The Meta Level
Aquifer StorageChapter

Depths, thicknesses and volumes

Generated by build_aquifer_volumes.py. Every body in aquifer_inventory.md, sized - with the confidence of every cell carried through and the weakest one governing.

Generated by build_aquifer_volumes.py. Every body in aquifer_inventory.md, sized - with the confidence of every cell carried through and the weakest one governing.

The three volumes, and which one this file stops at

volume formula status
IN GROUND area x thickness x porosity all the water the rock holds. Not available. Quoted only so the next row can be seen as the small fraction of it that it is.
DRAINABLE area x thickness x storativity what the rock would give up. The rock’s ceiling. This is what the table below reports.
ACCESSIBLE drainable x what wells can reach NOT COMPUTED, DELIBERATELY.

Why the last step is refused. Accessible volume is an ENGINEERING quantity, not a property of the rock. Water moves about 16 m through the Sherwood in the 229-day surplus-to-deficit lag, so recovery is set by how many wells are drilled and where - not by the size of a polygon. Every body here exceeds its own advective reach by three orders of magnitude. Multiplying a drainable volume by an area is the easiest way to produce a confident wrong answer in this project, so the module stops one step short and says why.

Headline

  • 15,801 Mm3 drainable across 335 bodies, range 2,033 - 92,140 Mm3 (x45 from bottom to top of the propagated range)
  • 90% of that total rests on inferred or guess inputs
  • intergranular only - the part that can actually store between grains: 9,855 Mm3 over 1,991 km2, of which 85% is inferred or guessed
  • 2,533 Mm3 of that total sits on ground our OWN screen calls the SEAL (16%). The 625k classes the Mercia Mudstone 2B/2C, so it enters an aquifer inventory legitimately - but it is the confining layer, and its volume must never be added to a store total. Filter on role before summing anything
  • units with parameters of their own: 9 of 32. The rest take a single shared fracture-flow default, which is an admission, not a parameterisation
volumes by unit
volumes by unit

Depth

Depth-to-top is 0 m for every body, by construction: the 625k maps aquifers at OUTCROP, so this is the source’s assumption and not our measurement. Where our own 50k model shows a younger formation over the same ground the body is concealed there, and cover thickness comes from core/stratigraphy.py - see depth_to_ssg_top(), which is the only depth chain in the project built from boundary definitions rather than from a guess.

THE UNSATURATED ZONE IS THE LARGEST UNQUANTIFIED TERM IN THIS FILE. Drainable volume uses the FULL unit thickness. True saturated thickness is that minus depth to the water table, which we hold at six groundwater stations for one aquifer and nowhere else. So every figure below is an overstatement, and the overstatement is largest where the ground is highest - which is exactly where outcrops are. This is left explicit rather than absorbed into a coefficient.

By unit

unit class flow bodies km2 thickness m storativity T m2/d drainable Mm3 range confidence
Bracklesham + Barton 1B intergranular 7 670 60 0.150 200 5,179 390 - 18,674 guess
Permian sandstone (Exeter Gp / Wiveliscombe) 1B intergranular 12 247 75 0.180 150 2,592 269 - 8,231 inferred
Triassic Rocks * 2C fractures 29 1,471 100 0.020 1,000 2,570 26 - 21,133 guess
Sherwood Sandstone (the target) 1A intergranular 16 241 70 0.125 122 1,525 1,220 - 8,698 published
Great Oolite Group * 2B fractures 14 493 100 0.020 1,000 761 4 - 6,830 guess
White Chalk Subgroup 2A fractures 6 1,975 200 0.002 1,400 486 87 - 1,438 guess
Great Oolite Group * 2A fractures 1 207 100 0.020 1,000 335 2 - 2,906 guess
Upper Devonian Rocks * 2C fractures 13 321 100 0.020 1,000 306 0 - 3,971 guess
Corallian Group * 2B fractures 9 170 100 0.020 1,000 274 2 - 2,391 guess
Upper Greensand 1B intergranular 38 757 50 0.150 100 262 5 - 4,569 guess
Bridport Sand 1B intergranular 10 52 60 0.120 100 239 23 - 816 guess
Triassic Rocks * 2B fractures 42 138 100 0.020 1,000 217 2 - 1,925 guess
Inferior Oolite Group * 2A fractures 33 138 100 0.020 1,000 202 1 - 1,890 guess
Holsworthy Group * 2C fractures 7 149 100 0.020 1,000 198 0 - 1,990 guess
Dinantian Rocks * 2B fractures 30 267 100 0.010 1,000 173 1 - 2,120 guess
Middle Devonian * 2C fractures 3 150 100 0.020 1,000 154 0 - 1,880 guess
South Wales Upper Coal Measures Formation * 2B fractures 4 36 100 0.020 1,000 68 1 - 533 guess
Lower Greensand 1A intergranular 4 21 40 0.150 300 52 0 - 297 guess
Warwickshire Group * 2B fractures 6 28 100 0.020 1,000 46 0 - 392 guess
Portland Group * 2B fractures 5 27 100 0.020 1,000 42 0 - 374 guess
Pennine Middle Coal Measures Formation And South Wales Middle Coal Measures Formation * 2B fractures 3 20 100 0.020 1,000 32 0 - 277 guess
Purbeck Limestone Group * 2B fractures 4 17 100 0.020 1,000 26 0 - 236 guess
Lower Devonian Rocks * 2C fractures 7 10 100 0.020 1,000 17 0 - 140 guess
Pennine Lower Coal Measures Formation And South Wales Lower Coal Measures Formation * 2B fractures 1 9 100 0.020 1,000 12 0 - 120 guess
Teign Valley Group * 2C fractures 2 9 100 0.020 1,000 11 0 - 115 guess
Wealden 1B intergranular 1 3 40 0.100 50 6 0 - 51 guess
Unnamed Extrusive Rocks, Permian * 2C fractures 3 2 100 0.020 1,000 3 0 - 27 guess
Grey Chalk Subgroup 2A fractures 20 255 60 0.006 1,400 3 0 - 39 guess
Wenlock Rocks * 2C fractures 1 1 100 0.020 1,000 2 0 - 19 guess
Millstone Grit Group * 2B fractures 2 1 100 0.020 1,000 2 0 - 18 guess
Unnamed Extrusive Rocks, Silurian * 2C fractures 1 2 100 0.020 1,000 2 0 - 26 guess
Ludlow Rocks * 2C fractures 1 1 100 0.020 1,000 2 0 - 13 guess

* marks a unit with no parameters of its own: it is carrying the shared fracture-flow default.

What would move these numbers most

  1. Bracklesham + Barton - guess, governs 5,179 Mm3 over 670 km2
  2. Triassic Rocks - guess, governs 2,787 Mm3 over 1,609 km2
  3. Permian sandstone (Exeter Gp / Wiveliscombe) - inferred, governs 2,592 Mm3 over 247 km2
  4. Great Oolite Group - guess, governs 1,097 Mm3 over 699 km2
  5. White Chalk Subgroup - guess, governs 486 Mm3 over 1,975 km2
  6. Upper Devonian Rocks - guess, governs 306 Mm3 over 321 km2
  7. Corallian Group - guess, governs 274 Mm3 over 170 km2
  8. Upper Greensand - guess, governs 262 Mm3 over 757 km2

Read in that order. The list is ranked by the volume each weak input governs, not by how weak it is - a guess over 3 km2 costs nothing to leave alone.

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