Landfill Airspace, Fill Rate and Compaction from Drone Surveys

Airspace remaining: the volume between today's surface and the permitted final surface, inside the permitted boundary. Airspace used in the period: the volume between the previous survey and today's. And the effective density: tonnes received in the period divided by the airspace used in the same period, often called the airspace utilisation factor.

The first number is the site's remaining life; the second is the period's consumption; the third tells operations whether compaction and cover practice are using the space well.

Three surfaces carry every calculation: the permitted final design — usually delivered as a TIN in LandXML or as a DEM; the current survey; and the previous survey. A fourth, the cell base or liner surface, is needed for total airspace consumed since the cell opened.

All of them must share one horizontal coordinate system and one vertical reference. A design in orthometric heights compared with a drone DEM in ellipsoidal heights is wrong by the local geoid separation — tens of metres in many places — across the whole site.

Load the permitted design as a surface and compute cut and fill between it and the current terrain inside the permit boundary. Where the ground is below the design, the difference is airspace still available. Where it is above, the site stands over the permitted level there — a compliance issue better found on the survey than at an inspection.

In STREAM, a LandXML surface opens as a TIN, and Volume vs Model computes cut and fill between the TIN and the terrain in the background without changing the DEM. A design delivered as a raster can be loaded as a second terrain scenario and used as the reference instead.

Compare the current survey with the previous one over the active area. The net change is the airspace consumed in the period — but only change larger than the combined noise of the two surveys should count. Change detection with a level of detection filters out differences below that threshold and reports the net volume with an uncertainty band, and co-registration removes a systematic vertical shift between the two surveys before the difference is taken.

Divide the weighbridge tonnes for the period by the airspace used in the same period. A rising figure means each tonne takes less space; a falling one points to compaction, cover practice or the survey itself.

Two cautions. The volume includes everything placed — waste, daily cover soil and construction materials — and settlement of older waste lowers the surface too, which the survey records as airspace regained. Keep the survey dates aligned with the tonnage period, or the ratio compares two different months.

The same survey answers operational questions. Slope analysis checks side slopes against the design gradient. Ponding analysis finds the closed depressions where rainwater will stand on the cap or the working area and reports their storage and spill level, and a watershed click shows the catchment that drains to any point. Both run on the surveyed surface, so they describe the site as it is, not as it was designed.

A drone surface includes whatever stands on it: compactors, trucks, litter screens. Fly when the working area is quiet or remove objects from the DEM before measuring. Keep ground control and the vertical reference identical between surveys, and measure the same boundary every time — a volume difference over two different boundaries measures the boundary, not the waste.