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1.
Saltwater wedge intrusion often renders the quality of water from the Shinkawa River in the city of Niigata (Japan) unsuitable for agricultural use. To determine an effective and economic strategy to limit this intrusion and prevent irrigation water from contamination by seawater, we propose a countermeasure, pushing the saltwater layer outside the river through submerged flow generated by sluice gates near the river mouth. To demonstrate this effect, an in situ experiment was conducted. During that experiment, longitudinal and vertical distributions of the saltwater wedge were observed by an acoustic profiling system and electrical conductivity meters. As a result, elevation of the density interface between freshwater and saltwater was reduced by 1.04 m on average and the longitudinal extent of the saltwater wedge was withdrawn by 1.08 km seawards over about 4 h. With the intrusion extent shortened and the density interface lowered, three of five intake pumping stations could operate without risk of saltwater mixture into irrigation water, and the risk to two other intake pumping stations was reduced. We conclude that the use of the sluice gates to generate submerged flow underneath them is an effective countermeasure to limit the saltwater wedge intrusion along the Shinkawa River and preserve the agricultural water quality during irrigation season. This method may be used in other estuaries suffering from saltwater wedge intrusion.  相似文献   

2.
In the absence of a reservoir on the downstream side, a river flow that increases temporarily by rainfall cannot be stored and discharged apart from requirements in a command area. This unused water (excess water) occurs to some extent even in a drought year and making effective use of this supply is considered as one of the countermeasures for water shortage. Setting up a regulating reservoir on the upstream side of head works is regarded as one of the methods for making effective use of excess water. The inflow to the river and water delivery loss occurred from rainfall are stored in the regulating reservoir and supplied to the command area on the downstream side as agricultural water. An operational method for the regulating reservoir to effectively utilize the excess water was examined for a canal system by simulation. In an investigated area, there was excess water even in drought years, and making use of it through the regulating reservoir whose capacity is smaller compared to that of a dam can become one of the countermeasures for the drought period. The simulation in this study could estimate quantitatively the effect of the regulating reservoir to make the excess water effective.  相似文献   

3.
The Japanese government started to construct two subsurface dams on Miyako Island in 1988, and the project was completed in 2001. Before the construction of the dams, the NO3-N concentration of groundwater on the island was about 10 mg/l, the upper limit for drinking water in Japan, owing to the application of fertilizer to sugarcane fields. Predicting the effect of these subsurface dams on the groundwater environment was difficult because they were probably the first mega-subsurface dams in the world. We measured the NO3-N concentration in the groundwater at observation wells before and after construction of the Sunagawa Dam and after the groundwater began to be used. We also measured the NO3-N concentration monthly at a typical observation well in the catchment over a period 14 years to evaluate the environmental impact of construction of the dam. The highest NO3-N concentrations were downstream before completion of the subsurface dam, and a high NO3-N concentration zone remained around the cut-off wall after its completion, but this high-concentration zone disappeared and the distribution of NO3-N became uniform after pumping of the groundwater began. Overall, the NO3-N concentration decreased gradually. These results show that the groundwater quality did not deteriorate as a result of the construction of the Sunagawa Subsurface Dam.  相似文献   

4.
Windbreaks present a porous obstacle to the approaching airflow, forcing air to flow through the windbreak at a reduced speed and accelerate over the top. In this research, windbreaks were considered as border structures to mitigate spray drift. Air flows, with an interspace between it, particles are filtered from the flow by deposition on the windbreak. Hence there is a reduction in deposition in the downwind sheltered area (the ‘quiet zone’) behind the windbreak. Peak deposition in the sheltered area can occur at minimum wind speeds. The deposition profiles of spray drift behind various border structures were measured. In the first part, drift tests were performed in a wind tunnel. Artificial screens with various heights and open areas were tested. A row of plastic Christmas trees and natural canopies were also tested. Subsequently, drift experiments were performed under field conditions in a grassland with the artificial screens and a row of Fagus sylvatica trees. The artificial screens reduced spray drift deposition in the sheltered region, but significant deposition peaks were found behind the screens. The natural structures had potential to reduce drift deposition when their height was at least equal to the height of the spray nozzle(s). The drift deposition at short distances behind the natural structures was higher than deposition behind artificial structures, but conversely peaks in deposition in sheltered areas were not created by the natural structures.  相似文献   

5.
Diversion dams are settled in river channels to dam water. They obstruct flood flow and also affect sediment movement on riverbeds. Dam structures break due to local scouring of the riverbed caused by local flow around them. The causes of such failures should be studied by investigating how flow meanders over alternate bars during floods. Diversion dam failures are classified into three types according to cause. The first type of problem is caused by the difference between the riverbed height and the sill height. If the present riverbed is higher than the sill, the mobile gates do not close easily due to sand deposition on the sill. If the riverbed is lower than the sill, the riverbed in the downstream area of the weir is scoured, and the weir may be damaged. The second type is caused by the relation of the weir position to the alternate channel bars. The bar area is usually higher than the sill, and sand deposition on the sill causes problems for mobile gate operation. The riverbed below the weir at the pool section is scoured because the bed height is lower than the sill height. The third type is caused by the migration of alternate bars. A low water course changes due to migration of alternate bars after a flood. The sand deposition area from the upstream reach blocks the intake entrance. Before a diversion dam structure is designed, the situation and the probable changes in riverbed form should be investigated.  相似文献   

6.
We investigated the post-passage movement patterns of three freshwater fish species, Carassius auratus, Hemibarbus longirostris, and Silurus asotus, frequently captured in a fishway trap as they were released into the lentic dam reservoir. Acoustic telemetry was used to monitor fish movement. Acoustic tags were attached to 10 individuals (C. auratus, [n = 6], Ca1–6; H. longirostris, [n = 2], Hl1 and Hl2; and S. asotus, [n = 2], Sa1 and Sa2). The individual (Sa1) was particularly monitored to changes of vertical distribution between day and night a depth transmitter. The lentic species, C. auratus and S. asotus, were grouped into those that moved into upper streams (Ca1, Ca2, Ca3, and Sa1) and those that stayed in the reservoir (Ca4, Ca5, Ca6, and Sa2); all individuals utilized almost the entire area of the reservoir. However, H. longirostris, which favor lotic environments, showed different responses; one (Hl1) immediately moved into one of upper the streams, whereas the other (Hl2) utilized the entire dam reservoir area. No significant correlations were observed between size of the C. auratus individuals (total length and total weight) and monitored parameters (total movement distance, movement distance per day, and number of receivers encountered). Moreover, S. asotus used the water at a mean depth of 2.89 ± 1.52 m, and its vertical distribution changed more actively during the night than that during the day. Therefore, the efficacy of the Jangheung Dam fishway could be improved through release of the confluence of the inflow streams at the dam reservoir, which would provide both lentic and lotic environments without extended migration for fish.  相似文献   

7.
This study aims to propose a methodology for establishing the optimal rule curves of reservoir operation based on a multi-use reservoir system. Located on the upper Saigon River, Dau Tieng Reservoir plays an important role in economic and social aspects: (1) flood control; (2) domestic and industrial demands; (3) flushing out salt water intrusion from the downstream area; and (4) agriculture irrigation. We propose a reservoir operation model using a constrained genetic algorithm (CGA), in which the fitness function was constrained by penalty functions. The proposed model was formulated by including various water demands configured into the objective function. The penalty functions were designed for various constraints and integrated into the objectives of the operation process to perform the fitness function. The model’s performance was simulated for the last 20 years with 1-month intervals and evaluated through a generalized shortage index (GSI). The derived results of three CGA cases with associated environmental flow requirements significantly improved the efficiency and effectiveness of water supply capability to various water demands as compared to current operation. Among the three cases, CGA case 3 achieved much better water releases from the reservoir as indicated by a small derived GSI value (0.33), the smallest shortage of environmental water (0.11 m3/s) and the highest water usage (63.8 %). Thus, the derived results of CGA case 3 were presented as the best rule curves for reservoir operation. To summarize, CGA was demonstrated as an effective and powerful tool for optimal strategy searching for multi-use reservoir operations.  相似文献   

8.
We investigated the applicability of a dredged pool formed at the inlet of a reservoir for pollution control. To quantify the effect of a dredged pool on the water quality of a reservoir, we monitored the water quality of the Masan Reservoir, located in the city of Asan, Choongnam Province, Korea, before and after dredging. In addition, a completely mixed box model was applied to simulate the water quality of the dredged pool and reservoir. The model included a water balance equation and chemical mass balance equation, into which several interactions among water quality components, such as phytoplankton, total nitrogen (T-N), total phosphorus (T-P), dissolved oxygen, and chemical oxygen demand (COD), were incorporated. The water quality monitoring and modeling results indicated that reservoir water quality was greatly affected by the dredged pool. The loads of T-N and T-P into the reservoir were reduced by the dredged pool, which may have induced the removal of nutrients by settling. However, the dredged pool may have had a negative effect on the reservoir in terms of COD and chlorophyll-a because of the internal production of organic matter and/or algae with water detention. Therefore, a dredged pool may be used for pollution control in a reservoir, as long as it is combined with measures to reduce concentrations of organic matter and/or algae.  相似文献   

9.
This paper introduces an irrigation system developed in the floodplain of a lake and studies the water management technique of the irrigation system by estimating the total water balance of the whole system. The system is characterized by a reservoir combined with a dike system in the floodplain of the Tonle Sap Great Lake and an irrigation system. Two main models are used for calculating the total water balance. The first model is the water balance of the reservoir. The inputs to the model are water level of the reservoir, precipitation, lake evaporation, infiltration, and area–volume curve of the reservoir. The outputs are inflow and outflow of the reservoir. The supply from the reservoir to paddy fields is computed from the outflow. The second model is the water balance of paddy fields, based on which the water requirement in paddy fields is derived. The reference evapotranspiration needed to calculate the water requirement is simulated for monthly time series using the FAO Penman–Monteith model. Since there is no drainage network in the irrigation system, surface drainage and runoff are not included in the calculation of the water balance, and seepage is considered negligible in the flat floodplain area. The evapotranspiration, rice variety, soil type and irrigated area are used to simulate water consumption in paddy fields. Finally, the two models are connected to produce the total water balance from the reservoir to paddy fields. The total outflow from the reservoir is estimated and the total water consumption for dry season cultivation is also determined. Finally, the efficiency of the whole system is examined.  相似文献   

10.
Agricultural production in the coastal wetlands of Asia is often hindered by salinity intrusion caused by tidal fluctuation. This paper reports changes in environmental and socio-economic conditions that followed the phased construction and operation of sluices for controlling seawater intrusion from 1994 –2000 in a coastal area of the Mekong River Delta, Vietnam. Canal water salinity decreased rapidly upstream of sluices, allowing rice cropping intensification and increased rice production in the eastern part of the study area. However, the livelihoods of farmers in the western part were adversely affected due to cessation of supply of brackish water that was needed for brackish-water shrimp farming, while the acid sulphate soils present there posed problems for rice cultivation. The poor farmers and landless people suffered more because the fishery resource that they depended on declined sharply due to reduced salinity and increased acidity in the canal water. The findings confirmed that the environment and resource use in the coastal lands are very sensitive to external intervention. A clear understanding of the socio-economic and environmental impacts of salinity control measures in coastal areas can help planning to enhance farmers' incomes while minimizing negative environmental impacts. Land-use policy formulation, planning and management should adopt a more holistic approach, taking into account the interests of all resource users, especially the poor, instead of focusing on any particular sector.  相似文献   

11.
《Plant Production Science》2013,16(4):522-528
Abstract

The contents of major nutrient components, and the composition and contents of medicinal substances were examined in Houttuynia cordata cultivated under field conditions and treated with natural light at full intensity, 40% intensity, and 20% intensity from sprouting to harvesting. The results indicated that the yield of the aboveground portion per unit area was highest at a 40% intensity and lowest at 20% intensity. The yield of the underground portion per unit area was highest under full intensity and lowest at a 20% intensity. As light intensity was reduced, protein and water content increased, while the contents of soluble sugar and fat, the contents of volatile oils both the aboveground and underground portion decreased. The total flavonoid content in both the aboveground and underground portions decreased with diminishing light intensity, but the composition of these flavonoids was hardly affected. In summary, although proper shading can increase the yield and the contents of some nutrients in H. cordata, this treatment reduces the net contents of medicinal components such as volatile oils and flavonoids, as well as the contents of active components. Therefore, it is necessary to provide sufficient light when growing H. cordata for medicinal and functional food purposes, but the crop may be treated with appropriate shading or intercropped when grown as food.  相似文献   

12.
This study of a water cycle was conducted in an evergreen forest located in the Mekong River Basin in central Cambodia. At the observation site, we measured the dynamics of the spatial distribution of groundwater levels. The groundwater movement was analyzed two-dimensionally using boundary conditions and parameters that had been observed in the field. The climate in the research area is dominated by two seasons, which occur annually: a rainy and a dry season. The groundwater levels are generally high during the rainy season and low during the dry season. Groundwater levels were measured along a stream, which flowed through the study site. The streambed was visible at the head of the stream in January. At the next downriver well point, the streambed appeared in March. Finally, it became visible at all well points in April, meaning that surface runoff had disappeared temporarily and instead flowed underground during the ensuing dry period. Groundwater levels of the studied lateral flow perpendicular to the stream that seeped and infiltrated into the stream were 1.2–2.5 m deep (in April), which was the lowest level recorded for the year. During that period, the depth of the groundwater of the studied lateral flow fell by as much as 56 mm per month. In addition, the lateral flow groundwater infiltrated into groundwater of the stream during that period. The groundwater level fluctuation was estimated based on a two-dimensional analysis of lateral flow perpendicular to the stream using a numerical simulation model with soil physical parameters and observed boundary conditions. The observations of ground water fluctuations were well reproduced. Deep seepage of groundwater was estimated using a uniform boundary condition that allowed efflux through the bottom, estimated as being approximately 30 mm per year. The simulated deep seepage rate was considered plausible considering other hydrological components such as soil water storage fluctuation.  相似文献   

13.
江西是我国双季稻的优势产区,在保障国家粮食安全方面发挥着重要作用。以世界稻作文化发源地之一、古时贡米之乡的江西省万年县为例,通过实地调研和文献资料收集,分析了万年县水稻生产的熟制结构和农户在熟制选择中的考虑因素。结果表明,与近40年江西省水稻种植面积呈现正反“W”型变化特点相似,万年县双季稻呈现先减后增再减的变化特点,而单季稻呈现出持续增加的特点;农户熟制选择受地块特征和地理位置影响较大,城郊和滨湖平原地区的双季稻面积占绝对优势,而丘陵地区的单季稻种植面积在进一步扩大;经济效益和政策因素是农户水稻熟制选择的重要原因,而绿肥种植主要依靠政府政策的引导;劳动力状况和农业生产技术也是农户熟制选择的两大因素。因此,要加强冬闲田的开发利用、恢复绿肥生产、提高复种指数,努力做到土地用养结合、地力常新。调整作物结构、优化种植模式、引导农户遵循“绿色协调发展” 的原则选择合适的种植模式,进行合理的熟制配置,以此构建水稻生产绿色发展结构体系。  相似文献   

14.
The study of the gill fishes of 176 Oreochromis niloticus (L.) was undertaken in the dam of Loumbila (Burkina Faso), in order to obtain the first information on the dynamics of population of the Monogeneans parasites in a population of wild hosts. These data are essential in the search for means to avoid the enormous losses that often occur in intensive pisciculture. This analysis revealed the presence of five species of Monogeneans (Cichlidogyrus tilapiae, Cichlidogyrus halli, Cichlidogyrus thurstonae, Cichlidogyrus rognoni and Scutogyrus longicornis). On the levels of the recorded infestations, these species taken individually probably do not control the population of Oreochromis niloticus. In the dam of Loumbila, the fluctuations of parasitic abundances are neither seasonal nor cyclic. The size either does not have an influence on parasitism. However, the sex effect was noted with C. halli, the females thus were more infested than the males. O. niloticus is parasitized all the year, because the recruitment of these organisms, although relatively weak, is continuous; this logically results in their accumulation in this fish.  相似文献   

15.
The subject of this study is water management in low-lying paddy fields. The objective of this study is to quantify the water requirement, and estimate an appropriate volume and facilitate management of irrigation water in areas where it is difficult to estimate the flow rate continuously. A field observation was conducted at a 14-ha study site located in the Kuwabara area, Fukuoka City, southwest of Japan, to evaluate water management conditions in the command area of the reservoir. This site near the reservoir was selected, because it was impossible to understand the water supply situation in the entire command area. The farmers in this region have been unable to retain sufficient irrigation water. The observation results indicate that the water depth fluctuates widely in every irrigation canal. The canals are frequently empty because rotational irrigation is conducted by water managers; this makes quantifying the flow rate in the irrigation canal very difficult. To quantify the water requirement, an improved tank model was introduced. The accuracy of the model was examined by comparing the observed and calculated ponding depths at a paddy field. The simulation results agreed with the observed data. Using this model, water management for the reduction of water managers’ labor was simulated. Simulation results indicated that rotational irrigation effectively reduces labor and saves irrigation water.  相似文献   

16.
There are many paddy fields and large amounts of groundwater in the Tedori River Alluvial Fan in Ishikawa Prefecture, Japan. Water infiltration from paddy fields during irrigation may significantly contribute to groundwater recharge. Groundwater recharge is known to be one outcome of paddy farming, and in general is usually related to land use. However, a decreased area of paddy fields because of socioeconomic factors such as urbanization and increasing area of fallow fields has possibly affected the groundwater environment. Evaluation of the quantitative effect of paddy fields on groundwater is necessary for groundwater conservation. This study examined the relationship between differences in the depth of groundwater from just before the irrigation period to just after the first irrigation of paddy fields (increments of groundwater levels) in observation wells and the area of paddy fields around each well. The paddy areas within circular buffer zones, which were delineated at 0.2 km intervals between 0.2 and 2.0 km centered on each observation well, were calculated. A positive relationship was found between the rise in groundwater and the area of paddy field within different buffer zones at most wells. In addition, in the middle or upper part of the fan, the effect of changes in the area of paddy fields surrounding the well on the groundwater level rise was greater than that on the lower part of the fan.  相似文献   

17.
调查研究浆果类水果主要病虫害及其防治措施、农药使用情况、国内外现行污染物的限量标准及检测方法，并对近年来浆果类水果主要污染物的检测结果进行分析。提出浆果类水果质量安全控制主要污染物的检测项目和限量值，为该类水果的质量安全日常监测提供一定的依据。  相似文献   

18.
In management of the Japanese scallop Mizuhopecten yessoensis culture, it is important to understand the phytoplankton bloom development in the coastal region of the Okhotsk Sea. Variations in food available to this benthic bivalve are a primary environmental factor affecting growth in nature. This paper determined the seasonal variability of Chlorophyll a (Chl a) at the scallop farming region in the Okhotsk Sea from 1998 to 2004 using satellite imageries. Satellite images were processed using default NASA coefficients and community-standard algorithms as implemented by Sea DAS. Spatial and temporal variation of Chl a was determined by EOF analysis. The Chl a concentration showed high seasonal and interannual variability. Peak of Chl a concentration occurred in spring followed by autumn and summer. This was evident in the Empirical Orthogonal Function (EOF) analysis. The spatial pattern of the first mode of EOF analysis of Chl a revealed intensified Chl a at the shelf and offshore areas in spring and autumn (51.8% of variance). The second mode explained 14.2% of the variance indicating enhancement of spring (April-May) Chl a pattern in the frontal area along the coast. Meanwhile, the third mode captured 9.0% of the variability demonstrating high Chl a extending seaward from the shelf area during late autumn. These seasonal variability of Chl a resulted from the variability in occurrences of physical processes associated with retreat of sea ice in spring, advection of Soya Warm Current in summer and intrusion of East Sakhalin Current in autumn.  相似文献   

19.
Low dose chemical stress has been shown to increase plant vegetative growth, though not all chemicals induce the response. Glyphosate is the most widely used herbicide by volume and treated area. At low doses, it can increase growth in a variety of species. Here we show that a glyphosate-induced growth increase can be transformed into an increase in crop yield, if applied at the right time. Glyphosate, in the dose range of 2.5–20 g a.e. ha−1, corresponding to less than 1% of the rate normally used for weed control in the field, increased grain yield of barley by 12–15% when applied at the time of grain filling. Straw yield and the quality of the grains in terms of nitrogen and starch content were not affected by the treatment. The physiological mechanism behind this counter intuitive increase in growth is still unknown, as are possible adverse effects. It is, however, evident that understanding the physiological processes behind chemically induced growth increases in plants holds the promise of improving food yield.  相似文献   

20.
Three stratified clip methods for the estimation of herbage mass and its vertical distribution in grass swards were compared. The first method used a herbage-gripping device, which held a sample from a 2 × 9 cm area while it was harvested and cut into layers in the field. For the other two methods, turfs of herbage were dug and brought into the laboratory where areas defined by 10 × 10 cm or 2 × 9 cm quadrats were cut into layers. For the comparisons, two operators collected independent samples from a sward shortly before it was cut for silage, a sward grazed by cattle and a sward grazed by sheep.
The total mass of herbage dry matter collected depended on the method used, with the herbage-gripping device producing greater estimates than the turf quadrats in two of the swards. The different methods produced similar estimates of the vertical distribution of mass. The larger quadrat usually produced the least variable results, while the herbage-gripping device collected samples most quickly. There were also small differences between the estimates produced by different operators. It was concluded that because the herbage-gripping device was the most cost-effective it would often be the most appropriate method to use. However, when a higher level of precision per quadrat is required the large quadrat, following turf collection, would be more appropriate.  相似文献   

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