ANALYSIS OF STREAMFLOW TRENDS AND THE EFFECTS OF CLIMATE IN PENNSYLVANIA, 1971 TO 20011

An understanding of temporal trends in total stream‐flow (TSF), base flow (BF), and storm runoff (RO) can help in the development of water management plans for watersheds and local communities. In this study, 47 streams across Pennsylvania that were unregulated and unaffected by karst environments or coal mining were studied for flow trends and their relationships to selected climate parameters for the period 1971 to 2001. LOWESS curves for annual flow showed that almost all of the selected streams in Pennsylvania had downward trends in total TSF, BF, and RO. Using a seasonal Mann‐Kendall analysis, downward trends were significant at an α= 0.05 level for 68, percent 70 percent, and 62 percent of the streams and at an α= 0.10 level for another 19, 17, and 13 percent of the streams for TSF, BF, and RO, respectively. The ratio of BF to TSF (RBS) had significant upward trends for 34 percent of the streams at an α= 0.05 level and for another 9 percent of the streams at an α= 0.10 level, indicating that TSF decreased relative to BF for more than 40 percent of the streams during the previous 30 years. Downward trends in TSF, BF, and RO were most common for the months of June, July, and December. Trend analyses using monthly and annual total precipitation and mean temperature showed some association between climate and the streamflow trends, but Spearman's correlation and partial Mann‐Kendall analyses revealed that the trends in TSF, BF, and RO could not be explained by trends in precipitation and temperature alone, and thus urbanization and development may have played a role.     

泥石流灾害的分形研究

复杂性是各个学科面临的共同难题,分形理论作为解决复杂性问题的有力工具被提出以来,得到了广泛的应用.在泥石流灾害中的应用也得到不断深入研究.本文在结合前人研究的基础上,从泥石流发生机理、泥石流堆积、泥石流沟谷形态和水系的发育演化以及泥石流预测四个方面论述了分形理论在泥石流灾害研究中的应用,将分维作为表征泥石流灾害系统的有效参量,揭示了泥石流灾害中的某些规律,反映了泥石流的一些本质现象.     

西部地区重大工程建设中的泥石流灾害 --兼论其与环境的互馈作用

在西部大开发过程中,许多重大工程建设涉及泥石流灾害的问题.讨论了工程活动、泥石流及山地环境之间的相互作用和影响.工程活动往往受到泥石流、山地环境的制约,同时它作为活的因素,又积极地影响着泥石流和山地环境,促使其产生次生演化,泥石流和山地环境的次生演化常会对工程活动产生次生制约.泥石流的发生会危及工程和人类的安全,破坏地表,破坏生态环境;人类工程活动若不遵守自然规律,过度向山地索取,必将导致山地环境退化和泥石流的广泛活动及频繁发生,甚至引起泥石流活动范围扩大和成灾规律改变.     

德宏“7.5”特大滑坡泥石流灾害分析及其对策

受滇缅高压外围强对流天气影响,2004年7月5日云南德宏州的陇川、盈江、瑞丽等县(市)普降暴雨,引发大面积的滑坡、泥石流和山洪灾害,造成死亡18人、失踪24人、直接经济损失4.8亿元的区内近几十年来最严重的灾害。在分析此特大滑坡、泥石流、山洪灾害的活动特点、形成条件和激发因素的基础上,得出今后一段时间该区地质灾害将处于活跃期的评估结论。针对这一状况,提出了应急措施和防灾减灾对策。     

滑坡转化为泥石流机理研究综述

对国内外有关滑坡转化为泥石流的机理的研究做了全面的综述,重点介绍了国外最新的研究成果,阐明了今后研究的方向.滑坡转化为泥石流机理的研究,处于滑坡动力学与泥石流形成学的交叉点,既是学科的边缘问题,也是学科的前沿问题.滑坡转化为泥石流的过程是一个和土体液化密切相关的流态化过程,是土体和水体强烈相互作用的结果.滑坡直接转化为泥石流的机理的两个核心问题是超静孔压的产生和超静孔压的保持.Iverson对这一问题的研究直接促进了滑坡流态化理论的发展,并形成了最新的泥石流运动模型--库伦混合流理论,是对传统的基于流变关系的泥石流模型的重大突破.土体中粘性颗粒对滑坡直接转化为泥石流过程的影响,需要进一步进行研究.滑坡转化为沟谷泥石流是一个更为复杂的过程,是今后研究的重点.     

1999年委内瑞拉阿维拉山北坡入海型泥石流

委内瑞拉阿维拉山呈东一西走向，北坡濒临加勒比海．１９９９年１２月１６日，阿维拉山北坡２０多条沟谷暴发泥石流，使沿海的城镇、村庄、港口、公路及各种设施遭到毁灭性破坏，造成数万人死亡，直接经济损失超过刀亿美元．泥石流发生在森林植被良好的山区，具低频率和群发性特征，规模大，直接入海．分析这次泥石流灾害，对我国的防灾减灾工作具有启示意义．     

The Ecological and Environmental Characteristics and Conservation of the Wetlands in the Changjiang Estuary, China

The natural wetlands in the Changjiang Estuary, China are important ecologically. The total area of the wetlands in the Changjiang Estuary amounts to 215000 ha. The wetlands consist of littoral and sandy estuarine island areas, and are rich in biological resources. There are 136 species of vascular plant, 150 species of bird, and 68 species of benthic macro-invertebrate in the wetlands. However, the wetland in the Changjiang Estuary is a vulnerable ecosystem. Development of the wetland is mainly influenced by intensive human reclamation, pollution, movement of sediments in the Changjiang River, and the effects of tides and waves. Investigations have shown that maintaining biodiversity, providing resources for the living organisms, purifying environments and resisting natural hazards could be regarded as important functions for the protection of the wetlands. It is proposed that sustainable principles should be supported in developing the wetlands in the future.     

APPLICATION OF ROSGEN ANALYSIS TO THE NEW JERSEY PINE BARRENS1

ABSTRACT: Rosgen analysis, developed for assessing channel stability in streams from the western United States, is applied to the Oswego River watershed in the New Jersey Pine Barrens. The Rosgen method requires calibration to local conditions due to the impact of peat substrates on channel morphology. In particular, the presence of peat induces low width to depth ratios and greater channel confinement, reversing typical downstream morphologic trends observed in other rivers. Therefore peat is added to those substrates already evaluated by Rosgen. A consistent sequence of Rosgen stream types develops along the Oswego River and its tributaries created by spatially overlapping processes of water table emergence, peat development, and channel formation. This sequence delineates a “natural” transition of stream channel morphology downslope through the watershed. First, as the water table reaches the surface of dry sloughs, Sphagnum growth is stimulated and peat substrates result. These substrates have lower permeability than the underlying gravelly sands. Next, surface runoff, through braided pathways over the peat, eventually erodes mainly anastomosing channels into the peat. Finally, single‐thread channels develop in underlying gravelly sands further downslope. This downslope sequence, expressed as Rosgen stream types, begins generally with DA7 streams arising from dry sloughs. These pass to E7, C7 or DA5 stream types that in turn pass to B5c, C5 and C4 stream types. Departures from the “natural” stream type sequence occur along the course of the Oswego and its tributaries due to human activities such as the construction of dams, bridges and drainage ditches, stream bank erosion at streamside camping and picnic areas and the clear‐cutting of adjacent stands of Atlantic white cedar.     

THE LODGING VELOCITY FOR EMERGENT AQUATIC PLANTS IN OPEN CHANNELS1

ABSTRACT: The growth of aquatic plants in open‐channels has many adverse environmental effects including, but not limited to, impeding the transport of water, hindering navigation, increasing flood elevations, increasing sediment deposition, and degrading water quality. Existing control strategies include physical removal and chemical treatment. Physical removal is only a temporary solution and chemical treatment is unacceptable if the water will be consumed by humans. The hydrodynamic method can wash out the encroached aquatic plants by keeping flow velocity higher than the critical velocity required to bend and rupture (lodge) their stems. This approach is a promising, physically‐based, efficient, economic, and permanent solution for this problem. However, the success of this approach requires the accurate prediction of the critical lodging velocity. This paper presents an analytic study of the lodging velocity for the submerged portion of aquatic plants of narrow leaved emergent stems that are wider at bottom than the top. Based on the principles of engineering materials and the theory of turbulent flow, a semi‐empirical formula is derived for the prediction of the critical lodging velocity. It indicates that the lodging of aquatic plants is controlled not only by flow conditions but also the geometric and mechanical characteristics of the plants. These analytic results provide a satisfactory explanation of the lodging phenomena observed in the field and are verified by the available experimental data.     

USING SUBSURFACE DRIP IRRIGATION FOR ALFALFA1

ABSTRACT: A test of the suitability of subsurface drip irrigation (SDI) for alfalfa (Medicago sativa L) compared to a sprinkler, was conducted on a Kansas producer's field where the soil is loam. The treatments included drip tape spacing of 60, 40, and 30 inches placed at depths of 18 and 12 inches. A nearby plot irrigated by a center pivot sprinkler was seeded to alfalfa and used for comparison. Seedling emergence and yield were adversely affected at 60 inch spacing, while the depth of placement of drip tapes (18 and 12 inches) showed no effect on yield. The site served for education and allowed comparison between SDI tape spacing and center pivot system.