Characteristics of long series data of groundwater quality and level in Kunming basin

Kunming basin is a representative of karst faulted basin, with a basin bottom area of 846.19 km² and a fluctuation of 1-82 m averaging at 19 m. With the city development, Kunming has gradually become one of the megacities in China. However, as the center of intensive human settlements and activities, the contradiction between human and land is prominent, and the problems of resources and environment are serious. Since the 1960s, the dynamic monitoring of groundwater in the urban and suburban areas of Kunming has been carried out in a comprehensive and systematic manner. In this study, hydrogeology method, data statistics method, Piper and Matlab software were used to establish models to analyze the dynamic characteristics and change of water quality and water level, based on the comparative analysis of monitoring data of water quality and level in Kunming basin, especially in the main urban area. The main underground chemical types of Kunming basin are HCO₃-Ca and HCO₃-Ca·Mg. In recent years, with the gradual increase of Na⁺ + K⁺ and ${\rm{SO}}_4^{2-} $ +Cl, the hydrochemical types have also gradually been increasing and become more complex. According to the water quality evaluation, the groundwater quality in Kunming basin has generally shown a downward trend in recent 15 years. The pore water quality is mainly of Class IV and Class V, and the proportion of Class V water has increased rapidly, from 30.2% to 62.5%. The bedrock water quality is mainly of Class III and Class IV. The proportion of Class IV water and Class V water has risen rapidly from 11.1% and 8.6% to 33.3% and 26.7%, respectively. Mn, NH$_4^{+}$, ${\rm{NO}}_3^{-}$ and COD are the main items exceeding permitted levels in pore water. Mn, NH$_4^{+}$ and F are the main items exceeding permitted levels in karst water. In recent years, I, ${\rm{SO}}_4^{2-}$, As, Cd and other toxic, harmful and organic substances have exceeded permitted levels, showing a compex tendency. The reason for the change of water quality is the intensification of industrial and domestic pollution. The results show that the interannual variation of groundwater level in Kunming basin is mainly affected by industrial and agricultural production, mining amount and engineering activities, and pore water decreased from 2002 to 2009, but increased after 2009. Karst water showed a downward trend from 2002 to 2012, and an upward one after 2012. The groundwater levels of Puji-Liangjiahe, Beijiaochang, the urban area of Kunming, Jinmasi-Guanshang and other water-rich blocks have risen significantly. The rising trend of groundwater levels in Cuihu, Heilongtan, Beijiaochang, Majie, Heilinpu and other five falling funnel areas is significant, which is closely related to the measures of restricting groundwater exploitation and sealing groundwater exploitation wells in Kunming City. Based on the dynamic analysis of water quality and water level, countermeasures and strategies to protect groundwater should be proposed through enhancing administrative management, strengthening the investigation, evaluation and monitoring of basic groundwater environment, and furthering the research on technology of preventing groundwater pollution.