Spacing of tube wells to limit regional drawdown For minimal cumulative impact on the groundwater table in an aquifer, a common planning thumb-rule is to space tube wells approximately one well per:

Introduction / Context:
Well spacing affects interference (overlap of drawdown cones) and long-term aquifer response. Over-densification causes excessive regional drawdown, higher pumping lifts, and declining yields.

Given Data / Assumptions:

• Homogeneous unconfined or semi-confined aquifer for a rule-of-thumb estimate.
• Moderate pumping rates typical of municipal/agricultural wells.
• Planning guidance rather than an exact analytical design.

Concept / Approach:
Interference theory shows that superposition of cones of depression increases drawdown when wells are too close. Many textbook rules adopt a nominal spacing near 1 well per square kilometre to reduce interference at community-scale abstractions, pending detailed aquifer testing and modeling.

Step-by-Step Solution:

Verification / Alternative check:
Field designs refine spacing via transmissivity, storativity, and permissible drawdown; preliminary spacing near 1 km² is commonly used where data are limited.

Why Other Options Are Wrong:
Closer densities (0.5–0.75 km²) increase interference; very sparse networks (≥1.25 km²) may be conservative but not a “least effect” standard rule.

Common Pitfalls:
Ignoring well-field layout (line vs staggered grid) and boundary effects; neglecting seasonal recharge variability.

Final Answer:
1.0 km²