A simple method to assess unsaturated zone time lag in the travel time from ground surface to receptor

2013 ◽  
Vol 144 (1) ◽  
pp. 138-151 ◽  
Author(s):  
Marcelo R. Sousa ◽  
Jon P. Jones ◽  
Emil O. Frind ◽  
David L. Rudolph
Keyword(s):  
Travel Time ◽  
Unsaturated Zone ◽  
Time Lag ◽  
Ground Surface ◽  
Simple Method

Evaluation of the vulnerability of the Western Mountain aquifer to pollution

2000 ◽  
Vol 42 (1-2) ◽  
pp. 417-421 ◽  
Author(s):  
Y. Bachmat ◽  
S. H. Wollman
Keyword(s):  
Travel Time ◽  
Unsaturated Zone ◽  
Winter Season ◽  
Ground Surface ◽  
Mediterranean Coast ◽  
Water Levels ◽  
Mountain Range ◽  
Travel Times ◽  
Recharge Area ◽  
The Mean

The paper introduces a preliminary physical measure of vulnerability of groundwater to pollution called “mean relative travel time of a pollutant”, which is defined as the time of passage through the unsaturated zone of a front of water containing a conservative pollutant and applied to the ground surface at a unit intensity of supply. A methodology for mapping the mean relative travel time is presented and applied to the recharge area of the Western Mountain, (Yarkon-Taninim) aquifer. The aquifer, which extends from the mountain range west of the Jordan River to the Mediterranean coast line, is subdivided into a set of 5×5 km2 cells, and a mean relative travel time is computed for each cell within the recharge area of the aquifer. The estimated mean travel times are directly proportional to the depth to groundwater and inversely proportional to the ratio between the coefficient of replenishment and the water content of the unsaturated zone. Estimates of the latter are obtained from regression of the rise in well water levels during the winter season on the corresponding seasonal rainfall depth. They show relative travel times in the range of one decade in the outcrops of the lower subaquifer and along the foothills, and relative travel times in the range of two to three decades along the mountain range outcrops of the upper subaquifer.

Contributions of Thermodynamic and Mass Transport Modeling to Evaluation of Groundwater Flow and Groundwater Travel Time at Yucca Mountain, Nevada

1994 ◽  
Vol 353 ◽  
Author(s):  
William M Murphy
Keyword(s):  
Mass Transport ◽  
Groundwater Flow ◽  
Travel Time ◽  
Unsaturated Zone ◽  
Ground Surface ◽  
Yucca Mountain ◽  
Transport Modeling ◽  
Transfer Model ◽  
Advective Flow ◽  
Mass Transport Modeling

AbstractConstraints on groundwater flow and groundwater travel time (GWTT) at the proposed HLW repository site at Yucca Mountain, Nevada, U.S.A., can be provided through thermodynamic modeling of relations between gas, liquid, and solid phases, and mass transport modeling. In the unsaturated zone at Yucca Mountain the observed distribution of 14C can be reasonably represented by a mass transport and mass transfer model representing diffusion of 14C02 in the gas phase from the ground surface and equilibrium between aqueous and gas phases, in the absence of net advective flow. This mechanism could also account for aqueous phase 14C activities in the unsaturated zone. Thermodynamic interpretations indicate that groundwaters extracted from boreholes in the water saturated tuffaceous aquifer at Yucca Mountain are undersaturated with respect to calcite, providing evidence that groundwater flow bypasses zones of rock containing calcite and therefore must be channelized. This conclusion is supported by published isotopic data for calcites and groundwaters.

scholarly journals Time lags of nitrate, chloride, and tritium in streams assessed by dynamic groundwater flow tracking in a lowland landscape

2021 ◽  
Vol 25 (6) ◽  
pp. 3691-3711
Author(s):  
Vince P. Kaandorp ◽  
Hans Peter Broers ◽  
Ype van der Velde ◽  
Joachim Rozemeijer ◽  
Perry G. B. de Louw
Keyword(s):  
Water Quality ◽  
The Netherlands ◽  
Groundwater Flow ◽  
Travel Time ◽  
Unsaturated Zone ◽  
Time Lag ◽  
Agricultural Fields ◽  
Drainage Network ◽  
Trend Reversal

Abstract. Surface waters are under pressure from diffuse pollution from agricultural activities, and groundwater is known to be a connection between the agricultural fields and streams. This paper is one of the first to calculate long-term in-stream concentrations of tritium, chloride, and nitrate using dynamic groundwater travel time distributions (TTDs) derived from a distributed, transient, 3D groundwater flow model using forward particle tracking. We tested our approach in the Springendalse Beek catchment, a lowland stream in the east of the Netherlands, for which we collected a long time series of chloride and nitrate concentrations (1969–2018). The Netherlands experienced a sharp decrease in concentrations of solutes leaching to groundwater in the 1980s due to legislations on the application of nitrogen to agricultural fields. Stream measurements of chloride and nitrate showed that the corresponding trend reversal in the groundwater-fed stream occurred after a time lag of 5–10 years. By combining calculated TTDs with the known history of nitrogen and chloride inputs, we found that the variable contribution of different groundwater flow paths to stream water quality reasonably explained the majority of long-term and seasonal variation in the measured stream nitrate concentrations. However, combining only TTDs and inputs underestimated the time lag between the peak in nitrogen input and the following trend reversal of nitrate in the stream. This feature was further investigated through an exploration of the model behaviour under different scenarios. A time lag of several years, and up to decades, can occur due to (1) a thick unsaturated zone adding a certain travel time, (2) persistent organic matter with a slow release of N in the unsaturated zone, (3) a long mean travel time (MTT) compared to the rate of the reduction in nitrogen application, (4) areas with a high application of nitrogen (agricultural fields) being located further away from the stream or drainage network, or (5) a higher presence of nitrate attenuating processes close to the stream or drainage network compared to the rest of the catchment. By making the connection between dynamic groundwater travel time distributions and in-stream concentration measurements, we provide a method for validating the travel time approach and make the step towards application in water quality modelling and management.

A method of obtaining P and S travel-time curves within a “Stripped Earth”*

1952 ◽  
Vol 42 (4) ◽  
pp. 313-314
Author(s):  
V. C. Stechschulte
Keyword(s):  
Travel Time ◽  
Depth Distribution ◽  
Epicentral Distance ◽  
Travel Times ◽  
Depth Of Focus ◽  
Distance Curve ◽  
Simple Method ◽  
Time Distance ◽  
Deep Focus

Abstract A simple method is outlined for obtaining from a time-distance curve of a deep-focus earthquake a table of travel times within an earth “stripped” to the depth h, the depth of focus. The method depends on the fact that such a curve for a deep-focus earthquake has a point of inflection and therefore has the same slope at two different values of epicentral distance. The Herglotz-Wiechert method may then be applied to these travel times to obtain a velocity-depth distribution.

scholarly journals Deep permafrost evolution in unstable slopes during the Holocene

2018 ◽  
Author(s):  
Julien Seguinot
Keyword(s):  
Slope Failure ◽  
Time Lag ◽  
Great Influence ◽  
Ground Surface ◽  
Heat Diffusion ◽  
Failure Initiation ◽  
Finite Element Software ◽  
Hand Model ◽  
The One ◽  
Ice Pressure

Large alpine landslides dynamics are generally associated with Quaternary glacier retreat. Some recent datations demonstrate that several thousand years can separate the slope failure initiation from ice pressure unloading. The current study addresses the question whether the persistence of deep permafrost could produce this time lag. A model of deep permafrost evolution is developed, including heat diffusion, phase change and a ground surface transfer function. It is numerically implemented by a 1D finite difference code on the one hand and into a 2D finite element software on the other hand. Model results reveals the great influence of porosity and near-ground processes in permafrost evolution, and illustrates the possible persistence of a permafrost core into the slope.

A Simple Method for Simultaneous Projection of a Schlieren Image on a Viewing Screen and into a Camera

1963 ◽  
Vol 67 (631) ◽  
pp. 454-454 ◽  
Author(s):  
C. Nebbeling
Keyword(s):  
Light Beam ◽  
Time Lag ◽  
Visual Observation ◽  
Schlieren Image ◽  
Steady Flows ◽  
Knife Edge ◽  
Simple Method ◽  
Schlieren System ◽  
Simple Arrangement ◽  
Viewing Screen

The toepler schlieren system of wind tunnels is usually designed in such a way that an image of the flow in the test section can be formed in a camera for taking flow pictures. For visual observation, a mirror is inserted in the light beam and the image is projected on a screen. When a photograph or film record of the flow is desired, the mirror is removed by some quick-acting mechanism to allow the light beam to enter the camera. Especially in the case of non-steady flows, the time lag involved in removing the mirror can prove to be a drawback. An interesting pattern observed upon the screen may have vanished by the time the light beam is switched over to the camera. At the same time the image disappears from the screen, leaving the operator in doubt whether or not the pattern lasted long enough to be recorded by the camera. In this note a very simple arrangement of the schlieren system is described, which gives simultaneously an image on the viewing screen and in the camera. So far as the author knows, it is not applied elsewhere. The method consists of the use of a mirror knife edge instead of the usual knife edge.

Uncertainty Analyses of Unsaturated Zone Travel Time at Yucca Mountain

Ground Water ◽  
1993 ◽  
Vol 31 (2) ◽  
pp. 293-301 ◽  
Author(s):  
William E. Nichols ◽  
Mark D. Freshley
Keyword(s):  
Travel Time ◽  
Unsaturated Zone ◽  
Yucca Mountain ◽  
Uncertainty Analyses

Transport and Time Lag of Chlorofluorocarbon Gases in the Unsaturated Zone, Rabis Creek, Denmark

2004 ◽  
Vol 3 (4) ◽  
pp. 1249-1261 ◽  
Author(s):  
Peter Engesgaard ◽  
Anker L. Højberg ◽  
Klaus Hinsby ◽  
Karsten H. Jensen ◽  
Troels Laier ◽  
...  
Keyword(s):  
Unsaturated Zone ◽  
Time Lag

scholarly journals Quantitative Assessment of Specific Vulnerability to Nitrate Pollution of Shallow Alluvial Aquifers by Process-Based and Empirical Approaches

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 269 ◽  
Author(s):  
Francesco Fusco ◽  
Vincenzo Allocca ◽  
Silvio Coda ◽  
Delia Cusano ◽  
Rita Tufano ◽  
...  
Keyword(s):  
Travel Time ◽  
Water Table ◽  
Unsaturated Zone ◽  
Nitrate Pollution ◽  
Shallow Aquifers ◽  
Alluvial Aquifers ◽  
Coupled Process ◽  
Nitrate Fertilizer ◽  
Specific Vulnerability ◽  
Empirical Approaches

Shallow aquifers of coastal and internal alluvial plains of developed countries are commonly characterized by the challenging management of groundwater resources due to the intense agricultural and industrial activities that determine a high risk of groundwater contamination. Among the principal origins of pollution in these areas are agricultural practices based on the amendment of soils by nitrate fertilizers, which have been recognized as one of the most severe environmental emergencies for which specific policies and regulations have been issued (e.g., EU Directive 2006/118/EC). In such a framework, the results of research aimed at assessing the specific vulnerability of shallow alluvial aquifers to nitrate fertilizer pollutants by coupled process-based and empirical approaches are here proposed. The research focused on assessing the specific vulnerability to nitrate pollution of a shallow alluvial aquifer of the Campania region (southern Italy), which was selected due to its representativeness to other recurrent hydrogeological settings occurring in alluvial plains of the region and worldwide. In this area, 1D hydro-stratigraphic models of the unsaturated zone were reconstructed and applied for simulating the transport of nitrate pollutants at the water table and estimating the associated travel times. Numerical modeling was carried out by the finite differences VS2TDI code and considered a 10-year time series of rainfall and evapotranspiration as well as typical local farming practices of nitrate fertilizer input. Results of the travel time calculated for the 1D hydro-stratigraphic models considered and at different depths were recognized as a proxy to assess the specific vulnerability to nitrate fertilizer pollution. Among the principal outcomes is an empirical multiple correlation between the travel time of the nitrate fertilizer pollutant, water table depth, and equivalent saturated hydraulic conductivity of the unsaturated zone or hydraulic resistance, which was used to assess the travel time at the distributed scale over the whole area studied as well as the related specific vulnerability. Given such results, the coupled process-based and empirical approach is proposed as generally applicable for assessing and mapping groundwater vulnerability in shallow aquifers, for which detailed stratigraphic and piezometric data are available.

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