The abrupt rises of water level in rivers by torrential rain or storm repeatedly cause inundation damage, such as erosion and deposition in floodplains. However, studies on identifying the abrasion of waterfront facilities or the accumulation of sediment near rivers under extreme flow conditions are seldom found because floodplains are utilized in various ways in each country. In this study, novel floodplain sustainability indices by spatial classification of erosion and deposition were developed for sustainable waterfront development. The indices can provide the relative spatial distribution of erosion and deposition in a floodplain by using only kinematic flow information, such as flow depth and velocity obtained by 2D numerical analysis. Accordingly, applying a complex sediment transport model that involves numerous assumptions and parameters can be moderately replaced with the present approach. The suitability of developed indices was tested in several flow problems by comparing the predicted erosional or depositional region with measured data. In addition, the developed indices were applied to a floodplain in a natural river to examine the relative spatial distribution of the erosion and deposition for a typhoon event, and the results were compared with field monitoring data. It was found that deposition was more likely to occur than erosion in most floodplains, and the developed floodplain sustainability indices accurately quantified the erosion and deposition phenomena.

Chemical accidents in rivers may be triggered by natural or anthropogenic causes and refer to the flow of large quantities of hazardous chemicals into rivers. In South Korea, domestic water is sourced from large rivers, such as the Nakdong River. However, owing to rapid industrialization, industrial facilities have become heavily concentrated in the middle and upper reaches of the Nakdong River. Therefore, severe problems could arise if harmful chemicals are leaked from industrial facilities into the river, and this contaminated river water is supplied to cities. Quantitative evaluation based on instrumental analysis during chemical accidents and prediction research based on modeling is actively being conducted however, research on the initial response is insufficient. Therefore, in this study, the variations in pH and EC were analyzed according to their chemical concentrations for seven chemicals. These seven chemicals are designated accident-preparedness substances that frequently cause chemical spills in South Korea. Additionally, we evaluated the possibility of identifying unknown substances by comparing the variations in pH and EC and statistics while diluting unknown substances. Thus, the potential of pH and EC as alternative indicators for detecting and identifying chemicals was evaluated in this study. NaF, NH₄HF₂, NaCN, and NH₄OH were classified by comparing their spatial distributions in a pH-EC relation curve. However, H₂SO₄, HCl, and SOCl₂ showed similar spatial distributions in the pH-EC curves and were difficult to identify. The results of this study provide information for chemical detection and identification using alternative sensors that permit easy and rapid field measurements in the event of a chemical spill and could be used as preliminary data for rapidly responding to accidents.

Climate change has intensified torrential rainfall and floods, causing frequent floodplain inundation with erosion and deposition. Large-scale waterfront facilities such as park golf courses are highly vulnerable, requiring systematic hydraulic safety evaluation. We simulated a recent flood in the Musim Stream using a two-dimensional FaSTMECH model to assess floodplain safety. The model showed excellent reproducibility (RMSE = 0.0176 m, NSE = 0.95 for depth; RMSE = 0.016 m/s, NSE = 0.87 for velocity). Flood risk indices—flood intensity (FI) and flood hazard rating (FHR)—and erosion–deposition indices—transient erosion and deposition index (TEDI) and steady erosion and deposition index (SEDI)—were applied. FI values were in the range of 0.3–6.4 (median 2.8) and FHR was in the range 0.7–10.2 (median 3.0), indicating that most floodplain areas exceeded the “high” to “extreme” risk range. TEDI was in the range of 0.004–4.15 (mean = 0.60), while SEDI was in the range of 0.001–5.59 (mean = 2.12). High TEDI values (0.6–0.9) occurred in curved and contracted sections, corresponding to observed erosion zones, whereas high SEDI values (0.8–1.0) were concentrated in the main channel. These results demonstrate that the indices effectively quantify and visualize floodplain risk, providing a practical basis for the design, placement, and maintenance of floodplain facilities.