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In deep tunnels with hydro-geological conditions, it is paramount to investigate the geological structure of the region before excavating a tunnel; otherwise, unanticipated accidents may cause serious damage and delay the project. The purpose of this study is to investigate the geological properties ahead of a tunnel face using electrical resistivity tomography (ERT) and tunnel seismic prediction (TSP) methods. During construction of the Nosoud Tunnel located in western Iran, ERT and TSP 303 methods were employed to predict geological conditions ahead of the tunnel face. In this article, the results of applying these methods are discussed. In this case, we have compared the results of the ERT method with those of the TSP 303 method. This work utilizes seismic methods and electrical tomography as two geophysical techniques are able to detect rock properties ahead of a tunnel face. This study shows that although the results of these two methods are in good agreement with each other, the results of TSP 303 are more accurate and higher quality. Also, we believe that using another geophysical method, in addition to TSP 303, could be helpful in making decisions in support of excavation, especially in complicated geological conditions.

We proposed a step-by-step approach to quantify the sensitivity of ground-water discharge by evapotranspiration (ET) to three categories of independent input variables. To illustrate the approach, we adopt a basic ground-water discharge estimation model, in which the volume of ground water lost to ET was computed as the product of the ground-water discharge rate and the associated area. The ground-water discharge rate was assumed to equal the ET rate minus local precipitation. The objective of this study is to outline a step-by-step procedure to quantify the contributions from individual independent variable uncertainties to the uncertainty of total ground-water discharge estimates; the independent variables include ET rates of individual ET units, areas associated with the ET units, and precipitation in each subbasin. The specific goal is to guide future characterization efforts by better targeting data collection for those variables most responsible for uncertainty in ground-water discharge estimates. The influential independent variables to be included in the sensitivity analysis are first selected based on the physical characteristics and model structure. Both regression coefficients and standardized regression coefficients for the selected independent variables are calculated using the results from sampling-based Monte Carlo simulations. Results illustrate that, while as many as 630 independent variables potentially contribute to the calculation of the total annual ground-water discharge for the case study area, a selection of seven independent variables could be used to develop an accurate regression model, accounting for more than 96% of the total variance in ground-water discharge. Results indicate that the variability of ET rate for moderately dense desert shrubland contributes to about 75% of the variance in the total ground-water discharge estimates. These results point to a need to better quantify ET rates for moderately dense shrubland to reduce overall uncertainty in estimates of ground-water discharge. While the approach proposed here uses a basic ground-water discharge model taken from an earlier study, the procedure of quantifying uncertainty and sensitivity can be generalized to handle other types of environmental models involving large numbers of independent variables. [ABSTRACT FROM AUTHOR]

The objective of this study was to use applied and naturally occurring geochemical tracers to study the hydrology of clay settling areas (CSAs) and the hydrological connectivity between CSAs and surrounding hydrological landscapes. The study site is located on the Fort Meade Mine in Polk County, Florida. The CSA has a well-developed, subangular-blocky, clay-rich surface layer with abundant desiccation cracks and other macropores, and a massive, clay-rich sublayer that is saturated below ∼1.0-2.5 m. A bromide tracer was applied to study hydrological processes in the upper part of the CSA. Bromide infiltrated rapidly and perched on a massive, clay-rich sublayer. Bromide concentrations decreased in the upper part of the profile without being transported vertically down through the lower part of the profile suggesting that bromide was lost to lateral rather than to vertical transport. Infiltration and lateral flow were rapid suggesting that preferential flow through desiccation cracks and other macropores likely dominates flow in the upper part of the CSA. Naturally occurring solute and stable isotope tracers were used to study the hydrological connectivity between the CSA and the surrounding hydrological landscape. Three-end mass-balance mixing model results indicate that shallow and/or deep CSA water can be found in all downgradient waters and must be as much as ∼50% of some downgradient waters. Discharge from the CSA to the surrounding surface water-bodies and surficial aquifer occurs laterally through the berms and/or vertically through the massive, clay-rich sublayer. However, the precise flow paths from the CSA to the surrounding hydrological landscape are unclear and the fluxes remain unquantified, so the precise effects of CSAs on the hydrology of the surrounding hydrological landscape also remain unquantified. [ABSTRACT FROM AUTHOR]

Ground-water flow paths constrain the extent of nitrogen (N) sinks in deep, stratified soils of riparian wetlands. We examined ground-water flow paths at four forested riparian wetlands in deep, low gradient, stratified deposits subjected to Southern New England’s temperate, humid climate. Mid-day piezometric heads were recorded during the high water table period in April/May and again in late November at one site. Coupling field data with a two-dimensional steady-state ground-water flow model, flow paths and fluxes were derived to 3 m depths. April/May evapotranspiration (ET) dominated total outflux (44-100%) while flux to the stream was <10% of total outflux. ET exerted upward ground-water flux through shallow carbon-rich soils, increasing opportunities for N transformations and diverting flow from the stream. Dormant season results showed a marked increase in flux to the stream (27% of the total flux). Riparian sites with deep water tables (naturally or because of increased urbanization or other hydrologic modifications) or shallow root zones may not generate ground-water upwelling to meet evaporative demand, thereby increasing the risk of N movement to streams. As water managers balance issues of water quality with water quantity, they will be faced with decisions regarding riparian management. Further work towards refining our understanding of ET mediation of N and water flux at the catchment scale will serve to inform these decisions. [ABSTRACT FROM AUTHOR]

Nonpoint source pollution, which contributes to contamination of surface waters, is difficult to control. Some pollutants, particularly nitrate ( ), are predominantly transmitted through ground water. Riparian buffer zones have the potential to remove contaminants from ground water and reduce the amount of that enters surface water. This is a justification for setting aside vegetated buffer strips along waterways. Many riparian zone hydrologic models assume uniform ground-water flow through organic-rich soil under reducing conditions, leading to effective removal of ground-water prior to discharge into a stream. However, in a small first-order stream in the mid-Atlantic coastal plain, base-flow generation was highly variable (spatially and temporally). Average base-flow loads were greater in winter than summer, and higher during a wetter year than in dryer years. Specific sections of the stream consistently received greater amounts of high ground water than others. Areas within the riparian zone responsible for most of the exported from the watershed are termed “critical areas.” Over this 5-year study, most of the exported during base flow originated from a critical area comprising less than 10% of the total riparian zone land area. Allocation of resources to address and improve mitigation function in critical areas should be a priority for continued riparian zone research. [ABSTRACT FROM AUTHOR]

This study used measured diurnal surface-water cycles to estimate daily evapotranspiration (ET) and seepage for a seasonally flooded sinkhole wetland. Diurnal surface-water cycles were classified into five categories based on the relationship between the surface-water body and the surrounding ground-water system (i.e., recharge/discharge). Only one class of diurnal cycles was found to be suitable for application of this method. This subset of diurnal cycles was used to estimate ET and seepage and the relative importance of each transfer process to the overall water budget. The method has limited utility for wetlands with erratic hydrologic regimes (e.g., wetlands in urban environments). This is due to violation of the critical assumption that the inflow/outflow rate remains constant throughout the day. For application to surface-water systems, the method is typically applied with an assumed specific yield of 1.0. This assumption was found to be invalid for application to surface-water systems with a noncylindrical pond geometry. An overestimation of ET by as much as 60% was found to occur under conditions of low pond stage and high water loss. The results demonstrate the high ET rates that can occur in isolated wetlands due to contrasting roughness and moisture conditions (oasis and clothesline effects). Estimated ET rates ranged from 4.1 to 18.7 mm/day during the growing season. Despite these large ET rates, seepage (recharge) was found to be the dominant water loss mechanism for the wetland. [ABSTRACT FROM AUTHOR]

In recent years the ground-water demand of the population of the island of Maui, Hawaii, has significantly increased. To ensure prudent management of the ground-water resources, an improved understanding of ground-water flow systems is needed. At present, large-scale estimations of aquifer properties are lacking for Maui. Seven analytical methods using constant-rate and variable-rate withdrawals for single wells provide an estimate of hydraulic conductivity and transmissivity for 103 wells in central Maui. Methods based on constant- rate tests, although not widely used on Maui, offer reasonable estimates. Step-drawdown tests, which are more abundantly used than other tests, provide similar estimates as constant-rate tests. A numerical model validates the suitability of analytical solutions for step-drawdown tests and additionally provides an estimate of storage parameters. The results show that hydraulic conductivity is log-normally distributed and that for dike-free volcanic rocks it ranges over several orders of magnitude from 1 to 2,500 m/d. The arithmetic mean, geometric mean, and median values of hydraulic conductivity are respectively 520, 280, and 370 m/d for basalt and 80, 50, and 30 m/d for sediment. A geostatistical approach using ordinary kriging yields a prediction of hydraulic conductivity on a larger scale. Overall, the results are in agreement with values published for other Hawaiian islands. 6 [ABSTRACT FROM AUTHOR]