PSD.13:5.1 - A pump comparison that cannot yet choose an investment

An East-District authority asks a separate analysis team for advice on flood-pump investment for the coming season. Its receiving decision is whether and how to commit funds. The live candidates include a baseline N, fixed pumping F, mobile pumping M and staged combination S.

The qualified numerical slice concerns pumping-service loss and incremental cost, not the whole public consequence. In the stated model, F has loss 2 in normal access and 3 with road loss, at cost 8; M has loss 1 and 9, at cost 5. The baseline and staged alternative are not closed by this two-option comparison. Reachable assistance, property consequences and protected conditions still require their direct evidence and value judgements.

A sensitivity result supplies the conditional boundary 7p > 1 + 3λ for F to have the lower weighted loss, where p is the assumed road-loss probability and λ the declared cost weight in this illustrative model. Neither value has been established for the actual investment question. With λ = 0.5, p = 0.2 favours M, while p = 0.6 favours F. This is evidence of a possible reversal, not evidence that either probability obtains.

The team returns:

Retain fixed and mobile pumping for the current pumping-service/cost comparison. A whole-investment recommendation is blocked by the unqualified road-access basis, unresolved assistance and protection consequences, and the unclosed baseline/staged branches. The current model favours different options under different declared assumptions; it does not justify a preferred investment. Reconsider the affected comparison when those results or the authority’s value and protection premises change.

A material objection about reachable assistance remains in the return, not buried below the numerical result. The authority can decide what further evidence to commission under its own mandate. A bounded consequence/access request is a useful continuation when an obtainable result can improve the investment decision enough to warrant its acquisition burden. Neither that request nor the conditional comparison authorizes spending, a public trade-off or an operational response.