International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

Evaluation of infiltration engineering and storage tank systems For improved stormwater management LARIYAH MOHD SIDEK Dept. of Civil Engineering, College of Engineering, Universiti Tenaga Nasional, Malaysia Email: lariyah@uniten.edu.my/lariyah70@hotmail.com KAORU TAKARA Disaster Prevention Research Institute (DPRI), Kyoto University, Kyoto 611-0011, Japan MOHD NOR MOHD DESA Humid Tropics Centre (HTC), Kuala Lumpur, Malaysia AMINUDDIN AB. GHANI River Engineering & Urban Drainage Research Centre (REDAC), University Sains Malaysia, Malaysia Abstract Urbanisation of a watershed with its associated impact on the quantity and quality of stormwater runoff has resulted in the implementation of a number of alternatives for storm-water management. The early stage of stormwater management initiatives in Malaysia is concentrated on the minimization of downstream flooding caused by urbanisation. The objective of the project is to implement the source control and distributed storage systems to resolve identified problems of flooding and hydraulic overloading using the infiltration engineering systems and storage tank system. This paper presents the concept and result for subsurface infiltration and storage tank system which are studied to control stormwater quantity in Engineering Campus Universiti Sains Malaysia, Tronoh, Perak. The purpose of this study is to attenuate the peak flood hydrograph and volume by using three different infiltration and storage techniques based on the surrounding soil conditions. These systems are module infiltration system, loose rock infiltration system and module storage tank system. This paper also discusses some results retrieved from automatic data acquisition system. The comparison of peak flow attenuation and volume attenuation for these infiltration engineering and storage tank systems are highlighted in this paper. The study shows that the peak flow attenuation rate varies with different rainfall magnitude and storm duration at three study locations. These characteristics are important for optimising the design of detention/retention facilities. Modification to the system has been carried out in stage II data acquisition period after encountering flow constraints from stage I data analysis. The simulation using XP-SWMM confirmed the results obtained from the experiment. Keywords Runoff reduction, infiltration facilities, storage tank, stormwater management

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

INTRODUCTION Rapid development in Malaysia, with the construction of new towns, may change the hydrologic and hydraulic characteristics of previously rural catchments. Urbanized areas in which development has altered the natural hydrology and infiltration characteristics of the land typically experience increased surface runoff. Land development alters the natural balance between runoff and natural absorption areas by replacing them with greater amounts of impervious surface. The result is increased rates and volumes of surface runoff. Instead of soaking into the ground, rainfall is converted quickly to runoff and is then eliminated (rapid disposal approach) from the site via pipes and man made channels. The effect of the urbanization on runoff has resulted in producing significantly more runoff volume than pre-development. The peak flows are increased by a factor of 2 to more than 10 times (Roesner et. al., 2001). Urbanisation of a watershed with its associated impact on the quantity and quality of stormwater runoff has resulted in the implementation of a number of alternatives for storm-water management. In order to reduce hydrologic impact such as flooding on that entire catchment and catchments at further downstream, the provision of detention/retention facilities to reduce peak flow are recommended in urban stormwater management manual for Malaysia (DID, 2001). Most methods of urban storm water management emphasize a relatively small number of retention and detention facilities that are distributed throughout a watershed. In contrast, on-site stormwater management controls storm water runoff produced at the site and delivers the runoff to the storm water collection network at reduced rates that will minimize harmful effects to stream habitat. On-site mitigative measures do not eliminate the need for distributed retention and detention facilities, but when implemented effectively, lead to smaller distributed facilities than would otherwise be required. Controlling stormwater at their source has the advantages of reduced hydraulic loading, greater ability to attenuate flows, reduced pollutant loads to downstream regional treatment facilities (such as wetlands and waterway protection/restoration works) and, in many cases, lower capital cost. To understand and control the interaction of urbanization and stormwater runoff a comprehensive view of the urban water cycle and the integrated water management of urban and surrounding area is necessary. The implementation of Urban Stormwater Management Manual for Malaysia (MaSMA) since January 2001 shows the transformation of urban stormwater management practice in Malaysia. The conveyance-oriented approach (rapid disposal) that has been adopted for the past few decades ago is substituted by storage-oriented approach (zero peak contribution). The concept of ‘control at source’ is emphasized in this context and the provision of storage system is essential for new development area. Source control approach is a site design strategy with a goal of maintaining or replicating the predevelopment hydrologic regime through the use of design techniques to create a functionally equivalent hydrologic landscape. Hydrologic functions of storage, infiltration, and ground water recharge, as well as the volume and frequency of discharges are maintained through the use of integrated and distributed micro-scale retention and detention areas, reduction of impervious surfaces, and the lengthening of flow paths and runoff time (Coffman, 2000). As a result, the impact of increased surface runoff due to urbanisation on the receiving waterbody can be minimized. Therefore, the risk of inundation at further downstream catchment is reduced. There are various types and levels of storage tank system can be designed to suit the real site condition. They are broadly categorized as surface storage system and subsurface storage system. They function as a detention/retention facility to attenuate peak flow hydrograph and discharge volume in achieving zero peak discharge. Three types of subsurface on-site detention/retention systems are constructed to study peak flow attenuation of stormwater in USM Engineering Campus, Tronoh, Perak. These systems are Module Storage Tank at Hydrology Lab, Loose Rock Infiltration Tank at Desasiswa Jaya and Module Infiltration Tank at Dewan Serba Guna. The project was carried out with the prime objective of improving natural hydrological cycle and reducing the effects of urbanization by applying infiltration engineering system and storage tank for improvements to be used as guidelines for local use. The infiltration engineering systems and storage tank are design to

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

attenuate about 50% of the runoff hydrograph which means only 50% of the runoff is allow to enter the nearby drain. SIZING ON-SITE DETENTION/RETENTION SYSTEMS These study are designed based on criteria recommended in the Planning and Design Procedure No. 1 “Urban Drainage Design Standards and Procedures for Peninsular Malaysia” (JPS, 1975), Atlantis Water Management Engineering Design Manual (Atlantis, 1998) and Infiltration Drainage – Manual of Good Practice (CIRIA, 1996). These criteria are adopted for tank system design based on site condition such as soil strata in surrounding medium, infiltration capacity and ground water level as detailed in Lau et. al. (2001) and DID (2001). Infiltration and storage tank design consider three important processes: infiltration assessment, geotechnical investigation and hydraulic design. The rate of water infiltrate into the adjacent soil is an important factor in the design. On-site infiltration test is carried out to determine the infiltration capacity which may varies for different sites. The soil infiltration coefficient q is given by

2575950

2575

−

−

×=

p

p

taV

q [1]

where tp75-25 is the time taken for the pit to empty from 75% to 25% of the depth of the pit,

Vp75-25 is the storage volume of the pit between 75% and 25% of the depth, and ap50 is the area of the base and sides of the pit at 50% of the depth.

Infiltration systems introduce water into the surrounding soil. The geotechnical investigation is conducted to identify the implication impact on the ground surrounding the infiltration system. The in-situ infiltration test on site is described in detail by Mohd Sidek et.al. (2000). The results were found to conform with the minimum recommended infiltration rates for Malaysian condition namely 13 mm/hr (DID, 2000). The hydraulic design is to select the dimensions of the infiltration system which are sufficient to dispose of the runoff from storms of any duration with a selected return period. The theory of the detention tank sizing is based on Flow Balance Approach as shown in Equation (2):

outin QQdtdS

−= [2]

where S = storage volume in infiltration system (m3),

Qin = inflow of infiltration system (m3/s), and Qout = outflow of infiltration system (m3/s).

However, storage capacity for infiltration system depends on the porosity of the fill material in infiltration system. Therefore, effective storage, Seffective

Seffective = n * V [3] where Seffective = effective storage volume due to porosity in infiltration system, V = storage volume due to dimension of infiltration system, and n = porosity of infiltration system. So, equation (2) can be solved to give

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

outin QQdtdh

dhdVn −= [4]

For a given return period, the volume of runoff to the infiltration system is given by

Volume of runoff = Q.D = C.i.Ad.D [5] where C = runoff coefficient,

i = rainfall intensity (m/h), D = rainfall duration (h), Ad = impermeable area drained (m2), and

Q = inflow (m3/h). For 3-D infiltration system, the hydraulic equations can be solved to give the maximum depth of water, hmax. The maximum depth of water corresponding to a particular storm duration is given by

)( )(max 1−= −bDeah [6]

where

PdiA

PA

a Db −=

bnAPqb = ,

P = the perimeter of the infiltration system, q = infiltration coefficient, from percolation test (m/h),

AD = area to be drained (m2), n = porosity of fill material (voids volume/total volume), and Ab = base area of infiltration system.

CIRIA (1996) recommended that the infiltration rate from the system should be sufficient to half-empty the storage in 24 hours to ensure the system’s readiness to deal with a rainfall event. For a 3-D infiltration system, the time for half-emptying (T50) is given by

+

+=

PAhP

Ah

PnA

Tb

b

eb

2

50max

maxlog [7]

The design parameters adopted in this study is summarized in Table 1. The dimension for the infiltration and storage tanks are tabulated in Table 2 based on CIRIA method (CIRIA, 1996). The design of the infiltration systems and storage tank was using three different methods i.e. CIRIA method (CIRIA, 1996), DID method (DID, 1975) and Karl Imhoff Method (Imhoff, 1998). However, the design parameter by CIRIA method was chosen as it computed the biggest tank sizing amongst the three methods. Even though the storage systems are design to accommodate 50% of 10-year design storm, the actual flow diverted into the storage is constrained by purification unit (gross pollutant trap). Two main components of purification unit control that deviated the flow are the geotextile (filter) and the 3 inches diameter of connection pipes.

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

Parameter Hydrology Lab

Desasiswa Jaya

Dewan Serba Guna

Infiltration Coefficient, q (m/hr) - 0.1 0.1 Parosity, n 0.96 0.35 0.96 Safety Factor, F 5.0 5.0 5.0 Catchment Area, AD (m2) 1926 1125 2500 Rainfall Intensity, i (mm/hr) 157.5 157.5 157.5 Return Period, T (year) 10 10 10 Rainfall Duration, D (hr) 0.5 0.5 0.5 Percentage of Runoff Attenuation (%) 50 50 50

Table 1: Design Parameter for Infiltration and Storage Tank

Location Hydrology Lab Desasiswa Jaya Dewan Serba Guna

Type of System Storage Tank System

Loose Rock System

Module System

Length (m) 14.568 20 29.75 Width (m) 4.05 4 2.43 Height (m) 1.341 1.50 1.341 Storage due to Dimension (m3) 79 120 98 Effective Storage (m3) 75.84 42 94.08 Time for Emptying 50% Storage Volume (hour)

Not Applicable 8.0 17.3

Table 2: Infiltration and Storage Tank Details

EXPERIMENTAL FACILITIES AND METHODS Storage Module Tank System – Hydrology Lab The first 15-meter from ground platform at Hydrology Lab consists of silty sand to silty clay. This low permeability soil layer is not suitable for infiltration. For most soil with low perviousness when infiltration is rarely feasible and detention is the only alternative to extensive amplification of the drainage network if the downstreams are to be protected as development density increases. Therefore, storage tank system (Figure 1) is recommended at Hydrology Lab. The components for storage tank system are gross pollutant trap, fine sediment trap and the tank covered by geomembrane. The deviated flow will be stored in the tank and the water can be recycled for domestic use hence another way to conserve water.

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

Hydrology Lab ( 1296)

Figure 1 Module Storage Tank System at Hydrology Lab Loose Rock Infiltration System – Desasiswa Jaya Soil layer of silty sand to coarse sand with high permeability is found at Desasiswa Jaya. Infiltration engineering by loose rock system (see Figure 2) is constructed. The system is made up of two main components namely gross and fine pollutant trap and loose rocks. A portion of surface runoff from the existing drainage system will be directed to the pond and hence reducing the peak flood. For optimum efficiency of the system, the design of the pond should satisfy the criteria that the pond should be half-empty within 24 hours. In order to avoid the sediments and silts from entering the facilities the gross pollutant trap (GPT) should be installed.

Desasiswa Jaya (1125)

Figure 2 Loose Rock Infiltration System at Desasiswa Jaya Module Infiltration System – Dewan Serba Guna The soil characteristic at Dewan Serba Guna is similar to Desasiswa Jaya. Infiltration engineering by module system is selected for comparison with loose rock system. The module system (Figure 3) is covered using geotextile to contain the deviated flow from the existing drain system. The stored runoff will slowly infiltrate into the soil around the modular infiltration systems. The module system has an advantage over loose rock system because it requires less area. The difference between infiltration and storage tank systems is the medium used to separate the tank and the surrounding soil. Infiltration tank system allows the water stored in the tank to infiltrate into the surrounding medium but not for the storage tank system because of the low infiltration capacity of the surrounding soil strata. Therefore, permeable geotextile is used for infiltration tank system as separator and filter medium while impermeable geomembrane is used for storage tank system as

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

separator. The construction method and processes are typically similar for both infiltration and storage tank systems except the system at Desasiswa Jaya using loose rock infiltration system rather than module tank for others. Loose rock tank is constructed with gabion which contains chip seal. Small amount of manpower and light machinery are sufficiently mobilised on construction sites. Experience on site has shown that the time required to construct each tank system is recorded less than 15 days.

Dewan Serba Guna

Figure 3 Module Infiltration System at Dewan Serba Guna RESULTS AND ANALYSIS The flow rate and volume attenuation for a particular runoff at Hydrology Lab, Desasiswa Jaya and Dewan Serba Guna are plotted in Figures 4 to 6. Each site consists of around 40 rainfall events which are recorded for a duration of 8 months from August 2000 to March 2001. Based on the effectiveness of the system, the infiltration systems at Dewan Serba Guna and Desasiswa Jaya attenuate higher percentage of stormwater peak flow and volume compared to the storage tank system at Hydrology Lab. The predicted peak flow attenuation for the infiltration and storage tank systems at Dewan Serba Guna, Desasiswa Jaya and Hydrology Lab are 8.5 %, 10 % and 0.3 % respectively for 2-years storm. However, the percentage of volume attenuation is higher than peak flow attenuation for these systems since the peak flow occurs for a shorter duration relatively for every storm event. The volume attenuation for the infiltration and storage tank systems at Dewan Serba Guna, Desasiswa Jaya and Hydrology Lab are extrapolated to 27 %, 19 % and 3.45 % respectively for 2-year storm. The variation between peak flow and volume attenuation differ for three study sites.

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

Figure 5 Comparison for Peak Flow and Volume Attenuation

De s as is wa Jaya

y = 100e-2 .3 0 6 3 x

R2 = 0 .8498

y = 100e-1 .6 8 1 1 x

R2 = 0 .8342

0102030405060708090

100

0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1Qin/Q2

% R

educ

tion

Peak Flow Volume

D e wan Se rba Guna

y = 123 .51e-1 .5 3 7 x

R2 = 0 .6789

y = 119 .67e-2 .6 5 5 7 x

R2 = 0 .5950102030405060708090

100

0 0.1 0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1Qin/Q2

% R

educ

tion

Peak Flow Volume

M akmal Hidrologi

y = 100e-5 .8 1 6 7 x

R2 = 0 .8689

y = 100e-3 .3 6 8 x

R2 = 0 .796

0102030405060708090

100

0 0 .1 0 .2 0 .3 0 .4 0 .5Qin/Q2

% R

educ

tion

Peak Flow Volume

Flow

Volum

Flow

Volum

Flow

Volum

Figure 4 Comparison for Peak Flow and Volume Attenuation

Figure 6 Comparison for Peak Flow and Volume Attenuation

Table 3 summarised selected recent rainfall event data and peak flow attenuation rate for stage I (July 2000 to March 2001) and stage II (April to September 2001) data acquisition at three study sites. Figures 7 to 9 show the relationship of inflow and outflow discharge with the rainfall distribution for stage I data acquisition at Hydrology Lab, Desasiswa Jaya and Dewan Serba Guna respectively. Intense rainfall magnitude for shorter storm duration gives higher peak inflow for the entire catchment. Flow attenuation is apparently lower for higher inflow. The effectiveness of the system is

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

governed by flow capacity of the purification unit. Stage II data acquisition was executed after removing the purification unit and enlarging pipe connecting between infiltration/storage tank and sump. The increased pipe capacity diverts more stormwater quantity into tank system and increases flow attenuation subsequently. Infiltration tank system at Dewan Serba Guna has improved peak flow attenuation significantly compared to other tank systems. These results are depicted in Figures 7a to 9a.

Figure 7 Hydrology Lab – Stage I

Figure 7a Hydrology Lab – Stage II

Figure 8 Desasiswa Jaya – Stage I

Figure 8a Desasiswa Jaya – Stage II

Figure 9 Dewan Serba Guna – Stage I

Figure 9a Dewan Serba Guna – Stage II

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

RESULTS OF MODEL SIMULATION XP-SWMM is a popular stormwater software that routinely used in assessing the impact of proposed land-use changes on runoff quantity as the basis for designing storm-water management facilities to prevent flooding problems. The XP-SWMM model was chosen to simulate a runoff hydrograph and the behaviour of the system for all three sites. The simulation is emphasised on the impact of minor flood event on the drainage system. Hence, the basis of the evaluation is the frequent occurrence storm with design duration and average recurrence interval of 60 minute and 10 years, respectively. The magnitude of peak discharge located at Hydrology Lab was computed by SWMM to be 0.13m3/s and 0.0665 m3/s at the inlet and outlet respectively with 51.0% runoff attenuation as shown in Table 4. The SWMM also predicted the target of 50% runoff attenuation can be achieved for Desasiswa Jaya and Dewan Serba Guna.

Discharge (m3/s) Location Catchment

Area Inlet Outlet

% Runoff Attenuation

Depth of water in the Tank (m)

Hydrology Lab 0.1356 0.1356 0.0665 51.0 1.25 Desasiswa Jaya 0.1043 0.1039 0.0516 50.3 2.88 Dewan Serba Guna

0.2079 0.2071 0.1006 51.4 1.40

Table 4 Summary of result predicted by SWMM for 10 years ARI design storm

The results generated from XP-SWMM modeling have given a good indication that the model is capable of simulating the characteristic infiltration engineering and storage tank system and capable of attenuating flood discharge and managing storm water at source. Table 5 to 7 show how the computed hydrograph is compared to the observed hydrograph at Hydrology Lab, Desasiswa Jaya and Dewan Serba Guna respectively. The simulated hydrograph and flow for all three sites can be illustrated in Figure 10 to 12 respectively. The result from Hydrology Lab (see Table 5) shows the percentage runoff attenuation for observed value always less than the percentage runoff attenuation for computed values except for the event on 15 January 2001. This was affected by the characteristics of the rainfall where the higher rainfall intensity with shorter duration will be smaller the percentage runoff attenuation. By demonstrating that SWMM has comparable results to observed values, it can be concluded that the SWMM can help to optimize the design of urban runoff systems.

Discharge (m3/s) Inlet Outlet

Percentage Runoff Attenuation (%)

Event

Observed Computed Observed Computed Observed Computed 18 Dis 2000 0.0249 0.0243 0.0182 0.0085 26.9 65.0 15 Jan 2001 0.0054 0.0061 0.0006 0.0024 88.9 60.7 12 Feb 2001 0.0118 0.0134 0.0076 0.0049 35.6 63.4 15 Feb 2001 0.0290 0.0228 0.0266 0.0081 8.3 64.5 27 Apr 2001 0.0435 0.0412 0.0352 0.0144 19.1 65.0 8 Aug 2001 0.0163 0.0169 0.0067 0.0061 58.9 63.9

Table 5 Comparison results between observed and simulated at Hydrology Lab

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

Discharge (m3/s) Inlet Outlet

Percentage Runoff Attenuation (%)

Event

Observed Computed Observed Computed Observed Computed 25 July 2000 0.0065 0.0076 0.0014 0.0025 78.5 67.1 27 Sept 2000 0.0392 0.0371 0.0231 0.0099 41.1 73.3 8 Nov 2000 0.0534 0.0553 0.0401 0.0146 24.9 73.6 13 Mar 2001 0.0086 0.0082 0.0026 0.0027 74.4 67.1 25 April 2001 0.0530 0.0447 0.0381 0.0117 28.1 73.8 8 May 2001 0.0157 0.0138 0.0018 0.0042 88.5 69.6

Table 6 Comparison results between observed and simulated at Desasiswa Jaya

Discharge (m3/s)

Inlet Outlet Percentage Runoff

Attenuation (%) Event

Observed Computed Observed Computed Observed Computed 4 Aug 2000 0.0147 0.0075 0.0025 0.0024 83.0 68.0 28 Nov 2000 0.0285 0.0182 0.0116 0.0059 59.3 67.6 12 Jan 2001 0.0639 0.0973 0.0536 0.0314 16.1 67.7 9 Feb 2001 0.0792 0.0988 0.0575 0.0326 27.4 67.0 29 Apr 2001 0.0178 0.0208 0.0004 0.0069 97.8 66.8 8 Aug 2001 0.0341 0.0249 0.0023 0.0078 93.3 68.7

Table 7 Comparison results between observed and simulated at Dewan Serba Guna

Figure 10 Simulated Hydrograph and Flow by SWMM at Hydrology Lab

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

Figure 11 Simulated Hydrograph and Flow by SWMM at Desasiswa Jaya

Figure 12 Simulated Hydrograph and Flow by SWMM at Dewan Serba Guna CONCLUSION The study has shown that the implementation of infiltration engineering and storage tank system will attenuate flow rate and volume of stormwater runoff with the percentage of reduction varies for different sites. However, higher percentage for volume attenuation than peak attenuation is observed for three study sites. At the early stage of the experiment it was found that the target to achieve 50% attenuation for 10-years design storm is not fulfilled. The reduction is governed by the characteristics of inlet and outlet control structures of the system. After some rectification for the existing purification unit and pipe connections in Stage II, the percentage for peak attenuation was drastically growing up even in certain cases more than 50% attenuation was achieved.

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International Conference on Urban Hydrology for the 21st Century 14 – 16 October 2002, Kuala Lumpur

Direct connection systems that are constructed at three infiltration and storage tank systems have encountered disadvantages of the clogging possibility and flow attenuation decrement subsequently. The adoptions of gross pollution traps and sediment control devices are essential for these systems to improve stormwater quality. Furthermore, the inlet control structures such as weir, orifice or others also play an important role to divert stormwater inflow into tank system. Apart from infiltration assessment and hydraulic design, these are the issues that should be taken into consideration so that the system could effectively perform as stormwater quantity and quality control mechanism.

As a conclusion, the stormwater management facilities such as infiltration engineering and storage tank systems are able to attenuate the postdeveloped runoff rate to be less than or equal to the predeveloped peak flow rate up to 50% attenuation of the peak flow. However, the study has shown that the results may be varies based on the design and actual facilities constructed on-site. In the long term the infiltration and storage tank systems will manage to mitigate the initial peak discharge rates and capture the initial runoff pollutants. Then, the community/regional detention should be incorporate to the whole system to hold back the increased volume in water for the overall catchment, while also reshaping the outflow hydrograph to closely match the predeveloped state for the overall catchment.

ACKNOWLEDGEMENT The authors would like to express sincere gratitude to the Department of Irrigation & Drainage, Malaysia for granting a contract research (JPS (PPP) /S/7/98) to conduct the on-going research. Appreciation also goes to Mr Lau Tze Liang, Mr. Shanker Kumar a/l Sinnakaudan, Mr. Paker Mohamad and Mr. Fauzi Shah for their involvements in this project. REFERENCES Ab. Ghani, A., Zakaria, N. A., Abustan, I., Mohd. Sidek, L., Abdullah, R. , Adlan, M. N., and Wan Hussin, W. M. A, 1999. Water Resources and Conservation - Attenuation of Flood Hydrograph and Increase of Groundwater Replenishment. World Water Day, Melaka , 21st - 22 nd March 1999 Atlantis (1998) Atlantis Water Management Engineering Design Manual, Atlantis Corporation Pty Ltd. Bettess, R. (1996) Infiltration Drainage – Manual of Good Practice, CIRIA Report 156 Bettess, R, Davis A., and Watkins, D.C. (1995) Infiltration Drainage – Hydraulic Design, CIRIA Project Report 23 Coffman, L. (2000), Coffman, Larry. 2000. Low-Impact Development Design Strategies, An Integrated Design Approach. EPA 841-B-00-003. Prince George's County, Maryland. Department of Environmental Resources, Programs and Planning Division. DID (2001), Urban Stormwater Management Manual for Malaysia, Penerbitan Nasional Berhad Jabatan Pengairan dan Saliran (1975) Urban Drainage Design Standards and Procedures for Peninsular Malaysia Lau, T. L., Ab. Ghani, A., Zakaria, N. A., Abdullah, R., Mohd. Sidek, L., S. Tan, B. K. (2001) Comparison of Subsurface Infiltration and Storage Tank Systems to Attenuate Stormwater Peak Flow and Volume, Kolokium R&D 2001, Penang, 15th-16th August 2001

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Mohd. Sidek, L, Abd Ghani, A., Zakaria, N. A., Abustan, I., Abdullah, R. & Adlan, M. N., 2000a. Hydraulic characteristics for infiltration systems at USM Perak. National Conference AWAM ’99, Lumut, 21-24 January 2000 Mohd. Sidek, L, Abd Ghani, A., Zakaria, N. A., Abustan, I. & Abdullah, R. , 2000b. New Ecological Drainage System as An Alternative to Conventional Drainage System: A new Concept in Malaysia. Seminar on Integrated Urban Drainage Improvement for the Cities, Melaka, 5-6 June 2000 Mohd. Sidek, L, Takara, K., Desa, M.N., Zakaria, N. A., Abd Ghani, A., Abustan, I. & Abdullah, R. , 2000c. Modelling of New Ecological Drainage Systems Under Malaysian Conditions, Proceedings of Fresh Perspectives on Hydrology and Water Resources in Southeast Asia and the Pacific, (Ed.) M. Paul Mosley, Christchurch, New Zealand, 21-24 November 2000, IHP-V Technical Document in Hydrology No. 7, UNESCO Jakarta Office, pp. 197--205. Mohd. Sidek, L, Abd Ghani, A., Zakaria, N. A., & Abdullah, R. The Use and Development of Bio-ecological Drainage Systems (BIOECODS) Under Tropical Climate. Proceedings of 2nd World Engineering Congress WEC’02, 22 – 25 July 2002, Kuching, Sarawak Roesner, L. A., Bledsoe, B. P., Brashear, R. W. (2001) Are Best-Management-Practice Criteria Really Environmentally Friendly?, Journal of Water Resources Planning and Management, May/June 2001

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