Simulation of the Irshalwadi Landslide
Event Context & Objective
On July 19th, 2023, a massive landslide struck the remote village of Irshalwadi, triggered by an anomalous spell of heavy rainfall combined with severe local deforestation and earth-digging. The resulting debris flow split into two lobes and wiped out almost the entire village.
Because such events are common during monsoons in the Western Ghats, the objective of this project was to simulate the disaster in order to derive local friction parameters and flow velocities. This data can be directly used to design preventive safety measures, such as protective dams, for similar communities.
Simulation Methodology
The simulation was conducted using RAMMS DebrisFlow, which relies on the Voellmy fluid friction model. This model calculates frictional resistance as a combination of a Dry-Coulomb friction coefficient (µ) and a Viscous-turbulent friction coefficient (ξ).
To build the input domain, we utilized a pre-event Digital Elevation Model (DEM) and modified it to account for local obstacles. Post-event photography, scaled using human references, combined with Google Earth imagery, allowed us to accurately chart the depth of the initial release area. During initial simulations, we identified anomalous flow splitting, which upon closer inspection was caused by a stand of trees blocking the flow. The DEM was further refined to account for this natural damming effect.
Findings & Analysis
Iterative simulations successfully matched the observed spread, height, and volume of the real-world deposition. The derived friction parameters were µ = 0.2 and ξ = 100m/s². The flow achieved a maximum pressure of 187.56 kPa and a peak velocity of 8.66 m/s, depositing a total volume of 10,144 m³.
The parameters offer a direct insight into the material: a lower µ drives a larger deposition spread, while a larger ξ pushes the deposition area further down the slope (indicating a more muddy, fluid-like landslide rather than a rocky one).
Preventive Measures
Based on the flow dynamics, building dams is a viable protective measure. However, due to Irshalwadi's extreme proximity to the release zone, a single dam would need to be 16m tall (double the highest flow height) to arrest the debris. If the village had been situated just 50m further downhill, a much smaller 7m dam would have been sufficient. Future preventative strategies in the Ghats might also consider digging catch-wells or utilizing consecutive smaller dams rather than single massive structures.