Evaporation from surface-exposed fractures (ESEF) was investigated experimentally. Surface-exposed fractures can act as major conduits of flow from land surface to underlying aquifers. This role is intensified for low- permeability matrix and deep vadose zone. ESEF can cause salt accumulation (SA) at and near the fracture surface and within the fracture aperture, drawing solution from the vadose zone towards the fracture walls. Surface waters which penetrate and flow through these fractures during flood or intensive rain events can dissolve the accumulated salt and carry it downwards towards underlying groundwater. In this laboratory study, artificial fractures were formed by placing two rock blocks, 50x50x20 cm, with 1 cm between them, mimicking a large-aperture fracture. Pore solution in the rocks was held under low tension, and flux was continuously monitored. The system was constructed in a way that loss of pore solution could occur only via evaporation from the two fracture surfaces. All measurements were taken under controlled ambient temperatures ranging between 9 and 25°C. It was found that decreasing the ambient atmospheric temperature, while the bottom of the rock blocks were kept at constant temperature of 23°C, increases the evaporation from the fracture surfaces by up to three folds. It is concluded that moist air convection is the controlling mechanism for ESEF rates. Long-term effects of SA on EFEF rates were also studied, where evaporation rates began decreasing after approximately 100 gram of salt per square meter of fracture surface had accumulated. Furthermore, ESEF decreased by ~50% compared to its initial value after approximately 160 gram per square meter had accumulated.
|Journal||Geophysical Research Abstracts|
|State||Published - 1 Dec 2007|
- 1818 Evapotranspiration
- 1843 Land/atmosphere interactions (1218
- 1875 Vadose zone