ESTIMATING DRAINAGE AREA ON STEEP UNIFORM SLOPES1

ABSTRACT: A study was conducted to derive a simple procedure for estimating the tributary drainage area that may potentially develop at the base of a uniformly graded, steep slope. Data were extracted from a nil development flume study in which 112 rills and their tributary drainage areas were documented. The tributary drainage area for each rill was correlated to the slope length and the slope gradient. The findings are considered applicable to planar, convex, and divergent slopes with lengths of up to 130 m. Field verification is needed to extend the applicability of the relation.     

Environmental and social implications of waste in U.S. agriculture and food sectors

Because the agriculture/food sectors appear to be driven by short-term economic and political forces, cheap energy, and agricultural-chemical technologies, waste and environmental/social problems in the agricultural/food sectors are estimated to cost the nation at least $150 billion per year. Most of the waste and environmental/social problems can be eliminated through better resource management policies and the adoption of sustainable agricultural practices.Based on a paper entitled Waste in U.S. Agricultural and Food Sectors—Environmental and Social Costs presented at the Gross National Waste Product Forum, Washington, D.C.     

黄土丘陵沟壑区土壤侵蚀专家系统试验研究

本文介绍了黄土丘陵的沟壑区土壤侵蚀专家系统的建造原理与方法.系统采用压缩编码方式存贮各种地学图形与遥感图象数据,具有效据与图象的存贮更新、查询检索、分析处理、图象显示和自动制图功能.该系统可对黄土地区的土壤侵蚀进行准确、快速的预测、预报,并对土壤侵蚀的综合治理,水土保持规划提出几种可行性建议供用户选择。用该系统对山西省离石县王家沟流域羊道沟的土壤侵蚀进行了试验研究,并对试验结果进行了系统评价。     

毁林与汉代居延垦区的衰落

本文根据历史史料，阐明了汉代居延垦区由兴旺发达到衰落的历史原因。进一步说明了乱破滥伐森林带来的恶果。开发大自然必须遵循自然规律，切不可盲目蛮干，毫无克制。     

ECONOMIC EFFECTS OF SOIL CONDITIONS ON FARM STRATEGIES TO REDUCE AGRICULTURAL POLLUTION1

ABSTRACT: Utilizing predictions of pollutant movement generated by the CREAMS model, the economics of reducing field losses of sediment and nitrate percolation were compared between two soil types on each of two slopes common to the Upper Eastern Shore of Maryland. The soils considered were Matapeake silt loam and Sassafras sandy loam textures on field slopes of 3.5 percent and 7.5 percent. A representative cash grain farm was used as a basis of comparison. Under assumptions of profit maximization, economic optimal cropping systems varied by slope. Results further indicated that relative cost-effectiveness of sediment or nitrate percolation control varied by soil type for both slopes considered. Unit costs of sediment control were less on silt loam soils, while unit costs of nitrate percolation control were less on sandy loam soils.     

GIS支持下的土壤侵蚀量估算——以江西省泰和县灌溪乡为例

在地理信息技术（ＧＩＳ）的支持下，应用通用土壤侵蚀方程（ＵｎｉｖｅｒｓａｌＳｏｉｌＬｏｓｓＥｑｕａｔｉｏｎ，简称ＵＳＬＥ）估算了江西省泰和县灌溪乡的土壤侵蚀量。研究结果表明，当地表覆盖率大于１５％时，计算的结果与实测的数据有良好的相关性（０８７）。     

区域开发中的生态补偿量化分析--以珠江温泉城为例

区域开发建设会对生态环境造成一定程度的破坏。利用一些简单适用的模型或参数,对珠江温泉城开发中的主要生态因子进行了量化研究,结果表明珠江温泉城水土流失增加、绿量减少、林地的景观优势度降低。依据开发前后的变化结果,确定了补偿其开发应该采取的具体对策。     

GRASS VERSUS TREES: MANAGING RIPARIAN AREAS TO BENEFIT STREAMS OF CENTRAL NORTH AMERICA1

ABSTRACT: Forestation of riparian areas has long been promoted to restore stream ecosystems degraded by agriculture in central North America. Although trees and shrubs in the riparian zone can provide many benefits to streams, grassy or herbaceous riparian vegetation can also provide benefits and may be more appropriate in some situations. Here we review some of the positive and negative implications of grassy versus wooded riparian zones and discuss potential management outcomes. Compared to wooded areas, grassy riparian areas result in stream reaches with different patterns of bank stability, erosion, channel morphology, cover for fish, terrestrial runoff, hydrology, water temperature, organic matter inputs, primary production, aquatic macroinvertebrates, and fish. Of particular relevance in agricultural regions, grassy riparian areas may be more effective in reducing bank erosion and trapping suspended sediments than wooded areas. Maintenance of grassy riparian vegetation usually requires active management (e.g., mowing, burning, herbicide treatments, and grazing), as successional processes will tend ultimately to favor woody vegetation. Riparian agricultural practices that promote a dense, healthy, grassy turf, such as certain types of intensively managed livestock grazing, have potential to restore degraded stream ecosystems.     

页岩气压裂弯管中液固两相流冲蚀磨损的数值模拟

为了研究超高压水力压裂下支撑剂颗粒进入弯管后冲蚀磨损区域的变化特性。基于液-固两相流理论、Fluent冲蚀模型建立弯管冲蚀模型,结合弯管内流场分析颗粒运动轨迹,引入斯托克斯数（St）探究冲蚀磨损区域变化,并进行数值分析。研究结果表明:弯管中冲蚀磨损发生区域有5处,主要严重区域有3处,弯管流场会改变固体颗粒数量及对壁面冲击动能与运动轨迹,St变化会明显引起冲蚀磨损区域的规律性变化;随着St从0~1至St>1变化,弯管段内壁面外侧（液体进入弯管后的正对区域）与直管段靠近弯管段的侧方区域的冲蚀磨损情况呈现“此消彼长”的规律性差异;管径越小,最大冲蚀速率的增长幅度越明显,增大管径,是减小冲蚀磨损的有效途径。研究结果对压裂弯管的改进设计及管道安全防护具有指导作用。