Conversion of a Missouri River Dam and Reservoir to a Sustainable System: Sediment Management1

Abstract: A present and future challenge for water resources engineers is to extend the useful life of our dams and reservoirs. Ongoing reservoir sedimentation in impoundments must be addressed; sedimentation in many reservoirs already limits project benefits and effective project life. Sustainability requires that incoming sediment be moved downstream past the impounding dam. We use Lewis and Clark Lake, the most downstream of the six Missouri River main stem reservoirs, to demonstrate how a reservoir in advanced stages of its project life could be converted to a sustainable system with local benefits exceeding costs by a factor of 1.5. Full consideration of benefits would further enhance project justification. The proposed strategy involves four phases that will take about 50 years to complete. Cost estimates for this potential project range from the quantitative to the plausible, but it is clear that the results justify a full engineering, environmental, and economic study of this model project. If implemented, the project will create scientific knowledge and develop technologies useful for achieving sustainability at many other reservoirs in the Mississippi River basin and beyond.     

Climate dynamics and extreme precipitation and flood events in Central Europe

Past changes and possible future variations in the nature of extreme precipitation and flood events in Central Europe and the Alpine region are examined from a physical standpoint. An overview is given of the following key contributory physical processes: (1) the variability of the large-scale atmospheric flow and the associated changes of the North-Atlantic storm track; (2) the feedback process between climate warming and the water cycle, and in particular the potential for more frequent heavy precipitation events; and (3) the catchment-scale hydrological processes associated with variations in major river flooding events and that are related to land-use changes, river training measures, and shifts in the proportion of rain to snowfall. In this context an account is provided of the possible future forecasting and warning methodologies based upon high-resolution weather prediction and runoff models. Also consideration is given to the detectability of past (future) changes in observed (modeled) extreme events. It is shown that their rarity and natural fluctuation largely impedes a detection of systematic variations. These effects restrict trend analysis of such events to return periods of below a few months. An illustration using daily precipitation from the Swiss Alps does yield evidence for pronounced trends of intense precipitation events (return period 30 days), while trends of stronger event classes are not detectable (but nevertheless can not be excluded). The small detection probability for extreme events limits possible mitigation of future damage costs through an abatement of climate change alone, and points to the desirability of developing improved early forecasting/warning systems as an additional no-regret strategy. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Vegetation of Wet Meadows in Relation to Their Land-use

Wetland biomonitoring approaches are needed to determine when changes in response to stressors are occurring and to predict the consequences of proposed land-use changes. These approaches require an understanding of shifts in biota that occur in response to land-use, data that are lacking for most kinds of wetlands. Changes in floristic composition corresponding to land-use differences at multiple scales (site to 2500 m radius) were characterized for 40 wet meadows associated with prairie glacial marshes in Minnesota (U.S.A.). In general, guild was more useful than species composition for indicating land-use impacts. Site impacts (stormwater, cultivation) and landscape disturbance (agriculture and urbanization, combined), coincide with a reduction in native graminoid and herbaceous perennial abundance (e.g., Carex lasiocarpa, Calamagrostis canadensis, Spartina pectinata). This vegetation is replaced with annuals (e.g, Bidens cernua, Polygonum pensylvanicum) in recently cultivated sites or introduced perennials (e.g., Phalaris arundinacea, Typha angustifolia) and floating aquatics (lemnids) in stormwater impacted wetlands. Ditches also reduce native perennial importance and increase perennials, but only when they are in highly impacted landscapes.     

Effect of spatial variation on salinity tolerance of macroinvertebrates in Eastern Australia and implications for ecosystem protection trigger values

Salinisation of freshwater has been identified as a serious environmental issue in Australia and around the world. Protective concentrations (trigger values) for salinity can be used to manage salinity impacts, though require locally relevant salinity tolerance information. 72-h acute salinity tolerance values were determined for 102 macroinvertebrates collected from 11 locations in four biologically distinct freshwater bio-regions in Northeast Australia and compared with sensitivities observed in Southeast Australia. The salinity tolerance of individual taxa was consistent across Northeast Australia and between Northeast and Southeast Australia. However, two distinct communities were identified in Northeast Australia using distributions of the acute tolerance values and a calculated index of salinity sensitivity. Salinity trigger values should therefore be representative of local or regionally relevant communities and may be adequately calculated using sensitivity values from throughout Eastern Australia. The results presented provide a basis for assessing salinity risk and determining trigger values for salinity in freshwater ecosystems at local and regional scales in Eastern Australia.     

Changes in Streambed Composition in Salmonid Spawning Habitat of the Elwha River during Dam Removal

One uncertainty associated with large dam removal is the level of downstream sediment deposition and associated short‐term biological effects, particularly on salmonid spawning habitat. Recent studies report downstream sediment deposition following dam removal is influenced by proximity to the source and river transport capacity. The impacts of dam removal sediment releases are difficult to generalize due to the relatively small number of dam removals completed, the variation in release strategies, and the physical nature of systems. Changes to sediment deposition and associated streambed composition in the Elwha River, Washington State, were monitored prior to (2010‐2011) and during (2012‐2014) the simultaneous removal of two large dams (32 and 64 m). Changes in the surface layer substrate composition during dam removal varied by year and channel type. Riffles in floodplain channels downstream of the dams fined and remained sand dominated throughout the study period, and exceeded levels known to be detrimental to incubating salmonids. Mainstem riffles tended to fine to gravel, but appear to be trending toward cobble after the majority of the sediment was released and transported through system. Thus, salmonid spawning habitats in the mainstem appear to have been minimally impacted while those in floodplain channels appear to have been severely impacted during dam removal.     

城市生活垃圾处理方式生命周期评价的比较研究

生命周期评价理论与方法作为一种量化环境影响的工具,在诸多领域中得到了广泛的应用。在垃圾处理领域,生命周期评价最早在20世纪90年代得到应用。生命周期评价与城市生活垃圾处理的有效结合,将促进城市生活垃圾的减量化、资源化、无害化目标的实现。总结了生命周期评价理论与方法在城市生活垃圾处理中的应用现状。对国内不同城市生活垃圾处理方式环境影响因子进行比较分析,诸如全球变暖潜力、酸化潜力和富营养化潜力等因子。针对其目标范围定义、数据收集、评价方法的选择、结果解释及工艺改进等方面指出了目前研究的局限性和不足。并对未来城市生活垃圾处理生命周期评价的发展方向进行展望。     

古城旅游地旅游影响的居民感知研究——以黄山市歙县徽州古城为例

古城旅游地是独具中国传统魅力的重要旅游目的地,而古城居民是古城生命力之所在。以黄山市歙县徽州古城为案例地,运用因子分析法,提取了古城居民感知的3个积极影响公因子和2个消极影响公因子,通过均值的比较,分析了居民对旅游影响的总体感知与态度。在此基础上,采用Bonferroni多变量协方差分析法（MNOVA）进一步分析不同细分居民群体对旅游影响感知的差异,展望了未来居民利益诉求的转变方向,以期为政府部门、旅游管理部门、旅游规划部门提供有益参考,促进古城旅游业的可持续发展。     

Impact of Sea Level Rise on Groundwater Salinity in a Coastal Community of South Florida1

Guha, Hillol and Sorab Panday, 2012. Impact of Sea Level Rise on Groundwater Salinity in a Coastal Community of South Florida. Journal of the American Water Resources Association (JAWRA) 48(3): 510-529. DOI: 10.1111/j.1752-1688.2011.00630.x Abstract: Freshwater resources of coastal communities in the United States and world over are threatened by the rate of sea level rise. According to recent estimates by various governmental agencies and climate researchers, the global sea level rise is likely to be between 0.6 and 2.1 m by the year 2100. South Florida is a coastal community and much of its coastline is subject to sea level rise and potential impacts to wetlands and the water resources of the area. To understand what the impact of sea level rise would cause to the groundwater level and salinity intrusion, an integrated groundwater and surface water model was developed for North Miami-Dade and Broward Counties of South Florida. The model was calibrated against daily groundwater heads, base flows in canals, and chloride concentrations for a period of one year and six months. Three separate sensitivity analyses were conducted by increasing the sea level by 0.6, 0.9, and 1.22 m. Results of the simulations shows increase of groundwater heads in some areas from 4 to 15%; whereas the average relative chloride concentrations increased significantly by 100-600% in some wells. The increase in groundwater elevations and chloride concentrations varies from location of the wells and its proximity to the coast. The model results indicate that even a 0.6 m increase in sea level (which is the conservative estimate) is likely to impair the vital freshwater resources in many parts of South Florida.     

The Water Table: The Shifting Foundation of Life on Land

Hyperarid, arid, and semi-arid lands represent over a third of the Earth’s land surface, and are home to over 38 % of the increasing world population. Freshwater is a limiting resource on these lands, and withdrawal of groundwater substantially exceeds recharge. Withdrawals of groundwater for expanding agricultural and domestic use severely limit water availability for groundwater dependent ecosystems. We examine here, with emphasis on quantitative data, case histories of groundwater withdrawals at widely differing scales, on three continents, that range from the impact of a few wells, to the outcomes of total appropriation of flow in a major river system. The case histories provide a glimpse of the immense challenge of replacing groundwater resources once they are severely depleted, and put into sharp focus the question whether the magnitude of the current and future human, economic, and environmental consequences and costs of present practices of groundwater exploitation are adequately recognized.