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Nonleaky Artesian Radial Flow
Published in William C. Walton, Principles of GROUNDWATER ENGINEERING, 2020
The volume of the cone of depression depends on the time after pumping started, aquifer hydraulic characteristics, and the discharge rate. The radius of the cone of depression is often called the radius of investigation (Streltsova, 1988, p. 78). It is commonly defined as the distance from the production well beyond which drawdown is <0.01 ft or 0.003 m. The radius of investigation may be calculated by first substituting assumed values of Q and T and a value of 0.01 ft or 0.003 m in Equation 2.1 and solving for W(u). Next, the value of u corresponding to the calculated value of W(u) is obtained from Appendix G. This value of u is substituted in Equation 2.3 with assumed values of S, T, and t to obtain r which is the radius of investigation. A BASIC program listed by Clark (1987, pp. 3.1–3.12) calculates u when W(u) is known.
Full-face tunnel borers (TBMs) & special methods
Published in Ratan Raj Tatiya, Surface and Underground Excavations, 2013
Lowering of water table25 (fig. 11.21(a))10 in granular soils can be effective by using techniques such as digging well points, pumping from deep wells or by allowing the water to drain out to a lower horizon than the tunnel’s datum.25 Well points are the tubes that are sunk to a maximum depth of 6 m (the limit of effective suction head) and water is pumped using suction pumps. These are spaced at 1m or so and the tubes are perforated at their bottoms and fitted with a strainer to exclude sand. Continuous pumping for several weeks lowers the water level within the cone of depression. But the method is effective for depths not exceeding 6 m. Using deep-water wells and submergible pumps, water can be pumped effectively from sufficient depth; and the water table can be lowered after a continuous pumping from these wells that surround the tunneling site. Digging an array of wells around the tunnel as it progresses and continuous pumping from them is a costly affair, which can limit application of this technique. Sometimes it is practicable to drive a pilot tunnel below the main tunnel. Arrangement is made to drain off the water, that surrounds the main tunnel, by gravity into a sump which is located at the pilot tunnel and from there it can be pumped to the surface through a shaft or some other openings. This practice is practicable and applied in mines while driving drives and openings at the upper levels or horizons.
Constant Discharge Test Analysis
Published in William C. Walton, Groundwater Pumping Tests, 2019
When a production well is pumped near a stream hydraulically connected to an aquifer, water is first withdrawn from storage within the aquifer in the immediate vicinity of the production well. The cone of depression then spreads, drawing water from storage within an increasing area of influence. Water levels in the vicinity of the stream are lowered, and more and more of the water which under natural conditions would have discharged into the stream as groundwater runoff is diverted toward the production well. Water levels are lowered below the surface of the stream in the immediate vicinity of the production well, and the aquifer is recharged by the influent seepage of surface water (see Walton, 1963).
An empirical test of groundwater pumping effects on river flow and temperature: Chemainus River case study
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2023
In the area of the wells is another thin aquifer of sand and gravel above the confining unit that is thought to be in direct connection with the river (Thurber Engineering Limited, SRK Consulting (Canada) Inc., and Eakins Hydrological Consulting (EHC) 2006), though the nature of aquifer/river interaction is complex and varies along the length of the Chemainus River as it flows over the aquifers. Data from multiple observation wells located above, within, and below the confining till layer in the Chemainus aquifer show that a cone of depression forms when the production wells (which are located primarily in the lower medium to coarse sand and gravel unit) are operating. The cone of depression appears to affect the deeper aquifer and, to a lesser degree, the shallower aquifer above the till (Thurber Engineering Limited, SRK Consulting (Canada) Inc., and Eakins Hydrological Consulting (EHC) 2006).