What factors influence groundwater levels?

What factors influence groundwater levels?

The primary variables influencing groundwater flow are topography and geology. Storativity refers to an aquifer's ability to store water. Hydraulic conductivity is assessed by a pumping test, which involves pumping one well and noting the changes in hydraulic head in surrounding wells. The rate at which water moves through the soil profile is affected by many factors, including soil type, root density, moisture content, and temperature. Geologic factors that affect groundwater quality include rock composition, fracture systems, and depositional processes. Groundwater flows primarily into three major types of surface-distributed systems: regional groundwaters, confined basins, and unconfined aquifers.

Groundwater levels are determined by the balance between precipitation infiltration into the soil profile and withdrawal for human use. Infiltration depends on soil type, vegetation coverage, and other factors. Withdrawal includes losses by evaporation, seepage into lower-lying areas, and discharge back into streams or other bodies of water. Overwithdrawal can lead to surface drying or even groundwater depletion. If all or most of the water is withdrawn, then the resource will be depleted.

Confined basins are areas where groundwater is retained within layers or zones beneath the land surface. These may be natural formations such as caves or karst topography, or they may be man-made such as reservoirs or irrigation channels.

Does groundwater return to the surface?

The "permeability" of the soil is the rate at which water runs through it. Aquifers are the areas where water travels laterally. Groundwater rises to the surface via these aquifers (arrows), where it drains into lakes, rivers, and the seas. This process is called "recharge." Recharged layers of sediment form a new base for the next layer of withdrawal.

When an aquifer is depleted of water, it becomes vulnerable to contamination from surface sources such as run-off from farms and homes. As this contaminated water enters deeper levels of the aquifer, it begins to affect more distant sources of water. Eventually all the water in the deeply buried portion is lost due to depletion or contamination. These deep wells can no longer supply water and must be abandoned.

Groundwater also returns to the surface through natural pathways without being depleted of water. Some examples include puddles after rain, springs, and seepage into nearby ditches or low-lying land. The amount of recharge that reaches the surface depends on how much precipitation falls as well as the type of soil. If the soil is porous, it will allow water to penetrate further down into its structure before it gets trapped in shallow layers near the ground's surface. Porous soil includes sand, silt, and clay. Non-porous soil types include rock and concrete.

How does topography affect groundwater?

Subsequent research demonstrated that topography influences groundwater movement at multiple spatial scales; steeper topography is associated with deeper water table depths, greater regional groundwater flow, and increased groundwater imports and exports to surface water bodies [Marklund and Worman, 2007; Schaller and Fan. 2008]. Steep slopes may also lead to the formation of rock depressions or "chasms" that can capture and accumulate groundwater, causing local water levels to drop [Schaller and Fan, 2008]. Loose soils on steep slopes tend to be more permeable than stiff clay soils, so they allow water to drain away faster if there is precipitation upstream.

Topography can also influence the distribution of subsurface water by limiting its access to shallow wells or surface streams. If the water table is deep enough, it will not reach the ground even if all the surface water sources are open aboveground. Deep wells must be drilled into this inaccessible water supply to benefit from it.

Finally, topography can have a direct effect on the quantity of rainfall that reaches the ground by altering atmospheric pressure patterns. On mountain peaks, cooler air flows in from higher altitudes toward warmer air at lower elevations, causing precipitation to fall as snow rather than as rain. The amount of precipitation that falls as snow versus liquid water depends on the temperature difference between the peak and low elevation, as well as the distance over which these differences exist.

How are groundwater and earthquakes related?

A water level oscillation is the most typical groundwater level reaction. Step changes in groundwater levels occur "near the field" of an earthquake because the earthquake stresses and strains the earth's crust, including its aquifer systems (deformation). The amount of strain that any particular volume of rock can sustain before failing depends on many factors such as grain size, type of rock, moisture content, and other factors. But even under normal conditions, large volumes of rock may fail without an earthquake being necessary.

When this stress exceeds the sustainable limit of the surrounding rock, small fractures or fissures may develop into full-scale cracks that allow the water to flow into the void left by the rock fragment. The amount of water that can enter through a single crack is limited only by how much pressure it can withstand. Once the fracture reaches the surface, it will cause local flooding which may result in damage to buildings and roads. However, these surface floods do not usually reach heights where they would be dangerous to walk near or drive vehicles over.

Groundwater flows toward areas where there is space available for it to go, which is why you often find high concentrations of groundwater close to the coast or in low-lying areas where there is room for it to spread out.

Why is it important to monitor groundwater levels?

Groundwater monitoring may assist decision-makers in better understanding the long-term viability of an aquifer as a source of water supply and making appropriate policy decisions by: 1. Monitoring changes in groundwater levels. 2. Determining the relationship between surface water and groundwater flows 3. Detecting contamination 4. Assessing the effectiveness of treatment practices 5. Responding to natural or man-made disasters

Groundwater supplies about 20% of the total freshwater used in the United States. It also serves as a major environmental factor affecting the quality of nearby surface waters. Groundwater is withdrawn for various purposes including drinking water production, agriculture, industry, and municipal use. If this activity increases beyond what can be replenished naturally, then some form of management is required to avoid serious consequences for people and animals. Deforestation, overgrazing, urban expansion, and industrial pollution are just a few factors that can affect groundwater levels.

Groundwater levels are usually reported in feet below sea level (fmsl). Monitoring networks collect data on rainfall, snowmelt, streamflow, and ground moisture content for use by scientists in determining how much water is available in the soil and rock layers under different conditions. This information allows them to make forecasts and projections about future water needs/availability.

Groundwater levels are important for several reasons.

About Article Author

Alisa Wagner

Alisa Wagner is a biologist who has been conducting research for over two decades. Alisa loves to teach others about the biology of living creatures and enjoys sharing her knowledge with those around her. She started out as an undergraduate student studying zoology at Cornell University before going on to receive a PhD in developmental biology from the University of Michigan.


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