SCENARIO
A · Cheapest storageDams4
Storage132,378 m³
Swales26.2 km
Earthworks13,971 m³
DistributionPumped
Shortfall covered36%
Dams sited where the storage-to-earthworks ratio is best, which puts them in the valley throats. The most storage for each cubic metre of earthworks. Seven of the ten troughs sit above the highest dam, so distribution needs a 2.6 km pumped rising main to a header tank at 1,903.7 m.
SITES
D12.5 m × 72 m wall42,262 m³67.7 ha
D22.5 m × 56 m wall25,733 m³18.3 ha
D32.5 m × 59 m wall19,094 m³3.0 ha
D44.0 m × 164 m wall45,289 m³53.2 ha
Storage is not retentionStorage and retention are not the same quantity. A cubic metre in a dam can be moved where it is wanted; a cubic metre kept in the soil profile is only available where it fell. The comparison is a ranking of strategies, not an equivalence.
Scenario A is the drawn design: its figures and sites are D1 to D4 as drawn in dams.geojson and recorded in analysis-structures.json. B and C are computed from a separate site survey by the method in basis, so the three are ranked against each other as strategies rather than derived identically.
Nothing here has been sited on the ground. Field boundaries, crop areas and the forage layout are indicative; analysis-structures.json is the record.
THE FINDING
Seven of the ten troughs sit above the highest dam.
Dam full-supply levels run 1,868 to 1,881 m; the grazing ground averages 1,885 m. Sited for cheapest storage, the dams sit in valley throats below the stock. Only one trough can be gravity-fed from them. A header tank at 1,903.7 m, filled by a 2.1 km pumped rising main from D4 against 27 m of head, commands all ten by gravity.
Keyline practice sites storage high so it distributes by gravity, accepting a worse storage ratio. This design took the cheap-storage siting and pays for it with a pump. Re-siting dams higher is the alternative, and the pilot document explicitly left that question open for the scale-up.
THE DESIGN
— fields.
4 dams storing 132,378 m³.Each dam is a straight homogeneous embankment, a pond bounded by full supply level, a spillway sized by the rational method against the 194 mm wettest recorded day, a borrow pit downstream, a silt trap at the main inflow and a lockpipe at the wall low point.
55 swales, 26.2 km.
— grazing camps in — blocks.Derived from the field layout.
10 troughs from one header tank.
36% of the shortfall covered.Four dams cover about a third of the shortfall the water budget established. That is a statement about this design, and it belongs here rather than in the budget: the budget establishes the gap before any structure exists.
THE FIELD SYSTEM
The property is divided into rectilinear fields with tracks so every field has frontage, and land use is assigned to whole fields by the majority of the suitability analysis. Terrain-derived shapes are analytically right, and no farm is laid out that way.
PASTURE IS NOT ONE THING
It carries the pilot’s forage treatments, randomised in blocks as the pilot’s Figure 6 does, with silvopasture lines through a third of the pasture fields.
SURFACE
The illustrated plan is a drawing of the geometry below, not a computed layer.
DESIGN LAYERS
▦Fields and tracksLand use per field, farm tracks
◉DamsEmbankment, pond, spillway, borrow pit, silt trap, lockpipe
≈Soil worksSwales, contour bunds, zai pit fields
⋮PlantingTree beds, alleys, planting rows
▢GrazingBlocks, camps, permanent fence, gates
◌Livestock waterHeader tank, rising main, pipeline, troughs
WHAT THIS STEP CANNOT TELL YOU
Diversion drains and gradient roads. Both need a surveyed 1:200 to 1:400 gradient held over a kilometre, which a 4.64 m DEM cannot set. A channel that runs uphill fails destructively. The project schema has a diversion_drain slot; this is a recorded gap.
The barn. No known location.
Pipeline routing. Lines are drawn point to point; a built network follows tracks and fence lines.
Regulatory review. Dam construction and abstraction are regulated by the Water Resources Authority.
