Project Description:

Protecting riverbanks from erosion during flood events is critical for ensuring the safety of transportation infrastructure located near rivers. Such erosion can undermine roadways and bridge foundations, leading to failures such as those observed on I-40 in North Carolina following Hurricane Helene. In locations where riverbank erosion poses a significant transportation asset risk, porous riverbank protection structures such as engineered logjams (ELJs) have been implemented as alternatives to traditional revetment approaches. The geometric design of ELJs deflects flow away from banks while their porosity reduces drag and toe scour, thereby limiting additional flood-related failure risks. Additionally, ELJs can be constructed incrementally using off-channel crane equipment, which reduces construction costs associated with channel diversion and dewatering. 

Improved tools are needed to predict how flow deflection and scour vary with ELJ porosity and internal structure. Advancing this knowledge will support more reliable ELJ design and reduce the risk of over- or under-design. A larger database of flow and scour depth measurements for ELJs with a range of porosities and characteristics is needed to improve scour prediction methods and provide flow validation data for two- and three-dimensional hydraulic models.

To address these research gaps, laboratory experiments will be conducted in a 32-foot-long open-channel flume to quantify flow and scour at porous bank protection structures. Model ELJs will be fabricated using 3D printing to have identical external geometry but systematic variation in porosity and pore configuration. Flow fields will be measured using UMKC’s particle image velocimetry (PIV) system that can measure turbulent flow fields around channel obstructions with high resolution (<1 mm vector resolution). These PIV measurements will be used to quantify flow deflection and shear stress amplification. In addition, clear-water scour experiments will document the maximum scour depth for each ELJ configuration. 

_{Figure 1. Diagram of the flume system used to measure flow and scour at model porous bank protection structures.}

Outputs:

This research will generate a new experimental dataset documenting flow deflection, shear stress amplification, and maximum scour depth at porous bank protection structures. This dataset will be used to calculate correction coefficients for scour prediction formulas and evaluate correlations with bulk structure parameters like porosity. Existing scour estimation methods will be tested to identify the best predictors for porous bank protection structures.

The relationship between shear stress amplification and maximum scour depth will also be examined experimentally. Several scour estimation approaches, such as the shear stress decay method, assume that such a relationship exists. However, more experimental testing of this assumption for a broader range of conditions including varied structure porosity is needed. The findings of this research will support refinement of advanced mechanics-based approaches for estimating scour at bank protection structures, bridge abutments, and bridge piers.

Outcomes/Impacts:

Scour and riverbank erosion are common failure modes for transportation infrastructure. Flood-induced failures disrupt transportation services and increase public safety risks. The recent roadway failure on I-40 near the North Carolina–Tennessee state line during Hurricane Helene illustrates the consequences of inadequate bank protection. Estimated repair costs for this interstate are over a billion dollars and significant additional economic losses occurred due to road closures. 

Porous bank protection structures such as ELJs provide an approach to protect critical roadways while limiting additional hydraulic resistance during floods. The results of this study will provide DOT engineers with experimentally validated guidance to improve design confidence, reduce over-conservatism, and lower long-term repair and maintenance costs. These outcomes will enhance transportation infrastructure safety, reliability, and durability under extreme flood conditions.