Modeling infiltration capacity of permeable channels under static and dynamic hydraulic conditions
Increasing infiltration rate of stormwater is important for improving the control of stormwater quantity to foster sustainable urban stormwater management. In the design of stormwater channels, the effect of infiltration on the channel flow and the effects of hydraulic parameters such as water...
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| Format: | Thesis |
| Language: | English |
| Published: |
2018
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/75668/1/FK%202018%20132%20-%20IR.pdf |
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| Summary: | Increasing infiltration rate of stormwater is important for improving the control of
stormwater quantity to foster sustainable urban stormwater management. In the design
of stormwater channels, the effect of infiltration on the channel flow and the effects
of hydraulic parameters such as water level, channel cross section, flow velocity, and
vegetation, on the infiltration capacity of channels are usually ignored. The present
study aimed to examine the effects of hydraulic parameters on the infiltration capacity
of permeable channels through laboratory investigation on channel models under
static and dynamic hydraulic conditions. The study also aimed to develop empirical
models for the variations of infiltration capacity with flow hydraulic parameters, in
order to improve the design of permeable stormwater channels. Different channel
models were constructed for each of the above condition, and different sets of
hydraulic and channel boundary conditions were used to characterise the channel flow
considering the effect of infiltration and to develop empirical models for predicting
infiltration capacity for permeable channels. The effect of channel cross section on the
flow reduction by seepage and infiltration processes were first examined under static
or standing water condition, with various initial water levels, channel base widths and
side slopes. Regression analysis was used to develop an equation for predicting the
rate of unsteady seepage over time, and the equation was used to examine several
cases of different flow cross-sectional areas and channel dimensions, and
subsequently, to determine the section that produced highest infiltration and seepage
under the unsaturated soil condition. Moreover, five existing infiltration models,
namely, the Kostiakov, Horton, Modified Kostiakov, Philip, and Soil Conservation
Service (SCS) models were evaluated, and then they were modified by incorporating
the cross-sectional flow area parameters (depth y, side slope m, and bottom width b)
into them. Under the dynamic or flowing water condition, the mass-balance method
was used for the estimation of infiltration rate, and the experimental tests employed
five inflow rates (Qin = 5.5, 7.5, 9.5, 11.5, 13.5 l/s), with three downstream check dam heights (hw = 10, 15, 20 cm). In addition, two other sets of experiments were conducted
to investigate the effects of grass cover and subsurface water on infiltration rate. The
findings were used to quantify and compare the different cases in terms of the
infiltration rate and cumulative infiltration, and then to develop predictive equations
that include the effect of hydraulic parameters for estimating the infiltration rate in
permeable channels. The results indicated that the infiltration and seepage rates
increase with increasing initial water level irrespective of the base width and side
slope. Moreover, an increase in the side slope increases both the infiltration and
seepage rates, with the effect becoming more significant as the initial water level
increases, while the effect of varying the base width is insignificant. It has also been
found that increasing the wetted perimeter or top width of a channel enhances the
infiltration rate if this is achieved by varying the side slope, and not by increasing the
base width. In the evaluation of the five infiltration models, a comparison using the
coefficients of determination R2 obtained before and after the parameters were added
into the models reveals that the difference between the observed and predicted values
using the modified models was significantly reduced, and R2 increased sharply from
0.14, 0.158, 0.164, 0.146 and 0.162 for the Kostiakov, Horton, Modified Kostiakov,
Philip, and SCS models, respectively, to 0.732, 0.621, 0.735, 0.718 and 0.609. Two
predictive equations were developed finally using the nonlinear regression analysis
after introducing the four hydraulic parameters (y, m, b and v) into the Kostiakov and
Modified Kostiakov models, which were chosen to be improved because they have
been shown to give better performance than the other models during the previous
analysis. The latter model with the new parameters was used for the analysis of a
channel section to determine the best conditions to obtain the highest infiltration rates
for given flow rates and then to plot graphs of the variation of cumulative infiltration
F over time for a grassed channel with different check dam heights and inflow rates.
Cumulative infiltration quantity after 90 min for two cases of channels, with and
without check dams, were compared and the results reveal that the percentage of total
infiltrated water volume increased from 8% to 14% when using check dams with 20-
cm height and 10-m spacing compared to the channel without the check dams.
Modeling the variations of infiltration capacity with hydraulic parameters in
permeable channels using the models developed in this study therefore promises better
storm water management and provides a valuable decision support tool for designing
the permeable channels. |
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