基于形态开闭滤波二值标记和纹理特征合并的分水岭算法

为了防止分水岭算法过分割问题 ,研究了一种基于形态处理和纹理分析的图象分水岭分割方法 ,该方法是在分水岭算法的基础上 ,首先对形态梯度图象运用形态开闭滤波器组的方法来获得较好的参考图象 ,然后将提取的二值化初始分割结果作为区域标记来进行分割 .另外 ,为了获得整体目标 ,还定义了一个基于纹理特征的一致性和对比度的检验准则 ,并将其作为区域合并的根据 .该方法应用于多个视频序列初始目标分割的结果表明 ,形态滤波器组的引入很好地防止了过分割 ,并证明基于纹理特征均匀性和对比度的准则对分割区域进行进一步的纹理合并是行之有效的 .     

Past and future trends in nutrients export by rivers to the coastal waters of China

We analyzed the past and future trends in river export of dissolved and particulate nitrogen (N), phosphorus (P) and carbon (C) to the coastal waters of China, for sixteen rivers, as calculated by the Global NEWS models (Nutrient Export from WaterSheds). Between 1970 and 2000, the dissolved N and P export increased significantly, while export of other nutrients changed less. We analyzed the future trends (2000-2050) for the Millennium Ecosystem Assessment (MEA) scenarios. In general, the largest increases of dissolved nutrients export are projected for the Global Orchestration scenario, assuming a globalized world and a reactive approach toward environmental management. Future trends in river export of nutrients vary largely among basins, nutrient forms and scenarios. We calculate both increasing and decreasing trends between 2000 and 2050. We also identify the sources contributing to the nutrient export. For selected river basins we present results for alternative scenarios, which are based on the Global Orchestration scenario, but assume more environmental management. This illustrates how the NEWS models can be useful in regional analyses for decision making.     

Aerial Assessment of Ephemeral Gully Erosion from Agricultural Regions in the Pacific Northwest

Soil erosion from agricultural areas continues to be problematic in terms of both financial and environmental measures. Ephemeral gullies contribute to the soil loss both by the volume of sediment eroded from the gullies and because they act as delivery channels for surface erosion. High resolution aerial imagery was used to quantify the amounts and locations of ephemeral gullies in the subbasins of the Potlatch River system. Areal ephemeral gully erosion rates varied from 33.6?mt/km2 (0.15 U.S. t/acre) in the Big Bear Creek Subbasin to 88.4?mt/km2 (0.39 U.S. t/acre) in the Middle Potlatch Creek Subbasin representing 2.3–7.7% of the total surface sediment load. An erosion potential index was proposed to assist resource managers predict gully locations at the watershed scale using readily available remote sensing and geographic information system layers.     

Upland Erosion Modeling in a Semihumid Environment via the Water Erosion Prediction Project Model

The major water quality impairment in the midwest United States is sediment eroded from agricultural lands. Yet, few understand the spatial and temporal variability of erosion, or soil erosion dynamics, in relation to precipitation, topography, land management, and severe events. The objectives of this paper are to (1) develop a methodology for estimating long-term spatial soil erosion and water runoff losses and (2) explore issues in applying an established physical-based process model, Water Erosion Prediction Project (WEPP), to a large area by establishing a prototype system for the state of Iowa. This study for the first time provides a comparison of the model predictions against long-term measurements of the sediment delivery ratio (SDR) in the South Amana Catchment of the Clear Creek Watershed (CCW), a heavily instrumented watershed that is roughly 10 times the maximum WEPP fold size. To further examine the performance of WEPP in a semihumid environment, such as the CCW, where runoff and raindrop impact to erosion may be significant, the SDR was plotted as a function of the runoff coefficient, defined as the runoff/rainfall ratio. In addition, the WEPP predictions are compared against the statistical relation of SDR vs. runoff coefficient developed by Piest et al. in 1975) for watersheds in Iowa. It is shown that WEPP follows the trend shown by Piest et al. quite closely and performs well for continuous simulations extended up to 300?years.     

Bacteria Loads from Point and Nonpoint Sources in an Urban Watershed

A pathogen impaired watershed in Houston, Tex., was studied to assess the spatial and temporal nature of point and nonpoint bacterial load contributions. End-of-pipe sampling at wastewater treatment plant effluent and storm sewers discharging under dry weather conditions was undertaken. Relatively low concentrations of E. coli were found in wastewater treatment effluent, with a geometric mean of 5 MPN/dL, while dry weather storm sewer discharges exhibited a geometric mean concentration of 212 MPN/dL. Loads from both point and nonpoint sources of E. coli were calculated and compared to in-stream bacteria loads. Nonpoint loads were estimated using an event mean concentration approach on an annual basis. Nonpoint source (NPS) loads were the primary source of bacteria loading to the bayou. Wastewater treatment plant and dry weather storm sewer loads, however, dominated in dry weather conditions. While NPS loads remained relatively constant from headwaters to the mouth of the bayou, point source loads exhibited greater spatial variability depending on the distribution of the discharging pipes. The study points to the need for spatial and temporal considerations in managing bacterial pollution in streams.     

Modeling Storm Water Mass Emissions to the Southern California Bight

Storm water runoff is perceived as a major source of pollutants that results in adverse environmental effects, but large-scale assessments are rarely conducted. The problem is particularly pronounced in southern California where 17 million people have rapidly developed coastal watersheds. The goal of this study was to make regionwide estimates of mass emissions, assess the relative contribution from urbanized watersheds, and compare pollutant flux from different land uses. A geographic information system-based storm water runoff model was used to estimate pollutant mass emissions based on land use, rainfall, runoff volume, and local water-quality information. Local monitoring data were used to derive runoff coefficients; over 1,700 storm water sampling events were used to calibrate and validate annual loadings. An average rainfall year produced 1,073×109?L of runoff, 118,000 metric tons (MT) of suspended solids, 1,940 MT of nitrate-N, 108 MT of zinc, and 15 kg of diazinon. The majority of mass emissions were from urbanized watersheds except for suspended solids, total DDT, and chlorpyrifos. Agricultural areas had the greatest fluxes for pesticides, including total DDT and chlorpyrifos while open areas typically had the smallest.     

Seepage Velocity and Piping Resistance of Coir Fiber Mixed Soils

In the context of sustainable watershed management, natural fibers mixed with soil have applications in irrigation and drainage projects such as river levees, contour bunds, temporary canal diversion works, temporary check dams, soil structures, stream restoration, etc., for controlling seepage. In this study, a number of experiments were carried out for determining the seepage velocity and piping resistance of different types of soils mixed randomly with coir fibers. Three types of soils are used in this study. The experiments were carried out for various hydraulic heads, fiber contents, and fiber lengths. Discharge velocity and seepage velocity of flow of water through soil is calculated in each case and compared with plain soil. It is observed that fibers reduce the seepage velocity of plain soil considerably and thus increase the piping resistance of soil. Regression equations based on experiments are developed for quantifying the seepage velocity and piping resistance considering hydraulic gradient, fiber contents, and fiber lengths. Suitability of coir fibers for field applications with typical examples is also highlighted. The results show that coir fiber mixed soil can be used to increase the piping resistance and reduce seepage velocity in the above mentioned applications.     

Variability, Seasonality, and Persistence of Fecal Coliform Bacteria in a Cold-Region, Urban Stream

Fecal coliform (FC) analyses were conducted on weekly water samples collected from a single watershed over a 2-year period in Anchorage, Alaska. Although peak FC concentrations (>100?FC/100?mL) were observed primarily during the warmer months, lower FC levels (>20?FC/100?mL) could be observed throughout the year in the urbanized portion of the watershed. Median annual FC counts ranged from 3 FC/100 mL at an undeveloped site to 49 FC/100 mL at one of the urbanized sites. Median FC concentrations were found to be significantly higher in the summer compared to the winter at two locations directly downstream from a lake (p = 0.011 and 0.029), but not at the sites upstream or distant from the lake. FC-discharge relationships indicated a significant negative correlation between FC concentration and discharge at two sites (p = 0.030 and 0.035) and no significant correlation at the remaining three sites. In total, the results indicated that the water quality was impacted not only by peakwarm season loading events, but also by chronic low-level loading throughout the year.     

Event and Continuous Hydrologic Modeling with HEC-HMS

Event hydrologic modeling reveals how a basin responds to an individual rainfall event (e.g., quantity of surface runoff, peak, timing of the peak, detention). In contrast, continuous hydrologic modeling synthesizes hydrologic processes and phenomena (i.e., synthetic responses of the basin to a number of rain events and their cumulative effects) over a longer time period that includes both wet and dry conditions. Thus, fine-scale event hydrologic modeling is particularly useful for understanding detailed hydrologic processes and identifying the relevant parameters that can be further used for coarse-scale continuous modeling, especially when long-term intensive monitoring data are not available or the data are incomplete. Joint event and continuous hydrologic modeling with the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) is discussed in this technical note and an application to the Mona Lake watershed in west Michigan is presented. Specifically, four rainfall events were selected for calibrating/verifying the event model and identifying model parameters. The calibrated parameters were then used in the continuous hydrologic model. The Soil Conservation Service curve number and soil moisture accounting methods in HEC-HMS were used for simulating surface runoff in the event and continuous models, respectively, and the relationship between the two rainfall-runoff models was analyzed. The simulations provided hydrologic details about quantity, variability, and sources of runoff in the watershed. The model output suggests that the fine-scale (5?min time step) event hydrologic modeling, supported by intensive field data, is useful for improving the coarse-scale (hourly time step) continuous modeling by providing more accurate and well-calibrated parameters.