| Popis: |
This paper introduces an approach to the problem of characterizing flow and transport in a fractured basalt vadose zone. We propose the development of physically based conceptual models on a hierarchy of scales. This approach is derived from field investigations that were conducted in the vadose zone of the Snake River Plain in southeastern Idaho. Three scales of ponded infiltration tests were carried out: a Large Scale Infiltration Test (LSIT) conducted at the Idaho National Engineering and Environmental Laboratory (INEEL) (pond area ∼26,000 m 2 ), intermediate-scale infiltration tests (pond area 56 m 2 ) conducted at the Box Canyon site (near Arco, Idaho), and small-scale infiltration tests (pond area 0.5 m 2 ) conducted at the Hell's Half Acre Lava Flow Site (near Shelly, Idaho). Laboratory water-dripping experiments were also conducted using fracture models with constant and variable apertures. We find that, at each scale of investigation, different models for flow phenomena must be used to explain the observed behavior. These models can be used to describe the flow processes on different scales, with no apparent scaling principles evident. To characterize flow phenomena in fractured basalt, we recommend that investigations be carried out at four scales: elemental, small-scale, intermediate-scale, and large-scale. An elemental component is a single fracture or a block of homogeneous porous media. Small-scale components include one or a few fractures and the surrounding matrix. Intermediate-scale (mesoscale) components include a basalt flow with its fracture network and other parts (fracture zones, vesicular lenses, soil, massive basalt, rubble zone) of a single basalt flow. Large-scale (regional) components include multiple basalt flows and their surrounding network of rubble zones and sedimentary interbeds. |
