TITLE:
Modeling 3D Ex-Filtration Process of a Soak-Away Rain Garden
AUTHORS:
Sivarajah Mylevaganam, Ting Fong May Chui, Jiangyong Hu
KEYWORDS:
COMSOL Multiphysics, 3D Ex-Filtration, Soak-Away Rain Garden, Average Vertical Ex-Filtration Rate, Horizontal Flow Coefficient
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.3 No.3,
May
11,
2015
ABSTRACT: This paper presents a
three-dimensional (3D) model developed using COMSOL Multiphysics to understand the 3D ex-filtration process of a
soak-away rain garden. With a design hyetograph of 3-month average rainfall
intensities of Singapore, it is found that the average vertical ex-filtration
rate that is obtained by dividing the average vertical ex-filtration (drained
through bottom of the soak-away rain garden, averaged over the simulation
period = 720 min, and expressed in m3) by the surface area of the
soak-away rain garden and the simulation time step is almost constant regardless
of increase in saturated hydraulic conductivity (K) of the in-situ soil and the surface area of
the soak-away rain garden as a percentage of catchment area. However, as depth
to groundwater table which is measured from bottom of the filter media
increases, in between 0.5 m and 1 m of depth
to groundwater table, the average vertical ex-filtration rate decreases
significantly (by around 15 - 20 mm/hr) and the decrease is almost
twice, compared with that between 1 m and 1.5 m of depth to groundwater table.
Furthermore, this study shows that for a given K of in-situ, K of filter media, and depth to groundwater table, as the
surface area of the soak-away rain garden increases, the horizontal flow
coefficient which is defined as the ratio between total horizontal ex-filtration (drained through sides of the soak-away rain
garden, summed over the simulation period, and expressed in m3) and
total vertical ex-filtration (drained through bottom of the soak-away rain
garden, summed over the simulation period, and expressed in m3) decreases.
Moreover, for a given surface area of the soak-away rain garden, K of in-situ, and depth to groundwater table,
the horizontal flow coefficient decreases as K of the filter media increases.
However, it is found that for a given surface area of the soak-away rain
garden, K of in-situ, and K of filter
media, the horizontal flow coefficient increases as depth to groundwater table
increases.