Evaluating the Impact of Irrigation and Drainage Policies on Agricultural Sustainability

Farmers in the Broadview Water District in central Californiahave been improving irrigation practices in response to risingirrigation water prices and reductions in water supply since1989, when incentive policies were first implemented to reducethe volume of subsurface drain water generated in theDistrict. The average salinity of water deliveries hasincreased, over time, as the District has recycled largeamounts of drainage water to achieve regional restrictions ondrainage water discharge. We review irrigation and drainageactivities in Broadview since 1986 with an emphasis on thesustainability of crop production when drainage discharge islimited. Average cotton yields in Broadview have declined inrecent years, both nominally and in comparison with averageyields reported for the large county in which Broadview islocated. Average tomato yields in Broadview have increased inrecent years, but county-wide yields have exceeded Broadviewyields with greater frequency than in the late 1980s. Theseobservations suggest that average crop yields in Broadview maybe starting to reflect the increasing salinity of soil andwater resources, which may be due in part to persistentrestrictions on drainage water discharge.     

Salinity, drainage and selenium problems in the Western San Joaquin Valley of California

Highly productive, irrigated agriculturecan be found in California's Central Valleymade up of the Sacramento, San Joaquin, andTulare Lake basins. High water tablesthroughout much of the San Joaquin andTulare Lake portions of the Valley threatenthis highly productive region. Due totopographic and environmental constraintsmuch of the region is currently withoutdrainage. In 1990 State and Federalgovernment agencies combined to produce areport that outlined possible steps to dealwith the drainage issue. These stepsincluded: 1) Source control (practices toreduce the amount of drainage water); 2)Drainage reuse; 3) Evaporation systems; 4)Land retirement (cease irrigation); 5)Groundwater management; and 6) Discharge tothe San Joaquin River. General backgroundinformation to the history and hydrology ofthe Valley as well as a discussion of thefeasibility and constraints of providingdrainage by discharging drain water to theSan Joaquin River are presented. Inaddition a general discussion of thetechnical and political limitations ofproviding drainage in the River arediscussed.     

高港泵站水利枢纽自动化系统

详细介绍了江苏省泰州引江河高港泵站水利枢纽自动化系统的功能，介绍了系统采用的分布式体系结构、设备分布及其功能分配。     

干旱缺水灌区节水灌溉评价标准及其分析

在分析节水灌溉定义内涵的基础上，提出了评价干旱缺水灌区农田节水灌溉的目标标准和技术标准，并对这些评价标准的运用进行了讨论。     

Simulation of drainage water quality with DRAINMOD

The design and management of drainage systems should consider impacts on drainage water quality and receiving streams, as well as on agricultural productivity. Two simulation models that are being developed to predict these impacts are briefly described. DRAINMOD-N uses hydrologic predictions by DRAINMOD, including daily soil water fluxes, in numerical solutions to the advective-dispersive-reactive (ADR) equation to describe movement and fate of NO₃-N in shallow water table soils. DRAINMOD- CREAMS links DRAINMOD hydrology with submodels in CREAMS to predict effects of drainage treatment and controlled drainage losses of sediment and agricultural chemicals via surface runoff. The models were applied to analyze effects of drainage intensity on a Portsmouth sandy loam in eastern North Carolina. Depending on surface depressional storage, agricultural production objectives could be satisfied with drain spacings of 40 m or less. Predicted effects of drainage design and management on NO₃-N losses were substantial. Increasing drain spacing from 20 m to 40 m reduced predicted NO₃-N losses by over 45% for both good and poor surface drainage. Controlled drainage further decreases NO₃-N losses. For example, predicted average annual NO₃-N losses for a 30 m spacing were reduced 50% by controlled drainage. Splitting the application of nitrogen fertilizer, so that 100 kg/ha is applied at planting and 50 kg/ha is applied 37 days later, reduced average predicted NO₃-N losses but by only 5 to 6%. This practice was more effective in years when heavy rainfall occurred directly after planting. In contrast to effects on NO₃-N losses, reducing drainage intensity by increasing drain spacing or use of controlled drainage increased predicted losses of sediment and phosphorus (P). These losses were small for relatively flat conditions (0.2% slope), but may be large for even moderate slopes. For example, predicted sediment losses for a 2% slope exceeded 8000 kg/ha for a poorly drained condition (drain spacing of 100 m), but were reduced to 2100 kg/ha for a 20 m spacing. Agricultural production and water quality goals are sometimes in conflict. Our results indicate that simulation modeling can be used to examine the benefits of alternative designs and management strategies, from both production and environmental points-of-view. The utility of this methodology places additional emphasis on the need for field experiments to test the validity of the models over a range of soil, site and climatological conditions.     

泵站配电变压器优化选型设计研究

根据泵站排涝运行特点，从降低变压器损耗入手，采用综合经济比较等优化选型方法，从初选的三种系列变压器方案中优选出最佳方案，以取得良好的综合效益。     

灌区评估指标的选取及灰关联分析

该文探讨了灌区评估指标体系的建立方法,对评估指标的选取与预处理进行了系统分析,并尝试应用灰色系统理论中的灰关联度分析法,对灌区评估指标进行关联分析,从而很方便地进行灌区之间的评估、排队及比较,与传统的强制打分法相比,此法简便易行,无需预先建立评判标准,因此是一种新的评估分析法。     

Using drainage systems for supplementary irrigation

The use of drainage systems for supplementary irrigation is widespread in The Netherlands. One of the operating policies is to raise the surface water level during the growing season in order to reduce drainage (water conservation) or to create subsurface irrigation. This type of operation is based on practical experience, which can be far from optimal.To obtain better founded operational water management rules a total soil water/surface water model was built. In a case study the effects of using the drainage system in a dual-purpose manner on the arable crop production were simulated with the model. Also, the operational rules for managing this type of dual-purpose drainage systems were derived.The average annual simulated increase in crop transpiration due to water conservation and water supply for subsurface irrigation are 6.0 and 5.4 mm.y^–1, respectively. This is equivalent with 520 × 10³ and 460 × 10³ Dfl.y^–1 for the pilot region (2 Dfl 1 US $). The corresponding investments and operational costs are 600 × 10³ Dfl and 9 × 10³ Dfl.y^–1 for water conservation and 3200 × 10³ Dfl and 128 × 10³ Dfl.y^–1 for subsurface irrigation. Hence, water conservation is economically very profitable, whereas subsurface irrigation is less attractive.Comparing the management according to the model with current practice in a water-board during 1983 and 1986 learned that benefits can increase with some 50 and 500 Dfl per ha per year, respectively.     

葡萄干彩色图像的背景分割研究

背景分割是分析葡萄干其他特征的基础。为此,经研究提出一种改进的迭代算法,用来获取葡萄干灰度图像阈值;基于RGB阈值法与亮度阈值法,对葡萄干进行背景分割后的图像分析比较,证明亮度阈值法能较好地进行葡萄干彩色图像背景分割,保存图像的颜色信息。     

搅拌机的研制

介绍了搅拌机最基本的设计步骤,首先确定了执行机构的运动机构,确定四杆机的长度,验证是否合适;验证曲柄存在的条件,检查连杆是否干涉,验证四杆机构的传力性能以验证四杆机构是否有较高效率;计算出溶液阻力从而列出力矩平衡方程求出平衡力,求出阻力矩,利用阻力矩与等效驱动力矩之间的关求出最大盈亏功,从而确定飞轮惯量;最后确定了电动机的功率。