Relationships among Seepage, Water Level, and Rainfall of a Fill Dam by Decision Tree Analysis

This study is to present acceptable measurement values through decision tree analysis for the seepage, which is an important measuring item of the fill dam. The seepage of the dam under study increases rapidly when rainfall occurs, when the direct inflow of rainfall from the downstream slope and both sides occur. Therefore, the allowable seepage of fill dam considering rainfall and water level is required. Decision tree analysis was conducted for one domestic fill dam by setting the seepage as a response variable and setting rainfall and water level as explanatory variables. At this time, in order to analyze the effects of rainfall on the seepage more closely, the data subject was classified into two groups consisting of a rainfall-free group and a rainfall-occurring group. Group A, which is a rainfall-free group, had 97.7% of the seepage data distributed under the conditions of 98.50 mm/day of the antecedent 5-day rainfall selected as the first explanatory variable. The average seepage of the group was between 12.01 L/min and 26.35 L/min. Group B, which is a rainfall-occurring group, had 85.7% of the water leakage data distributed under conditions of 38.50 mm/day of daily rainfall selected as the first explanatory variable, with an average of 23.70 L/min.