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A numerical investigation of the deep well free surface-seepage face boundary condition

A numerical investigation of the deep well free surface-seepage face boundary condition
A numerical investigation of the deep well free surface-seepage face boundary condition

There is a long history of research dating back to 1932. This thesis revisits the previous work carried out to investigate the seepage surface in order to establish benchmarks and verify the validity of a recent numerical analysis, which permits the seepage surface to be modelled more accurately. After selecting an appropriate numerical code, various steady state and transient flow problems in unconfined aquifers with free surface-seepage face boundary conditions are analyzed.

The investigations of steady state, radial flow problems show that it is important that the impact of the seepage surface on the design of groundwater control and remediation schemes is fully appreciated. In particular caution should be used in applying a Dupuit-Forchheimer analysis to the design of such systems because flow velocities into a well will be overestimated, as will the shape of the free surface drawdown depth commonly known as the cone of depression. In the case of multiple well configurations, it is shown that the seepage surface is eliminated by the inter-action of the wells in the system and it appears that the seepage face surface phenomenon is not a significant factor in the performance of an array of wells.

An extended investigation of the transient seepage-face for single well configurations concludes that a fast decline of the phreatic surface takes place during the early stage of pumping due to the specific storage effect. As time progresses, the specific storage effect decreases and its effect is almost negligible after a period of time depending on the hydraulic conductivity. Intuitively, as the value of the hydraulic conductivity is increased, the faster soil tends to drain, and therefore the level of the phreatic surface is lowered more rapidly. In the case of the landfill investigation, the flow to the well appears to be taking place through the lower layers so that the yield from the well is controlled by the hydraulic conductivity in these layers. Finally, this research provides two algebraic representations. The first gives an estimated solution for both the hydraulic limiting gradient and seepage face elevation. The second estimates the leachate elevation in a landfill after a certain period of pumping.

University of Southampton
Al-Thani, Abdulla A
Al-Thani, Abdulla A

Al-Thani, Abdulla A (2002) A numerical investigation of the deep well free surface-seepage face boundary condition. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

There is a long history of research dating back to 1932. This thesis revisits the previous work carried out to investigate the seepage surface in order to establish benchmarks and verify the validity of a recent numerical analysis, which permits the seepage surface to be modelled more accurately. After selecting an appropriate numerical code, various steady state and transient flow problems in unconfined aquifers with free surface-seepage face boundary conditions are analyzed.

The investigations of steady state, radial flow problems show that it is important that the impact of the seepage surface on the design of groundwater control and remediation schemes is fully appreciated. In particular caution should be used in applying a Dupuit-Forchheimer analysis to the design of such systems because flow velocities into a well will be overestimated, as will the shape of the free surface drawdown depth commonly known as the cone of depression. In the case of multiple well configurations, it is shown that the seepage surface is eliminated by the inter-action of the wells in the system and it appears that the seepage face surface phenomenon is not a significant factor in the performance of an array of wells.

An extended investigation of the transient seepage-face for single well configurations concludes that a fast decline of the phreatic surface takes place during the early stage of pumping due to the specific storage effect. As time progresses, the specific storage effect decreases and its effect is almost negligible after a period of time depending on the hydraulic conductivity. Intuitively, as the value of the hydraulic conductivity is increased, the faster soil tends to drain, and therefore the level of the phreatic surface is lowered more rapidly. In the case of the landfill investigation, the flow to the well appears to be taking place through the lower layers so that the yield from the well is controlled by the hydraulic conductivity in these layers. Finally, this research provides two algebraic representations. The first gives an estimated solution for both the hydraulic limiting gradient and seepage face elevation. The second estimates the leachate elevation in a landfill after a certain period of pumping.

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Published date: 2002

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Local EPrints ID: 464978
URI: http://eprints.soton.ac.uk/id/eprint/464978
PURE UUID: aefa1b4e-bcd2-4a91-8aca-a2b6eaeff046

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Date deposited: 05 Jul 2022 00:14
Last modified: 05 Jul 2022 03:48

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Author: Abdulla A Al-Thani

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