Fine Sediment Modeling During Storm-Based Events in the River Bandon, Ireland

Abstract

The River Bandon located in County Cork (Ireland) has been time-continuously monitored by turbidity probes, as well as automatic and manual suspended sediment sampling. The current work evaluates three different models used to estimate the fine sediment concentration during storm-based events over a period of one year. The modeled suspended sediment concentration is compared with that measured at an event scale. Uncertainty indices are calculated and compared with those presented in the bibliography. An empirically-based model was used as a reference, as this model has been previously applied to evaluate sediment behavior over the same time period in the River Bandon. Three other models have been applied to the gathered data. First is an empirically-based storm events model, based on an exponential function for calculation of the sediment output from the bed. A statistically-based approach first developed for sewers was also evaluated. The third model evaluated was a shear stress erosion-based model based on one parameter. The importance of considering the fine sediment volume stored in the bed and its consolidation to predict the suspended sediment concentration during storm events is clearly evident. Taking into account dry weather periods and the bed erosion in previous events, knowledge on the eroded volume for each storm event is necessary to adjust the parameters for each model. This is achieved by predicting three points of the SSC-time curve: the maximum concentration, C max ; the time to the peak concentration, TPE; and the time from descent from the peak concentration, TDE. From these three points, exponential and logarithmic curves are proposed to represent the complete curve. Other classical models [9,10] are based on shear stress values in the bed, proportional to the bed erosion transported due to the streamflow. These models based on shear stress use an erosion rate, M, with erosion commencing when a critical value of shear stress, τ c , is exceeded. Other authors have previously studied storm events to quantify the fine sediment transport within a reach in a gravel bed river [11,12] through field measurements, considering important aspects such as sediment storage in the mainstream channel and its evolution during inter-event periods. The relationship between suspended sediment concentration, SSC, and fine sediment ingress into gravel bed rivers has been experimentally studied through sediment traps installed in the bed of the stream [13,14]. In general, factors that influence the suspended sediment load during storm events have been extensively studied in recent decades, although much effort is still needed to provide models with the capacity to predict the SSC with low uncertainty indices [5][6][7][8][15][16][17].

Sanitation Network Sulfide Modeling as a Tool for Asset Management. The Case of the City of Murcia (Spain)

“…The values obtained from the EMU-SANETSUL code are less than 57% in the case of the AI index and less than 15% in the case of the Er index. According to several quality models, a model simulation can be judged as being satisfactory if Er is in the range of ±55%, and AI < 40% [49][50][51]. Here, n is the number of observed data, H2Sg measured and H2Sg calculated are the concentration of sulfide in the air phase corresponding to each of the nodes measured in the field and simulated, respectively, and H2Sg is the average total sulfide corresponding to the measured values (ppm).…”