Aquifer Recharge Pit Design Guide: Aquifer Type, Sizing, and Filter Media
Aquifer recharge pit design is aquifer-specific: an unconfined alluvial aquifer accepts water very differently from a hard-rock fractured aquifer. This guide covers CGWB-recommended pit dimensions, filter media grading, and when to combine a pit with a borewell recharge shaft for hard-rock terrain.
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Aquifer-type decision matrix
Unconfined alluvial aquifers (Indo-Gangetic Plain, coastal Andhra) accept large recharge volumes through simple pits — 1.5 m × 1.5 m × 3 m handles 100–300 m² catchment. Hard-rock fractured aquifers (peninsular India — Karnataka, Telangana, Maharashtra) need pit + borewell-recharge combination to bypass the low-permeability weathered zone. Confined aquifers require pressure injection through a sealed casing.
- Unconfined alluvial — pit only, 100–300 m² per pit
- Hard-rock fractured — pit + borewell recharge shaft
- Confined aquifer — sealed pressure recharge through casing
- Coastal saline — recharge above water table only, monitor for salinity
CGWB filter media grading
The graded filter is identical across pit types — what changes is the discharge mechanism below the filter.
- Bottom 0.75 m — boulders 65–100 mm
- Next 0.50 m — gravel 20–40 mm
- Next 0.25 m — coarse sand 2–4 mm
- Top 0.50 m — free space for water column
- Cover — removable RCC slab with lockable inspection hatch
Integration with borewell recharge
In hard-rock terrain, the pit acts as the settling and filtration chamber, and a perforated PVC pipe connects to a borewell recharge shaft below to bypass the low-permeability zone. Rain GEO SAT's Expert engine auto-selects this hybrid design when top-layer infiltration falls below 15 mm/hr.
Frequently asked questions
- Do I need CGWA permission to recharge my own aquifer?
- For domestic self-use, no. Commercial or industrial deep recharge and any injection into a confined aquifer typically requires CGWA/SEIAA clearance depending on state and abstraction volume.
- How is this different from the recharge pit design guide?
- This guide focuses on aquifer-type-driven design and hybrid pit+borewell configurations. The general recharge pit guide covers standard urban rooftop pits regardless of aquifer.
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Rain GEO SAT calculators use IMD, NASA POWER, Open-Meteo, and CGWB data to deliver engineer-grade rainwater harvesting and groundwater recharge designs.
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