FLOOD ASSESSMENT AND DETENTION BASED PERFORMANCE AS MITIGATION MEASURES AT KOTA SAMARAHAN, SARAWAK

• Main Author: Lukman, Mohd Najib
• Format: Thesis
• Language: English; English
• Published: UNIVERSITI MALAYSIA SARAWAK 2025
• Subjects: TA Engineering (General). Civil engineering (General)
• Online Access: http://ir.unimas.my/id/eprint/48514/

Continuous rainfall coupled with tidal effects brings floods, particularly in the urban lowlying areas that led to the overflowing of river and stormwater drainage system. Open channels and their network system play a crucial role to mitigate stormwater runoff in the prevention of flood. The network is specifically designed by following the watershed in which, the water drains into a particular watercourse. The drainage system network is commonly designed to cater rainfall event Average Recurrence Interval (ARI) between 5 to 100 years return period. This research evaluate the flood problem at Tanjung Bundong and Uni Garden area in Kota Samarahan, Sarawak. Parameter being investigated consist of empirical relationship between hydrological properties and hydraulic conditions. Hydrological properties include land use changes, rainfall and flood event and catchment area, while hydraulic conditions are open channel system and proposed flood mitigation infrastructures. Storm Water Management Model (SWMM) is used to develop the drainage model to investigate the drainage’s performance for Tanjung Bundong and Uni Garden in Kota Samarahan. The site conditions were assessed through site visits and fieldwork at the study areas. Next is the case study, which was simulated using the hydrology and hydraulic modelling in SWMM for the implementation of detention storage (Dry Detention Pond and StormPav) as a mitigation strategy comprises of alteration of existing drainage system components, application of dry detention pond to detent water and permeable pavement with detention storage (StormPav). The results, show that for an analysis of development trends from 2015 to 2022 reveals a substantial increase in impervious surfaces in both areas, leading to higher water runoff. Tanjung Bundong experienced a development rate of 4.20%, with impervious surfaces increasing from 33.00% to 37.20%. Uni Garden's development rate was 19.50%, with impervious surfaces rising from 48.00% to 67.50%. The correlation betweenincreased development with positive linear relationship between rainfall and runoff of flood severity. In example, analysis on relationship between maximum hourly rainfall and daily rainfall at Tanjung Bundong shows that each additional millimetre of rainfall leads to an increase in runoff by approximately 3082 m³ and 1142 m³, respectively for maximum hourly rainfall and daily rainfall. While Uni Garden, the results illustrates that, each additional millimetre of rainfall raises runoff by about 692 m³ for hourly maximum rainfall and 318 m³ for daily rainfall. The model calibration showed a strong correlation with manual calculations, with Nash-Sutcliffe Efficiency (NSE) value of -0.91 to 1 in average. The analysis indicated that longer return periods result in increased of runoff, highlighted the generation of increasing node flooding at Tanjung Bundong and Uni Garden across longer return periods. Subsequently, the study also found that dry detention storage effectively reduced flooding, significantly lowering outlet link’s velocities for various rainfall events. Tanjung Bundong resulted in reductions ranged between 0.07 to 0.80 m/s for dry detention ponds and 0.17 to 1.85 m/s for StormPav. While Uni Garden shows a velocity reductions between 0.12 to 0.52 m/s for dry detention ponds and -0.49 to 0.12 m/s for StormPav. In sum, this study provide the insight of flood behaviour, drainage system performance, and stormwater management effectiveness in Tanjung Bundong and Uni Garden.