Stephen Mathers

The use of 3D geological models in the development of the conceptual groundwater model

The conceptual groundwater model is heavily dependent on the geological framework which is used to defi ne the aquifer being studied. In the past, two-dimensional datasets such as geological maps and cross-sections were used in coordination with site-specifi c point data to build a conceptual understanding at the site or catchment scale. This is then simplified and it is this simplifi ed version which is used to build the framework for the numerical groundwater fl ow model. Due to the way the geological framework model and the conceptual groundwater model were generated they could not be viewed together; this inevitably led to a signifi cant loss of information and understanding. With the current rapid developments in 3D modelling software and the increasing availability of digital geological data it is now possible to produce detailed 3D geological models of complex aquifer sequences. In this paper we will use two case studies (Chalk aquifer of the London Basin and the Jurassic limestone aquifer of the Cotswolds) to demonstrate that by developing a detailed 3D geological model signifi cant benefi ts are gained in the understanding and development of the conceptual groundwater model.

Geological 3D modelling : scientific discovery and enhanced understanding of the subsurface, with examples from the UK

In recent years, with the improvement of computer processing power and the development of sophisticated visualisation software, the traditional static views of geological maps, cross-sections and other analogue representations have been replaced by digital, three-dimensional (3D) models. Building these 3D models involves the assembly of many previously isolated and disparate datasets into a single 3D spatial framework for visualisation and analysis. This enables the construction of the best possible geological 3D model using all available information. This paper gives examples of how geoscientific understanding has benefited from the construction of 3D models by the British Geological Survey using several examples to illustrate how structural, stratigraphical and sedimentological discovery can result from the construction of 3D models.

A gravel beach-rip channel system: the Westleton Beds (Pleistocene) of Suffolk, England

The Westleton Beds of northeast Suffolk, England, represent a Pleistocene gravelly shoreline within which three facies are distinguished. A large-scale, cross-stratified, gravel-dominated facies (A) dips predominantly offshore and is interpreted as a beach-face deposit. This facies passes seawards into a ‘transitional’ zone characterized by a horizontally stratified sand facies (B). This is incised into, and replaced seawards, by a third facies (C) deposited in channel-forms. Nearshore these channels are gravel-filled; further offshore they are regularly spaced, up to 2 m deep, their bases commonly being rimmed by gravel which fines upwards into sand. Several such fining-upward pulses are present in the infill of some of the larger channel-forms. It is suggested that these channels were cut and infilled by sporadic high-energy seaward-directed rip-currents.