Beyond ‘Longkang Cities’: Rethinking urban stormwater management in Sarawak through Low Impact Development (LID)
By Ir. Dr. Tan Yee Yong
Flooding remains the most common natural disaster in Malaysia, causing significant damage to property, infrastructure, and economic activity. According to the Department of Irrigation and Drainage (DID) Sarawak, major cities such as Kuching, Miri, Sibu, and Bintulu frequently experience flash floods due to dense urban populations, inadequate flood-mitigation infrastructure, and limited emergency response capacity.
One of the primary drivers of flash flooding in Sarawak is the high rainfall intensity during the Northeast Monsoon season. Sarawak records among the world’s highest annual rainfall levels, averaging approximately 3,300 mm in coastal regions. Under natural conditions, part of the stormwater infiltrates into the soil. However, when rainfall intensity exceeds the soil’s infiltration capacity, or when urban surfaces are highly impervious, excess water becomes surface runoff that rapidly accumulates and contributes to flash flooding. Climate change is expected to intensify rainfall patterns further, increasing flood risks while reducing the resilience of urban areas.
In response, the federal government has allocated billions of ringgit toward flood-mitigation infrastructure, including drainage upgrades, detention ponds, and pumping stations designed to improve stormwater storage and conveyance. While these measures help reduce flooding caused by excessive runoff and rapid discharge, questions remain regarding their long-term sustainability. Continuous urbanisation reduces permeable surfaces, while climate change accelerates rainfall extremes, leading to ever-increasing runoff volumes. Under such conditions, continually enlarging drains and detention facilities may not be sufficient or economically sustainable in the long term.
Another concern is that stormwater facilities are typically utilised only during periods of heavy rainfall, raising issues of land-use efficiency and the long-term costs of operation and maintenance. The large land areas required for detention ponds and drainage reserves must be balanced against their actual flood-mitigation benefits. In addition, many urban drainage systems also receive grey wastewater from surrounding communities. During dry periods, stagnant water and the retention of organic-rich wastewater can create environmental and public health problems, including foul odours, degraded water quality, and unpleasant urban living conditions.
Figure 1: Despite the presence of large detention ponds, reduced storage capacity caused by excessive water hyacinth growth and slow discharge rates to nearby water bodies continue to contribute to flash flooding in the localised area.
Figure 2: Oil and grease pollution contaminates the drainage channel, reducing hydraulic efficiency, degrading water quality, and increasing the risk of blockages and localised flooding.
Against this backdrop, Low Impact Development (LID) has emerged as a promising alternative approach to urban stormwater management. LID seeks to replicate natural hydrological processes by reducing runoff at its source through infiltration, storage, and evaporation. Instead of rapidly conveying stormwater away through conventional drainage systems, LID promotes the retention and infiltration of rainwater using features such as green roofs, permeable pavements, bioswales, rain gardens, and constructed wetlands.
This concept closely resembles China’s “Sponge City” initiative, which aims to enable urban areas to “store, infiltrate, and purify” stormwater like a sponge. Stormwater is detained and slowly released while also creating opportunities for reuse as an alternative water resource. More broadly, the LID framework offers a pathway to transform today’s inefficient and aesthetically unappealing “drainage-oriented” urban landscapes into resilient, multifunctional environments that improve both environmental quality and urban liveability.
LID enhances on-site stormwater retention and infiltration through the integration of green infrastructure within existing urban spaces. By reducing peak runoff, LID helps alleviate pressure on conventional drainage systems and improves resilience to extreme rainfall events. Simulation studies conducted in Sarawak have shown that converting roads and roundabouts into permeable pavements and vegetated detention areas can significantly reduce peak stormwater flow. In addition, bioretention systems integrated with vegetated swales have demonstrated the ability to improve stormwater quality by removing suspended solids and nutrients such as phosphorus and nitrogen.
These findings highlight the potential of LID to reduce dependence on oversized concrete drains and detention structures that often create environmental, safety, and aesthetic concerns in urban areas. More importantly, the shift from rapid stormwater conveyance toward distributed retention, infiltration, and treatment provides Sarawak’s cities with an opportunity to move beyond the image of “Longkang Cities” toward more resilient, liveable, and sustainable urban environments.
This transition is particularly significant for Miri, which aspires to strengthen its identity as a resort city and serves as a gateway to two UNESCO World Heritage sites, Gunung Mulu National Park and Niah National Park. For a city positioned around tourism and environmental appreciation, urban liveability and environmental quality are critical components of its long-term development vision.
Figure 3: A rain garden integrating a public park with on-site detention facilities as a Low Impact Development (LID) approach in Penang.
Despite its potential, the implementation of LID in Malaysia, including Sarawak, remains limited. One major challenge is the lack of flexibility in planning approaches due to environmental constraints and legislative requirements. Current urban stormwater management practices in Sarawak are primarily guided by the Urban Stormwater Management Manual 2nd Edition (MSMA 2) and the Sarawak Urban Stormwater Management (SUStoM) guidelines issued by the DID. However, these references provide limited technical guidance on the hydrological functions and detailed design requirements of LID systems.
Another challenge lies in the direct adoption of design standards developed in other countries. Rainfall intensity and frequency in Malaysia are substantially higher than in many regions where these standards originated, which may result in inappropriate or misleading designs if applied without adaptation. For instance, green roof systems intended for high water retention under tropical rainfall conditions may require significantly greater structural capacity, leading to increased construction and maintenance costs, as well as potential safety and performance concerns.
Given Malaysia’s frequent high-intensity rainfall events, existing LID guidelines require careful revision to suit local climatic and urban conditions. Equally important is the development of a comprehensive implementation framework that can support local authorities and government agencies in integrating LID into urban master planning and addressing existing knowledge gaps.
Ultimately, rethinking stormwater management in Sarawak through Low Impact Development is not about replacing conventional drains and detention ponds entirely, but about strengthening urban resilience against growing flood risks. By slowing, detaining, infiltrating, and treating stormwater at its source, cities can reduce flood risks while creating healthier, greener, and more sustainable urban environments without continually expanding drainage infrastructure that may constrain future urban development.
The transition toward LID not only offers a pathway away from “Longkang Cities,” but also strengthens Sarawak’s capacity to confront the increasing challenges posed by climate change and rapid urbanisation.
Ir. Dr. Tan Yee Yong is a Senior Lecturer and Associate Dean (Learning and Teaching) at the Faculty of Engineering and Science, Curtin University Malaysia. A Fellow of Advance HE and a registered professional engineer with the Board of Engineers Malaysia and Engineers Australia, he specialises in water and environmental engineering. Ir. Dr. Tan has contributed to various government projects in waste management, wastewater treatment, and flood mitigation, reflecting his strong commitment to sustainable development. He can be contacted via email at tan.yee.yong@curtin.edu.my.
