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1.
This article reviews the method for allocating flow to irrigation plots proposed by Clément and Galand in (1979). Mention is made of its shortcomings, such as the lack of consideration given to the specific technical and economic factors governing current pressurized (drip or sprinkler) irrigation systems and how they provide water to plots. We propose a method for fixed irrigation systems, which takes into account the irrigation method on the plot and the existence of an optimum block area. The result is to allocate a constant flow of water to plots up to an established value of maximum surface area. From there on, we propose applying linear increases related to the total plot area. We also present a formula for calculating the maximum number of blocks based on variables that are easily obtainable during the project phase.  相似文献   

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The study presents hydrologic simulations assessing the potential impact of climate change on subsurface drainage and its pattern in Iowa’s subsurface drained landscapes. The contemporary (representing the decade of 1990s) and future (representing the decade of 2040s) climatic scenarios were generated by downscaling the projections of global climatic model HadCM through two regional climatic models RegCM2 and HIRHAM to a regional grid box of 52–55?km2, which contains Perry, IA. These climatic scenarios were used to drive the field scale deterministic hydrologic model DRAINMOD to simulate subsurface drainage from one of Iowa’s predominant hydric soils, WEBSter, cultivated with Continuous Corn (WEBS_CC), and equipped with a conventional drainage system (30-m drain spacing at 1.2-m drain depth). The simulation results consistently indicate an increase in subsurface drainage from WEBS_CC under future climatic scenario as compared to contemporary climatic scenario. This increase in subsurface drainage would be more in the winter months (from December to March) and early spring months (from April to May) than summer and fall months. Since subsurface drainage is a primary carrier of nitrate-nitrogen (NO3–N) from the agricultural lands, the extrapolation of this study simulations suggest that there would be a potential for increased NO3–N loss from Iowa’s subsurface drained landscapes under future (in the decade of 2040s) climatic conditions.  相似文献   

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A modified form of Horton’s infiltration equation was used to model advance trajectory of the wetting front as well as for predicting cumulative infiltration in a furrow-irrigated system using experimental data obtained in a Yolo loam soil (Typic Xerorthents) planted to a furrow-irrigated tomato crop. Two distinct cases were considered: (1) furrows with deposional crusts at the bottom (uncultivated) and (2) furrows in which a crust breaking device was used to remove the deposional crust (cultivated). The model was used to successfully predict infiltration parameters, which are important for design and management of furrow irrigation systems. Simulation studies were also conducted to determine cumulative infiltration along a furrow.  相似文献   

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The hydrant pressure head in an on-demand water distribution system can be subject to high fluctuation depending on the discharge flowing inside the pipes, with consequent impacts on the performance of on-farm irrigation systems. In this work, an Italian water distribution system was analyzed using the AKLA model at upstream discharges of 1,200 and 600?L?s?1 to estimate the range of hydrant pressure variation. A computer model was developed, calibrated, and used to evaluate the performance of a drip irrigation system by relating the on-farm network with the hydrant characteristic curve at a certain operating status. The flow regulator within the hydrant played an important role in stabilizing the performance of the network at hydrant pressures higher than 27 m. At lower hydrant pressures, to apply the same amount of water, irrigation time must be extended by 17 and 95% for pressure heads of 20 and 12 m, respectively. These approaches described have great utility to ensure adequate irrigation management when water is delivered by pressurized on-demand systems.  相似文献   

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Manning’s roughness coefficient is one of the input parameters in many surface irrigation simulation models. It affects the velocity of flow and thereby its variation with time and distance along the field length influence water application. In this study, variation of Manning’s roughness coefficient was studied for a furrow plot consisting of three 40 m long free drained furrows of parabolic shape and having a top width of 0.30 m, a depth of 0.15 m and a slope of 0.5%. The irrigation experiments were carried out with the inflow rates of 0.2, 0.3, 0.4, and 0.5?L?s1; and 0.3, 0.4, 0.5, 0.6, and 0.7?L?s?1 under bare; and cropped field conditions, respectively. Furrow cross-section data were collected before each irrigation event at 0.5, 13, 26 and 39.5 m from the head end along the center furrow using a profilometer. During the irrigation event, water depth and velocity of flow were measured at these locations at an interval of 15 min using point gauge and color dye, respectively. The furrow cross-section data were fitted into a second-degree polynomial equation to determine the furrow shape parameters that were used along with the flow depth data for determining the wetted area and wetted perimeter. The wetted area, wetted perimeter, and the velocity data were used to estimate Manning’s roughness coefficient spatially and temporally. It is found that for both bare and cropped field conditions, Manning’s roughness coefficient was more at second and last quarter of the furrow due to soil erosion at these locations. Manning’s roughness coefficient at these locations varied from 0.019 to 0.022 and 0.015 to 0.018 for bare field whereas from 0.02 to 0.024, and 0.019 to 0.022 for cropped field, respectively. The temporal variation of Manning’s roughness coefficient for both bare and cropped furrow conditions decreased with the elapsed time. However, these decreasing trends were observed more for lower inflow rates. Further, the average Manning’s roughness coefficient for the subsequent irrigations was varied from 0.018 to 0.02 and from 0.019 to 0.0245 for bare and cropped conditions, respectively. Thus, the values of Manning’s roughness coefficients were more for cropped furrow conditions than for bare furrow.  相似文献   

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In many river basins, upstream development and interannual variations in rainfall can cause both episodic and chronic shortages in water supplies downstream. Continued rapid development of surface and groundwater throughout the Krishna Basin in southern India resulted in historically low inflows to the main canals of the Nagarjuna Sagar irrigation project (8,955?km2) during a recent drought (2002–2004). This paper presents an integrated approach to assess how cropping patterns and the spatial equity of canal flow changed with water supply shocks in the left canal command area (3,592?km2) of Nagarjuna Sagar. We combined 3?years (2000–2003) of canal release data with census statistics and high temporal resolution (8–10?days) moderate resolution imaging spectrometer (MODIS) 500-m resolution satellite imagery. The impact of water scarcity on land use pattern, delineated by MODIS images with moderate spatial resolution, was comparable with the census statistics, while the MODIS data also identified areas with changes and delays in the rice crop area, which is critical in assessing the impact of canal operations. A 60% reduction in water availability during the drought resulted in 40% land being fallowed in the left-bank canal command area. The results suggest that head reach areas receiving high supply rates during a normal year experienced the highest risks of fluctuations in water supply and cropped area during a water short year compared to downstream areas, which had chronically low water supply, and better adaptive responses by farmers. Contrary to expectations, the spatial distribution of canal flows among the three major zones of the command area was more equitable during low-flow years due to decreased flow at the head reach of the canal and relatively smaller decreases in tail-end areas. The findings suggested that equitable allocations could be achieved by improving the water distribution efficiency of the canal network during normal years and by crop diversification and introduction of alternative water sources during water shortage years. The study identified areas susceptible to decreases in water supplies by using modern techniques, which can help in decision-making processes for equitable water allocation and distribution and in developing strategies to mitigate the effects of water supply shocks on cropping patterns and rural livelihoods.  相似文献   

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Water resources are limited in many agricultural areas. One method to improve the effective use of water is to improve delivery service from irrigation canals. This can be done by applying automatic control methods that control the gates in an irrigation canal. The model predictive control (MPC) is one such advanced control method. In this article, the MPC is used to deliver irrigation water to the WM Canal at the Maricopa-Stanfield Irrigation and Drainage District. The tests show that the water is efficiently delivered to the users and water level deviations at all locations are small. The control is compared to the results from an advanced Linear Quadratic Regulator control method, also tested on the actual canal.  相似文献   

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In closing river basins where nearly all available water is committed to existing uses, downstream irrigation projects are expected to experience water shortages more frequently. Understanding the scope for resilience and adaptation of large surface irrigation systems is vital to the development of management strategies designed to mitigate the impact of river basin closure on food production and the livelihoods of farmers. A multilevel analysis (farm-level surveys and regional assessment through remote-sensing techniques and statistics) of the dynamics of irrigation and land use in the Nagarjuna Sagar project (South India) in times of changing water availability (2000–2006) highlights that during low-flow years, there is large-scale adoption of rainfed or supplementary irrigated crops that have lower land productivity but higher water productivity, and that a large fraction of land is fallowed. Cropping pattern changes during the drought reveal short-term coping strategies rather than long-term evolutions: after the shock, farmers reverted to their usual cropping patterns during years with adequate canal supplies. For the sequence of water supply fluctuations observed from 2000 to 2006, the Nagarjuna Sagar irrigation system shows a high level of sensitivity to short-term perturbations, but long-term resilience if flows recover. Management strategies accounting for local-level adaptability will be necessary to mitigate the impacts of low-flow years but there is scope for improvement of the performance of the system.  相似文献   

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Information technology (IT) change is difficult to implement successfully. Cultural (people) issues are a major barrier to IT implementation in the architecture, engineering, and construction (AEC) industry and existing change models have limitations, particularly with respect to cultural issues, which directly affect the ability of companies within the AEC industry to successfully implement IT change. This paper discusses research exploring the relationships between a resistance to change index (RTCI) and the demographics of individuals to understand different AEC participants’ resistance to IT change. Identifying individuals that exhibit different intensities of resistance to IT change efforts and their attendant demographics provides benchmark data to organizations. The ability to identify potential resistors is the first step in helping ensure that new technology implementations succeed. Data was collected from a 156-person sample of the AEC population to determine the relationships among different demographic groups within the AEC population and differences in their RTCI. The data analysis found several demographic groups that were different in their likelihood of resistance, including profession, gender, computer understanding and experience, and awareness of past or future changes occurring in their company. Age and education level were expected to have relationships with RTCI, based on industry stereotypes. The data analysis found that these stereotypes have no scientific basis. Two other stereotypes, gender and computer understanding and experience, were supported by the data analysis.  相似文献   

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Nine therapy clients were interviewed regarding their experiences of giving gifts to therapists. Data were analyzed using consensual qualitative research. In describing a specific event when they gave a gift that was accepted, participants described having a good relationship with the therapist and usually identified their therapy concerns as relationship or family struggles or both. Most bought a relatively inexpensive gift they thought their therapist would like and gave it during a nontermination session to express appreciation or mark an important life event. Most participants acknowledged mixed emotions when giving the gift and noted that any discussion of the gift was brief and did not explore its deeper meaning. Nevertheless, most participants perceived that gift events positively affected them and their therapists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

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The prospective relations between five types of parental reactions to children’s negative emotions (PRCNE) and children’s psychological adjustment (behavioral problems and social competence) were examined in a two-wave longitudinal study of 425 school-age children in China. Parents (mostly mothers) reported their own PRCNE. Parents, teachers, and children or peers reported on children’s adjustment. Parental punitive reactions positively predicted externalizing problems (controlling for baseline), whereas emotion- and problem-focused reactions were negatively related to internalizing problems. Parental minimizing and encouragement of emotion expression were unrelated to adjustment. Concurrent relations were found between PRCNE and parents’ authoritative and authoritarian parenting dimensions. However, PRCNE did not uniquely predict adjustment controlling for global parenting dimensions. The findings have implications for cultural adaptation of parent-focused interventions for families of Chinese origin. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

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