INTEGRATED ASSESSMENT OF SEEPAGE AND INTERNAL EROSION RISK IN EARTH DAMS UNDER VARIABLE RESERVOIR LEVELS USING FIELD MONITORING AND NUMERICAL MODELLING

Abstract

Seepage is an inherent process in earth dams, but concentrated leakage, excessive pore-water pressure, filter incompatibility, and high local hydraulic gradients may initiate internal erosion and progressively reduce embankment safety. Reliable assessment is complicated by spatial variability in soil properties, uncertain construction quality, reservoir-level fluctuations, drainage deterioration, and the limited ability of visual inspection to identify subsurface defects. This study proposes an integrated framework combining field monitoring, engineering inspection, geotechnical testing, saturated-unsaturated seepage analysis, and risk-based interpretation. The framework uses reservoir level, piezometric head, drain discharge, turbidity, deformation, hydraulic conductivity, grain-size distribution, filter compatibility, and drainage performance. Steady and transient numerical scenarios are considered for minimum, normal, and maximum reservoir levels, partial drain blockage, a localized high-permeability defect, and rapid drawdown. Model outputs include the phreatic surface, pore-water pressure, total and zonal seepage discharge, local hydraulic gradients, and concentrated-flow zones. A composite internal erosion risk index integrates hydraulic loading, material susceptibility, filter and drainage deficiency, observed anomalies, and failure consequences. A representative zoned earth-dam model demonstrates that total seepage alone is not a sufficient safety indicator: distributed flow through effective filters and drains may be acceptable, whereas a smaller concentrated flow through an unprotected exit can be critical. The proposed method supports decisions on enhanced monitoring, drainage rehabilitation, filter improvement, grouting, cutoff construction, reservoir restrictions, and urgent intervention.