Abstract
A groundwater mound (or pressure mound) is defined as a volume of fluid dominated by viscous flow contained within a sediment volume where the dominant fluid flow is by Knudsen Diffusion. High permeability self-sealing groundwater mounds can be created as part of a sustainable urban drainage scheme (SUDS) using infiltration devices. This study considers how they form, and models their expansion and growth as a function of infiltration device recharge. The mounds grow through lateral macropore propagation within a Dupuit envelope. Excess pressure relief is through propagating vertical surge shafts. These surge shafts can, when they intersect the ground surface result, in high volume overland flow. The study considers that the creation of self-sealing groundwater mounds in matrix supported (clayey) sediments (intrinsic permeability = 10–8 to 10–30 m3 m–2 s–1 Pa–1) is a low cost, sustainable method which can be used to dispose of large volumes of storm runoff (
Highlights
Studies [1,2] of drainage failure associated with a Sustainable Urban Drainage Scheme (SUDS (Appendix 1, A.1)) at Greenloaning, Perthshire, Scotland, UK (Appendix 1, A.2), have identified that the infiltrating water is held in a sealed groundwater mound which does not dissipate over time into the underlying water table
The relict water volume approximates to τ = 10 (Figure 56). This analysis indicates that (i) the seepage discharges can access stored relict water held in the groundwater mound at elevations, which are located above the seepage zone; and (ii) the seepage discharge can include relict water, which was placed in the groundwater mound over a period of >360 hrs
This study has analyzed a groundwater mound constructed by storm water infiltration into clay
Summary
Studies [1,2] of drainage failure associated with a Sustainable Urban Drainage Scheme (SUDS (Appendix 1, A.1)) at Greenloaning, Perthshire, Scotland, UK (Appendix 1, A.2), have identified that the infiltrating water is held in a sealed groundwater mound which does not dissipate over time into the underlying water table. The flow regime across the mounds boundary cyclically changes from viscous flow (during recharge) to Knudsen diffusion. Groundwater mounds (associated with infiltration devices) in impermeable sediments follow a cyclic three stage pattern of growth [3,4]. Following the cessation of recharge the water body within the groundwater mound is held in place by the change in flow regime at the mounds boundaries [2]. This results in a flow rate for the descending groundwater mound which is controlled by Knudsen diffusion [3,4]. The field observations from Greenloaning (Appendix 1, A.2) are used to develop a model, which can be used in two situations: (i) the disposal of large volumes of storm water runoff into an impermeable clay sequence; and (ii) the storage and recovery of large volumes of water from groundwater mounds contained within a clay sequence
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