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Submission for an ACEM award
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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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ACEM Engineering Awards Competition 2010
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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ACEM Engineering Awards Competition 2010
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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ACEM Engineering Awards Competition 2010
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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ACEM Engineering Awards Competition 2010
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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ACEM Engineering Awards Competition 2010
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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