environmental flow released from upstream reservoirs, the stormwater generated in the areas between the reservoirs and the estuary can also reduce the saltwater intrusion to some extent by increasing the freshwater discharge in the estuary. It will be a valuable approach for efficiently regulating the saltwater intrusion during the drought by jointly using estuarian stormwater and upstream reservoir release to drainage the salt from the estuary.