Abstract: The high-frequency monitoring results of groundwater seepage line of the debris landslide in Three Gorges reservoir show that monitoring error is usually caused by low frequency. The reasonable frequency of monitoring can be obtained through error analysis. According to the results of high frequency monitoring on the groundwater seepage line of three landslides,we designed a “simulation monitoring test” to research the errors of monitored groundwater seepage line in the presence of different monitoring frequencies. Results showed that as monitoring frequency continuously decreases,the error of monitored seepage line gradually reaches an unacceptable level. For debris landslide in Three Gorges reservoir area,with average error of 0.15m and maximum error of 1.5m as tolerance value,the monitoring cycle should be no greater than 4 days,and the monitoring frequency should be no less than 0.25 times per day.

Key words: reservoir landslide, groundwater seepage line, monitoring frequency, error