When ground water withdrawl is more than its recharge rate the sediments in the aquifer become compacted.this is called

3.2 Quantifying Rates of Groundwater Recharge In an unconfined aquifer, groundwater age generally increases with depth. If the recharge rate is high, then the age will increase slowly with depth, and if the recharge rate is low, age will increase rapidly with depth. Although it is not necessarily intuitive, Vogel (1967) showed that if recharge is constant across an aquifer, then the age profile will also be constant, and contours of groundwater age will be horizontal (Figure 14). The curvature of flow lines means that vertical water velocity decreases with depth (and is zero at the base of the aquifer). Thus, not only does groundwater age increase with depth, but it does so more rapidly towards the base of the aquifer. The groundwater age profile will therefore be concave upward (Figure 15). For an aquifer of uniform geology, constant thickness ( H), and receiving constant recharge ( R), the groundwater age ( t) as a function of depth below the water table ( z) will be given by Equation 10. (10) where: θ = porosity The vertical component of the groundwater velocity will decrease from R/ θ at the water table to zero at the base of the aquifer. If groundwater age is measured at any discrete depth, then the recharge rate can be determined by re-arrangement of Equation 10. However, if sampling takes place near the water table ( z/ H small) then the recharge rate may be approximated by Equation 11. (11) where: z = depth below the water table (L) In fact, comparison of evaluatio...

Figure 1: Schematic of the Hydrologic Cycle, showing how water moves from the oceans by evaporation, falls as precipitation back to the land and moves through streams, into lakes and into the subsurface as groundwater. All water on the surface of the earth and underground are part of the hydrologic cycle (Figure 1), driven by natural processes that constantly transform water from liquid to solid or vapor and back to liquid while moving it from place to place. Water evaporates from ponds, lakes, oceans, reservoirs, and soils. Plants take water from the ground and emit water vapor into the air, a process called evapotranspiration. Water vapor forms clouds that eventually condense and return to the earth’s surface as precipitation such as fog, rain, sleet, or snow. During storms, water runs off the surface into streams or water bodies or seeps into the ground. Water that sinks into soils or surface rock becomes groundwater, “recharging” groundwater reservoirs or aquifers. Groundwater can discharge at seeps or springs, or into rivers, streams, lakes and oceans, or wells. In arid areas and during the summer, precipitation may first infiltrate into the ground, but much of it quickly returns to the atmosphere through evapotranspiration. Figure 3: Recharge of groundwater, groundwater flow and interconnection of surface water. The unsaturated zone is located immediately beneath the ground and above the water table. Here, the pore spaces contain both air and water. Since an unsatura...

AQUIFERS FACT SHEET Imagine if all of the water that fell onto the location where you lived in a single year stayed right where it landed. Everyone would be wading through water higher than their waists! Fortunately, the precipitation runs into lakes, rivers, oceans, or into underground storage areas called aquifers. As you may have read, most of the void spaces in the rocks below the water table are filled with water. Rocks have different porosity and permeability characteristics, which means that water does not move around the same way in all rocks. When a water-bearing rock readily transmits water to wells and springs, it is called an aquifer. Aquifers are underground reservoirs. Worldwide, 97% of the planet’s liquid fresh water is stored in aquifers. Major aquifers are tapped on every continent, and groundwater is the primary source of drinking water for more than 1.5 billion people worldwide. The aquifer that lies beneath the Huang-Huai-Hai plain in eastern China alone supplies drinking water to nearly 160 million people. Asia, as a whole, relies on its groundwater for nearly one-third of its drinking water supply. Some of the largest cities in the developing world - Jakarta, Dhaka, Lima, and Mexico City, among them - depend on aquifers for almost all their water. In rural areas, where centralized water supply systems are undeveloped, groundwater is typically the source of water. More than 95% of the rural U.S. population depends on groundwater for drinking. Some aqui...

Groundwater separated from atmospheric pressure by relatively impermeable material is termed confined groundwater.When such zones are penetrated by wells, the water rises above the point at which it was first found becausea confined aquifer is under pressure exceeding that of atmospheric pressure. Confining beds vary in permeability and, hence, in their ability to confine artesian aquifers. A major difference from the unconfined aquifer is thatwhen an artesian aquifer is pumped, there is no dewatering of the saturated zone by gravity discharge. A well that taps an unconfined aquifer above a confined aquifer can dewater the former by gravity drainage and not affect the artesian aquifer if the confining bed between them has negligible permeability. Thepotentiometric surface is an imaginary surface above the aquifer, to which water from an artesian aquifer would rise in a pipe. The term potentiometric surface means head- or potential-indicating surface and is preferable to the term piezometric surface, which is found in some literature. In the early development of some artesian basins, the potentiometric surface was above the land surface giving rise to a flowing artesian well. More commonly, the potentiometric surface is above the top of the artesian aquifer, but below the land surface. This type of well is referred to simply as an artesian well. The release of water from artesian storage differs significantly from the way water is released in an unconfined aquifer. The best...

Groundwater recharge or deep drainage or deep percolation is a The most common methods to estimate recharge rates are: chloride mass balance (CMB); soil physics methods; environmental and isotopic tracers; groundwater-level fluctuation methods; water balance (WB) methods (including groundwater models (GMs)); and the estimation of baseflow (BF) to rivers. Processes [ ] Diffused or focused mechanisms [ ] Groundwater recharge can occur through diffuse or focused mechanisms. Diffuse recharge occurs when precipitation infiltrates through the soil to the water table, and is by definition distributed over large areas. Focussed recharge occurs where water leaks from surface water sources (rivers, lakes, wadis, wetlands) or land surface depressions, and generally becomes more dominant with aridity. Natural recharge [ ] Water is recharged naturally by Recharge can help move excess salts that accumulate in the root zone to deeper soil layers, or into the groundwater system. Tree roots increase water Wetlands [ ] Artificial groundwater recharge [ ] Managed aquifer recharge (MAR) strategies to augment freshwater availability include streambed channel modification, :110 Artificial groundwater recharge is becoming increasingly important in India, where ₹1,800 crore (equivalent to ₹46billionorUS$580million in 2020) to fund dug-well Pollution in stormwater Depression-focused recharge [ ] If water falls uniformly over a field such that depression focused recharge. Water tables rise under su...