Preliminary Research on Optimal Sampling Frequency of Hydrochemistry Under Different Rainfall Levels in Typical Karst Small Watershed

Abstract

[Objective] Current research mainly focuses on long-term frequency studies in non-karst areas, but there is insufficient research on hydrochemical sampling frequency under different rainfall levels in karst areas Inorder on determining the optimal sampling frequency of hydrochemistry at different rainfall levels in Karst small watersheds. [Methods] Based on high-frequency electrical conductivity (EC) data of different rainfall levels (heavy rainstorm, heavy rain and moderate rain) with a 1 hour interval from June 2022 to July 2023 in the typical Karst small watershed of the central Guizhou Plateau, low-frequency data of 2~15 hours were resampled. Combined with various evaluation indicators and catastrophe point theory, the optimal sampling frequency of hydrochemistry under different rainfall levels in the Karst small watershed was determined. [Results] (1) Due to the influence of geological background, the hydrochemistry response to rainfall in the small watershed of the Karst area is characterized by rapid rise and fall, and the loss of sampling error is large. (2) Factors such as I60 (maximum 60 min rainfall intensity), the number of rain-free days, and the amount of rainfall all impacted the hydrological process, which in turn altered the characteristics of hydrochemical changes and ultimately affected the sampling frequency; (3) It was recommended to use a sampling frequency of 4 hours during heavy rain events, a frequency of 5 hours during moderate rain events when I60>10 mm/h, and 6 hours frequency when I60 was small (I60<10 mm/h). [Conclusion] The research results provide reference for hydrochemical monitoring in karst small watershed.

Keywords

• karst
• small watershed
• optimal sampling frequency
• rainfall level
• hydrochemistry