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This study identifies and summarizes potential risks to operations, regulatory compliance, supply chains, and infrastructure of the electric power industry from changing surface water conditions resulting from global climate change. The results help inform companies/utilities seeking to incorporate climate change risk in their planning and decision‐making processes by ranking risk severity and likelihood of occurrence on both a regional basis and by risk receptor. The assessment includes identification of potential risks to: (1) thermal generating, (2) hydroelectric, (3) land‐based renewable generating, and (4) transmission and distribution assets. These risks may result from such projected changes as reduced water availability (e.g., for hydroelectric or once‐through cooling), increased water temperatures (e.g., decrease in cooling efficiency, inability to meet discharge permit conditions), increased flood severity (e.g., increased streambank erosion and/or damage to river‐adjacent infrastructure), and decreased water quality (e.g., from increased transport of sediment and dissolved solids). The potential risks identified from this qualitative risk‐assessment are documented in a graphical format depicting both severity and likelihood. This approach allows for comparison of risks across a portfolio and for future prioritization of adaptation strategies. A total of 32 risks were identified in the study, including nine risks to infrastructure, six risks to operations, four risks to supply chain, and 13 environmental/regulatory risks. [ABSTRACT FROM AUTHOR]

In this study, a new remote sensing tool was used in conjunction with sampling of river bank sediments to map channel migration patterns and estimate the net contribution of bank erosion to the sediment and phosphorus (P) budget of the Nishnabotna River in southwestern Iowa. Between the years 2009 and 2018, we found that at least 1.81 ± 0.57 × 107 Mg of sediment and 8.26 ± 2.5 × 103 Mg of P entered the Nishnabotna River due to channel migration. This equates to 0.87 Mg of sediment per meter of channel per year and 0.40 kg of P per meter of channel per year. Barring additional deposition elsewhere in the river corridor, these values represent as much as 77% of annual suspended sediment and 46% of the annual P export from the watershed. Our results also indicate that the contribution of net sediment and P volume loss by stream order increases sharply from third to sixth order, even though the total channel length is much smaller in the higher orders. These results suggest that bank erosion is an important source of sediment and P within the watershed and that future attempts to decrease riparian exports of sediment and P should focus on high‐order reaches. [ABSTRACT FROM AUTHOR]

The drawdown of reservoirs behind dams is an important management strategy (e.g., for removal of aging infrastructure, flushing of sediment), and an opportunity to study erosional processes. A numerical model was developed to examine retrogressive bank erosion across reservoir drawdown scenarios and to evaluate factors controlling the rate, volume, and mechanisms of lateral erosion. Modeled processes included dynamic drawdown of groundwater, sequential slope failures via limit equilibrium analysis, and retrogression considering stress interaction between failing blocks. Field measurements were coupled with Staged, Slow, and Rapid drawdown scenarios. Results highlight the importance of including retrogression as an avenue for lateral erosion, as sequential block failures were found to occur in all scenarios except Slow drawdown. This result indicates that bank stability models without some means of characterizing the evolution of slope failure during drawdown are likely underestimating bank failure rates and volumes. In contrast, dynamic groundwater was not found to be a dominant control for any drawdown scenario. Model results also demonstrate that the drawdown increment is a first‐order control on slope instability via the development of drained or undrained conditions. A majority of failures occurred under undrained conditions. To maximize slope stability, using slow drawdown to activate internal friction under drained conditions is essential. The design of the drawdown rate created a tradeoff between the amount of impact created and when the impact is produced. The study also articulated the need for coupling models and field observations for rapidly changing systems. [ABSTRACT FROM AUTHOR]

A total maximum daily load for the Chesapeake Bay requires reduction in pollutant load from sources within the Bay watersheds. The Conestoga River watershed has been identified as a major source of sediment load to the Bay. Upland loads of sediment from agriculture are a concern; however, a large proportion of the sediment load in the Conestoga River has been linked to scour of legacy sediment associated with historic millpond sites. Clarifying this distinction and identifying specific segments associated with upland vs. channel sources has important implications for future management. In order to address this important question, we combined the strengths of two widely accepted watershed management models — Soil and Water Assessment Tool (SWAT) for upland agricultural processes, and Hydrologic Simulation Program FORTRAN (HSPF) for instream fate and transport — to create a novel linked modeling system to predict sediment loading from critical sources in the watershed including upland and channel sources, and to aid in targeted implementation of management practices. The model indicates approximately 66% of the total sediment load is derived from instream sources, in agreement with other studies in the region and can be used to support identification of these channel source segments vs. upland source segments, further improving targeted management. The innovated linked SWAT‐HSPF model implemented in this study is useful for other watersheds where both upland agriculture and instream processes are important sources of sediment load. Research Impact Statement: Novel SWAT‐HSPF linkage to simulate sediment sources in legacy sediment‐impacted agricultural watersheds. [ABSTRACT FROM AUTHOR]

Abstract: Geomorphic change from extreme events in large managed rivers has implications for river management. A steady‐state, quasi‐three‐dimensional hydrodynamic model was applied to a 29‐km reach of the Missouri River using 2011 flood data. Model results for an extreme flow (500‐year recurrence interval [RI]) and an elevated managed flow (75‐year RI) were used to assess sediment mobility through examination of the spatial distribution of boundary or bed shear stress (τb) and longitudinal patterns of average τb, velocity, and kurtosis of τb. Kurtosis of τb was used as an indicator of planform channel complexity and can be applied to other river systems. From differences in longitudinal patterns of sediment mobility for the two flows we can infer: (1) under extreme flow, the channel behaves as a single‐thread channel controlled primarily by flow, which enhances the meander pattern; (2) under elevated managed flows, the channel behaves as multithread channel controlled by the interaction of flow with bed and channel topography, resulting in a more complex channel; and (3) for both flows, the model reach lacks a consistent pattern of deposition or erosion, which indicates migration of areas of erosion and deposition within the reach. Despite caveats and limitations, the analysis provides useful information about geomorphic change under extreme flow and potential implications for river management. Although a 500‐year RI is rare, extreme hydrologic events such as this are predicted to increase in frequency. [ABSTRACT FROM AUTHOR]

Complex relationships between stream functions and processes make evaluation of stream modification projects difficult. Informed by vague objectives and minimal monitoring data, post-construction project evaluations can often be a subjective attribution of success or failure. This article provides a simple framework to rapidly describe the degree of damage in stream modification projects performed in constrained settings. Based on widely accepted evaluations of physical habitat quality and stream stability, the damage states framework describes a continuum of damage in multiple categories that relate natural stream functions to the often desired state of static equilibrium. Given that channel form is closely related to stream function, it follows that changes to the channel form result in changes in function. The damage states focus on damage to flow hydraulics, sediment transport and channel equilibrium, hydraulic, and geomorphic parameters that describe basic stream functioning and support higher level functions in the modified channel. The damage states can be used in decision making as a systematic method to determine the need for repair and design adjustments. [ABSTRACT FROM AUTHOR]