Evaluation of Seepage Barrier Wall Performance Using Instrumentation-Paper

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The paper presents methods for evaluating seepage barrier performance using piezometer data, drawing on projects at Center Hill Dam in Tennessee and Mosul Dam in Iraq. Both dams sit on karst foundations and use seepage barriers to reduce seepage and the risk of internal erosion. Monitoring is needed not only during construction and post-implementation evaluation, but throughout a project’s life to confirm that the barriers continue to meet their design intent.<br /><br />Reliable analysis depends on understanding each instrument’s location, the geological zone it monitors, its baseline behavior, and factors that influence readings, such as reservoir and tailwater levels, rainfall, barometric pressure, and construction activity. Data must be collected frequently enough to capture important responses: monthly or daily readings may miss short-lived pressure changes during grouting, whereas automated monitoring can provide much finer resolution.<br /><br />The authors recommend using several complementary methods. Time-series plots reveal short- and long-term trends, but should be viewed at multiple time scales and alongside relevant water levels and other variables. Piezometric profiles help interpret readings in their geological and three-dimensional context. Net Head Dissipation calculations estimate barrier effectiveness between paired upstream and downstream instruments, and can show changes over time or variation along a barrier. Correlation plots and statistical analyses can identify changing relationships between piezometric response and reservoir levels.<br /><br />Examples show that instrumentation at Center Hill responded to grouting and barrier-wall construction, while Mosul Dam data revealed changing grout-curtain effectiveness and the need for maintenance grouting. The paper emphasizes that no single analytical method is sufficient. Instrumentation provides information only at monitored locations, so sound assessment also requires engineering judgment, visual observations, and ongoing review of performance.

Keywords

seepage barrier

piezometer data

karst foundation

Center Hill Dam

Mosul Dam

internal erosion

time-series analysis

net head dissipation

grouting effectiveness

instrumentation monitoring