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951.
大型灯泡式贯流泵CFD计算 总被引:2,自引:0,他引:2
大型灯泡式贯流泵在国内的研究与运用远远滞后于水轮机,导致国内低扬程泵站的选型一直突破不了传统的结构模式。为了研究解决国内低扬程泵结构选型问题,结合南水北调东线工程的蔺家坝泵站大型灯泡贯流泵,对适用低扬程工况的大型灯泡式贯流泵结构形式、流道水力损失、压力分布、流速分布进行了流体数值计算,并与模型试验作了比较。结果表明,流体数值计算的结果与试验数据非常接近,这为今后国内低扬程泵站设计选型提供了参考。 相似文献
952.
953.
The root zone water quality model (RZWQM) was developed primarily for water quality research with a generic plant growth module primarily serving as a sink for plant nitrogen and water uptake. In this study, we coupled the CERES-Maize Version 3.5 crop growth model with RZWQM to provide RZWQM users with the option for selecting a more comprehensive plant growth model. In the hybrid model, RZWQM supplied CERES with daily soil water and nitrogen contents, soil temperature, and potential evapotranspiration, in addition to daily weather data. CERES-Maize supplied RZWQM with daily water and nitrogen uptake, and other plant growth variables (e.g., root distribution and leaf area index). The RZWQM-CERES hybrid model was evaluated with two well-documented experimental datasets distributed with DSSAT (Decision Support System for Agrotechnology Transfer) Version 3.5, which had various nitrogen and irrigation treatments. Simulation results were compared to the original DSSAT-CERES-Maize model. Both models used the same plant cultivar coefficients and the same soil parameters as distributed with DSSAT Version 3.5. The hybrid model provided similar maize prediction in terms of yield, biomass and leaf area index, as the DSSAT-CERES model when the same soil and crop parameters were used. No overall differences were found between the two models based on the paired t test, suggesting successful coupling of the two models. The hybrid model offers RZWQM users access to a rigorous new plant growth model and provides CERES-Maize users with a tool to address soil and water quality issues under different cropping systems. 相似文献
954.
Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency 总被引:9,自引:0,他引:9
J. A. Tolk T. A. Howell J. L. Steiner D. R. Krieg A. D. Schneider 《Irrigation Science》1995,16(2):89-95
Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (Igross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated area as compared to a non-irrigated area can be subtracted from Igross irrigation application losses for a reduced, or net, interception (Inet) loss. This study was conducted to determine the extent in which transpiration suppression due to microclimatic modification resulting from evaporation of plant-intercepted water and/or of applied water can reduce total sprinkler irrigation application losses of impact sprinkler and low energy precision application (LEPA) irrigation systems. Fully irrigated corn (Zea Mays L.) was grown on 0.75 m wide east-west rows in 1990 at Bushland, TX in two contiguous 5-ha fields, each containing a weighing lysimeter and micrometeorological instrumentation. Transpiration (Tr) was measured using heat balance sap flow gauges. During and following an impact sprinkler irrigation, within-canopy vapor pressure deficit and canopy temperature declined sharply due to canopyintercepted water and microclimatic modification from evaporation. For an average day time impact irrigation application of 21 mm, estimated average Igross loss was 10.7%, but the resulting suppression of measured Tr by 50% or more during the irrigation reduced Igross loss by 3.9%. On days of high solar radiation, continued transpiration suppression following the irrigation reduced Igross loss an additional 1.2%. Further 4–6% reductions in Igross losses were predicted when aerodynamic and canopy resistances were considered. Irrigation water applied only at the soil surface by LEPA irrigation had little effect on the microclimate within the canopy and consequently on Tr or ET, or irrigation application efficiency. 相似文献
955.
The vertical K-sat of a clay layer, occurring between 30 and 60 cm below the soil surface, was measured in situ in early spring at thirteen sites, using large soil columns. Gypsum was used to form a barrier around the column and K-sat values were measured with an infiltrometer in columns that were first attached and then detached from the subsoil. This procedure allows an estimate of the occurrence of large continuous pores, such as vertical worm channels. Highest values were found in tile-drained grassland, followed by grassland with surface drainage only, and by tile-drained arable land. Relatively low K-sat for the silty subsoil, rather than the (high) vertical K-sat for the clay layer, is considered to be responsible for high groundwater tables in the wet season.Undisturbed, large columns were taken to the laboratory and saturated for a period of three months to simulate prolonged swelling after a very wet season, and to measure chloride-breakthrough curves, for characterizing soil-pore continuity. The clay layer, sampled in the surface-drained grassland, showed no significant reduction of K-sat after prolonged swelling, but the one for arable land was reduced. Moreover, flow in the latter occurred through only a few relatively large, continuous pores, whereas a more heterogeneous pore system was found for the column from grassland. The already high K-sat of the clay layer in surface-drained grassland increased as a result of tile drainage. Compaction of the clay layer in tile-drained arable land reduced K-sat well below the level found in surface-drained grassland. 相似文献
956.
L. Wartena 《Agricultural Water Management》1976,1(1):99-100
957.
Jan L. M. H. Gerards 《Irrigation and Drainage Systems》1992,6(3):223-247
The inability to properly maintain irrigation systems over time forced the Government of Indonesia (GOI) to seek cost recovery from water users through introduction of an irrigation service fee. The plan is to introduce this fee in all of the technical irrigation systems of Indonesia, covering about 4 million hectares, over a 12 year period. Design and Introduction of this service fee in 4 pilot areas of the 4 major rice producing provinces (West, Central and East Java, and South Sulawesi) during 1989–1991 has shown that users are willing to pay. Results of first ISF collection from over 11,000 farmers in Central and East Java in pilot systems was an encouraging 95%. However that acceptance to pay by users depends on their structured and systematic involvement in defining systems needs. They need to understand a differentiation in payment if service levels are different. They appreciate use of collected funds in the system where collected. They understand the organization of water users associations but this requires their active role in fee determination and collection. They understand the establishment of federations of these associations. ISF requires also active involvement of Local Government officials as facilitators and intermediaries between service receivers (the water users) and service providers (personnel of the Public Works irrigation department) in the introduction period. This article describes the experience of the first 21 months of the ISF project, the concept developed, the principles used as basis for ISF, the introduction at the field level, issues related to acceptance by users and by the institutions involved, and the first results.Abbreviations/Acronyms DGWRD
Directorate General of Water Resources Development (Ministry of Public Works)
- EOM
Efficient Operation and Maintenance
- Gabungan
group of WUAs
- IPAIR
Indonesian abbreviation for ISF
- ISF
Irrigation Service Fee
- Juru
gate keeper
- PBB
land tax on irrigated lands
- PPL
agricultural field extension agent
- P3A
Indonesian abbreviation for Water Users Associations
- PU
Indonesian abbreviation for Public Works
- SM
Special Maintenance
- WUA
Water Users Associations 相似文献
958.
Can carbon sequestration markets benefit low-income producers in semi-arid Africa? Potentials and challenges 总被引:1,自引:0,他引:1
The Clean Development Mechanism (CDM) of the Kyoto Protocol of the United Nations Framework Convention on Climate Change allows a country that emits C above agreed-upon limits to purchase C offsets from an entity that uses biological means to absorb or reduce greenhouse emissions. The CDM is currently offered for afforestation and reforestation projects, but may apply subsequently to sequestration in agricultural soils. Additionally, markets outside of the Protocol are developing for soil C sequestration. 相似文献
959.
960.
Landscape Ecology - Landscape and local factors govern tree regeneration across heterogeneous post-fire forest environments. But their relative influence is unclear—limiting the degree that... 相似文献