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Geology in reservoir site selection

Short answer

A site needs watertight impermeable rock (shale, clay, massive crystalline) and no cavernous limestone, open joints or permeable faults. Beds dipping upstream are preferred; groundwater level must be higher than reservoir level. Avoid landslide-prone slopes, active faults, erodible catchments causing siltation, and soluble rocks that degrade water quality.

Describe the geological considerations for reservoir site selection.

A reservoir must hold water, remain stable and stay silt-free as long as possible.

Geological considerations

  1. Watertightness of the basin and rim: impermeable rocks (shale, clay, massive crystalline rock) are suitable. Avoid cavernous limestone, highly jointed or fractured rock, coarse gravel and permeable fault zones, which cause leakage. Check there is no low saddle or permeable gap along the rim and divide.
  2. Geological structure: beds dipping upstream or toward the reservoir are favourable; downstream dip may lead to leakage. Faults and folds may be leakage channels.
  3. Stability of reservoir banks: avoid landslide-prone slopes; filling can reactivate old slides; slide into the reservoir causes waves.
  4. Water table: the groundwater level on both sides should be higher than the reservoir level, to avoid loss.
  5. Sedimentation: catchment with weak, erodible rocks and landslides leads to quick siltation.
  6. Seismicity: reservoir-induced seismicity; avoid active faults.
  7. Water quality: soluble salts (gypsum, rock salt) spoil the water.
  8. Valuable resources (minerals, forests, settlements) that would be submerged.
  9. Construction materials nearby.

✓ Answer checked by Claude Opus 5.5 (high effort)

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