Kristine Joy B. Mallari

Analysis of effects of climate change on runoff in an urban drainage system: a case study from Seoul, Korea

Both water quantity and quality are impacted by climate change. In addition, rapid urbanization has also brought an immeasurable loss of life and property resulting from floods. Hence, there is a need to predict changes in rainfall events to effectively design stormwater infrastructure to protect urban areas from disaster. This study develops a framework for predicting future short duration rainfall intensity and examining the effects of climate change on urban runoff in the Gunja Drainage Basin. Non-stationarities in rainfall records are first analysed using trend analysis to extrapolate future climate change scenarios. The US Environmental Protection Agency Storm Water Management Model (SWMM) was used for single event simulation of runoff quantity from the study area. For the 1-hour and 24-hour durations, statistically significant upward trends were observed. Although the 10-minute duration was only nearly significant at the 90% level, the steepest slope was observed for this short duration. Moreover, it was observed that the simulated peak discharge from SWMM increases as the short duration rainfall intensity increases. The proposed framework is thought to provide a means to review the current design of stormwater infrastructures to determine their capacity, along with consideration of climate change impact.

Evaluation of an erosion-sediment transport model for a hillslope using laboratory flume data

Climate change can escalate rainfall intensity and cause further increase in sediment transport in arid lands which in turn can adversely affect water quality. Hence, there is a strong need to predict the fate of sediments in order to provide measures for sound erosion control and water quality management. The presence of microtopography on hillslopes influences processes of runoff generation and erosion, which should be taken into account to achieve more accurate modelling results. This study presents a physically based mathematical model for erosion and sediment transport coupled to one-dimensional overland flow equations that simulate rainfall-runoff generation on the rill and interrill areas of a bare hillslope. Modelling effort at such a fine resolution considering the flow connection between interrill areas and rills is rarely verified. The developed model was applied on a set of data gathered from an experimental setup where a 650 cm×136 cm erosion flume was pre-formed with a longitudinal rill and interrill having a plane geometry and was equipped with a rainfall simulator that reproduces natural rainfall characteristics. The flume can be given both longitudinal and lateral slope directions. For calibration and validation, the model was applied on the experimental results obtained from the setup of the flume having 5% lateral and 10% longitudinal slope directions under rainfall intensities of 105 and 45 mm/h, respectively. Calibration showed that the model was able to produce good results based on the R2 (0.84) and NSE (0.80) values. The model performance was further tested through validation which also produced good statistics (R2=0.83, NSE=0.72). Results in terms of the sedigraphs, cumulative mass curves and performance statistics suggest that the model can be a useful and an important step towards verifying and improving mathematical models of erosion and sediment transport.

Assessment of porous pavement effectiveness on runoff reduction under climate change scenarios

AbstractClimate change has affected both water quantity and quality by increased rainfall, runoff, and associated pollutant loading in urban areas. Stormwater Best Management Practices (BMPs) are now being popularly considered for the reduction of increased runoff due to urbanization. Most research has been conducted on the analysis of BMP effectiveness under current conditions. However, there is no extensive literature on BMP effectiveness studies considering climate change. In this study, the effectiveness of BMP, porous pavement in particular, has been assessed under climate change scenarios. Climate change scenarios were generated by trend analysis of the historical rainfall data. The 2-year and 100-year design storms having 24-h durations were determined for three scenarios: current conditions, 2020, and 2050 using frequency analysis. Storm Water Management Model was then calibrated and used to evaluate the impact of climate change and the effect of incorporating porous pavement on runoff. Geographic...

Characteristics of hydrochemical variations and contaminant load during rainfall in an acid mine drainage-impacted watershed, Korea

AbstractAcid mine drainage (AMD) refers to the outflow of acidic water from usually abandoned metal mines. Since AMD is closely related to the rainfall–runoff process, it is important to monitor rainfall events for its characterization. This work aims to study the characteristics of hydrochemical variations of metals during rainfall in the Geopung Mine Watershed, Korea. Eleven dry-weather and five rainfall event monitorings were conducted in 2010 at two locations (GP-1 and GP-2). At GP-1, concentrations significantly increased during the fifth event, which was the largest one (As from 0.0003 to 0.0046 mg/l; Cd from 0.0114 to 0.2188 mg/l; Cu from 0.0206 to 3.1512 mg/l; Pb from 0.0006 to 0.1857 mg/l; Zn from 0.5823 to 15.9194 mg/l; Ni from 0.0011 to 0.0294 mg/l). Similar though less-marked trend of increase in metal concentration was found at GP-2 during the fifth rainfall event. As for the load, as much as 62–97% of the annual metal loads were accounted for by rainfall at GP-1 and GP-2. This pattern implie...

Modelling of suspended sediment in a weir reach using EFDC model

Construction of hydraulic structures often leads to alteration of river dynamics and water quality. Suspended solids entering the upstream of the weir cause adverse effects to the hydroecological system and, therefore, it is necessary to build a modelling system to predict the changes in the river characteristics for proper water quality management. In this study, the discharges and total suspended solids upstream and downstream of the Baekje Weir installed in Geum River, Korea, was modelled using the environmental fluid dynamics code (EFDC) model. The resulting trend of four rainfall events shows that as rainfall increases, the total suspended solids (TSS) concentration increases as well. For the two larger events, at the upstream of the weir, TSS was observed to decrease or remain constant after the rainfall event depending on the lowering of the open gate. At the downstream, TSS supply was controlled by the weir during and after the rainfall event resulting in decline in the TSS concentration. The modelling produced good results for discharge based on %Diff. (4.37-6.35), Nash-Sutcliffe efficiency (NSE) (0.94-0.99) and correlation coefficient (r) (0.97-0.99) values as well as for TSS with acceptable values for %Diff. (12.08-14.11), NSE (0.75-0.81) and r (0.88-0.91), suggesting good applicability of the model for the weir reach of the river in the study site.

Parameter sensitivity and uncertainty analysis of a stormwater runoff model

AbstractIn this study, Generalized Likelihood Uncertainty Estimation (GLUE) methodology was used to perform uncertainty analysis of a stormwater model, which randomly generates parameter sets and identifies behavioral ones with higher likelihood. Latin Hypercube Sampling (LHS) is used to generate parameter sets. The Model for Urban Stormwater Improvement Conceptualization was chosen as an appropriate model for stormwater runoff. Prediction limits are determined by selecting the cutoff threshold for likelihood function. Study area is Goonja Drainage Basin located in the city of Seoul, Korea. From the results, maximum likelihood value for calibration is 0.78 and 0.73 for validation. The p-factors for the calibration and validation are 87 and 83%, respectively. The p-factor for all storm events is 85%. These are all acceptable values as the results are considered good when 60% or more of the observed data are bracketed by prediction limits. Overall, it was shown that, using GLUE methodology with LHS, the mod...