No abstract

Groundwater has a predictable thermal signature that can beused to locate discretezones of discharge to surface water. As climate warms, surface water with strong groundwater influence will provide habitat stability and refuge for thermally stressed-aquatic species, and is therefore critical to locate and protect. Alternatively, these discrete seepage locations may serve as potential point sources of contaminants from polluted aquifers. This study compares two increasingly common heat tracingmethods to locate discrete groundwater discharge: directcontact measurements made withfiber-optic distributed temperature sensing (FO-DTS) and remote sensing measurements collected with thermal infrared (TIR) cameras. FO-DTS is used to make high spatial resolution (typically m)thermal measurements through time within the water column using temperature-sensitive cables. The spatial-temporal data can be analyzed with statistical measures to reveal zones of groundwater influence, however, the personnelrequirements, time to install, and time to georeferencethe cables can be burdensome, and the control units need constant calibration. In contrast, TIR data collection, either from handheld, airborne, or satellite platforms, can quickly capture point-in-time evaluations of groundwater seepage zones across large scales. However the remotenature of TIR measurementsmeans they can be adversely influenced by a number of environmental and physical factors, and the measurements are limited to the surface "skin" temperature of water features.We present case studies from a range of lentic to lotic aquatic systemstoidentify capabilities and limitations of both technologies and highlight situations in which one or the other might be a better instrument choice for locating groundwater discharge. FO-DTS performs well in all systems across seasons, but data collection was limited spatially by practical considerations of cable installation. TIR is found to consistently locate groundwater seepage zones above and along the streambank, but submerged seepage zones are only well identified in shallow systems (e.g. <0.5 m depth) with moderate flow. Winter data collection, when groundwater is relatively warm and buoyant, increases the water surface expression of discharge zones in shallow systems.

International audienceA 1.6 km riser borehole was drilled at site C0009 of the NanTroSEIZE, in the center of the Kumano forearc basin, as a landward extension of previous drilling in the southwest Japan Nankai subduction zone. We determined principal horizontal stress orientations from analyses of borehole breakouts and drilling-induced tensile fractures by using wireline logging formation microresistivity images and caliper data. The maximum horizontal stress orientation at C0009 is approximately parallel to the convergence vector between the Philippine Sea plate and Japan, showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous NanTroSEIZE sites C0001, C0004 and C0006 but orthogonal to the stress orientation at site C0002, which is also in the Kumano forearc basin. These data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike-slip and thrusting. In addition, the stress orientations at site C0009 rotate clockwise from basin sediments into the underlying accretionary prism

[1] In this paper we quantify the influence of geometry and distribution of surface roughness to the directional anisotropy of fluid flow and transport properties of a single fracture. Roughness of fractures appears to have first order control on how they behave mechanically and hydraulically. We directly quantified the surface roughness of a single fracture using high-resolution laser scanning confocal microscopy. This roughness was input into directly coupled numerical models of fluid flow and transport. We simulated the transport of colloids (microspheres) through the fracture. We found tailing in the breakthrough and sensitivity of the breakthrough to flow direction in the fracture. Microspheres were observed to be trapped in low velocity zones on the lee side of fracture walls. This was not observed in smooth or sinusoidal varying fracture wall geometries. These observations have significant implications for quantifying the transport of dissolved and solid phase materials (colloids) through fractured rock.