Deepening a Hand-Dug Well in the Dry Season, Priced as a Gamble: The Yield Bought per Metre and the Depth at Which It Stops Paying

A hand-dug well 9 m deep, with the water table at 6.0 m falling 4.2 m over a 180-day season on a 90-day recession timescale, yields nothing by day 180. Deepening buys yield at 2.5 m³/day per metre of submerged thickness regained: a well deepened to 11 m yields 3.42 m³/day at day 180 and one deepened to 12 m yields 5.92 m³/day. Priced honestly, at a deepening cost of 120 US dollars per metre and a water value of 0.50 dollars per m³ over the remaining 90 days, each metre returns 112.5 dollars against its 120 dollar cost — a net of -7.5 dollars per metre. Deepening therefore does not quite pay on water value alone in this case; it pays, if at all, as the price of continuity against a new borehole at 3,500 dollars, and only inside the window above the falling water table and below the 12 m collapse-risk threshold for unlined shafts in sand. SIMULATED, NOT MEASURED.