Proposal A — Rebuild
£1.4m · 14 monthsRubric
Proposal B — Repair
£620k · 5 monthsFull design life restored.
New structure carries a 60-year design life with a current-code safety factor.
Design life
Extends by 15–20 years.
Repair addresses the observed movement but not the underlying drainage.
Reservoir out of service 14 months.
Requires full drawdown and a temporary supply agreement.
Disruption
Out of service 6 weeks.
Partial drawdown only; no temporary supply needed.
Low residual risk.
Nothing of the original east wall is retained.
Residual risk
Moderate, and not fully characterised.
Depends on the seasonal hypothesis, which the panel has not accepted.
Committed at award.
Fixed-price contract, one contractor, no staged decision point.
Optionality
Preserves the choice.
Repair now does not preclude rebuild in 2032, and buys five years of monitoring.