Urbanization, if not properly managed, can lead to stream channel degradation termed Urban Stream Syndrome (USS). However, the effects of different levels of urbanization and thresholds for degradation are not well understood. The USS is characterized by increased frequency and magnitude of flood flows, increased rates of channel erosion, and degradation of aquatic habitat. In this study, changes over time in Flow Duration Curves (FDC) and Sediment Rating Curves (SRC) and resulting changes in sediment and phosphorus loads in watersheds undergoing various levels of urbanization were examined as candidate indices for detecting the presence of USS. We observed that watersheds undergoing urbanization show substantial shifts in the FDC, causing a notable increase over the whole range of stream flows and tilt in the SRC, raising the exponent and decreasing the scalar coefficient. The scalar coefficient in the SRC correlates with the percentage of the catchment area with exposed soils available for erosion, which decreases notably due to urbanization, and the exponent of the SRC increases in concert with increases in impervious cover. Changes in the exponent of the SRC associated with increased urbanization in the watershed, provide an additional diagnostic tool for identification of watercourses prone to developing urban stream syndrome. The combined effects of increased peak flows and the increase in the exponent of the SRC magnify the contribution of flood flows to the annual sediment and phosphorous loads in urbanizing watersheds. The study findings support the hypothesis that destabilized stream channels subjected to USS from increased stormflow have a significant non-point source of sediments and phosphorus from within the stream corridor in addition to off-channel upland urban area sources.

城市化如果管理不当，可能会导致河流渠道退化，称为城市河流综合症 (USS)。然而，不同城市化水平和退化阈值的影响尚不清楚。USS 的特点是洪水的频率和幅度增加，河道侵蚀率增加，水生栖息地退化。在这项研究中，作为检测 USS 存在的候选指标，研究了流动持续时间曲线 (FDC) 和沉积物等级曲线 (SRC) 随时间的变化以及流域经历不同城市化水平的沉积物和磷负荷的变化。我们观察到，正在经历城市化的流域在 FDC 中表现出显着变化，导致 SRC 的整个河流流量和倾斜范围显着增加，提高指数并降低标量系数。SRC 中的标量系数与流域面积中可用于侵蚀的裸露土壤的百分比相关，该百分比由于城市化而显着下降，并且 SRC 的指数随着不透水覆盖的增加而增加。与流域城市化进程增加相关的 SRC 指数的变化为识别容易发展为城市河流综合征的水道提供了额外的诊断工具。峰值流量增加和 SRC 指数增加的综合影响放大了洪水流量对城市化流域中年沉积物和磷负荷的贡献。