干流径流过程突变对通江过水型湖泊河湖转换过程的影响研究

The hydrological regime of Dongting Lake has become significantly dry since 2003, and this had affected the water using, shipping and water environment in the area of the Lake. Hydrologic process change of the middle and lower reaches of Changjiang River caused by the operation of the Three Gorges Reservoir is the other important factor besides the reduction of the runoff caused by the climate change. Research on the hydrological regime of Dongting Lake influenced by the runoff regulation of the Three Gorges Reservoir is existed, but the Three Gorges Reservoir would change the three diversion of the Jingjiang River in flood period and the water level of the Chenglingji in impoundment period of the Reservoir, both would affect each other, then influence the water level of the Lake in the period of the lake changing to the river, when the dry hydrological regime often happened. Based on analyzing of the characteristic that three diversion flow changing along with the flow change of the Jingjiang River, this research would study the different way of flood regulation influencing the three diversion flow, then find out the water level change of the Dongting Lake at the end of the flood period caused by the changing of the three diversion flow in flood period, the meth model would be used to analyze the influence of the water level sudden change of the Chenglingji caused by the impoundment of the Three Gorges Reservoir on the Lake changing to the river process of the Dongting Lake, finally, the reason of the hydrological regime changing of the Dongting Lake would be found out.

2003年以来洞庭湖水情显著偏枯，严重影响湖区取水、航运及水环境。除去气候变化导致的来流减少因素外，三峡水库运行改变长江中下游水文过程是另一重要因素。国内学者针对三峡水库径流调节作用对洞庭湖水文情势的影响进行了一定的研究，而对三峡水库汛期影响三口分流、蓄水期影响城陵矶水位对洞庭湖湖河相转换期湖内水位的叠加影响机理研究较少，而洞庭湖偏枯水情往往发生在该时期。本项目以分析荆江三口分流能力随干流流量的变化特性入手，研究三峡水库汛期不同调洪方式对三口分流量及分流过程的影响，进一步分析分流量变化对汛末洞庭湖湖内水量及水位的影响，通过数学模型分析洞庭湖汛末湖河转换期，不同湖内起始水位，三峡水库蓄水过程造成城陵矶水位突变对洞庭湖湖河转换过程的影响，最终得到洞庭湖枯水水文情势的变化原因。本研究对认识水库径流调节作用对下游河湖水文情势的影响有重要理论意义，为制定科学合理的水库调度方案提供技术支撑。

本研究首先建立并验证长江上游控制性梯级水库调度模型，在分析梯级水库应对长江中下游洪水的库容分配及调蓄方式后，重点研究三峡单库及梯级水库抵御荆江大洪水的限制下泄流量。明确梯级水库调蓄方式，分析三峡水库蓄水后荆江三口分流影响因素、分流比变化特性及三峡水库运行前后的三口分流比变化规律，阐明水库改变径流过程对荆江三口分流量的影响；基于三口分流比随干流流量的变化特性，以大洪水年为例，分析水库不同调洪下泄流量对三口分流洪量的影响，提出利用水库调节下泄洪水过程，进而改变分流河道分流总量的调控技术。.主要特点：（1）明确了三峡水库运行后荆江三口分流比变化趋势。.三峡水库后，荆江三口分流比变化不大，并未延续近50年来的萎缩趋势，荆江干流同流量下三口分流比，低流量略有减小，中高流量相比蓄水前基本变化不大，而分流量受水库调蓄影响，相比蓄水前减小。荆江干流中高流量持续天数的变化，受天然来流减少以及三峡水库调蓄改变荆江干流径流过程二方面因素的共同影响。三峡水库175m 运行期，汛期中小洪水拦蓄及蓄水期蓄水影响荆江中高流量持续时间，造成三口年分水总量减少83.1亿m3。.（2）研究了三峡水库运行后荆江三口分流变化的影响因素。.荆江干流同流量下三口分流比的变化主要受干流同流量水位变化以及洪道口门冲淤影响；三峡水库蓄水后，荆江干流中高流量下水位相比蓄水前无明显变化，而三口洪道冲刷有利于维持分流比，两个主要因素相比蓄水前变化不明显，故共同作用致使干流同流量下三口分流比维持不变。三峡水库调蓄下径流过程变化引起三口年均分流量减少值占总减少量的20%，长江干流径流量减少引起年均分流量减少量占总量的约80%。.（3）明晰了三峡水库运行对洞庭湖河湖转换过程的影响.以90年代资料为基础，推算三峡水库日均蓄水量在5000m3/s时，城陵矶水位10月份相比天然情况，下降1.64m，入湖水量减少24.23亿m3，城陵矶出流水量增加16.77亿m3，蓄水期洞庭湖水量相比天然情况下共少41亿m3。