Groundwater Exploration• Involves Mapping of potential aquifer horizons.• Location of water table through field investigation helps to define the saturated zone of the aquifer.• Several surface and subsurface investigations are carried out.
Movement of Groundwater• Groundwater velocity. Most groundwater moves slowly relative to stream flow. Water velocity varies greatly for a variety of reasons. Water flow underground flows in response to differences in water pressure and elevation.• Elevation. Water within the upper part of the saturated zone (phreatic zone) moves down hill from high head to low head. The greater the change in elevation, the faster it will flow.• Water table slope. The slope of the water table strongly influences ground water velocity where the steeper the slope the faster the water flows. Slope is controlled by topography .Groundwater will not move if the water table is flat.• Permeability. Groundwater flows faster in aquifers with high permeability.• Pressure. Water under pressure will move faster than water not under pressure.
Effective Porosity of Ground• Some of the pore spaces may be too small or too poorly connected to permit the water they contain to flow out easily• The effective porosity can be thought of as the volume of pore space that will drain in a reasonable period of time under the influence of gravity
Velocity of Groundwater Flow• Velocity of Flow is calculated using Darcy’s Law.
• Groundwater flow is very slow compared to surface water movement.• This is thousands of times slower than river flow (typically measured in feet per second), and means that a parcel of groundwater takes over a decade to move a mile, and about a century to cross a township.• This natural time scale underscores the importance of long-term planning and management, and helps explain why resource depletion or contamination cannot be quickly or easily rectified
Rock Interaction• Things are not as simple as that of a stream flow, flow beneath the earth surface occurs through the rocks and soil.• So, velocity and pattern of flow depends highly on the nature of the rock present at any particular location.• More the permeability, more will be the velocity.
Factors affecting the flow underneath Type of Rock:• Igneous and Metamorphic rocks both have primarily low porosity i.e. 8-10 %, but in Basalt porosity is higher due to vesicles.• Sedimentary Rocks includes sandstone, siltstone, shale, clay stone and limestone1. Sandstone possesses variable porosity depending on its concentration. Coarse Grained sandstone and partly consolidated sandstones perform better as aquifers.
2. Limestone are better aquifers as solutioncavities are present within them.3. Claystones, clay and shale have lowpermeability values and are poor aquifers. Effect of Faults in rocks• Joints and Cracks contribute to secondary porosity.• Joints decrease in their frequency with depth• Occurrence of impervious dykes and sills contribute to the groundwater localization.
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