Uncontrolled seepage through earth dams can cause internal soil erosion, leading to piping failure. The phreatic line (top seepage line) within a homogeneous earth dam with a horizontal toe drain is modeled as a parabola using Casagrande’s Method. The total seepage discharge (q) per unit length of dam is: $q = K \cdot S$ Where $K$ is hydraulic conductivity and $S$ is focal distance of the parabolic phreatic line: $S = \sqrt{b^2 + H^2} - b$ Here $H$ is water depth upstream and $b$ is horizontal distance from top of slope to toe drain entry. To prevent soil particle migration along seepage paths, critical filter design follows Terzaghi’s Filter Criteria: $$\frac{D_{15 \text{ (filter)}}}{D_{85 \text{ (base)}}} < 5 \quad$$ $$\text{and}$$ $$\quad \frac{D_{15 \text{ (filter)}}}{D_{15 \text{ (base)}}} > 5$$ Aging earth dams across India face structural threats from internal piping and unmonitored seepage paths during peak reservoir storage. Under India's Dam Rehabilitation and ...