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Abstract. On-site measurements from rain gauge provide important information for the design, construction, and operation of water resources engineering projects, groundwater potentials, and the water supply and irrigation systems. A dense gauging network is needed to accurately characterize the variation of rainfall over a region, unfitting for conditions with limited networks, such as in Sarawak, Malaysia. Hence, satellite-based algorithm estimates are introduced as an innovative solution to these challenges. With accessibility to dataset retrievals from public domain websites, it has become a useful source to measure rainfall for a wider coverage area at finer temporal resolution. This paper aims to investigate the rainfall estimates prepared by Tropical Rainfall Measuring Mission (TRMM) to explain whether it is suitable to represent the distribution of extreme rainfall in Sungai Sarawak Basin. Based on the findings, more uniform correlations for the investigated storms can be observed for low to medium altitude (>40 MASL). It is found for the investigated events of Jan [5][6][7][8][9][10][11] 2009: the normalized root mean square error (NRMSE = 36.7 %); and good correlation (CC = 0.9). These findings suggest that satellite algorithm estimations from TRMM are suitable to represent the spatial distribution of extreme rainfall.

An evaluation on the applicability of bio-retention system in grassed road divider under high rainfall of equatorial region was conducted by developing computer-aided stormwater models using USEPA SWMM 5.1. The models simulated road runoffs with and without bio-retention systems. A single unit of bio-retention system tested here was 3 m in width, 6 m in length with 150 mm of ponding depth and 600 mm of soil/storage depth. Results indicated that soil types of loamy sand, sandy loam and loam showed similar performance in reducing runoff. With installation of bio-retention system, road runoff could be reduced 40-50% when subjected to 60 minutes of 2-, 5- and 10-year ARI rain events. The results obtained from the simulation were encouraging that bio-retention system in grassed road divider could function to augment the existing urban road drainage.

Bioretention system is one of the best management practices for rainwater runoff redirecting and storing before discharge into existing stormwater system. On the other hand, road divider is designed for dividing the traffic flow for road safety. However, it may be a blockage for surface runoff on road and possibly created ponding during heavy rainfall event. This scenario could become a hazard for motorised vehicles. In this study, a grassed road divider in Broga Road, Semenyih, Malaysia, is modelled as bioretention system by EPA's Storm Water Management Model (SWMM) to investigate the performance of its application. A case of grassed road divider without bioretention cell was also modelled for comparison. A series of simulations were carried out for the ARI of 2, 5, and 10 years to further study the performance of grassed road divider as a bioretention system. Four different types of soil including sand, loamy sand, loam, and sandy loam are selected as filler soil in the bioretention cell. Results from the model simulations showed that the performances of grassed road divider as a bioretention system can reduce the surface runoff into the stormwater system up to 49.9% and 56.77% for different ARIs. The effect of this implication is more significant on the reduction as the ARI increased. Results also showed that the impact of soil types is insignificant. The findings show that a bioretention system in a grassed road divider may supplement conventional urban road drainage and provide an effective stormwater management.

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