Introduction of Flood in Dharampur Mandi
In month of August and September 2025 sudden flood in Dharampur caused widespread damage and loss. The Soan Khad river swelled unexpectedly, inundating the town and sweeping away vehicles at the local bus stand.
Three people were killed and around 20 HRTC buses were damaged, the Dharampur bus stand’s ground floor filled with silt, and several private vehicles were washed away. The flood also inflicted heavy damage on the electricity network — 12 transformers and 9.5 km of lines were hit, with losses estimated at over ₹4.6 crore.
3D Model of Dharampur, Mandi
Soan river Catchment
Soan river is the main river that cause all these floods. It is a Torrential river, with local catchment area of 229.9 Sq Km. Town itself is enclosed by mountain from all sides. Prolonged rainfall can easily exceed the river water carrying capacity.
Orographic rainfall
Altitude of of region range from 622 mtr to 2012 mt. Change in Altitude is very rapid , which make perfect condition for orographic rainfall. Thus in monsoon , saturated wind get trapped in valley at rapidly rise again the mountain and caused intense rainfall in short span. Thus regional Landscape play critical role in rainfall and flooding.
Flood-Prone Index (FPI) Analysis
The FPI raster map (Map 2) shows terrain vulnerability based on slope, flow accumulation, and proximity to channels.
| FPI Range | Interpretation | Color | Flood Susceptibility |
|---|---|---|---|
| 5.4230 – 6.2998 | Low | Light green | Stable uplands |
| 6.2998 – 7.1766 | Moderate | Orange | Gently sloping plains |
| 7.1766 – 8.0534 | High | Red | Near channel banks |
| > 8.0534 | Very High | Dark red | Flood-prone core zones |
The total area analyzed is 244.853 sq km, with the high to very high FPI zones concentrated along the Dharampur–Mini Haridwar–Shivdwala corridor.
Geology of Region
The lithology of Dharampur belongs to the Siwalik Group, with exposures of Dagshai and Lower Dharamshala formations forming the structural basement. The sequence represents a fluvial to piedmont depositional environment associated with Himalayan foreland basin evolution. (see this Basic Geology of Himachal Pradesh .)
Map 3: Dharampur, Mandi Rock System shows four dominant geological units:
- Upper Siwalik Group (Code 299; Pliocene–Pleistocene)
This formation consists of thick beds of boulder conglomerates and coarse sandstones. These deposits are relatively young and occur mainly in the western part of the study area. Their composition indicates deposition by high-energy rivers that once drained the frontal Himalayan zone. - Middle Siwalik Group (Code 314; Miocene–Pliocene)
The central region of Dharampur is dominated by pebbly sandstone, siltstone, and mudstone. The alternation of coarse and fine beds signifies variable fluvial energy, suggesting a meandering to braided river system. These rocks are moderately consolidated and form the most inhabited belt. - Lower Siwalik Group (Code 327; Miocene)
Represented by fine-grained sandstone and shale, these rocks are relatively weaker and occur along the inner valley flanks. Due to their soft, laminated nature, they are more prone to erosion and slope instability. - Dagshai Formation (Code 358; Eocene–Miocene)
The southeastern margin shows older fine sandstone and shale units belonging to the Dagshai or Lower Dharamshala formation. These rocks form elevated ridges that act as a natural drainage divide between Dharampur and adjoining basins.
Unscientific construction in River channel
Overlaying infrastructure with FPI shows that several key institutions lie close to or within high FPI zones:
- HRTC Bus Stand Dharampur – Very high FPI
- Govt. Degree College Dharampur – Moderate to high
- Block Development Office Dharampur – High
- 33 kV Substation and Kendriya Vidyalaya – High to very high
- Shiv Mandir Shivdwala and Mini Haridwar – Very high, located near flood accumulation paths
Solution
1. Restore and Maintain Natural Drainage Networks
- Many high FPI zones coincide with encroached or constricted drainage paths, especially around the HRTC Bus Stand–Shivdwala corridor.
- Conduct a drainage line demarcation survey and clear all obstructions (temporary structures, debris, silt deposits).
- Maintain a minimum buffer of 10–20 meters on both sides of natural channels for safe discharge.
- Create stone-pitched channel linings in high-energy reaches to prevent bank erosion.
2. Slope Stabilization and Landslide Control
- The Middle and Lower Siwalik formations are made of soft sandstone and mudstone that easily erode.
- Stabilize steep slopes using bioengineering measures such as:
- Vetiver or napier grass plantation.
- Jute/coir netting with deep-rooted shrubs.
- Contour trenching on 20–30° slopes.
- In critical slopes near habitations, construct retaining walls with proper weep holes to prevent waterlogging behind structures.
3. Rainwater Harvesting and Recharge Structures
- The compacted urban areas have lost infiltration capacity.
- Promote rooftop rainwater harvesting in all government and school buildings.
- Construct percolation pits and recharge wells in moderate FPI zones (values 6.2–7.1).
4. Micro-Watershed and Check Dam Planning
- Divide the Dharampur basin into micro-watersheds (2–5 sq km each) and prioritize those with high FPI values.
- Build gabion or boulder check dams in first-order streams to retain silt and delay runoff.
- Use silt traps near bridge crossings and culverts.
- Encourage vegetative filter strips along drainage lines to reduce sediment load.
5. Urban and Infrastructure Management
- Strictly restrict new construction in very high FPI zones (>8.0), especially near Mini Haridwar and Shivdwala.
- Redesign stormwater drains with separate channels for domestic discharge and surface runoff.
- Introduce permeable pavements and rain gardens around the bus stand, sub-station, and college areas to enhance infiltration.
- Relocate or raise the plinth level of key infrastructure within flood-susceptible corridors.
6. Sediment and Channel Capacity Management
- The Siwalik terrain produces high sediment yield during monsoons.
- Conduct annual desilting of main nallahs before monsoon season.
- Maintain minimum channel cross-section standards—width-to-depth ratios optimized for high discharge.
- Introduce settling ponds or sediment traps upstream of built-up areas to capture coarse debris.
7. Early Warning and Community Preparedness
- Install automated rainfall and stream-level gauges connected to district emergency control rooms.
- Develop real-time flood warning SMS alerts for local residents.
- Conduct annual mock drills and awareness workshops in schools and panchayats.
- Train local volunteers to monitor land cracks, drain blockages, and unusual runoff patterns.
8. Long-Term Policy and Land Use Planning
- Integrate FPI data into District Disaster Management Plans (DDMP).
- Declare high FPI corridors as “No-Construction Flood Buffer Zones.”
- Include geological suitability assessment in all new urban development projects.
- Establish a Dharampur Basin Management Authority under district administration to coordinate flood control, slope stability, and land-use enforcement.
9. Reforestation and Catchment Conservation
- Increase forest and vegetation cover in upper catchments dominated by Dagshai and Lower Siwalik formations.
- Promote mixed native plantations (Acacia, Dalbergia, Albizia, and grasses) to increase canopy interception and reduce runoff velocity.
- Prevent grazing and deforestation on ridge slopes, especially near Rakhra and Laxman Jhula ridges.
10. Scientific Monitoring and Continuous Mapping
- Update FPI and DEM maps every 3–5 years using high-resolution Sentinel or LiDAR data.
- Monitor changes in slope and surface roughness to identify new risk zones.
- Collaborate with IIT Mandi or HP State Disaster Management Authority (HPSDMA) for advanced hydrological modeling.
