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We present a sediment transport modelling study for the 2010 removal of the 3.3-m tall Simkins Dam on the Patapsco River, MD that released more than 56,000 m3 of sediment downstream. Our objectives are to validate the pre-removal model forecasts with detailed post-removal monitoring data, and through hindcast modelling, examine the effects of using approximate channel geometry data or more accurate data on model results. Comparisons of DREAM-1 model predictions using approximate data and field observations indicate that reach-scale model predictions were generally accurate, but some discrepancies between predicted and observed magnitudes of sediment deposition at specific locations occurred. A refined model, developed post-dam removal with more accurate channel geometry as model input, produced slightly improved results in reaches where input data were significantly improved. However, more accurate input data did not change the general conclusions nor substantially improve the model performance for the entire study reach. In conjunction with two previous studies, our results support a simplified data collection approach that enables timely predictions for decision making and minimizes study costs. [ABSTRACT FROM AUTHOR]

Aging infrastructure coupled with growing interest in river restoration has driven a dramatic increase in the practice of dam removal. With this increase, there has been a proliferation of studies that assess the physical and ecological responses of rivers to these removals. As more dams are considered for removal, scientific information from these dam-removal studies will increasingly be called upon to inform decisions about whether, and how best, to bring down dams. This raises a critical question: what is the current state of dam-removal science in the United States? To explore the status, trends, and characteristics of dam-removal research in the U.S., we searched the scientific literature and extracted basic information from studies on dam removal. Our literature review illustrates that although over 1200 dams have been removed in the U.S., fewer than 10% have been scientifically evaluated, and most of these studies were short in duration (<4 years) and had limited (1-2 years) or no pre-removal monitoring. The majority of studies focused on hydrologic and geomorphic responses to removal rather than biological and water-quality responses, and few studies were published on linkages between physical and ecological components. Our review illustrates the need for long-term, multidisciplinary case studies, with robust study designs, in order to anticipate the effects of dam removal and inform future decision making. WIREs Water 2017, 4:e1164. doi: 10.1002/wat2.1164 For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

Armstrong, William H., Mathias J. Collins, and Noah P. Snyder, 2012. Increased Frequency of Low-Magnitude Floods in New England. Journal of the American Water Resources Association (JAWRA) 48(2): 306-320. DOI: 10.1111/j.1752-1688.2011.00613.x Abstract: Recent studies document increasing precipitation and streamflow in the northeastern United States throughout the 20th and early 21st Centuries. Annual peak discharges have increased over this period on many New England rivers with dominantly natural streamflow - especially for smaller, more frequent floods. To better investigate high-frequency floods (<5-year recurrence interval), we analyze the partial duration flood series for 23 New England rivers selected for minimal human impact. The study rivers have continuous records through 2006 and an average period of record of 71 years. Twenty-two of the 23 rivers show increasing trends in peaks over threshold per water year (POT/WY) - a direct measure of flood frequency - using the Mann-Kendall trend test. Ten of these trends had p < 0.1. Seventeen rivers show positive trends in flood magnitude, six of which had p < 0.1. We also investigate a potential hydroclimatic shift in the region around 1970. Twenty-two of the 23 rivers show increased POT/WY in the post-1970 period when comparing pre- and post-1970 records using the Wilcoxon rank-sum test. More than half of these increases have p < 0.1, indicating a shift in flow regime toward more frequent flooding. Region wide, we found a median increase of one flood per year for the post-1970 period. Because frequent floods are important channel-forming flows, these results have implications for channel and floodplain morphology, aquatic habitat, and restoration. [ABSTRACT FROM AUTHOR]

Armstrong, William H., Mathias J. Collins, and Noah P. Snyder, 2012. Increased Frequency of Low-Magnitude Floods in New England. Journal of the American Water Resources Association (JAWRA) 48(2): 306-320. DOI: 10.1111/j.1752-1688.2011.00613.x Abstract: Recent studies document increasing precipitation and streamflow in the northeastern United States throughout the 20th and early 21st Centuries. Annual peak discharges have increased over this period on many New England rivers with dominantly natural streamflow - especially for smaller, more frequent floods. To better investigate high-frequency floods (<5-year recurrence interval), we analyze the partial duration flood series for 23 New England rivers selected for minimal human impact. The study rivers have continuous records through 2006 and an average period of record of 71 years. Twenty-two of the 23 rivers show increasing trends in peaks over threshold per water year (POT/WY) - a direct measure of flood frequency - using the Mann-Kendall trend test. Ten of these trends had p < 0.1. Seventeen rivers show positive trends in flood magnitude, six of which had p < 0.1. We also investigate a potential hydroclimatic shift in the region around 1970. Twenty-two of the 23 rivers show increased POT/WY in the post-1970 period when comparing pre- and post-1970 records using the Wilcoxon rank-sum test. More than half of these increases have p < 0.1, indicating a shift in flow regime toward more frequent flooding. Region wide, we found a median increase of one flood per year for the post-1970 period. Because frequent floods are important channel-forming flows, these results have implications for channel and floodplain morphology, aquatic habitat, and restoration. [ABSTRACT FROM AUTHOR]

A correction to the article "Evidence for Changing Flood Risk in New England Since the Late 20th Century," that was published in the earlier issue is presented.