A Protected Spring Capture Sized from Its Own Hydrograph: Night Storage for the Morning Peak, and the Dry-Season Flow at Which a Borehole Wins

A protected spring capture is sized from a stated Maillet recession (1.2 L/s falling to 0.459 L/s over a 120-day dry season) for 300 people at 6,000 L/day. Volume is never binding (worst-day supply margin 6.62x); timing is. With 45% of demand in a one-hour morning peak, required standing storage grows to 1,046 L on the final day, met by a 2,000 L tank within a total capital cost of US$1,450, delivering at US$0.056 per 1,000 L over 15 years against a borehole's US$0.239. The binding crossover is a service limit, not cost: below a dry-season minimum flow of about 0.076 L/s overnight flow cannot fill the storage the morning peak requires, and the borehole wins, although cost alone favours capture down to 0.016 L/s. SIMULATED, NOT MEASURED.