Bridge Scour and Stream Stability
Bridge scour and stream instabilities, such as channel widening, lateral migration and channel bed degradation, are common at many bridges. Road crossings can also have a significant influence on local hydraulics and sediment transport, resulting in an altered flow pattern that can cause backwater, increased erosion, debris and sediment deposition, and channel instability. Thus, managing rivers and streams that include one or more road crossings requires some knowledge of the flow hydraulics over a range of flows in order to create a smooth, stable transition through the bridge opening. Attention to channel conditions in the vicinity of bridges is an important aspect of bridge maintenance. Channel stability is also critical to goals of river management, which include maintaining high standards for water quality, aquatic habitat and protection of infrastructure and property.
Uncertainty, Risk, and Vulnerability
There are several broad categories of uncertainty that are common to most design processes. These include: model uncertainty, resulting from the use of simplified mathematical expressions to describe a complex physical process or phenomenon; parameter uncertainty, resulting from difficulties in estimating model parameters, such as Manning's roughness coefficient channel slope, and critical shear stress; randomness, due to fluctuation in parameters, such as flow discharges and velocities, and human error, such as calculation and construction errors. Scour and channel instability processes, including local scour at the piers and abutments, contraction scour, channel bed degradation, channel widening, and lateral migration, are very complex processes that can occur separately or simultaneously. The sum and interaction of all of these river processes create a very complex phenomenon that have, so far, eluded mathematical modeling. To further complicate a mathematical solution, mitigation measures, such as riprap, grout bags, and gabions, may be in place at the abutments, piers, and stream banks. Any mathematical model would have to account for these structures as well. There are a number of methods useful in qualitatively or quantitatively assessing the risk or reliability of systems. Some of the more commonly used methods include Monte Carlo simulation, fault tree analysis, failure modes and effects analysis (FMEA), and vulnerability analysis. Current research by Dr. Johnson and her students is focused on risk matrices and vulnerability analyses.
Bridge scour and stream instabilities, such as channel widening, lateral migration and channel bed degradation, are common at many bridges. Road crossings can also have a significant influence on local hydraulics and sediment transport, resulting in an altered flow pattern that can cause backwater, increased erosion, debris and sediment deposition, and channel instability. Thus, managing rivers and streams that include one or more road crossings requires some knowledge of the flow hydraulics over a range of flows in order to create a smooth, stable transition through the bridge opening. Attention to channel conditions in the vicinity of bridges is an important aspect of bridge maintenance. Channel stability is also critical to goals of river management, which include maintaining high standards for water quality, aquatic habitat and protection of infrastructure and property.
Uncertainty, Risk, and Vulnerability
There are several broad categories of uncertainty that are common to most design processes. These include: model uncertainty, resulting from the use of simplified mathematical expressions to describe a complex physical process or phenomenon; parameter uncertainty, resulting from difficulties in estimating model parameters, such as Manning's roughness coefficient channel slope, and critical shear stress; randomness, due to fluctuation in parameters, such as flow discharges and velocities, and human error, such as calculation and construction errors. Scour and channel instability processes, including local scour at the piers and abutments, contraction scour, channel bed degradation, channel widening, and lateral migration, are very complex processes that can occur separately or simultaneously. The sum and interaction of all of these river processes create a very complex phenomenon that have, so far, eluded mathematical modeling. To further complicate a mathematical solution, mitigation measures, such as riprap, grout bags, and gabions, may be in place at the abutments, piers, and stream banks. Any mathematical model would have to account for these structures as well. There are a number of methods useful in qualitatively or quantitatively assessing the risk or reliability of systems. Some of the more commonly used methods include Monte Carlo simulation, fault tree analysis, failure modes and effects analysis (FMEA), and vulnerability analysis. Current research by Dr. Johnson and her students is focused on risk matrices and vulnerability analyses.