Japanese farmers manage their irrigation water based on their past experiences and preferences, considering such factors as weather and available water (hereafter defined as empirical water management). They elaborately control the intake and drainage rates of their own paddy fields to maintain optimal ponding depths. But these well-managed systems will drastically change because of the decreasing number of farmers. Therefore, it is necessary to clarify if the optimal ponding depth will be maintained within the limits of traditionally-allowed water intake rate from the main river. The first objective of this study was the quantification of actual water use in the paddy fields, resulting from the farmers water management on the basis of their experience. The significance of the present water intake rate under empirical water management was studied for a paddy field command area of about 230 ha. Water intake rates and the water requirements of the whole area were investigated by measuring the flow rate at 17 points of irrigation and drainage canals. Characteristics of the farmers empirical water management were investigated by measuring the hourly changes in inflow and outflow rates for a sub-area using an automatic measurement system, and an inferential method of determining water management patterns for the paddy fields was proposed. The newly-proposed inferential method was introduced in the tank model, which expresses the characteristics of water management in the command area. The Shuffled Complex Evolution Algorithm (SCE-UA) method was used for optimizing the model parameters. It was proven that the model accuracy improved when the farmers empirical water management was taken into account. The optimal amount of water to be applied to the command area was quantified by the simulation. The second objective was to predict the effect of the decreasing number of farmers on future water use conditions. The simulated result indicates the difficulty of maintaining optimal ponding depth for the whole command area when the farmers empirical water management is not maintained. In other words, results indicated that efficient water use requires an automatic water management system or a new pipeline system to replace the farmers present empirical water management. 相似文献
Chiyoda basin is located in Saga Prefecture in Kyushu Island, Japan, and lies next to the tidal compartment of the Chikugo
River to which the excess water in the basin is drained away. Chiyoda basin has a total area of about 1,100 ha and is a typical
flat and low-lying paddy-cultivated area. The main environmental issue in this basin is total nitrogen (TN) and total phosphorus
(TP) load management because TN and TP, which loaded from farmlands, degrade surface water as a result of anthropogenic eutrophication.
This paper presents a mathematical model of TN and TP runoff during an irrigation period in Chiyoda basin in order to elucidate
the pollutant fluxes that accompany water transportation in paddy fields and drainage canals, and to evaluate pollutant removal
from the study area to the Chikugo River. First, the water flow and the algorithm of gate operation were simulated by a continuous
tank model and the accuracy of the model was then evaluated by comparing the simulated water levels with observed ones during
an irrigation period. The observed and simulated water levels were in good agreement, indicating that the proposed model is
applicable for drainage and water supply analyses in flat, low-lying paddy-cultivated areas. Second, the TN and TP runoff
during an irrigation period was simulated based on the TN and TP loads that were determined by observed data in paddy fields.
For TN runoff, the simulated results and observed data were in good agreement whereas for TP runoff, the simulated results
were higher than the observed data. However, if the settled TP within the paddy tank was calculated as 6%, then the simulated
results and the observed data were in good agreement. We concluded that TN runoff from paddy field to the drainage canal system
was not affected much by the sediment related process. The present study could provide farmers and managers with a useful
tool for controlling the water distribution in an irrigation period, and the TN and TP loads in the downstream area as well
as the Chikugo River. 相似文献
A cell-based distributed watershed model is developed which enables us to simulate the hydrological and hydraulic aspects
of the watershed in a refined fashion. With three-zoned cell profiling, the model is composed of three sub-models; tank model
for a surface water zone, soil moisture model for a surface soil zone, and unconfined shallow groundwater flow model for a
subsurface zone. Inclusion of the soil moisture sub-model modified to reroute the infiltration, routed from the tank sub-model,
into the return flow and the groundwater recharge features the model. The groundwater flow sub-model, numerically approximated
by use of the finite volume method and the implicit time-marching scheme, considers a network of on-farm drainage canals as
internal boundaries, which is an essential need for modeling the watershed including farmlands. Cascade-linking of the three
sub-models in a cell and assembling of all the cells over the entire watershed domain provides the global equations system
to be solved. Applicability of the model is demonstrated with its practical application to a real watershed in that paddy
and upland crop fields take great part of the land-use practice. It is then indicated in a quantified manner that rice farming
significantly contribute as a major groundwater recharger in an irrigation period to fostering and conservation of regional
water resources. Along with appropriately profiling a cell, the model is so versatile and tough that it can be applied without
difficulty to a watershed of diverse terrains and land-uses and the computations can stably be carried out. It is thus concluded
that the model presently developed could be a powerful “watershed simulator” to investigate and assess the time-varying hydro-environmental
properties of a watershed while separating and integrating the hydrological and hydraulic components of particular importance. 相似文献
In vivo digestibility determination in shrimp is a challenge because these animals are coprophagous, benthic and slow feeders and the small amount of feces that they produce is difficult to collect. The objective of this study was to evaluate an efficient tank design for the purpose of studying shrimp digestibility. Different tank designs were evaluated considering drain system (dual-drain and single-drain), water inlet flow rate (8, 12, and 16 L min−1) and bottom drain diameter (6, 13, 19, 25 and 50 mm) and their effects on tank hydraulics, water velocity and solids flushing. A circular and slightly conical 500 L tank was adapted with a clarifier for the two dual-drain designs (Cornell-type and central-type) and settling columns for the two single-drain designs (Guelph-F and Guelph-L). Results showed that: (1) water rotational velocity profile was more homogeneous in tanks with larger bottom drain outlets, and water velocity increased with water inlet flow rate from almost zero up to 14.5 ± 0.7 cm s−1; (2) solids flushing, measured as the percentage of feed pellets retained at both the bottom drain and in the settling devices, was positively correlated with the surface loading rate (L min−1 flow per m2) and was more effective at the Guelph-L design fitted with a 150 mm diameter settling column. In this system 100% of the solids were removed at the inflow rate of 16 L min−1. It can be concluded that among the systems evaluated, the Guelph-L at an inflow-rate of 12 L min−1 was most efficient for both solids removal and water velocity profile and thus seemed more suitable for shrimp digestibility studies in high performance conditions. Technologies involving hydrodynamic must be intensively applied to solids removal for aquatic species production as well as research purposes like digestibility, which is highlighted in this study. 相似文献
Field-collected tetrasporophytes of Palmaria palmata were tumbled in 300-L outdoor tanks from January to August at ambient daylength or in a constant short-day (SD) regime (8 h light per day), both at 10 or 15 °C. Tetrasporangia were massively induced after 2.5 months under SD conditions at 10 °C and completely lacking at 15 °C, both under SD or ambient daylength conditions, with a few tetrasporangia present at 10 °C and ambient daylength. Elongation rates of tagged tetrasporophytic thalli peaked from March to April in all four conditions, when the biomass densities in the outdoor tanks were close to 2.5 kg fresh weight m− 2. Under all four conditions, juvenile proliferations started to appear in June from the margins of the old fronds, and attained approximately 1 cm in length by the end of July.Approximately 80% of the tetraspores were released during the first three dark phases in a light/dark regime, and the remaining 20% during the light phases. A minimum of 10 min darkness was observed to trigger spore release. White light inhibited tetraspore release, while a similar number of spores were released in continuous red light or in the light/dark regime, although with no significant differences of spore release during subjective days and nights.Sporelings were successfully derived from the released tetraspores for mass propagation of the male gametophyte in 2000-L outdoor tanks in a greenhouse. Mass production of male gametophytic sporelings of P. palmata was completed two times by SD induction of tetrasporangia at 10 °C, release of spores in darkness and culturing the sporelings until they were ready to be propagated vegetatively in greenhouse tanks. One experiment lasted from January to October 2001, with spore release in June, and the second from September to April 2003, with spore release in January. These results may support the development of sustainable, year-round Palmaria farming. 相似文献
The design and operation of aquaculture tanks should minimize stagnant areas especially in the immediate vicinity of the fish. In tanks with pelagic fish, mixing caused by the water flow and by fish swimming is sufficient to maintain dissolved oxygen and metabolite concentrations in the immediate vicinity of the fish that are similar to those in the main water body. Given the behavior of sedentary benthic species, such as the California halibut (Paralichthys californicus), and their tendency to remain motionless on the bottom of aquaculture tanks, often in layers that are several fish deep, water quality may stratify with the worse conditions occurring in the area where they fish are lying. The purpose of this study was to evaluate the influence that California halibut (450 g average weight) may have on the vertical profile of oxygen concentration in a raceway (239 cm long, 28 cm wide) and a circular tank (92 cm diameter) operated at two water depths (10 and 20 cm). Oxygen was measured at each centimeter of the vertical profile both in an area with fish and without fish to assess their influence.
Results showed a lower oxygen concentration in the near-bottom region of the raceway and circular tanks. The phenomenon was most pronounced in the raceway operated at a 20 cm depth, but was also observed in the circular tank operated at 20 cm and in the raceway at 10 cm.
Measurements were also taken in samples collected just in front of or directly from a fish's mouth. A zone of depressed oxygen concentration in the immediate vicinity of the fish was documented, with oxygen concentrations as low as 50% of the measured tank effluent concentration. The magnitude of the depression was greater in raceways than in circular tanks and in 20 cm water depth than in 10 cm depth. The fish remained sedentary in these zones of depressed oxygen concentration for extended periods of time and frequently exhibited hyperventilation. The oxygen concentrations in the vicinity of the fish were consistently lower than the concentrations measured in the tank effluent. Therefore, effluent measurements did not provide an accurate representation of conditions to which the fish were exposed. 相似文献