Surface Coal Mining Effects on Ground Water Recharge (1990) / Chapter Skim
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3. Hydrology of Ground Water Recharge
3. Hydrology of Ground Water Recharge
Pages 24-40
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From page 24... ...
Surface mining activities may alter many hydrologic processes, including infiltration, overland flow, surface runoff, surface storage and detention, interception, evapotranspiration, percolation, vadose zone storage, ground water storage, ground water flow, streamflow, and water quality. In fact, about the only part of the cycle not generally considered to be influenced potentially is precipitation.
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From page 25... ...
- 2 5 Precipitation Surface Divide Infiltration 1 Percola: Vadose Zone Overland Flow Surface Runoff / \\~/ / Transpiration ~~ / Channel Precipitation InterRow Surface ~~ Storage Evaporation \ 7/ Rae ~ Interception \ Ground Water ~ Divide Ground :: Ground Water Water Flow Zone FIGURE 3.1 Schematic of hydrologic cycle SOURCE: Barfield et al .., 1981.
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From page 26... ...
A capillary fringe exists immediately above the water table. A confined aquifer has a relatively impervious layer as its upper boundary.
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From page 27... ...
- 2 7 R - 8r8e k" 1 l ~tm ~ ~ Scat ~ _~ Recherp ken Tabb ~ _ _ i_ ~ ~ ~ A,~ \~\—~ ~jr~ing Layers u'~confined _,~l~ ~ FIGURE 3 .
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From page 28... ...
Perched aquifers may be seasonal or permanent. For a given section or finite element of an aquifer, inflow or water accretion may consist of downward-moving water from the vadose zone, flow through semiconfining layers, or lateral flow from upgradient portions of the aquifer.
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From page 29... ...
The solid material may be in the form of individual particles or more massive rock formations. The void spaces occur between the particles and as cracks, fractures, or solution channels in the rock.
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From page 30... ...
All of the water contained in a formation will not drain solely due to gravity. The amount of water that will drain from a saturated material due to gravity is referred to as the specific yield, while the amount of water retained is known as the specific retention.
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From page 31... ...
-31 PRIMARY OP[N1N#$ "ELI-SORTED S^ND ~~% AL `~.'/`1 ^~: _- r ', ;/~: ;~ ~ ~ ~ / `~ ~ fR^CTuRES 1W GRA~TE FIGURE 3.3 Exampl porosity.
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From page 32... ...
-32TABLE 3.1 Typical Values (Percent by Volume) for Porosity, Specific Yield, and Specific Retention Material Specific Specific Porosity Yield Retention Soil 55 40 15 Clay 50 2 48 Sand 25 22 3 .
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From page 33... ...
. Unhactwed Fed Lava flaw SANDSTONE Fractured S~ldated SHALE Unfractured Fractured CARBONATE ROa |
From page 34... ...
'=^h='rrm hack - e GROUND WATER RECHARGE Ground water recharge is the addition of surface or precipitation water to the ground water reservoir, and is expressed as volume per unit time or depth of water per unit time. Natural recharge occurs as a result of the natural movement of water through the vadose zone.
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From page 35... ...
0.1 to O.o. O <0.04 0 1000 2000 - ~~e FIGURE 3.5 Spatial distribution of ground water recharge rates based on field data for pre-mining conditions .
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From page 36... ...
The actual recharge rate cannot exceed the rate at which water is available to supply the recharge process. Deep percolation of infiltrated precipitation is a common and widespread means of natural recharge.
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From page 37... ...
fracture zones and solution channels through rock material may increase recharge if they reach the surface or are otherwise located so that they come in contact with water at atmospheric pressure or act as localized sinks and rapidly transmit water to the ground water reservoir. Most fractures tend to terminate at depths of about 30 m (Bouwer, 1978~.
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From page 38... ...
This mound would continue to build until the hydraulic gradients in the aquifer were sufficient to cause lateral flows in the aquifer equal to the recharge rate or until the mound limited the recharge rate itself. Sometimes recharge rates are controlled by perched mounds on restricting layers in the vadose zone.
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From page 39... ...
The perched water then flows laterally out toward the hillsides along bedding planes until it can move vertically downward where fractures penetrate the confining bed. Wet-weather springs form on the hillside where the confining bed is relatively unfractured, and ground water is forced out to the surface.
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From page 40... ...
C0~1~1~. sell _ _ ,.,..,, '.AC'UR'' FIGURE 3.6 Conceptual model of fracture flow in a ground water system.
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