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[1] A sequential, geostatistical inverse approach was developed for electrical resistivity tomography (ERT). Unlike most ERT inverse approaches, this new approach allows inclusion of our prior knowledge of general geological structures of an area and point electrical resistivity measurements to constrain the estimate of the electrical resistivity field. This approach also permits sequential inclusion of different data sets, mimicking the ERT data collection scheme commonly employed in the field survey. Furthermore, using the conditional variance concept, the inverse model quantifies uncertainty of the estimate caused by spatial variability and measurement errors. Using this approach, numerical experiments were conducted to demonstrate the effects of bedding orientation on ERT surveys and to show both the usefulness and uncertainty associated with the inverse approach for delineating the electrical resistivity distribution using down-hole ERT arrays. A statistical analysis was subsequently undertaken to explore the effects of spatial variability of the electrical resistivity-moisture relation on the interpretation of the change in water content in the vadose zone, using the change in electrical resistivity. Core samples were collected from a field site to investigate the spatial variability of the electrical resistivity-moisture relation. Numerical experiments were subsequently conducted to illustrate how the spatially varying relations affect the level of uncertainty in the interpretation of change of moisture content based on the estimated change in electrical resistivity. Other possible complications are also discussed.

tion, 1995 through 1997(Faybishenko et al., 1998, and the Hell's Half Acre BasaltThe behavior of unsaturated flow was investigated in a laboratory Infiltration tests, 1997 through 2000 (Wood and Podgormodel. A constant and uniform supply of chemically equilibrated ney, 1999;Podgorney et al., 2000;Wood et al., 2000b). water was introduced to the upper surface of three artificial fractures These tests were conducted at the 100-, 10-, and 1-m in a surrogate fracture network consisting of a thin wall of uncemented limestone blocks. Water was collected from the lower boundary via scales, respectively. Due to the very different behavior fiberglass wicks placed at the bottom of each artificial fracture. Eight observed at these different scales, it can be concluded experiments were conducted to evaluate the repeatability of flow that fractured basalt vadose zone must be conceptualunder nearly identical conditions and to characterize general patterns ized at a hierarchy of scales (Faybishenko et al., 2001). in flow behavior. Collected data revealed that flow generally con-Although the hierarchy of scales approach describes verged to a single fracture in the bottom row of blocks. Periods of behavior of a fractured basalt vadose zone at multiple pathway switching were observed to be more common than periods scales of observation, it fails to provide a means for with steady, constant flow pathways. We noted the importance of scaling between scales of observation and does not defracture intersections for integrating uniform flow and discharging a scribe the unit processes generating flow dynamics ob-"fluid cascade," where water advances rapidly to the next capillary served during field testing. barrier creating a stop and start advance of water through the network. Under very similar initial moisture and boundary conditions, flow in Common to this conceptualization, and indeed to the system was less repeatable than expected. The results of this other studies conducted on a wide variety of fractured simple experiment suggest that the interaction of multiple fracture rock types, is the suggestion that at large spatial scales intersections in a network creates flow behavior not generally recogand relatively short temporal scales, fracture networks nized in popular conceptual and numerical models, (i.e., convergence can facilitate the deep penetration of dissolved contamiof flow, pathway switching, and fluid cascades).

Many forested steeplands in the western United States display a legacy of disturbances due to timber harvest, mining or wildfires, for example. Such disturbances have caused accelerated hillslope erosion, leading to increased sedimentation in fish-bearing streams. Several restoration techniques have been implemented to address these problems in mountain catchments, many of which involve the removal of abandoned roads and re-establishing drainage networks across road prisms. With limited restoration funds to be applied across large catchments, land managers are faced with deciding which areas and problems should be treated first, and by which technique, in order to design the most effective and cost-effective sediment reduction strategy. Currently most restoration is conducted on a site-specific scale according to uniform treatment policies. To create catchment-scale policies for restoration, we developed two optimization models -dynamic programming and genetic algorithms -to determine the most cost-effective treatment level for roads and stream crossings in a pilot study basin with approximately 700 road segments and crossings. These models considered the trade-offs between the cost and effectiveness of different restoration strategies to minimize the predicted erosion from all forest roads within a catchment, while meeting a specified budget constraint. The optimal sediment reduction strategies developed by these models performed much better than two strategies of uniform erosion control which are commonly applied to road erosion problems by land managers, with sediment savings increased by an additional 48 to 80 per cent. These optimization models can be used to formulate the most cost-effective restoration policy for sediment reduction on a catchment scale. Thus, cost savings can be applied to further restoration work within the catchment. Nevertheless, the models are based on erosion rates measured on past restoration sites, and need to be updated as additional monitoring studies evaluate long-term basin response to erosion control treatments. Figure 2. Three treatment options for road crossings. (A) No treatment: drainage structure and road fill remain in stream channel. (B) Basic excavation: culvert and road fill are excavated from stream channel. (C) Total excavation: culvert, road fill and excess sediment are excavated from stream channel and stream banks are reshaped extensively. In this example a mulch of wood and branches was applied on the newly excavated stream banks.focused treatments on the steeper, lower hillslopes where erosion risks are usually highest. However, for crossing treatments, the DP prescribed 'total excavation' slightly more frequently as a technique for crossing removal, whereas the GA used a greater mix of crossing treatments. With a US$250 000 budget, the GA prescribed 'no treatment' or 'rip and drain' for many road segments located on gentle slopes far from the stream (upper and some middle hillslope sites), whereas the DP recommended at least partial outsloping on middle hillslo...

The behavior of unsaturated flow was investigated in a laboratory model. A constant and uniform supply of chemically equilibrated water was introduced to the upper surface of three artificial fractures in a surrogate fracture network consisting of a thin wall of uncemented limestone blocks. Water was collected from the lower boundary via fiberglass wicks placed at the bottom of each artificial fracture. Eight experiments were conducted to evaluate the repeatability of flow under nearly identical conditions and to characterize general patterns in flow behavior. Collected data revealed that flow generally converged to a single fracture in the bottom row of blocks. Periods of pathway switching were observed to be more common than periods with steady, constant flow pathways. We noted the importance of fracture intersections for integrating uniform flow and discharging a “fluid cascade,” where water advances rapidly to the next capillary barrier creating a stop and start advance of water through the network. Under very similar initial moisture and boundary conditions, flow in the system was less repeatable than expected. The results of this simple experiment suggest that the interaction of multiple fracture intersections in a network creates flow behavior not generally recognized in popular conceptual and numerical models, (i.e., convergence of flow, pathway switching, and fluid cascades).