| dc.description.abstract | Erosion and sediment control (E&SC) practices are commonly installed on construction projects to prevent soil loss and prevent the impacts of sediment-laden runoff on surrounding areas, including protected natural resources and waterbodies that can be adversely affected by sediment pollution. The conditions on a construction project can considerably impact the performance of practices. Severe upstream conditions, such as large drainage areas, erodible soils, and steeper slopes, can increase the stormwater and sediment loading subjected to practices. Severe conditions can increase a practice’s susceptibility to failure unless it is sufficiently robust and can withstand such conditions. Practice failure can lead to adverse downstream impacts, both on- and off-site. Downstream practices may be subjected to more severe conditions and be at risk of failure due to the failure of upstream practices. Failed practices can also have adverse impacts on adjacent natural resources. Additionally, more disruptive conditions may cause practice failure unless practices are designed with resilience to remain effective and recover when subjected to disruptive conditions.
A review of 176 documents was completed to determine existing guidance and the level of existing risk- and resilience-based design guidance. Common trends were identified in existing design guidance, with the guidance primarily focusing on the selection, placement, and sizing of practices. Additionally, limited risk-based design guidance was identified that related to the susceptibility of failure or the impact of practice failure. Guidance aimed at reducing the susceptibility of failure for practices primarily considers the adjustment of practices designs based on the presence of severe upstream conditions to ensure adequate robustness. However, guidance may also consider the design life of the practice due to either an increased likelihood of material degradation or a higher probability of experiencing a severe stormwater runoff event. Guidance may also recommend more robust practices in instances where the impact on surrounding areas, such as adverse impacts on sensitive natural resources, damage to nearby properties, or a safety risk to adjacent roadways, is present. Little resilience-based design guidance was also found, primarily related to overflow capabilities, dewatering components, or incorporating natural infrastructure.
To improve the state of risk- and resilience-based design guidance in E&SC, previously developed risk- and resilience-based design frameworks, specifically the Performance-based Resilience Evaluation Program (PREP), were implemented on E&SC practices to evaluate practices or systems of practices. The risk-based design framework consisted of three main components: the probability of a specific design storm occurring, the likelihood of the practice failing, and the potential impact of practice failure. If a practice is found to have an unacceptable level of expected adverse impact, it can be modified to increase robustness, a more robust practice can be selected, or upstream conditions can be mitigated through the use of other practices. The implementation of the resilience-based design framework aimed to determine the adaptive capacity and recoverability of practices through either quantitative or qualitative means, allowing for comparisons with other practices or modifications, and allowing for the application of the PREP framework on E&SC practices.. Both frameworks were applied to previously completed silt fence research to evaluate how modified installations can decrease the risk of failure and impact, and improve the resiliency of the practice.
To improve performance, reduce the likelihood of failure, and increase the resiliency of rock check dam installations, full-scale testing was conducted on Iowa Department of Transportation (DOT) standard rock check dams. This testing led to the development of efficient and cost-effective recommendations for the practice. The standard rock check dam installation was found to fail due to high flow-through rates, as it only protected approximately 10% of the test channel from erosive flows with an average of 6 ft (1.8 m) of impoundment formed. A modified installation, with the use of a smaller rock, installed on grade, with a geotextile overlay with dewatering holes, and a reduced profile, outperformed the standard installation, with impoundment increasing to 57.5 ft (17.5 m), protecting over 90% of the channel, while decreasing approximate material costs by 55%. Additionally, the increased impoundment facilitated by the modified installation, under sediment-laden conditions, increased sediment capture from 9.4% by the standard to 72.4% and lowered average discharge turbidity by 396 NTU. The improvements made to the Iowa DOT rock check dams increased the resilience of the practice by enhancing adaptive capacity through effective overflow and recoverability, thanks to the implementation of dewatering holes that facilitate efficient dewatering. Modifications also reduces the risk of soil loss in channels where the modified practice is implemented.
Finally, research was proposed on four practices (alternative sediment barriers, slash mulch berms in inlet protection and ditch check applications, vegetated buffers, and limiting and delaying soil disturbance). The completion of these four research efforts would increase the body of knowledge on these practices and provide additional data for the use of risk- and resilience-based design frameworks. | en_US |
