Available via license: CC BY 4.0
Content may be subject to copyright.
Numerical modelling of urban stormwater
management with grassed road divider as bio-
retention system
Jin Sian Lim1, Cha Yao Tan1*, Yau Seng Mah2, Min Lee Lee1, and Fang Yenn Teo1†
1University of Nottingham Malaysia, Jalan Broga, 43500, Selangor, Malaysia
2Universiti Malaysia Sarawak, Jln Datuk Mohammad Musa, 94300 Kota Samarahan, Sarawak
Abstract. Bioretention system is one of the best management practices for
rainwater runoff redirecting and storing before discharge into existing
stormwater system. On the other hand, road divider is designed for dividing
the traffic flow for road safety. However, it may be a blockage for surface
runoff on road and possibly created ponding during heavy rainfall event.
This scenario could become a hazard for motorised vehicles. In this study, a
grassed road divider in Broga Road, Semenyih, Malaysia, is modelled as
bioretention system by EPA's Storm Water Management Model (SWMM)
to investigate the performance of its application. A case of grassed road
divider without bioretention cell was also modelled for comparison. A series
of simulations were carried out for the ARI of 2, 5, and 10 years to further
study the performance of grassed road divider as a bioretention system. Four
different types of soil including sand, loamy sand, loam, and sandy loam are
selected as filler soil in the bioretention cell. Results from the model
simulations showed that the performances of grassed road divider as a
bioretention system can reduce the surface runoff into the stormwater system
up to 49.9% and 56.77% for different ARIs. The effect of this implication is
more significant on the reduction as the ARI increased. Results also showed
that the impact of soil types is insignificant. The findings show that a
bioretention system in a grassed road divider may supplement conventional
urban road drainage and provide an effective stormwater management.
1 Introduction
Malaysia is a developing country with a territory of approximately 320000 km square.
Majority of the population is living in the country's capital which is Kuala Lumpur. Evidently,
urbanization has boosted economic activity and aided in the expansion of the global
population. Simultaneously, urban development disrupted the ecological system by
deforestation, paving over dirt, and polluting atmosphere and water source. Effective
management techniques that are commonly used include wetlands, detention basins, gross
pollutant barriers, and bioretention. The centre business district (CBD) of Kuala Lumpur has
* Corresponding author: keey5tcy@nottingham.edu.my
† Corresponding author: fangyenn.teo@nottingham.edu.my
E3S Web of Conferences 347,
ICCEE 2022
0 (2022) https://doi.org/10.1051/e3sconf/202234704007
4007
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative
Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).
limited lands for the development of gigantic civil structures for stormwater management
such as detention ponds and wetland.
A grassed road divider can be commonly observed in Kuala Lumpur. The fact of limited
space in Kuala Lumpur inspires an idea about applicability of road divider as a stormwater
storage facility [1]. There is a lack of understanding in Malaysia about the use of grassed
road dividers as a mechanism of natural system to retain stormwater [2]. By redirecting
stormwater from the pavement further into grassed road divider, the divider becomes a
valuable component on the road, providing a green space in the urban road drainage
mechanism. As a result, an effort is made here to explore the appropriateness of grassed road
dividers as bio-retention systems in the equatorial region's heavy rains [2].
Usage of bio-retention system method on existing locations aims to establish more
appealing perspective on urban landscape which are typically applied to small places. Bio-
retention systems are typically positioned throughout building, alongside highway and road
drainage riverbeds, next to parking lots, and then within landscaping in impervious or high-
density environment [3].
The objectives of this study are:
1) To simulate the numerical model of grassed road divider as bio-retention system.
2) To study the effectiveness of grassed road divider as bio-retention system.
2 Methodology
2.1 Study area
Broga Road has been selected as the field of study. After a strong storm event, the road
pavement around the Broga road complex is regularly flooded, it is inconvenience for the
road user. The grassed road divider along the Broga road is modelled as normal road divier
and bio-retention system road divider.
Fig. 1.
Street
view of Broga main road with grassed divider.
E3S Web of Conferences 347,
ICCEE 2022
0 (2022) https://doi.org/10.1051/e3sconf/202234704007
4007
2
2.2 Model setup
The methodology used directly targeted storm water runoff management through the use of
green infrastructure, which further contributes towards the achievement of sustainable
development goals. Using EPA SWMM 5.1, model was simulated to investigate the influence
of green infrastructure on storm water runoff control. Example of model setup is showed in
Figure 2, where the shaded regions are the designated sub-catchment of the study.
Fig. 2.
Plan view of mode setup.
2.3 Soil type of bio-retention road divider
Appropriate soils can increase the infiltration rates of surface runoff discharged to the stream,
regulate infiltration rates for pollutant removal, and promote plant growth and long-term
sustainability [2]. For bio-retention systems, sandy loam, loamy sand, or loam texture is
suggested. Depending on water flow calculations performed in a research, soils with
infiltration rates greater than 0.5 in/hr were favoured for bio-retention systems. Minimum
infiltration values ranged between 0.52 in/hr to 2.41 in/hr for loamy sand, sandy loam, and
loam soils. Loamy soils also including silt loams and sandy clay loams with penetration and
infiltration rates equivalent to or less than 0.27 in/hr were not ideal. For the system to work
optimally, the soil must contain 15 percent organic matter and not more than 25 percent clay
[4]. Table 1 displays the hydraulic conductivity, suction head, porosity, field capacity, and
wilting point of sand, loamy sand, sandy loam, and loam that may be used in simulation.
Table 1. Characteristics of soil used for bio-retention road divider
E3S Web of Conferences 347,
ICCEE 2022
0 (2022) https://doi.org/10.1051/e3sconf/202234704007
4007
3
2.4 Design rainfall
The design rainfall in the model is chosen according to Urban Stormwater management
Manial for Malaysia 2
nd
edition (MSMA 2
nd
edition) [5]. The design storm duration 1 hr
and with 3 different sets of ARI which are 2 years, 5 years and 10 years. The design rainfall
intensity is calculated according to the empirical equation (Equation 1) from MSMA 2
nd
edition as the input of the study model and listed in Table 2. The study area is Semenyih
which is near to Kajang, thus, the selected station for IDF constant is Sector JPS Kajang
(Station ID: 2917001).
Rainfall intensity : i =(λT
κ
)/(d+θ)
η (1)
Table 2. Design rainfall intensity by ARI.
ARI (Year) Duration of Storm (hours) Rainfall Intensity (mm/hr)
2 1 60.410
5 1 70.013
10 1 78.278
2.5 Bio-retention road divider specification
According to Malaysian Urban Stormwater Management Manual guideline, the length to
width ratio for constructing a bio-retention scheme is 2:1 as shown in Table 3. As a result, a
single unit of bio-retention system of 3 m x 6 m in scale was constructed. Since the selected
road strip had two-way lanes, the width was considered to be half for one lane and half for
the opposite lane. Conversely, the scale used for SWMM modelling was 1.5m x 6m.
Table 3. Physical specification and geometry of bio-retention system [5].
3 Result
According to Table 4, with the presence of bio-retention cell, the runoffs reduced with a
percentage range of 49.9% to 56.77% from the original scenario which is without the
presence of bio-retention cell. The 2 year ARI reduced the least percentage in runoffs whereas
the 10 year ARI reduced the highest percentage in runoffs which mean 10 year ARI is the
most accurate outcome. Despite so, all the estimate reductions were less than a percentage of
10%. Although the soil types were different, but they were having a same bio-retention
performance when subjected to 1 hour of increasing rain intensities.
For ARIs that is higher than 10 year, the percentage reduce will be higher and eventually
become 100% which does not make sense, so the optimum ARIs was not more than 10 year
to obtain an accurate result.
E3S Web of Conferences 347,
ICCEE 2022
0 (2022) https://doi.org/10.1051/e3sconf/202234704007
4007
4
Additional conclusion of the study showed that in the equatorial areas, roadside drainage
was required for rainfall distribution. In the face of heavy rains and runoff, eliminating a
roadside drain was a poor decision. Additionally, by including a bio-retention system,
portions of the flow as well as dust/soil elements from the road surface may be retained. To
save costs on construction and operation, the design of the roadside drainage may be
simplified.
Table 4. Result of simulated model with and without bio-retention system.
ARI
(Year)
Runoff (m3/s)
Without bio-
retention cell
Runoff (𝑚/s)
With bio-retention cell (different soil types) Average
Runoff
(𝑚/s)
Sand Loamy
San
d
Sandy
Loa
m
Loam
2 0.000341 0.000170 0.000170 0.000170 0.000171 0.00017025
5 0.000412 0.000223 0.000224 0.000224 0.000224 0.00022375
10 0.000480 0.000272 0.000272 0.000273 0.000273 0.00027250
Fig. 3. Runoff with and without bio-retention.
Fig. 4. Bio-retention percentage improvement.
4 Conclusion
From this research paper, we can determine the performance of the bio-retention cell presence
in grassed road divider to store water effectively. Other than storing water, bio-retention cell
0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
55 60 65 70 75 80
RUNOFF(m^3/s)
RAINFALLINTENSITY(mm/hr)
RunoffWithandWithoutBio‐retention
Series2
Series1
Withoutbio‐
retention
Withbio‐
retention
46 48 50 52 54 56 58
2
5
10
Percentagereduction(%)
ARIs(Year)
Averagerunoff
E3S Web of Conferences 347,
ICCEE 2022
0 (2022) https://doi.org/10.1051/e3sconf/202234704007
4007
5
also helps to infiltrate the stones and others particle from road surface to maintain a healthy
and sustainable environment of the urban area. Although the soil types are different from
each other but the performance and the outcomes from each are similar with the others which
are water retention/detention. Using SWMM 5.1, research investigated bio-retention systems
by constructing stormwater transportation systems. For road drainage situations with and
without bio-retention mechanisms, two models were constructed. Existing site constraints at
the site might be replicated using a case study. For discussion, a practical bio-retention
mechanism was tested to 1 hour of tropical rainfall of 2, 5 and 10 year ARIs.
References
1. D. B. Booth, D. Hartley, R. Jackson, J. Am. Water Resour. As. 38(3), 835–845 (2002)
2. Z. S. Lui, Y. S. Mah, F. Y. Teo, Int. J. Civ. Eng. Technol. 10(4), 400–409 (2019)
3. J. Liu, D. J. Sample, C. Bell, Y. Guan, Water, 6(4), 1069–1099 (2014)
4. Z. Y. Li, K. M. Lam, Water Sci. Technol. 71(11), 1742–1749 (2015)
5. Urban Storm Water Management Manual for Malaysia 2nd Edition, Department of
Irrigation and Drainage Malaysia, (2012)
E3S Web of Conferences 347,
ICCEE 2022
0 (2022) https://doi.org/10.1051/e3sconf/202234704007
4007
6
