SIMULATING THE EFFECTS OF REDUCED PRECIPITATION ON GROUND WATER AND STREAMFLOW IN THE NEBRASKA SAND HILLS1

ABSTRACT: The Nebraska Sand Hills have a unique hydrologic system with very little runoff and thick aquifers that constantly supply water to rivers, lakes, and wetlands. A ground water flow model was developed to determine the interactions between ground water and streamflow and to simulate the changes in ground water systems by reduced precipitation. The numerical modeling method includes a water balance model for the vadose zone and MOD‐FLOW for the saturated zone. The modeling results indicated that, between 1979 and 1990, 13 percent of the annual precipitation recharged to the aquifer and annual ground water loss by evapotranspiration (ET) was only about one‐fourth of this recharge. Ground water discharge to rivers accounts for about 96 percent of the streamflow in the Dismal and Middle Loup rivers. When precipitation decreased by half the average amount of the 1979 to 1990 period, the average decline of water table over the study area was 0.89 m, and the streamflow was about 87 percent of the present rate. This decline of the water table results in significant reductions in ET directly from ground water and so a significant portion of the streamflow is maintained by capture of the salvaged ET.     

非稳态过滤除尘压力损失的研究

提出用于建立过滤层非稳态过滤压力损失模型的微观分析法和宏观分析法新概念，归纳出无论是纤维层过滤，还是颗粒层过滤，所反映的压力损失随过滤时间变化的规律是相同的，由此提出筇同观分析法和宏观分析法相结合的对纤维层过滤和颗粒层过滤均适用的非稳态过滤简化式，通过实验探讨了非稳态过滤压力损失比例常数的确定方法，并由此验证了该简化式的正确性。     

曝气-两级过滤工艺用于地下水除铁除锰

深圳市平湖华宝（集团）有限公司采用曝气一两级过滤工艺进行地下水除铁除锰的处理，出水的各项指标均达到国家生活饮用水卫生标准（GB5749-85），吨水处理成本为0.31元。该工艺运行稳定，投资运行费用低，具有较好的经济效益。     

场地液化危害的概率分析

为使场地液化危害程度的估计建立在以概率论为基础的可靠性分析之上,本文提出二种估计场地液化危害程度的概率方法,二种方法分别采用不同的途径处理地震和岩土的不确定性,不仅分析了一点液化的概率,而且提供了估计整个土层住状液化概率的方法,文中最后通过算例简要讨论了液化概率分析结果的工程应用。     

PHYSICAL AND CONCEPTUAL SIMULATION OF EFFLUENTS FROM DREDGED MATERIAL CONFINEMENT FACILITIES1

ABSTRACT: Environmental protection dictates that effluents of desired quality should be dischargd from dredged material confinement facilities. In general, this can be accomplished by supplementing the solid-liquid separation obtained by simple sedimentation with appropriate filter systems which provide additional clarification. A methodology to estimate the sedimentation required in a disposal area was developed on the basis of classical sedimentation theories and compared favorably with field data. A procedure was then advanced and documented whereby effluents from dredged material confinement facilities can be successfully modeled for laboratory filtration tests. For these purposes inorganic suspended solids can be simulted reasonably well by adjusting the concentration of commercially available clays, and fresh or saline water environments can be simulated satisfactorily by tap water or sodium chloride solutions, respectively.     

EFFECT OF FILTRATION PRESSURE ON ANALYSES FOR CHLOROPHYLL1

ABSTRACT: Nine samples, each with different kinds and numbers of algae, were filtered at five pressures from 5 to 75 pounds per square inch and the amounts of chlorophylls a and b were measured. Pressures in the range tested had no effect on the measured amounts.     

EXPANDING WASTE WATER TREATMENT CONSIDERATIONS AT CORPS OF ENGINEERS RECREATION AREAS1

ABSTRACT. There have been many changes in the waste water treatment requirements at St. Louis District Corps of Engineers projects over the past few years. Discussed are the methods considered for treating these wastes. Extended aeration plant, followed by filtration, is the process used in most of the areas. The treatment plant operators have become key members of the project operation team. A discussion of the Districts operator training program is presented along with the operator's job requirements. Through a Spring inspection of all treatment plants in the District, a mechanism has been provided for encouraging feedback to the design engineer from the operator.     

黏性颗粒在滤料表面沉积的动态模拟及规律

为研究颗粒黏性对过滤除尘性能的影响,分析了颗粒沉积过程的受力情况,应用颗粒流计算软件PFC2D对颗粒在滤料表面的沉积行为进行了数值模拟。结果表明:颗粒形成粉尘层的过程中主要受到风流力、惯性力等压缩力和范德华力、滚动摩擦力偶矩等压缩阻力的作用,颗粒黏性的增加,会使颗粒间滚阻系数和摩擦系数显著增加;PFC可实现粉尘颗粒在滤料表面沉积过程的可视化,得到不同黏性颗粒在滤料表面的沉积形态,滚阻系数或摩擦系数越大,粉尘层孔隙率越大,过滤阻力越小,其中,摩擦系数的影响作用弱于滚阻系数。     

袋式除尘器滤袋接缝方法对PM_(2.5)过滤效率的影响

针对袋式除尘器超低排放及对PM_(2.5)细颗粒物的捕集控制问题,选用分别经缝合、热熔两种制袋工艺制作的滤袋进行试验,探讨不同袋身接缝方法对袋式除尘器滤袋PM_(2.5)过滤效率的影响。结果表明:1 m/min过滤风速时,清洁状态下热熔滤袋对PM_(2.5)的过滤效率要比缝合滤袋高12.59%,而集尘状态下随滤袋表面粉尘负荷的不同,热熔滤袋对PM_(2.5)的过滤效率要比缝合滤袋高8.68%~11.18%;随过滤风速增加,缝合滤袋对PM_(2.5)过滤效率的衰减幅度要远大于热熔滤袋;滤袋表面尘饼的形成和分布的均匀性是缩小缝合滤袋与热熔滤袋间过滤效率差距的重要因素。     

Hydrogeomorphic Reference Condition and Its Relationship with Macroinvertebrate Assemblages in Southeastern U.S. Sand Hills Streams

Defining stream reference conditions is integral to providing benchmarks to ecological perturbation. We quantified channel geometry, hydrologic and environmental variables, and macroinvertebrates in 62 low‐gradient, SE United States (U.S.) Sand Hills (Level IV ecoregion) sand‐bed streams. To identify hydrogeomorphic reference condition (HGM), we clustered channel geometry deviation from expectations given watershed area (Aws), resulting in two HGM groups discriminated by area at the top of bank (Atob) residuals <0.6 m² and >0.6 m² predicted to be HGM reference/nonreference streams, respectively. Two independent partial least squares discriminate analyses used (1) hydrologic/environmental variables and (2) macroinvertebrate mean trait values (mT) on 10 reference/nonreference stream pairs of similar Aws for classification validation. Nonreference streams had flashier hydrographs and altered flow magnitudes, lower organic matter, coarser substrate, higher pH/specific conductivity compared with reference streams. Macroinvertebrate assemblages corresponded to HGM groupings, with mT indicative of multivoltinism, collector‐gatherer functional feeding groups, fast current‐preference taxa, and lower Ephemeroptera, Plecoptera, and Trichoptera richness and biotic integrity in nonreference streams. HGM classifications in Sand Hills, sand‐bed streams were determined from channel geometry. This easily implemented classification is indicative of contemporary hydrologic disturbance resulting in contrasting macroinvertebrate assemblages.