Inviting geo-hazards: What an elevated corridor over the Bindal–Rispana will do to Doon’s subsurface & riverscape

GUEST COLUMN

Rakesh Kapoor  

The Rispana-Bindal elevated corridor being planned at an estimated cost of Rs 6,200 crore, a 26-kilometre long elevated corridor akin to a concrete monster will not only adversely affect ecology and the environment. It is being debated once again in the provisional State capital. Some believe it is important while others are opposing it. The fact is that if executed, this project may have many more implications than being officially stated now.

Geological & geohydrological implications

Since the culmination point funneling traffic from two branches near the Max hospital is located very near to the Main Boundary Fault (MBF) separating younger Siwaliks (highly unstable fragile nature) from older Cenozoic Mesozoic Rocks which are high sloped highly jointed, even a small magnitude earthquake beyond 5 on the Richter scale (which is most likely as studies predict) shall cause mass failure and tumbling blocks will trigger other problems. In such a scenario, the piers/abutments shall narrow and roughen the active channel and floodplain, raising water levels in peak flows and shifting inundation to currently “safe” banks. Expect higher flood depths/velocities near bends and pier groups. The second major fallout shall be on scour and foundation risk. A combination of cloudburst-driven flash flows and bedload from the hills will result in local/general scour around piles. This can undermine the supports if not founded into competent strata and protected with robust armoring sized for extreme events (not just Q100). The third causality will be the channel fixation and instability downstream. Confining/straightening reaches reduces lateral migration and bars, often causing incision immediately downstream and aggradation upstream of constrictions.

It shall also have a killer effect on aquifers and groundwater as it will become a permanent barrier to subsurface flow and recharge. The Doon Valley’s main aquifers are the highly permeable Doon gravels. Floodplains of Bindal/Rispana act as major recharge windows. Continuous pile caps, floodwall segments, approach embankments and utility corridors can act as partial cutoff walls, altering shallow groundwater gradients and lowering recharge to adjacent neighborhoods. Perched water and waterlogging will also be an issue. Where fill/approaches seal floodplain soils, rainfall can perch above compacted layers, raising local water tables upslope of the structure and increasing damp basements and pavement. It will further aggravate contamination pathways. Road runoff (metals, PAHs, oils) discharged to the river or into soak pits near the corridor can degrade shallow aquifers that many households still use. Recent studies report elevated heavy metal indices in Rispana and health-risk exceedances at some stretches—adding traffic-derived pollutants without advanced treatment worsens this.

Geotechnical/seismic

Valley-fill sands/gravels with shallow groundwater have moderate-to-high liquefaction potential during strong shaking; piles must be designed for downdrag, loss of lateral support and post-liquefaction kinematics. (Doon gravels + shallow GW documented across the valley.)  Transition zones over heterogeneous alluvium are prone to long-term settlements; utilities integrated into the structure are then stressed at the joints. Further, approach ramps on reclaimed floodplains can mobilise edge failures during monsoon saturation unless drainage and lightweight fills are used.

Fourthly, it will adversely change river ecology and morphodynamics with Loss of floodplain function. Converting a living river to a pier-lined conduit removes storage, nutrient exchange and bar dynamics—effectively “canalizing” a Himalayan foothill stream that needs room to spread in cloudbursts. Environmentalists have flagged this as a likely “death of the river ecosystem”.

 The adverse impact does not stop here alone as it will compound social risk (procedural + hazard) encroachment/ legal context. The Uttarakhand High Court has repeatedly intervened around Bindal–Rispana for unapproved riverside construction; more recently it paused acquisition/hearings tied to the 26-km, Rs 6,200–6,500 crore corridors. Any design that further fixes the rivers without first resolving floodplain governance magnifies risk to vulnerable settlements.

What a robust EIA/DPR must prove

*  Hydraulic modeling for Q10–Q500 and cloudburst scenarios, with pier layout alternatives and no-adverse-impact maps.

*  Sediment transport and scour with armoring design for extreme hydrographs; failure mode analysis for pier groups.

* Groundwater model : (MODFLOW/GSFLOW) showing effects on phreatic surface, seasonal storage and cross-valley gradients; identification of any subsurface cutoff created by foundations/embankments, with mitigation. It should be calibrated to Doon gravels parameters and local pumping tests.

*  Stormwater quality plan: first-flush capture, oil-grit separators, lined sumps, and zero untreated discharge to river; monitoring against heavy-metal benchmarks given the already high Heavy Metal Pollution Index (HPI).

* Seismic geotech: site-specific response spectra, liquefaction triggering plus lateral spreading checks, pile performance in liquefied layers and settlement management at transitions.

* Cumulative impact with existing/ approved river training works and encroachment removal sequence (per HC and Apex Court directives on encroachments and National Mission for Clean Ganga).

Still, if the city insists on a corridor, some minimum safeguards are necessary.

Keep the river free-spanning. Put piers outside the active channel along with designated floodway; use fewer, longer spans even if costlier.

There should not be continuous floodwalling. Where retaining is unavoidable, integrate porous seepage galleries/under-drains to maintain lateral groundwater movement.Design earth fill rock fill dam type embankment support for piers. Further, prohibit impervious reclamation on floodplain; add off-channel detention and infiltration parks upslope (with liners where GW quality is at risk).

When it comes to runoff treatment, one must focus on first-flush diversion, sedimentation, adsorption media and monitored outfalls while also designing for maintenance access.

Liquefaction-compatible deep foundations to competent strata, capacity-protected columns, seat extenders and restrainers are vital to address the seismic aspects.

Real-time stage/velocity sensors, debris booms upstream of piers outside floodway, and monsoon lane-closure protocols are also necessary.

At the same time there are preferred alternatives with lower risk and faster delivery, which could be considered by the authorities.

Blue-green mobility spine beside (not over) the rivers Continuous bus priority (or BRT-lite), junction fixes, transportation demand management and floodplain restoration—cost far less and avoid aquifer impacts flagged above. Recently, civic and expert groups have argued for such options instead of river-top expressways. These alternatives must be embedded and explained in the executive summary of the DPR /SIA/EIA for saving Doon and Doonites.

(A retired civil servant, the author is a geo-environmental and QCI NABT approved EIA expert; views expressed are personal)