Active Groundwater Flow Research Articles

A multiple-isotope (δ37Cl, 14C, 3H) approach to reveal the coastal hydrogeological system and its temporal changes in western Kyushu, Japan

Multiple isotopes were used to reveal the coastal hydrogeological system and its temporal changes, caused by transgression and deposition of marine clay, in a small catchment and its offshore extension in Kyushu, Japan. Chloride concentrations in extracted pore waters from an offshore borehole were higher than 16,400 mg/L at depths shallower than 1.5 meters below sea floor (mbsf), and decreased downwards gradually to become lower than 250 mg/L below 7.7 mbsf. Stable chlorine isotopic ratios were –1.50‰ at 6.2 mbsf and –1.27‰ at 5.6 mbsf, while those from other depths showed minor fluctuation. A one-dimensional diffusion-sedimentation model was successfully applied to explain both chloride and stable chlorine isotopic ratios. Apparent residence times of groundwater below the inter-tidal zone is on the order of 100 years while that below sea bottom is about 2,000 years, indicating that groundwater below the inter-tidal zone constitutes a part of the present-day active groundwater flow system while that below sea bottom moves extremely slowly. The coincidence of the apparent residence time of groundwater below sea-bottom and the age of the start of both deposition of marine clay and diffusion processes strongly suggests that the deposition of marine clay has controlled the hydrogeological system and resulted in the reduction of the extent of groundwater discharge.

山形盆地の鉄気水・塩水・どんこ水に関する水質化学的・水文地質学的考察

Groundwater quality in the relatively small Yamagata Basin exhibits considerable variation. The water obtained from artesian wells in the downstream of the Midaregawa Fan in Hairi district is referred to as donko-sui, and is one of the selected 100 exquisite and well-conserved waters. The donko-sui is used for fish farming and daily life water in this district. On the other hand, kanake-mizu from the Sagae district is not potable due to the high Fe content. The kanake-mizu is often used for snow melting in winter, and the iron hydroxide changes the color of road surfaces to redblown. In the Hirashio district on the western margin of the basin, salt is produced in a salt pan fed by a saline spring with a Cl- concentration of more than 10,000 ppm. To clarify the hydrogeological reasons why such various interesting groundwaters exist in the Yamagata Basin, the authors examined a three dimensional distribution of chemistry of groundwater including in Tertiary sediments, which has been assumed to a hydrological basement, by field surveys and reviews of previous studies. The results are summarized as follows.(1) The hydrogeology of the Hairi district is characterized as the discharge zone of very active groundwater flow system in the Midaregawa watershed. Donko-sui is confined and has low electric conductivity and oxidative potential due to the very short residence time.(2) Kanake-mizu is found not only in the Sagae district but in the lowland area where it becomes reductive and Fe-rich after a long residence time.(3) Groundwater from the deep zone in Tertiary sediments (>400 m) could be classified into two groups based on hydrochemical characteristics. One group had lowδ18O, δD and d values, and was obtained from the eastern, southern, and northern parts of the basin. The δ values and Cl- concentration suggested that the groundwater from this group was formed by mixing with paleo sea-water and precipitation in an ice age, which has low δ and d values. The other group had high δ value and low d values, respectively. The properties are similar to saline spring at the Hirashio district but differed markedly from the water samples of the first group. The second group would be originated from paleo seawater but needs some mechanism to form the high δ value.(4) Groundwater from the shallow zone in Tertiary sediments (<400m) has low Cl-concentration, and which suggested that this zone should not be assumed to a hydrological basement.

地下温度に関する研究の現状と水文学的知見の貢献

Subsurface thermal regime is affected not only by thermal conduction but also by advection owing to groundwater flow. The effect of thermal advection is especially large in shallow sedimentary layer with active groundwater flow. Subsurface temperature distributions in some basins and plains in Japan are affected by regional groundwater flow systems. Both field observation and simulation results in the study area show that thermal transport conducted by regional groundwater flow system, driven by topographic effect, distorts subsurface temperature distributions. Moreover, subsurface temperature distributions in the Yonezawa Basin and Nagaoka Plain show effect of groundwater pumping. Subsurface temperatures in shallow layers in these areas have seasonal change due to groundwater pumping for snow melting in winter season.In recent years, subsurface temperature data have been used for reconstruction of ground surface temperature (GST) history as well. The effects of temperature change at the ground surface in the past have conducted into subsurface and have been recorded as transient temperature perturbations onto the background thermal field. Many studies on GST history in North America and Europe are inferred from inversion of borehole temperature profiles in log data.On the other hand, direct utilization of low-temperature geothermal resources, such as geothermal heat pump system, is important from the viewpoint of reduction of CO2 that causes global warming. Such systems are gradually increasing in Japan. To evaluate the influence of direct utilization onto subsurface temperature, an areal simulation, which numerical model was cut out from regional 3D groundwater flow and heat transport model of the Sendai plains, was conducted.Subsurface temperature observed with comparative ease includes important clues to understand global environment problems and/or hints for development of new energy to preserve global environment.It is hoped that hydrological knowledge contributes to understand many problems in various studies with subsurface temperature.

Behaviour of chemical solutes during a storm in a rainforested headwater catchment

AbstractThe aim of this study is to identify, in a small catchment area located within a tropical forest, the pedological compartments in which the export of nutrients and chemical erosion of solutes occur during a stormflow event. The catchment area displays two types of lateral flow: (i) overland flow at the surface of the soil in the litter and root mat and (ii) groundwater flow in a macroporous subsurface horizon. We interpret the variations of stream‐water chemistry during a storm‐flow event using the separation of storm‐flow hydrograph data between overland and groundwater flow, and (Cl−) as a chemical parameter characterizing the residence time of water in the soil. It appears that K+ especially was released into the throughfall, whereas Ca++, Mg++ and Na+ were clearly released from the litter. K+ disappeared rapidly from soil solution, whereas Ca++ and Mg++ were more progressively absorbed by the vegetation. The Ca++ and Mg++ contents in groundwater increased with increasing residence time owing to the transpiration of trees. The export of H4SiO4 in the overland flow was moderate, i.e. 24% of total H4SiO4 export in the stream flow, as overland flow represented 39% of total runoff. The subsurface horizon—where active groundwater flow occurs—was successively affected by chemical erosion during the storm‐flow peak, and then by neoformation of kaolinite favoured by increasing water residence time. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Stress control of hydraulic conductivity in fracture-saturated Swedish bedrock

The granitoid bedrock exposed in the Äspö Hard Rock Laboratory is the best known rock mass in Sweden but is probably generally similar to most of the country in many characteristics relevant to the long term isolation of spent nuclear fuel. Like most Precambrian rocks in the Fennoscandian shield, the rocks of Äspö are saturated by fractures with a large range of orientations after long and complicated deformation histories.The ca. 11,000 fractures documented throughout the Äspö HRL belong to six sets with distinctive orientations. Only about 8% of the total fracture population were wet when they were excavated. Although the wet fractures belong to the same six sets as the total population, their numbers in each set change abruptly at a particular gently dipping fracture zone 240m deep in the laboratory. We correlate the numbers of wet fractures in particular sets to different regimes in the current stress field. Most wet fractures are subhorizontal in a stress regime prone to thrusting above a depth of 240m and subvertical with NW trends in an underlying stress regime prone to wrench faulting.Faults favourably orientated for slip or dilation in the ambient stress field have recently been shown to be the most active groundwater flow pathways near a plate boundary. Here we show a similar relationship for old fractures in a Precambrian shield embedded deep in the Eurasian plate. However, the stress regimes, and thus the anisotropy of transmissivity, are complicated by post-glacial uplift in the Fennoscandian shield and can change 90° within a few metres at depths and locations on the scale of tens and hundreds of metres.

Depth of fractures and active ground-water flow in a clayey till plain in southwestern Ontario : Ruland, W W; Cherry, J A; Feenstra, S Ground Water V29, N3, May–June 1991, P405–417

Depth of fractures and active ground-water flow in a clayey till plain in southwestern Ontario : Ruland, W W; Cherry, J A; Feenstra, S Ground Water V29, N3, May–June 1991, P405–417

Groundwater flow and the metal content of peat

Variations in the concentrations of metals in three peat profiles from the Lost River Peatland, Minnesota are related to the degree of groundwater discharge into the peat, rather than the metal content of the peat when it was originally deposited. Elevated concentrations of metals in the peat profile, particularly from a spring-fen, identify where the greatest volume of groundwater discharge occurs in the peatland. In each profile, the metal content of the peat corroborates previous hydrologic and geochemical sutdies showing active groundwater flow in the humified peat, which must have substantial permeability. Consequently, metal profiles in peat may be used as indicators of the condition of groundwater flow in peatlands where other hydrologic or geochemical information is lacking.

On the origin of saline soils at Blackspring Ridge, Alberta, Canada

Problems of soil salinity occur at Blackspring Ridge, Alberta, in four different settings. The most seriously affected area is at the base of the ridge where salinity appears as severe salt crusting on the surface, salt-tolerant vegetation, and areas of poor or no crop production. Blackspring Ridge is a structural bedrock high that is underlain by Upper Cretaceous sediment of the Horseshoe Canyon Formation. Bedrock is overlain by fluvial, glacial, lacustrine, and aeolian sediment. Piezometric data indicate that groundwater is recharged on and along the upper flanks of Blackspring Ridge and discharges in southern parts of a lacustrine plain that surrounds the ridge. Hydraulic conductivity data, water-level fluctuations, stable isotopes, and hydrochemical data indicate that the fractured near-surface bedrock and overlying thin-drift sediment constitute a zone of active groundwater flow within which salts are generated and transported. Water discharging from this shallow system evaporates and forms saline areas at the base of the ridge. The most seriously affected areas on the lacustrine plain coincide with places where the water table is less than 1.5m from the ground surface. A high water table occurs locally because of the changing topology of geologic units, and lows in the topographic surface that focus groundwater and surface water flows. Some proportion of the shallow groundwater salinized by evaporation is also transported down the flow system where it mixes with unevaporated water. Surface water, from snowmelt and precipitation events, dissolves salt that was deposited at the surface by evaporating groundwater and redistributes the salt to areas of lower elevation.

Origin of dissolved solids in groundwaters of Mayne Island, British Columbia, Canada

Hydrogeological, hydrochemical and isotope techniques were applied to determine the origin of saline groundwaters on Mayne Island in the Strait of Georgia, British Columbia. The saline groundwater is a sodium chloride type, with concentrations of Na + and Cl − as high as 4367 and 8008 mgl −1, respectively. Leach tests on twenty rock samples from boreholes indicate that the shale strata in the Cretaceous bedrock have Cl − concentrations ranging up to 900 ppm by weight and Na + concentrations up to 2070 ppm. The salt probably originated in the shale during periods of post-depositional compaction, or during periods of immersion in ocean water during episodes of glacial loading and erosion during Pleistocene time. The present flow regime of active flushing of meteoric water through the surficial sediments and sedimentary bedrock of Mayne Island began as the island emerged from below sea level during the last deglaciation. The salt content of the present-day groundwater can be accounted for by the slow release, through molecular diffusion, of Na + and Cl − from the low-permeability matrix of the shale to the active paths of groundwater flow in fractures in the shale and in sandstone strata. Intrusion of ocean water under the present hydrologic regime on the island, and upward flow of brine from deep zones within the regional sedimentary basin are believed to be relatively unimportant contributors of salt to the active groundwater flow systems. 18O, deuterium and tritium concentrations are rather uniform for both surface waters and groundwaters on Mayne Island and a meteoric origin is suggested. Saline spring waters on an adjacent island were found to have high 18O and D concentrations ( δ 18 O = + 6.5‰ , δ O = − 24‰ ), suggesting a sedimentary basin brine, but there is no evidence that these brines are mixing with Mayne Island groundwater.