ACEM Submission (Additions by CCM)

ACEM Engineering Awards Competition 2010

PROJECT NAME : FLOOD MITIGATION PROJECT FOR KLANG VALLEY AND MAINTENANCE SCHEME FOR SG KLANG, SG DAMANSARA, SG KAYU ARA, SG PENCHALA, SG BOHOL, SHAH ALAM MAIN DRAIN AND OTHER RELATED TRIBUTARIES – SG DAMANSARA (PKG 1)

ROLE OF FIRM : DESIGN & BUILT CONSULTANT

OTHER CONSULTANTS : MARITIME RESEARCH CENTRE, NANYANG TECHNICAL UNIVERSITY (NTU), SINGAPORE

STATEMENT OF PROPORTION

: 99.9% (LOCAL)0.1% (FOREIGN)

CLIENT : WIJAYA BARU SDN BHD

BRIEF PROJECT DESCRIPTION

This Project is a design and build flood mitigation project for the lower reaches of Sg

Damansara, commissioned by the Government of Malaysia through Jabatan

Pengairan dan Saliran Malaysia (JPS) under the Ninth Malaysia Plan. The Project

has a contract sum of RM340,519,678.12 commencing on 6 th August 2007. The

Project was successfully completed in August 2009.

In summary, the Project consists of the following flood mitigation works (see Figure 1 for Project Layout):

(i) Construction of the RRIM, Subang Airport East (SAE) and Subang

Airport South (SAS) flood detention ponds (refer Figures 2, 3 and 4 for pond layout).

(ii) Removal of bridge constrictions along Sg Damansara from its

confluence with Sg Klang to Taman Saujana Indah.

(iii) River protection works for six critical areas which include earth

bund, culvert, pumping station, RC flood wall at TTDI Jaya, etc.

CLIENT REQUIREMENTS

JPS specified that the main emphasis of the Project is to provide adequate protection

from the 100 year ARI overbank flooding at six important areas within the Sg

Damansara catchment, which were in the past frequently flooded.

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Priority was given to six prominent flood prone areas, namely:

(i) Taman TTDI Jaya

(ii) NKVE Highway

(iii) Section 13 Shah Alam

(iv) Batu Tiga at the Federal Highway and KTMB Railway

(v) Taman Mesra

(vi) Kampung Melayu Kebun Bunga

Besides protection from overbank flooding, four low lying areas along the river were

also identified for additional flood protection works by JPS. The areas are:

(i) Taman Saujana Indah

(ii) TTDI Jaya

(iii) Jalan Persiaran Kerjaya and Taman Mesra

(iv) Kampung Melayu Kebun Bunga

These areas were selected based on their susceptibility to flooding due to their

existing low platform levels (lower than surrounding catchments) and internal drain

levels. A 10 year ARI level of protection for the local drainage works was required.

JPS has also emphasized on the importance of maintaining the river in its natural

state, thus dictated that no permanent concrete structures and concrete lined

sections should be installed in the river, if possible.

FEATURES AND SOLUTIONS

a) FeaturesTo meet the client’s requirements, a thorough analysis of Sg Damansara’s

catchment was carried out. The design flow of the catchment and its main

triburtaries were derived using HEC-HMS hydrological modeling software.

With the availability of river cross sections and ground elevations obtained

from field survey and LiDAR survey respectively, the Digital Terrain Model

(DTM) of the catchment was incorporated into the hydrodynamic model setup

of the Sg Damansara network prepared using the software MIKE FLOOD, to

route the design flows through the river and its flood plain. The results of the

hydrodynamic model simulation allowed the client to visualize the design

flood scenarios and provided a better understanding of the river flow

characteristics which is important to derive the best possible solution. Figure

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5 illustrates the 100 year ARI flow flood profile in Sg Damansara prior to the

project while Figure 6 shows the flood extent within the catchment for the

same storm event.

b) SolutionsThrough the setting up of the hydrodynamic model, various scenarios were

simulated and evaluated to meet the requirements specified by the client.

Each design scenario was simulated sequentially in order to evaluate its

effectiveness against lowering the design flood profile in a favourable

hydraulic environment. As flow in the river is very much dynamic, any

changes upstream will impact downstream flow, therefore the proposed works

had to be added in from upstream to downstream, and evaluated again each

time changes were made. This way, the sensitivity of each activity can be

evaluated to obtain the maximum lowering of the design flood profile for each

proposed work involving the river flow.

In evaluating the proposed flood mitigation works, the following strategies

were adopted:

Maximize upstream flood storage (to resolve problem of downstream

bridge constrictions) by detention ponds and MSMA control

Maximize river corridor with minimum land acquisition and

resettlement of people

Earth sections preferred over lined sections wherever possible

Packaging of works to suit Government available allocations, urgency

and effectiveness, and to avoid repetition of works in the future

Ease of O/M works and low OPEX

i) Construction of flood detention ponds Since the publication of JPS’ Manual Saliran Mesra Alam in year 2000, flood

detention storage has been widely recognized as a necessity; provided

storage areas are available, in any flood mitigation project. Three ponds were

proposed and the potential storage for each pond determined. As river

improvement works were not included in the scope of works for the Package

1 phase, no structures were proposed in the river to encourage or divert flood

flows into the proposed detention ponds under the design flood events. To

allow flood flows into the detention pond, side spill weirs were proposed along

the river banks adjacent to the pond, forming the inlet structure of the pond.

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The pond outlets consist of culverts and flap gates to detain the flood waters

in the pond until the river flood level resides. The sizing of the pond inlets and

outlets were analyzed using the hydrodynamic model setup. The location,

length and height of the weir at the inlet are important to achieve the

maximum lowering of the flood profile along the river, downstream of the

proposed ponds. To further confirm the hydraulic effectiveness of the side

spill weir inlets, a physical model of the river and inlet (specifically the SAE

pond inlet) was constructed at NTU in Singapore to verify the design

configuration derived from the hydrodynamic model. The later verified the

designed configuration as per the hydrodynamic model and suggested some

additional bank protection works to prevent erosion adjacent to the

embankment at the inlet structure. The hydraulic design of the inlet structures

were also subject to external specialist review as part of the quality assurance

practiced by the consultancy.

The foundation design of the inlet structures also utilizes an innovative

“disconnected” piled raft system in order to resolve the technical challenge of

large lateral force imposed by water pressure onto the inlet structure while at

the same time, ensuring cost-effectiveness of the solution. Typical details of

the “disconnected” piled raft system are shown Figure 7. A technical paper

on the “disconnected” piled raft system has also been accepted for

publications in the coming 17th Southeast Asian Geotechnical Conference

(SEAGC) which will be held from 10-13th May 2010 in Taipei, Taiwan.

ii) Removal of bridge constrictionsBeing a heavily urbanized catchment, many crossings exist over Sg

Damansara connecting trunk roads, expressways and railway lines; servicing

daily commuters of nearby and far away developments. A total of 19

crossings fell within the scope of this Project. Most of the existing bridges had

very little vertical clearance beneath the bridges, causing overbank flooding

even during minor flood events to several flood prone areas. Demolition and

reconstruction of the bridges were not an option, as traffic disruptions at

especially the expressways were unthinkable. The only option was to create a

larger flow area beneath the bridges to reduce the constriction of these

crossings. The potential removal of the constriction within each bridge was

determined and the hydrodynamic model simulated each propose flow area

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beneath the bridges to assess and improves the flow conditions due to the

widening works under each bridge.

The removal of the constriction requires design of sheet pile retaining wall

system to be installed using “press-in” method due to the restricted headroom

at the bridge constriction area. The use of new technology from Japan has

enabled the works to be carried out in difficult conditions while fulfilling the

objective of providing increased flow area beneath the bridge.

iii) River protection works (bunding and flood wall)The extent and height of the flood bunding and flood wall works were

assessed using the hydrodynamic model to contain the flood flows within the

assigned river corridor according to the Client’s requirements. The design of

the flood bunding also takes into consideration long-term settlement of the

soft subsoil along the river alignment. The design of the river protection works

is based on the recommendations of USACE for the design of levee and flood

wall.

iv) Construction of pumping stationsWhile design flood flows along Sg Damansara is contained within the

downstream river corridor, certain existing low lying developments along the

river banks will be affected by the much higher tailwater conditions. Although

flood flows may be prevented from entering these low lying areas due to the

present check valves or flap gates installed, the internal drainage system may

not be able to cope with the built up of stormwater volume within its

conveyance. Thus a pumped drainage system was proposed in these areas

where if the flood profile of Sg Damansara is high resulting in a sizeable

internal flood volume, the operation of the pumps would be triggered to

continuously discharge the internal stormwaters into Sg Damansara.

ACHIVEMENT OF OBJECTIVES

The proposed flood mitigation works have solved the flood problems in Sg

Damansara by meeting the ’Client Requirements’ section mentioned earlier. The six

prominent areas are protected from overbank spilling from Sg Damansara with the

works designed up to a 25 year ARI storm, while the local drainage areas have been

designed to a 10 year ARI storm event.

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ATTACHED PHOTOGRAPHS AND DIAGRAMS

The relevant figures and photographs with descriptions for this project are attached.

TECHNICAL PAPERS

The relevant technical published papers to this entry submission are enclosed.

CLIENT AUTHORISATION

A copy of the letter of authorization from the project client to allow publication and

publicity is enclosed.

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Documents

ACEM Submission (Additions by CCM)