Scaling and Other Properties of Individual Fractures and Networks of Fractures in Crystalline Bedrock Underlying the Mirror Lake Watershed, Woodstock, NH, USA

Modeling of fluid flow through discrete fracture networks is conditioned by the distribution of the properties of individual fractures and of the network of fractures. Size-frequency scaling of the fracture properties as measured in the field is a critical input into discrete fracture network models.

The individual fracture and network properties have been quantified in the crystalline bedrock underlying the Mirror Lake watershed, a small (0.85 km2), steep, watershed located in and adjacent to the Hubbard Brook Experimental Forest, Woodstock, NH. Fracture and groundwater flow data were collected from 40 bedrock wells (Johnston and Dunstan, 1998) and from extensive bedrock outcrops in adjacent roadcut exposures (Barton, Camerlo, and Bailey, 1997).

The size-frequency distributions the properties of individual fractures are scale independent with power scaling exponents b as follows: trace length of fractures on the roadcuts b = -1.6; aperture for fractures on the roadcuts b = -2.0; spacing of fractures logged in the bedrock wells b = -0.2 to -1.6 and on the roadcuts b = -0.1 to -1.9.

The distribution of fracture orientation and fracture inter-connectivity (from fracture trace terminations and intersections mapped in bedrock roadcuts) is reported in frequency percent and their scaling was not studied. Fracture trace length and corresponding apertures show no correlation and no scaling. All fractures are open and reveal reactivation in shear prior to glacial loading and unloading (Barton and Angelier, 2020). There are no sub-horizontal fractures attributable to glacial unloading.