OR/13/001 Modelled volume, purpose and scale

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The model covers the 1:25 000 sheets TL 92 and TM 01,11,21,02,12,22, (Figure 1) covering approximately 500 km2. It was built in 2006–08 for the six TM 25K sheets as a systematic model build using combinations of the individual tiles (01-11-21, 02 and 12-22) and then amalgamated in 2008. In 2011 TL92 was added to produce a single unified model. The model was constructed using 1:10 000 digital linework with all the TM sheets produced as part of an integrated mapping-modelling resurvey. The TL 92 portion of the model will enabled revision of the approved 1:10 000 superficial and bedrock linework, the simple linework means that the 50K maps of these areas included in the combined Colchester, and Brightlingsea mapsheet closely resembles the 10K dataset.

Figure 1    Extent of the Colchester model in mauve, OS topography © Crown Copyright.

The model was funded as a science budget activity.

The model extends down to the base of the Cretaceous succession in the area at about -300 m OD, the Gault Formation is the lowest modelled unit. The model contains 3 artificial 17 superficial, 5 bedrock units, and a single lens unit within the Anglian glacigenic sequence at Marks Tey.

The final project file is saved as Colchester_V21.gsipr.

No faults are modelled within the area although one single small fault has been drawn into sections as a steep ramp in the base of the affected bedrock units on the TL92 mapsheet.

The model has been calculated using GSI3D 2012 utilising the superficial (sections and envelopes) calculation option. Figure 2 below shows the arrangement of cross-sections drawn to construct this model.

Figure 2    Cross sections in the Colchester model.

The complete model takes about 10 minutes to calculate on a Dell Precision M6700.