Groundwater in geologic processes download pdf

To develop, most systems of the right flank of composite topography. Other phenomena, such tively high and decrease with increasing depth; water as vegetation patterns, soil- and rock-mechanical insta- flow is downward and divergent.

In discharge areas, the bility, ice development, etc. The indi- subvertical and, consequently, flow is chiefly lateral. The middle segments function chiefly as relatively stable environments of mass and energy transfer.

A schematic overview of groundwater flow distribu- Figure 1 Effects and manifestations of gravity-driven flow in a tion and some typical hydrogeologic conditions and regionally unconfined drainage basin.

Geologic effects requiring long- flow systems and with depth; 4 chemically leached term permanency for their creation are therefore less soils and near-surface rocks in areas of inflow, but likely to develop at shallow depths. Owing, however, to the vastly system terminuses; 5 saline marshes in situations different conditions, different reactive matter, different where wetland conditions and intensive salt supply processes and different flow rates prevailing at coincide; 6 negative and positive anomalies of different locations and depths of the flow regime, the geothermal heat and geothermal gradients beneath rates and products of interaction between water and its areas of descending and ascending flows, respectively; environment will also be fundamentally different, 7 chemically oxidizing and reducing conditions in the although generated simultaneously and by the same near-surface environment of recharge and discharge agent: moving groundwater.

The disequilibria tend to be geomorphologic features, such as gullying and stream reduced in nature through numerous and different meanders; 10 accumulation of transported mineral processes, of which a brief, annotated enumeration is matter such as metallic ions uranium, sulfides , hydro- presented in this section.

Their detailed discussion is carbons, and anthropogenic contaminants, primarily in unwarranted in the present paper as they are all pro- regions of converging flow paths hydraulic traps or in cesses and material interactions dealt with in the regions where the fluid potential is minimum with present context by various works and they are well respect to a transported immiscible fluid oil, gas , e. The above examples pertain to gravity-driven systems of groundwater flow.

It affects both gases and solids. Typical regions of gas The history, geometry, and geologic effects of the dissolution by groundwater are the soil zone, unsatu- nongravitational flow systems are much less tractable rated or vadose zone, and zones of oil and gas accumu- and, therefore, not yet amenable to systematic and lations.

Gases commonly interacting with groundwater generalized discussions. The degree of disso- ; and Oliver More strictly, hydrolysis is the components of decreased solubility, such as the precipi- reaction of an ion with water to form an associated tation of ferric hydroxide Fe OH 3 from waters species plus H c or OH —. Hydrolysis of cations containing ferrous iron Fe OH 2 in solution. The most important removed from the solution, or 2 others that are substances capable of ion exchange are clay minerals, required for the hydrolysis are added to the solution.

Oxidation and reduction must occur based clay mineral. Oxidation, as Reduction of sulfate is due mainly to bacteria and a process of modifying water quality, is most important contact with organic matter coal, lignite, petroleum in the vadose zone, where there is a copious supply of and results in the removal of sulfates from the trans- O2 from the air and from CO2.

Below the water table in porting groundwater. One example is the reaction of the saturated zone, water is rapidly depleted in O2. Consequently, the importance of oxidation also Concentration of the total dissolved solids TDS decreases rapidly with depth. Typical and important content in groundwater may be effected also by evapo- oxidation processes include the oxidation of sulfides, ration of water and solution of mineral matter, in addi- producing Fe2O3, H2SO4, and CO2, with the acids tion to various chemical reactions indicated earlier.

In producing CO2. Reduction also is important in organic this zone, owing to evaporation of earlier rain water, deposits, which constitute reducing chemical environ- salt concentration increases and the dissolved salts are ments. In these cases, oxygen may be obtained from washed down to the water table by subsequent rains. As a result, ionic species may be gener- between rainfall events, the higher is the degree of salt ated, including H2, H2S, CH4, and other hydrocarbons, concentration in the groundwater.

The changes lead to increases in effective stresses, i. The result is for the water to dissolve mineral matter, a very small an increased vulnerability of the land surface to soil amount of soluble minerals in the rocks will result in erosion, landslides and other forms of mass wasting in relatively high water salinity.

Ultrafiltration by shale membranes is thought to be a possible mechanism for increasing ionic concentrations Kinetic or Transport Processes in groundwater. In addition to its functions as a cules are forced by differences in hydraulic heads. The medium of transport and a reactive agent in the subsur- ions of chemical species are left behind, thus increasing face environment, water is also a component of that the salt concentration on the high pressure side of the environment as well as of the hydrosphere of the land argillaceous beds.

The process is probably not as surface. By means of the systematized flow paths, the prevalent and general in nature as its original propo- water masses are regularly distributed in a gravitational nent thought Berry The process may be viewed as the subsurface Physical Processes portion of the hydrologic cycle and, as such, a key Lubrication by water of discontinuity boundaries in the element in the areal distribution of water bodies, their rock framework, such as grain surfaces in soils and in chemical characteristics, the type and magnitude of unconsolidated sediments or fracture and fault planes water-table fluctuations, and the many far-reaching in indurated rocks, reduces friction and enhances the ecological ramifications linked to these conditions.

As a consequence, shear movements of and by groundwater flow systems also is fundamental soil and rock material can be induced along the discon- among the subsurface geologic processes. A wide tinuities, ranging in magnitude from minor rearrange- variety of matter in many different forms is transported ment of mineral grains, as in compaction, to major land by groundwater flow, including aqueous solutions of slides and earthquakes.

The process is particularly organic and inorganic ions; particulate matter in effective in regions where large variations in precipita- colloidal form or larger size suspended grains; gases as tion cause large fluctuations in the water table Deere bubbles or in solution; globules, micelles, or ionic solu- and Patton The effect is further magnified by tions of liquid hydrocarbons; and viruses and bacteria. Relatively high or increased pore pressures are sustained processes resulting in the leaching and natural attributes to the discharge segments of ground- removing of minerals from soils and rocks, carrying water flow systems.

Reductions or increases in pore pres- concentrating contaminants at fluid-dynamically suit- sures, with respect to either space or time, affect the able subsurface locations. If a temperature systems is a dynamic effect. It changes systematically difference exists, i. The greater the controlled by the three components of the hydrogeo- rate of heat exchange the faster the temperature differ- logic environment, namely the topography, geology, ence the temperature anomaly is reduced between and climate.

In turn, the environmental components the water and the environment. This features of different permeabilities, e. Pe p 7 rm Cm km The controlling effect of the hydrogeologic environ- ment on the groundwater regime is easily seen when where n is porosity of the rock; rw, rm are density of the roles of the individual components are considered. Topo- is thermal diffusivity, in which lm is thermal conduc- graphy determines the amount of energy available to tivity and rmCm is specific-heat capacity of the satu- the water for motion at any given point in a drainage rated porous medium.

Finally, rock equilibrate. If, however, Pe 1 1, then advection, i. The process stored water. Geology also determines the chemical is enhanced by highly permeable discontinuities such as constituents and may contribute local or regional faults, fracture zones, cavities, and solution channels, sources of energy by, for instance, compaction, which are often major attributes in the formation of hot compression, or heat.

For instance, soil- Manifestations mechanical effects of discharging groundwater may be manifest simply by liquefaction quick sand, quick clay The geologic agency of moving groundwater is most in a flat, plains region; by soil creep, slumping, and plausibly revealed by the numerous and diverse effects landslides in hills and mountains; or ice mounds and and manifestations resulting from the various flow- frost heaving under cold climates. Discharging spring driven chemical, physical, and kinetic processes.

The ,main factor in the formation of land surface. Typically, total dissolved solids TDS all phenomena within each of these types is the effect content increases, the anionic facies of groundwater of groundwater itself.

Several levels of further divisions changes from bicarbonate through sulfate to chloride, can be made in each case until individual effects and carbon dioxide and free oxygen decrease, redox poten- manifestations of groundwater flow are identified as tial changes from positive to negative, and the pH from shaped by the hydrogeologic environments of parti- acidic to basic, in the direction of flow and with cular localities.

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