Background/Objectives
Unprecedented rainfall and flood events have caused massive stress to society and economy due to climate change. In 2020, the world lost 5886 lives due to floods, resulting in 0.07% of world GDP (about 5.9 trillion USD) in economic damages (source: Our World in Data based on EM-DAT,CRED). This paper will discuss the flood event on November 4-5, 2017 in the northeast district of Penang Island, Malaysia, which caused loss of lives and economy due to tropical depression 29W. The Government of Malaysia, via the Department of Irrigation and Drainage, has undertaken the task of performing flood mitigation works for the developed city of Penang. The project faced many challenges due to the aging drainage network, infrastructure and utilities. Data collection comprises soil investigation, topography and lidar survey, river hydrographic and coastal survey, hydrology and hydrodynamic analysis, changes in land use in the future, effects of sea water rise and climate change. The root causes of flooding were due to climate change, rising seawater levels and storm surges that prevented effective river water discharge, along with the release of dam water. The solution requires a new generation of flood mitigation approaches that address the seawater intrusion into rivers, the inadequacy of land to build conventional flood mitigation components and solve the undersized aging drainage network. We have used the combination of Aqueduct, Aqua Arteries and Nexus Weir to solve the flood and water resource issues.
Approach/Activities
The current mechanism of installing pumps, flood walls and flood gates at low-lying areas are incapable of functioning effectively when floodwater from the main river overflows the bank. As a result, we need a fail-proof system that can continuously discharge flood water without being affected by storm surges or high tides at sea. Aqueducts are used to solve this problem. In low-lying areas, Aqueducts will be coupled with a series of pumps to pump flood water up to the Aqueduct and channel it directly to the sea, above high tide levels or storm surge levels. As for the aging undersized drainage in the city of Penang, it is not feasible for upgrading works due to lack of land space. Hence, it is critical to have a supporting new drainage network that will indirectly improve the existing capacity of monsoon drains without the need for monsoon drain upgrades. Aqua Arteries' primary design considerations are to increase the discharge capacity of existing monsoon drains. Floodwaters are channeled into Aqua Arteries from monsoon drains. This floodwater will be directed to a large regulating pond for storage. If the storage becomes full, it will be pumped to Aqueduct, allowing for direct discharge to the sea. Aqua Arteries can eliminate urban flash floods caused by aging and insufficient capacity of drainage systems. To address seawater intrusion, Nexus Weir was deployed for flood flow enhancement and river water harvesting. The Installation of Nexus Weir will serve as a barrier against seawater intrusion, allowing for the rapid discharge of floodwater.
Results/Lessons Learned
Based on our design, Aqueduct and Nexus Weir were able to increase flood water flow efficiency by 40% and 23~63%, respectively. As per Aqua Arteries, it was able to increase the existing aging drainage system from 20~50 Average Recurrence Internal (ARI) to 100~200 ARI, eliminating urban flash floods immediately. With the integration of the Aqueduct’s infinite and dedicated flood water flow, together with Aqua Arteries capturing urban flood water from the aging drainage system and channeling it to the Aqueduct, we will have infinite uninterrupted, rapid flood water discharge above the rising sea water levels or storm surge and address flooding due to climate change.- With proper planning, the flood water channeled by Aqueducts and Aqua Arteries can be stored for water resource management and sustainability development. Together with Nexus Weir stopping seawater intrusion, it not only increases the flood water discharge efficiency and provides salinity free river water for harvesting and solves urban water shortages for sustainable growth.