Design Blueprint: Community Sand-Storage Dam — Build Specification Derived from Sand-Dam Extractable-Storage Sizing for a Seasonal River

DESIGN BLUEPRINT — SIMULATED, NOT MEASURED — NOT BUILT. Build specification for a community sand-storage dam serving 400 people at 20 L per person per day through a 180-day dry season, derived from the source paper at https://doi.org/10.5281/zenodo.24109218. The reservoir is the trapped sand body itself: 147.4 m long, 20 m wide and 2.0 m in mean saturated depth (5,895.8 m3 of sand at specific yield 0.25), holding 1,440 m3 of net extractable water after a 34.0 m3 evaporation loss through its 0.30 m dry crust, against 2,907.5 m3 lost by an open reservoir of the same plan area — a saving of 2,873.6 m3. The wall is raised in 7 lifts of 0.30 m so the deposit keeps only grains coarser than 57.8 micrometres. The specification covers dimensions and layout, bill of materials, staged construction sequence, operating envelope, tolerances, failure modes and maintenance. Site hydrology, flood and spillway design, and structural design are flagged as site-engineering duties outside the package, as the source paper states no flood hydrology.