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A multi-model approach was applied to reconstruct long-term flow records in 32 ungauged rivers developed with small diversion hydropower stations. Potential hydrologic alteration was assessed for flow records simulated by a catchment similarity model and the multi-criteria Streamflow Prediction under Extreme Data-scarcity (SPED) framework. Model validation based on limited observed data suggests that the SPED flow predictions are substantially more accurate than those generated by the catchment similarity model (NSE of 0.74 and 0.22, respectively and Correlation Coefficient of 0.87 and 0.72, respectively). Both flow prediction techniques indicated that flow signatures were altered substantially by diversion hydropower. Mean annual flows decreased by a mean of 76–86% across the 32 rivers and flow became more predictable in most rivers (47–94% mean increase in predictability). Frequency and duration of high flows decreased and duration of low flow events increased substantially. Slopes of rising hydrograph limbs and recession limbs increased respectively by a mean of 123–161% and 254–720%. While direction of detected flow alteration was similar regardless of model choice, severity of alteration was consistently greater based on the analysis of flows simulated by the multi-objective SPED model. Overall, the agreement of the multi-model analysis indicates that the signal of flow alteration by diversion hydropower in the study rivers supersedes uncertainty associated with flow prediction. While both models may be appropriate for applications such as change detection analysis, prescriptive management actions, such as establishing flow targets for environmental flow regimes, should be based on flow records generated by models adept at simulating rainfall-runoff processes targeted to individual basins, such as SPED. [ABSTRACT FROM AUTHOR]

Oyster reef living shorelines have been proposed as an effective alternative to traditional coastal defence structures (e.g. bulkheads, breakwaters), with the benefit that they may keep pace with sea‐level rise and provide co‐benefits, such as habitat provision. However, there remains uncertainty about the effectiveness of shoreline protection provided by oyster reefs, which limits their broader application.We draw evidence from studies along the east and gulf coasts of the United States, where much research and implementation of oyster reef restoration has occurred, to better define the existing gaps in our understanding of the use of restored oyster reefs for shoreline protection.We find potential disconnects between ecological and engineering functions of reefs. In response, we outline how engineering and ecological principles are used in the design of oyster reef living shorelines and highlight knowledge gaps where an integration of these disciplines will lead to their more effective application.Synthesis and applications. This work highlights the necessary steps to advance the application of oyster reef living shorelines. Importantly, future research should focus on appropriate designs and conditions needed for these structures to effectively protect our coasts from erosion, while supporting a sustainable oyster population, thereby providing actionable nature‐based alternatives for coastal defence to diverse end‐users. This work highlights the necessary steps to advance the application of oyster reef living shorelines. Importantly, future research should focus on appropriate designs and conditions needed for these structures to effectively protect our coasts from erosion, while supporting a sustainable oyster population, thereby providing actionable nature‐based alternatives for coastal defence to diverse end‐users. [ABSTRACT FROM AUTHOR]

Hydrologic changes caused by diversion hydropower are poorly described. Herein, we evaluate hydrologic alteration in 32 ungauged rivers developed for diversion hydropower. We simulated long-term unregulated discharge records before perturbing flows with the hydropower diversion and comparing periods with and without diversion. We detected statistically significant changes to flow regime metrics across all rivers. Magnitudes across a range of flows consistently decreased following diversion, flow variability decreased substantially, and transitions between flows of different magnitudes became more abrupt. Magnitudes of 7-day minimum flows were lower by a mean of 41 ± 23% ( p < .05 for 19 rivers), annual maximum flows decreased significantly ( p < .05) in 22 rivers, and 7-day maximum flows decreased by a mean of 52 ± 18% ( p < .05 for 26 rivers). Temporally dynamic low to moderate flows were replaced by static minimal flows, leading to a mean 184 ± 49% increase in flow constancy. Mean duration of events sustained below the prediversion Q75 increased ( p < .05 for 32 rivers) from a mean of 3 days to a mean of 27 days after diversion. Mean hydrograph rise and fall rates doubled and tripled, respectively ( p < .05 for 28 rivers). We detected few changes to peak flow timing. Although direction of observed change was consistent among the rivers, magnitudes and significance of response often varied between rivers. A proposed diversion index largely explained response variability among the 32 rivers. Results highlight that hydropower systems without storage reservoirs can profoundly affect river flow regimes when water is diverted from the river. [ABSTRACT FROM AUTHOR]

To manage flood risk, floodplains are often designated for uses that support flood storage and ecosystem conservation. In such cases, direct human uses of flood-prone land are often restricted. Despite effectiveness at reducing flood risk, the exclusion of direct human uses from flood-prone lands is not always possible. Additionally, where livelihoods are tied to the use of flood-prone land, such strategies may eliminate floodplain-related benefits. To support implementation of Integrated Flood Management suited to such contexts, we propose a framework in which the livelihood benefits of direct floodplain use are distinguished from those supplied through ecosystem services. Decision-makers may apply this approach where flood risk, ecosystem, and livelihood objectives must be balanced. Because flood adaptation strategies may involve risk-benefit trade-offs, we propose the integrated assessment of flood risk and probabilistic benefits to inform decision-making. Through parallel analysis of probabilistic damages and benefits, a broad suite of management actions may be evaluated to minimize flood risk while maximizing river-derived benefits. Application of the proposed framework and risk-benefit analysis may highlight effective solutions that reflect the pressures and opportunities of developing countries. For instance, measures that reduce flood risk by targeting coping capacity and adaptation, as opposed to flood exposure, may be emphasized. [ABSTRACT FROM PUBLISHER]

Flood risk assessments often overlook benefits of floodplain use and the influence of coping capacity. Herein we present a classic flood risk analysis, but simultaneously evaluate benefits of flood‐prone land use in Candaba, Philippines. By combining simulated flood probabilities with both damage and benefit functions, we estimate agricultural damages and livelihood benefits over flood hazards of varying frequency. We find that concurrent evaluation of both damages and benefits provides more complete information on which flood risk reduction decisions may be based. In Candaba, although "risky" uses of flood‐prone land are associated with rice‐crop damages, livelihood benefits exceed risks by a large margin (US $58 million) across the range of investigated flood hazards. Even considering risk, net benefits of direct human floodplain use far exceed benefits provided when direct "risky" human uses are excluded (difference of $85–87 million). We also find that individual coping strategies (adapting crop cycles to the flood pulse or shifting from farming to seasonal fishing) may minimise flood losses while supporting livelihood benefits (net benefit of $125 million). Risk‐benefit analysis can support floodplain management by elucidating practices that yield maximum socio‐ecological benefits for the minimum flood risk. [ABSTRACT FROM AUTHOR]

Oysters are recognized as ecosystem engineers that constitute vital parts of biodiverse and sustainable estuarine environments. Although their beneficial services are widely acknowledged, there has been a dramatic reduction in oysters population worldwide and current restoration projects aim to increase their numbers. In Mosquito Lagoon, on Florida's Atlantic coast, oyster restoration is accomplished by restoring existing degraded oyster reefs. Oyster reefs in Mosquito Lagoon are home to at least 150 additional species that include commercially and recreationally important fishes and invertebrates as well as foraging grounds for threatened/endangered birds. Successful restoration implies that oysters will recruit and the reef will obtain intricate structure similar to that of an intact natural oyster reef. Such a reef evolution will alter its surface roughness, which will subsequently affect the flow pattern and turbulence levels with significant implications on oyster recruitment and proliferation, sediment transport, and shoreline protection. The present experimental study compares flow and wave patterns on five oyster reefs with different surface roughness, in the intertidal environment of Mosquito Lagoon. These five oyster reefs comprise a natural, a degraded, and three restored oyster reefs with different restoration age (restored in 2014, 2016, and 2017). Three-dimensional flow velocity measurements were conducted on the oyster reefs with a Nortek Vectrino Profiler (3 cm velocity profile with 100 Hz sampling frequency) and at the adjacent channels with a Nortek Aquadopp acoustic Doppler current profiler (monitoring the whole water column at 2 Hz). Simultaneous measurements were conducted for wave height at these two locations, water level, and wind speed. Reef topography was measured with survey grade Global Navigation Satellite System (GNSS) equipment receiving real time kinematic (RTK) corrections from the Florida Permanent Reference Network. A Faro x330 laser scanner was used for detailed measurements of roughness elements, i.e., oyster clusters, that protrude into the flow. Two different sets of flow velocity measurements were collected for each reef during low- and high-water season, at the same location. For the former, flow measurements on the reefs were conducted at the bed vicinity, within the roughness sublayer defined by oysters, while for the latter measurements were conducted above the roughness sublayer. Results show that there is a gradual increase in turbulent kinetic energy dissipation rate with increasing restoration age, both for measurements within and above the roughness sublayer. This does not necessarily correlate with the number of live oysters counted on the reefs, due to their individual shape and random orientation. Reef roughness calculated with the aid of laser-scanner is compared to manual measurements of oyster shells that obstruct the flow and distributions of live oyster characteristics to infer appropriate measures for flow resistance and drag. Some of the well-known methodologies for bed shear stress calculation generate consistent results for the degraded reef; however, they derive a wide scatter for the natural reef, highlighting the insufficiency of current empirical formulae for bed shear stress estimation on oyster reefs. [ABSTRACT FROM AUTHOR]