Characteristics and modeling of bedrock spring runoff in a small catchment in granite mountains

Ikkei MATSUNAGA, Shin’ya KATSURA, Takahiko YOSHINO and Takamasa MATSUNAGA


Recent studies suggested that runoff of bedrock groundwater can influence shallow landslides. As a first step towards incorporating the effect of bedrock groundwater runoff into shallow landslide prediction models, we analyzed characteristics and developed models of bedrock spring runoff based on detailed observations of two bedrock springs in a small granitic mountainous catchment. Spring temperature and chemistry indicated that they originate from the same aquifer in deep bedrock. The increment in runoff in response to rainfall events was correlated with the total rainfall amount, and the lag time from the rainfall peak to the runoff peak was more than approximately 1 day. Runoff dynamics were reproduced by the functional models using antecedent precipitation indices with half lives of 156.0 and 211.9 h. These results imply that bedrock groundwater can influence shallow landslides through raising soil mantle groundwater level by its perennial runoff.

Key words

bedrock spring, runoff characteristics, shallow landslide, granite, antecedent precipitation index