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Groundwater recharge is part of the hydrology cycle's process of replenishing groundwater resources.^[1] Groundwater is water that has seeped underground and stored into aquifers which are made up of rock and sediment. Groundwater can be found as deep as 30,000ft below the surface. The majority of this stored groundwater is used for drinking, to irrigate crops and manufacturing.^[2] When this water needs to be replenished is when the process of groundwater recharge is implemented. Recharge happens incidentally and intentionally but it is the primary method through which groundwater enters an aquifer. It occurs both naturally (through the water cycle) and through anthropogenic processes (i.e., "artificial groundwater recharge"), where rainwater and or reclaimed water is routed to the subsurface.

Processes[edit]

Groundwater can be recharged naturally or artificially. Naturally recharging groundwater can be from rainfall, snowmelt and stream flow. This method often is not able to keep up with the demands of water use. Especially during drought years which we are becoming more common.

Artificially recharging groundwater can by done by using recharge ponds and injection wells. Recharge ponds are constructed on the surface of land and allow water to infiltrate the soil into the underground aquifer. When water demand is not so high, this water can come from the overflow of streams and lakes although some areas are using recycled water and agricultural run off water to fill the ponds in turn recharging the aquifers. Injection wells function similar to recharge ponds but use a pumping system to fill the aquifers quicker.^[3]

Natural Groundwater Recharge [edit]

Natural groundwater recharge is the simplest way to recharge groundwater aquifers. When precipitation (or rainfall) falls onto land surface, it then moves through the soil and pore spaces crossing the water table replenishing the supply of groundwater. Streamflow can also recharge groundwater by soaking into the ground and into an underlying aquifer. Wetlands also provide groundwater recharge but more often are a source of groundwater discharge. ^[4]

Artificial Groundwater Recharge [edit]

\Unfortunately, naturally recharging groundwater cannot keep up with the demands of its use so anthropogenic methods have been implemented to help recharge the aquifers. The two most common methods for artificial recharge are using recharge ponds and injection wells. Recharge ponds are artificial ponds made just for groundwater recharge. Depending on water supply, water from stream overflow or redirected streamflow is released into the ponds which then seeps into the ground replenishing groundwater. Injection wells are wells constructed to pump water back into the deep ground and into the aquifers. Injection wells get their water from stormwater, agricultural runoff and also treated waste water and this water is then injected into the aquifers. Injection wells are ideal were soil surface is not as permeable or if land space is limited. ^[5]

Estimation methods[edit]

Estimates of groundwater recharge are important for evaluating and managing groundwater resources. Estimation by any method leaves room for error and uncertainty because of the limitations. It is often recommended that multiple methods be used to estimate recharge. ^[6]

Physical[edit]

Physical methods use the principles of soil physics to estimate recharge. The direct physical methods are those that attempt to actually measure the volume of water passing below the root zone. Indirect physical methods rely on the measurement or estimation of soil physical parameters, which along with soil physical principles, can be used to estimate the potential or actual recharge. After months without rain the level of the rivers under humid climate is low and represents solely drained groundwater. Thus, the recharge can be calculated from this base flow if the catchment area is already known.

Chemical[edit]

Chemical methods use the presence of relatively inert water-soluble substances, such as an isotopic tracer or chloride, moving through the soil, as deep drainage occurs.

Numerical models[edit]

Recharge can be estimated using numerical methods, using such codes as Hydrologic Evaluation of Landfill Performance, UNSAT-H, SHAW, WEAP, and MIKE SHE. The 1D-program HYDRUS1D is available online. The codes generally use climate and soil data to arrive at a recharge estimate and use the Richards equation in some form to model groundwater flow in the vadose zone.

Factors affecting groundwater recharge[edit]

Climate change[edit]

Natural processes of groundwater recharge. Adjustments affecting the water table will drastically enhance or diminish the quality of groundwater recharge in a specific region. The future of climate change introduces the opportunity of implications regarding the availability of groundwater recharge for future drainage basin. Recent studies explore different results of future groundwater recharge rates based on theoretical moist, medium, and arid climates. The model projects a series of various rainfall patterns. From the results, it is predicted that groundwater recharge rates will have the smallest impact on a climate of equal humidity and dryness. Research predicts the insignificant impact of groundwater recharge rates on a medium climate due to predictions of decreased basin size and rainfall. Precipitation trends are predicted to relay minimal change quantitatively in the near future, while groundwater recharge rates are subject to increase as a consequence of global warming. This phenomenon is explained through the physical attributes of vegetation. With increasing temperature as a result of global warming, leaf area index (LAI) decreases. This leads to higher rates of infiltration into the soil and less interception within the tree itself. A direct result of increasing infiltration into the soil is elevated rates of groundwater recharge. Therefore, with increasing temperatures and insignificant changes of precipitation patterns, groundwater recharge rates are subject to increase.

Other research initiatives also reveal that different mechanisms of groundwater recharge have different sensitivities in response to climate change. Increasing global temperatures generate more arid climates in some regions, and this can lead to excessive pumping of the water table. When rates of pumping are greater than the rate of groundwater recharge, there is an enhanced risk of overdrafting. The depletion of groundwater is evidence of the water table's response to excessive pumping. Severe consequences of groundwater depletion include lowering of the water table and depleting water quality. The quantity of water in the water table can change rapidly depending on the rate of extraction. As the level of water decreases in the aquifer, there is less available water to be pumped. If the rate of potential groundwater recharge is less than the rate of extraction, the water table will be too low for access. A consequence of this includes drilling deeper into the water table to access more water. Drilling into the aquifer can be a costly endeavour and it is not guaranteed that the quantity of available water will be exact to previous yields.

Urbanization[edit]

Further implications of groundwater recharge are a consequence of urbanization. Research shows that the recharge rate can be up to ten times higher in urban areas compared to rural regions. This is explained through the vast water supply and sewage networks supported in urban regions in which rural areas are not likely to obtain. Recharge in rural areas is heavily supported by precipitation and this is opposite for urban areas. Road networks and infrastructure within cities prevents surface water from percolating into the soil, resulting in most surface runoff entering storm drains for local water supply. As urban development continues to spread across various regions, rates of groundwater recharge will increase relative to the existing rates of the previous rural region. A consequence of sudden influxes in groundwater recharge includes flash flooding. The ecosystem will have to adjust to the elevated groundwater surplus due to groundwater recharge rates. Additionally, road networks are less permeable compared to soil, resulting in higher amounts of surface runoff . Therefore, urbanization increases the rate of groundwater recharge and reduces infiltration, resulting in flash floods as the local ecosystem accommodates changes to the surrounding environment.

Adverse factors[edit]

References[edit]

Aquaoso. (2021, February 21). Groundwater recharge - its importance and scalability. AQUAOSO. Retrieved May 8, 2022, from https://aquaoso.com/how-to-conserve-water-in-agriculture/groundwater-recharge/
What is groundwater. The Groundwater Foundation. (n.d.). Retrieved April 22, 2022, from https://www.groundwater.org/get-informed/basics/groundwater.html
Hashemi, H., Berndtsson, R., Kompani-Zare, M., & Persson, M. (2013). Natural vs. artificial groundwater recharge, quantification through inverse modeling. Hydrology and Earth System Sciences, 17(2), 637–650. https://doi.org/10.5194/hess-17-637-2013
Escriva-Bou, A., Sencan, G., & Hanak, E. (2021, August). Groundwater recharge - PPIC. www.ppic.org. Retrieved May 8, 2022, from https://www.ppic.org/wp-content/uploads/groundwater-recharge.pdf
"Wetland Functions and Values: Surface and Ground Water Protection | Department of Environmental Conservation". Retrieved 2022-05-08.
Khan, Roohul & Islam, Saiful & Singh, Ram. (2016). Methods of estimating groundwater Recharge. International Journal of Engineering Associates. 5.