Flashing out flood forecasts

Containing heavy rainfall: The Batu retention pond receives floodwaters from Sungai Batu before slowly releasing it back into the river.

A SYSTEM is being developed to better predict flash floods in Kuala Lumpur.

The National Flood Forecasting Warning System (NaFFWS), which comprises three phases, is expected to be completed by the end of 2023.

The warning system will allow the Kuala Lumpur Drainage and Irrigation Department (WPKL DID) to use data provided by the Malaysian Meteorological Department to forecast floods and alert people in time.

The first phase of the project costing RM8mil started in May. This phase is intended to increase the number of hydrological stations to collect data such as rainfall, river water level and stream flow from remote areas in real time.

The information will be used in the Malaysia Flash Flood Model that will be developed in the second phase.

In the third phase, upon developing NaFFWS, DID will be able to issue flood warnings between three hours and two days in advance.

WPKL DID deputy director Ratna Rajah Sivapiragasam said the system would help the department detect possible floods earlier.

“Currently, the contractor is installing instruments to collect hydrological data which will be used in developing a flood forecasting model in the second phase.

“We are also engaging a consultant to develop the flood forecasting model which goes concurrently with the installation of hydrological instruments,” he said.

The Malaysia Flash Flood Model is a risk assessment to identify the source and extent of potential flooding before proposed mitigation and protection measures can be taken.

The NaFFWS was introduced following major floods in December 2014 that hit eight states, namely Kelantan, Terengganu, Pahang, Perak, Perlis, Johor, Sabah and Sarawak.

Ratna Rajah said one of the challenges in Kuala Lumpur was that water levels in rivers were rising rapidly.

“From cloud formation to a downpour, it can happen within one or two hours, which gives us a small window to alert people.

“We are also exploring various ways for an early warning system, including through mobile phone notifications.

“This is so they can make better travel plans, move their vehicles from low-lying areas or postpone their plans to avoid getting caught in traffic jams due to flash floods,” he said.

The NaFFWS had been developed for the east coast of the peninsula, targeting rivers such as Sungai Kelantan, Sungai Terengganu and Sungai Pahang where the surrounding areas were flood-prone.

“However, those are big rivers where the rise in water level is slow and thus, there’s more time to alert the people on potential flooding incidents.

“DID has taken on the challenge and begun working with experts in the industry to develop the system,” Ratna Rajah said.

Flood mitigation plans

Kuala Lumpur records average annual rainfall of 3,050mm.

The northeast monsoon is expected to last until January.

To date, the highest monthly rainfall recorded was in August – at 370mm.

As of Nov 25, 285mm of rainfall had been recorded.

Ratna Rajah said due to climate change, the intensity of rainfall had increased.

“Rain that previously fell over three hours now falls over an hour.

“For example, we have recorded 120mm of rainfall within an hour.

“When that happens, it might exceed the river capacity, causing it to overflow its banks.

“Normally, DID will be on alert if rainfall exceeds 60mm per hour as the probability of a flood occurring would be high,” he explained.

Currently, there are three main components in the Kuala Lumpur Flood Mitigation (KLFM) plan.

KLFM is based on the control-at-source approach whereby the flood flow will be diverted and stored in flood mitigation ponds until the river level subsides in the city centre, prior to releasing the stored water gradually into rivers.

This prevents excess water from flowing into the city during a downpour, causing flooding.

KLFM A is the Stormwater Management And Road Tunnel (Smart Tunnel) bypass with 3mil cubic metre capacity, while KLFM B consists of Jinjang and Batu flood retention ponds with a combined capacity of 7.1 million cubic metres.

The Jinjang retention pond receives floodwaters from Sungai Jinjang and Sungai Keroh Diversion.

The Batu pond receives floodwaters from Sungai Batu and Sungai Gombak Diversion.

Both ponds store the excessive water at the retention ponds before slowly releasing it into Sungai Jinjang and Sungai Batu, respectively.

The third KLFM is the Sungai Bunus flood mitigation that consists of six retention ponds and a diversion.

One of the retention ponds, Kolam Pulapol, is still under construction and expected to be completed in 2023.

The Sungai Bunus flood mitigation helps control water volume as the river flows from Setapak through Jalan Tun Razak and Kampung Baru to Sungai Klang, near the Flat PKNS Kampung Baru.

“DID Flood Management Division has engaged a consultant to look into the effectiveness of KLFM through a feasibility study and this might take about two years.

“Based on the study, we may propose additional flood mitigation measures,” he added.

The previous feasibility study was done in 2003, and might not reflect the current situation as more development had taken place, in addition to climate change issues.

“We are also working with the Environment and Water Ministry (KASA) to minimise the impact of floods in the city.

“We want to ensure Kuala Lumpur city centre is protected from flooding during a downpour,” he added.

Ratna Rajah said fortunately, there had been no incidents of water breaching the riverbanks this year.

“The most recent would be the flash floods on Sept 10 last year, which hit Masjid Jamek when Sungai Klang spilled its banks.

“One of the reasons for the river overflow was a utility crossing that had obstructed water flow.

“We have spoken to the utility company and they are in the process of rectifying the problem,” he said.

Collaborative effortAddressing flash floods in the city is a collaborative effort across several agencies, said Ratna Rajah.

DID works closely with Kuala Lumpur City Hall (DBKL) and mayor Datuk Seri Mahadi Che Ngah to address flash floods.

“While we are the technical department that looks into the hydrology, hydraulics and flood mitigation system for main rivers in Kuala Lumpur, DBKL is responsible for the drainage system.

“DBKL’s Enforcement Department and their emergency response team will help clear blockages in the drainage system that obstruct water flow, to prevent flash floods and water ponding on roads.

“DID is in charge of the main rivers while DBKL takes care of the smaller tributaries.

Ratna Rajah said DID was pleased that Mahadi, who is also a certified town planner, decided to rope them in as specialist advisor to adopt a control-at-source approach to flooding.

“The existing flood mitigation plans are meeting their outcomes and we hope to receive sufficient funds for the maintenance of these systems.

“This includes removing rubbish collected every time we activate and operate KLFM.

“Rubbish thrown into the rivers range from mattresses and sofas to plastic bottles and motorbike frames.

“The frequency of clearing is based on the annual allocation received,” he said.

Meanwhile, taking care of riverbanks is essential to the National River Trails (DSK) project by KASA to build river trails for recreational activities.

In a StarMetro report in March, Minister Datuk Seri Tuan Ibrahim Tuan Man said KASA aimed to build 1,000km of river trails by 2023.

In total, 10,000km are targeted for completion by 2030.

The project, placed under DID’s supervision, is a government effort to beautify, restore and preserve rivers.

Improvements seenKuala Lumpur residents are already seeing improvements at flash flood hotspots in the city.

Taman Mutiara Barat resident CK Chew said Jalan Cheras used to have flash floods along the road.

Water would pond on the main road whenever there was a flash flood and traffic jams would occur.

“However, there were fewer flash floods this year,” he said.

Wangsa Maju MP Datin Paduka Dr Tan Yee Kew’s special assistant Andre Lai agreed that flash floods had reduced.

“Jalan Genting Klang in Setapak was one of the hotspots for flash floods whenever there was a downpour.

“The Prima Setapak commercial area often got flooded too with water flowing into shoplots.

“But drainage upgrades since last year had improved the situation and Jalan Genting Klang is no longer flood-prone even when it rains heavily,” he said.

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