桂林市会仙岩溶湿地水资源特征及有效调控

Study on characteristics and regulation technology of water resources of karst wetland in Huixian,Guil

会仙湿地是“漓江之肾”,对漓江补水和生态环境改善具有重要作用,但湿地水资源调蓄功能较弱,严重制约了湿地功能的发挥。本研究以会仙湿地为示范区,对湿地核心区狮子岩地下河系统和睦洞湖分散排泄系统流量进行了一个水文年的观测,并实施水资源调控措施。结果表明:会仙湿地岩溶含水层对大气降雨具有一定的调蓄作用,但调蓄功能较弱,雨季后若连续2个月无降雨地下河基本断流;会仙河通过桂柳古运河补给睦洞湖,补水效果取决于会仙河大坝的蓄水高度,当会仙河大坝蓄水高度小于149.25 m时,会仙河无法对湿地进行有效补水,对该大坝重修可增加对睦洞湖湿地的补水效果。针对狮子岩地下河系统具有管道集中径流、流量大、水量充足的特征,在地下河采取了上游“蓄”和“引”,中游“堵”,下游“拦”的三级调控工程使地下河水位从出口到八仙湖段1 km范围内提高70 cm,可缩短狮子岩地下河溶洞湿地低水位期1个月以上。针对睦洞湖分散排泄系统地下水具有分散排泄的特征,采取出口“拦”的水资源调控技术,成功将出口水位抬高30 cm,核心区水位抬高10~20 cm,使睦洞湖湿地低水位期推迟2个月以上。

Known as"the kidney of the Lijiang river",Huixian karst wetland is the largest original ecological wetland of karst landform in the Lijiang river basin;therefore,it plays an important role in water replenishing and improvement of ecological environment of the Lijiang river.However,the regulation of water resources and storage capacity of Huixian karst wetland is limited because the area of the wetland varies greatly in season,and the regulation and storage function of water resources is weak in both the waterlogging season and the drought season.In a hydrological year,the water surface elevation of wetland fluctuates between 147.5-150.20 m,and the surrounding ground elevation ranges from 149.6-150 m.Thus,when the water level is higher than 149.8 m,a large area of cultivated land will be flooded,while the water level of wetland will easily drop below 149 meters resulting in the water shortage of wetland in the dry season.The frequent fluctuation of wetland water surface in a hydrological year leads to the reduction of wetland area or the inundation of cultivated land,which seriously affects the wetland landscape and villagers'water consumption of farming and living.Water resource problem has become a key factor restricting the development and protection of Huixian karst wetland.Previous studies have been carried out on the geological background,hydrogeological conditions,water level dynamics,groundwater balance,groundwater pollution and other aspects of the formation of Huixian karst wetland.However,less attention is paid to the dynamics of groundwater flow and the technology of regulating water resources,which may seriously influence the implementation of effective regulation of wetland water resources.In 2022,Guilin City launched the flood control and drainage upgrading project of the Xiangsi river in Guilin New District.The municipal government planned to invest 650 million yuan for the improvement of water resource regulation and storage function of Huixian karst wetland and the improvement of water ecological environment.It also intended to develop the landscape resources of karst cave wetland at the outlet of the Shiziyan underground river.In this study,the discharge of Shiziyan underground river system and Mudong lake dispersed drainage system in the core area of wetland were observed for one hydrological year,and the dynamic characteristics and controlling factors of wetland groundwater flow were systematically analyzed.On this basis,different regulation techniques were adopted to control water resources for the centralized runoff system of the Shiziyan underground river pipeline and the dispersed drainage system of Mudong lake.As a result,the water level of Huixian wetland was controlled within a reasonable range,achieving a good demonstration effect.This study provides scientific and technological support for the improvement of water resource regulation and storage function of Huixian karst wetland.It also provides a typical example for water resource regulation of karst cave pipeline wetland and dispersed drainage wetland in the karst area of Southwest China.The results show that groundwater plays a certain role but a weak function in regulating and storing atmospheric rainfall.If there is no rainfall for two months after the rainy season,the flow will be basically cut off.The Huixian river supplies water to Mudong lake through the ancient Guiliu canal,and the amount of water replenishment depends on the water storage height of the Huixian river dam.In the rainy season,the water storage height of the Huixian river dam is greater than 149.25 meters,which can guarantee the water replenishment of the wetland,but in the dry season,the water storage height can easily fall below 149.25 meters,which cannot replenish the wetland.Considering that the Shiziyan underground river system has the characteristics of concentrating runoff from pipelines,a three-level control project—"storing"and"diverting"in the upper reaches,"blocking"in the middle reaches,and"intercepting"in the lower reaches—has been adopted to increase the level of the underground river by 70 cm from the outlet to Baxian lake.This project can shorten the period of keeping a low water level by more than one month.In view of the dispersed drainage characteristics of the Mudong lake system,the technology of regulating water resources by"diverting"at the entrance and"intercepting"at the outlet was adopted.The water level at the exit was raised by 30 cm and the water level in the core area by 10-20 cm,delaying the time of keeping the low water level for more than two months.