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Sea-level rise (SLR) is a projected consequence of global climate change that will result in complex changes in coastal ecosystems. These changes will cause transitions among coastal habitat types, which will be compounded by humanmade barriers to the gradual inland migration of these habitat types. The effect of these changes on the future viability of coastal species will depend on the habitat requirements and population dynamics of these species. Thus, realistic assessments of the impact of SLR require linking geomorphological models with habitat and population models. In this study, we implemented a framework that allows this linkage, and demonstrated its feasibility to assess the effect of SLR on the viability of the Snowy Plover population in Florida. The results indicate that SLR will cause a decline in suitable habitat and carrying capacity for this species, and an increase in the risk of its extinction and decline. The model projected that the population size will decline faster than the area of habitat or carrying capacity, demonstrating the necessity of incorporating population dynamics in assessing the impacts of SLR on coastal species. The results were most sensitive to uncertainties in survival rate and fecundity, and suggested that future studies on this species should focus on the average and variability of these demographic rates and their dependence on population density. The effect of SLR on this species' viability was qualitatively similar with most alternative models that used the extreme values of each uncertain parameter, indicating that the results are robust to uncertainties in the model.

Seepage may be a significant mechanism of streambank erosion and failure in numerous geographical locations. Previous research investigated erosion by lateral subsurface flow and developed a sediment transport model similar to an excess shear stress equation. As a continuation of this earlier research, slope destabilization driven by lateral, subsurface flow was studied to further verify the recently proposed sediment transport model. Laboratory experiments were performed using a two‐dimensional soil lysimeter. The experiments were conducted on two sandy soils: a field soil (loamy sand) and sieved sand with greater sand content and less cohesion. A series of seven lysimeter experiments were performed for the two different sands by varying the bank slope (90, 60, 45, 36, and 26°). Flow and sediment concentrations were measured at the outflow flume. Pencil‐size tensiometers were used to measure soil pore‐water pressure. A slight modification of the existing seepage sediment transport model adequately simulated lysimeter experiments for both noncohesive soils without modifying the seepage parameters of the excess shear stress equation, especially for bank angles >45°. The research then determined whether integrated finite element and bank stability models were capable of capturing both small‐ and large‐scale sapping failures. The models predicted large‐scale failures for bank angles >45° in which tension cracks formed on the bank surface. The models failed to predict collapses for bank angles <45° in which tension cracks formed on the seepage face. The failure to predict collapse was hypothesized to be due to the assumption of circular arc slip surfaces. More analytically complex stability approaches are needed to capture bank slope undermining.

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Undercutting, primarily considered due to fluvial mechanisms, has been reported to have a major impact on slope failure. Predicting bank collapse specifically due to seepage erosion undercutting by particle mobilization on layered streambanks has not been fully studied or modeled, even though its role in streambank erosion may be important. The limitation originates from the limited field measurements or laboratory experiments as well as the unavailability of discrete element models that can effectively simulate seepage particle mobilization, undercutting, and the corresponding mass wasting. The objective of this research was to demonstrate a procedure for incorporating seepage undercutting into bank stability models and to investigate the role of seepage undercutting on bank instability. The question to be addressed is whether seepage particle mobilization can lead to distances of undercutting that are a significant cause of bank instability. A numerical finite-element model, SEEP/W, was used to model soil-water pressure variations during seepage observed in laboratory experiments with two-dimensional soil lysimeters. Flow parameters were calibrated using measured soil-water pressure and cumulative discharge. A general limit equilibrium bank stability model ͑SLOPE/W͒ was used to simulate bank stability with and without seepage erosion undercutting by comparing the computed factor of safety, Fs, at different stages of the seepage erosion process with regard to input parameter uncertainty using Monte Carlo analysis. The percentage decrease in the mean Fs ranged between 42 and 91% as the depth of undercutting increased, dependent upon the initial stability of the bank. A stable bank ͑i.e., FsϾ 1͒ can quickly become unstable ͑i.e., FsϽ 1͒ when seepage undercutting is considered. For stable banks, the probability of failure reached 100% when the depth of the undercutting reached approximately 30 to 50 mm under these experimental conditions. The results derived are specific to the streambank simulated but are expected to be comparable for similar layered streambank lithologies reported to occur in numerous geographical locations. This research also highlights the need to incorporate the dynamic process of seepage erosion undercutting into integrated subsurface flow and streambank stability models.

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