Investigation of Seepage and Piping Risk in Earthen Embankment Dams in Anambra State

Earthen embankment dams in Anambra State, South East Nigeria, serve agricultural irrigation and rural water supply functions but are susceptible to internal erosion and piping failure if seepage is not adequately controlled. This study investigates seepage conditions and piping risk in three earthen embankment dams in Ogbaru, Awka South, and Ihiala LGAs of Anambra State. Piezometer readings from installed instruments at each dam were compiled for the 2020 to 2023 period. Visual inspection of downstream slopes and toe areas was conducted to identify evidence of seepage, sinkholes, or wet spots. Seepage flow rates were measured by bucket and stopwatch methods at downstream collection points. Grain size analysis was performed on samples from five embankment cross-sections per dam to assess internal erosion susceptibility using the Kenney and Lau criteria. Results indicate that two of three dams exhibit seepage rates above the threshold associated with potential internal erosion initiation. Phreatic line positions estimated from piezometer data suggest inadequate filter drain performance in the Ogbaru dam. Wet spots on the downstream slope of the Ihiala dam indicate preferential seepage paths requiring investigation. Grain size analysis indicates susceptibility to internal erosion in three sampled zones. The study recommends emergency seepage remediation at the Ogbaru and Ihiala dams, including installation of reinforced filter drains and regular phreatic line monitoring.

Keywords: earthen dam, seepage, piping risk, internal erosion, Anambra State