Humberto Ávila

Development of Effluent Concentration Models for Sediment Scoured from Catchbasin Sumps

The ability of catchbasin sumps and hydrodynamic separators to remove sediment must be balanced with their ability to retain the previously captured material by preventing scour. The sediment scour process in these storm-water structures differs from the unidirectional scour and sediment transport process that occurs in pipes and channels. The hydrodynamics is affected by the particular characteristics of the hydraulic structure. The study of sediment scour in these devices requires incorporation of all the factors involved in the scour phenomenon and is best supported through computational fluid dynamic modeling (CFD) verified experimentally. Scour can be documented in the effluent as suspended sediment or total suspended solids concentration, a parameter of critical importance in storm-water quality management. This paper presents two simplified models for estimating effluent suspended sediment concentration attributable to scour of previously captured sediment. These models are based on results obtained from full-scale physical experimentation and calibrated and validated CFD modeling over a wide range of operating conditions where different particles sizes would be scoured. This paper also shows the effects of the armoring layer and of homogeneous and heterogeneous sediment sizes on the effluent concentration patterns.

ESTIMATING EFFECTIVE PERMEABLE AREAS IN CONSOLIDATED URBAN WATERSHEDS BASED ON SATELLITE IMAGE ANALYSIS AND FIELD SURVEY

This paper describes a methodology developed to estimate permeable and impermeable areas from consolidated urban areas based on satellite image analysis and field survey. The methodology allows inventorying vegetated cover and potential permeable areas that are actually not effective to reduce runoff due to lack of urban drainage management practices. It includes the selection of the parameters, definition and distribution of the sample units, definition of the sample size, and design of the field work protocol to collect information. This methodology was applied to an urban subcatchment in Barranquilla, Colombia. Based on the satellite images 52% of the area was identified as permeable and 48% as impermeable. In contrast, based on the field survey the effective permeable area was reduced to 27% increasing the effective impermeable area to 73%. These results showed that with only the satellite image analysis the permeable area is overestimated, underestimating the runoff coefficient. Therefore, an structured methodology to identify and estimate ineffective permeable areas is required for consolidated urban areas. This analysis allows performing a diagnosis oriented to define a more realistic starting point for urban watershed retrofitting with sustainable urban drainage systems.

Physical Experimentation and CFD Modeling to Evaluate Sediment Scour in Catchbasin Sumps

The sediment removal capacity in catchbasin sumps and other hydrodynamic separators does not necessarily imply the ability to prevent the sediment from being scoured, especially when the remaining sediment capacity volume of the device is small and the flow rates are high. The sediment removal ability of catchbasin sumps and hydrodynamic separators must be balanced with their ability to retain the captured material by preventing scour. Therefore, understanding and quantifying scour processes in catchbasin devices is an important need when considering these devices as part of a stormwater management plan. This study investigated the sediment scour from a conventional catchbasin sump for different particle sizes, sediment depths, and flow rates. Full-scale physical experimentation and Computational Fluid Dynamics (CFD) modeling were conducted to determine a wide range of conditions at which different particles sizes are scoured.

Evaluating the Natural Development of the Meta River for Proposing Hydraulic Works Oriented to River Training for Fluvial Navigation

The navigability capacity under the natural development of the Meta River was evaluated to identify the hydrologic, hydrodynamic, sedimentologic, and morphologic conditions to propose hydraulic works for establishing a navigation channel. The Meta River is one of the main rivers in Colombia with a high economical potential through its fluvial navigation. A 2D numerical modeling was conducted by using MIKE-21C for a representative sector of 75 km with braided and sinuous segments. The 2D model was calibrated by using water level and flow rate time series data, sediment data, and field data of velocity with ADCP, bed sediment sampling, and bed morphological changes with bathymetries performed in August 2012 and February 2013. The evaluation also included hydrological analysis; the morphology of banks, islands, and sandbars; and the analysis of satellite images from 2000 to 2012. Results of depth, velocity, shear stress, and spatial and temporal bed level changes were obtained and analyzed. The results showed that the natural development of the river allows navigation eight months per year on average (between May and December) without need of hydraulic works. However, between January and April, the depths are not enough for navigation. The river has a high morphological dynamic linked to the wide flow rate variation that influences the hydrodynamic and sedimentologic conditions. This dynamic causes important short-term morphological changes on the thalwegs alignment, changes in the flow rate distribution percentage on river branches, and other morphological changes that modify the active river channel. These results suggested that, based on the natural river behavior, the hydraulic works oriented to river training, which progressively establish the alignment and depth of a navigation channel, are more appropriate for the Meta River than fixed and hard solutions.

An experimental design based methodology for calibrating 2D hidromorphodynamic numerical models for rivers

The confidence level of a numerical model is strongly related to the calibration and validation processes and the quality of their adjustment. Typically, numerical 2D models for rivers that involve hydrodynamics, sediment transport and morphology processes are calibrated sequentially under the assumption that the morphology changes do not significantly affect the hydrodynamics. However, in some cases, the morphologic processes modify substantially the hydrodynamic due to the quick bed level accession and erosion as a function of the hydrological regime. These changes require a more efficient procedure reduce the amount of scenarios with indicators that allow to asset the quality of the calibration. This paper shows a methodology proposed to take into account the interaction of hydrodynamic, sedimentology and morphology in rivers based on an experimental design that allow evaluating simultaneously the significance and the sensitivity of the variables in order to select the best set of scenarios based on quantitative and qualitative indicators. The methodology was implemented in the Magdalena River and the Meta River in Colombia, which have different hydromorphodynamic conditions. The calibration and validation was supported with field data of water elevation, velocity vectors obtained by ADCP, flow rate measurements, sediment transport, and bed level changes, showing that is applicable either to straight, meandered, or braided rivers.

Susceptibility Analysis of River Bank Erosion Based on Exposure to Shear Stress and Velocity Combined with Hydrologic and Geomorphologic Variables

This paper presents the results of evaluating the susceptibility and risk analysis of bank erosion in rivers by evaluating the exposure of banks to shear stress and velocity combined with hydrologic and geomorphologic variables. A 75 Km sector of the Meta River was taken as a case study for this research by conducting 2D numerical hydrodynamic and morphologic modeling with MIKE-21C. The study integrated hydrographs for different exceedance probabilities, bank resistance and bank variability maps, shear stress, velocity and bed level change, in order to achieve a complete analysis to determine the susceptibility and risk of bank erosion. A time exposure analysis was conducted to determine the percentage of time that velocity and shear stress are higher than threshold values for different soil materials. These results were analyzed conjointly with the river’s bank resistance and the probabilities associated with different hydrographs. It was found that specific geomorphologic resistances (low, medium, or high) have different susceptibilities depending on the hydrodynamic conditions acting on the bank, as well as the time exposure and probability of occurrence. These results allowed identifying areas with high risk of bank erosion and predicting potential river bank mobility under different hydrological scenarios.