Prediction of floatable litter using hydrological response modeling at Sungai Batu catchment

The emergence of floatable litter in river system with vast quantity was remained as a challenge in environmental issue. The rapid developments have influenced the hydrological process and catchment characteristics. Indirectly, it will contribute to the high runoff generation during high rainfall intensity and extreme event. The significant impact of rainfall-runoff process toward the accumulation of floatable litter in river system was still hindered in Malaysia. Therefore, the primary objective of this research is to predict the floatable litter load from hydrological response in upper part of Sungai Batu catchment, Selangor. The research on floatable litter sampling was conducted in two different periods and highly subjected to cleaning operation schedule. The floatable litter load was obtained through the bucket conveyer by employing the time interval approaches for every nth hour, where the floatable litter will be elevated based on the same time interval. The Guidelines on Solid Waste Composition and Characterization analysis from Department of Standards Malaysia and the American Society for Testing and Materials Standard test method (ASTM D5231) were used to determine the floatable litter composition captured at Floating Debris Boom (FDB) structure. Prior to exact date of floatable litter sampling, the 15-minutes interval of rainfall data have been used as an input in Hydrologic Modeling System (HEC-HMS) to simulate the rainfall– runoff processes in the catchment and Soil Conservation Service Curve Number (SCSCN) method to generate runoff. The flood frequency analysis for extreme event was performed in order to estimate the cumulative of floatable litter over the return period. Statistical analysis for accumulation of floatable litter load and its composition in two different periods was carried out, as well as their association with hydrological data where the correlation analysis between these two variables were conducted and assessed. The results revealed that the highest accumulation of floatable litter load was 711434.44 kg/km²/day. In terms of compositions, the plastic and organic waste load were the highest load with 21505.20 kg/km²/day during first sampling and 12222.48 kg/km²/day during second sampling, respectively. In this study, the mean percentage of runoff generations derived from rainfall events prior to the floatable litter collection during first sampling and second sampling were 49.95% and 48.77%, respectively. The runoff generations have a major potential in transporting the floatable litter towards the downstream area until being intercepted by FDB structure. This condition can be proved as there were highly correlated between cumulative floatable litter loads and cumulative runoff generation during first sampling with R² = 0.9572, r = 0.978 (p<0.01); and second sampling with R² = 0.9806, r = 0.990 (p<0.01). During the extreme event, the estimated discharge derived from Gumbel distribution method was 52.58 m3/s where it can estimate about 408352.83 kg/km²/day of the cumulative floatable litter load at 5 years return period. The capability to predict the accumulation of floatable litter load captured by FDB structure based on annual peak discharge data which can be served as the main knowledge contribution in this study.

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