How long does it take for an aquifer to recharge?

Well pumping can have a great influence on groundwater levels, especially in the vicinity of the well. If groundwater is withdrawn at a faster rate than it is replenished, either by infiltration from the surface or by input from surface water bodies, then the water table may become lower, resulting in a “cone of depression” around the well. Depending on the geological and hydrological conditions of the aquifer, among others, the impact on the level of the water table can be short-lived or last for decades and can fall a small amount or many meters. Excessive pumping can lower the water table so much that wells will not supply water; they can “dry out”.

The rate of entry of water into an aquifer (called the recharge rate) varies greatly in a country, local region, or specific location. Factors influencing the recharge rate include the following:

• Climate

• Terrain or topographic relief

• Geology

• Type and amount of vegetative ground cover

• Hydrogeologic conditions

Climate includes the amount of local precipitation. Lower precipitation means less water is available for recharging groundwater levels, while more precipitation means more water is available.

The terrain, or topographic relief, will affect the runoff rate. Rapid runoff does not allow percolation, while standing water allows more percolation.

Geology and the amount of vegetation cover will influence the ability of the earth’s surface to accept infiltrated water. The types of rocks or sediments (including the presence of karst terrain and fractured rocks) also affect the rate of recharge, as does the amount of soil that has impervious surfaces (i.e., impermeable layers and sealing beds).

In areas with many layers of seals, the soil is effectively “sealed” from precipitation. This means that water cannot enter the ground, nor can it percolate through the soil to reach the water table.

Hydrogeology is concerned with how water gets into the ground (recharge), how it flows underground (through aquifers), and how groundwater interacts with the surrounding soil and rock (geology).

The size of the recharge area for a given well depends on the depth of the well and the factors listed above.

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