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How can rerouting surface drainage reduce the risk of landslides?

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landslide This 1995 landslide at La Conchita, a coastal town in California, swept away a hillside road and destroyed a number of houses.

Rerouting surface drainage is a direct method used to prevent landslides by managing the water content within a slope.12

Landslides occur when gravitational shear stresses exceed the shear strength of the slope materials. Water plays a critical role in this process; an inflow of water or a rise in the groundwater table increases the load on a slope and can significantly weaken its material. In sandy materials, increased water content reduces interparticle friction, while in clays, it leads to the dissolution of cements and the hydration of clay minerals.2

By rerouting surface drainage, engineers can prevent water from infiltrating and saturating the slope, thereby maintaining the material's frictional and cohesive strength and reducing the likelihood of slope failure. This approach is one of several engineering interventions, such as modifying slope geometry or installing retaining walls, used to mitigate landslide hazards.12