The fundamental effect of the change in saltwater level on velocity distribution is important in understanding the effect of tidal fluctuation in coastal aquifers. This study applied the laboratory experiments using the image analysis method and the numerical model to study the effect of varying the saltwater level on velocity distribution in coastal aquifers. It was established that the change in saltwater level affected the velocity distribution, such that; the velocity at the interface was more than twice the one in freshwater. In addition the tracer in the freshwater zone moved to the intersection between the saltwater level and the coastal slope while the tracer in the saltwater zone went along to the shape of the interface. The numerical model revealed that the drastic high velocities at the interface were due to the great buoyancy effects resulting from the varying fluid density between the saltwater and freshwater in the transition zone. The velocity in the freshwater zone was proportional to the global hydraulic gradient while in the saltwater zone, the velocity was inversely proportional to the global hydraulic gradient. Therefore the changes in saltwater level influence velocity distribution in coastal aquifers.
This paper focuses on the application of a particle tracking approach that incorporates temporal moment analysis to dispersivity estimation linked with an inverse analysis under a limited number of observation points. Laboratory solute displacement experiments in saturated homogeneous porous media are conducted to observe a time series of NaCl concentrations at four observation points in 80-cm long, horizontally placed flow field under a steady state and unidirectional flow condition. Breakthrough data measured at the same two coordinates as the source along a flow direction permit the proper estimation of the longitudinal dispersivity without the evaluation of concentration variation at a control plane perpendicular to the flow direction. Breakthrough data also are utilized to estimate transport and source parameters such as transverse dispersivity, retardation factor and source magnitude using genetic algorithm. The good agreement between the measured concentration variation and the recovered breakthrough curves corresponding to the identified set of values suggests that a combined use of temporal moment and inverse analysis can provide an additional useful means of parameter estimation for transport in homogeneous porous media.
During April 2006-December 2006, an investigation was conducted on aquatic insects and river flow rate in mountainous areas upstream of the Ibi and Neo Rivers in Gifu Prefecture, Japan. These mountainous areas experience extremely high annual rainfalls, and many streams have been destroyed due to frequent debris flow disasters in the past. In July 2006, a high river flow rate with maximum velocity of 1.78 m/s (St.1) and 2.63 m/s (St. 2) was observed due to extremely heavy rainfall with total rainfall in a month of 976 mm (St. 1) and 482 mm (St. 2). Although prior to this, the number of aquatic insects was 452 (St. 1) and 124 (St. 2) respectively, the numbers significantly reduced to 42 (St. 1) and 28 individuals (St. 2) after the storm. During this period, the number of individuals dropped to 10% (St. 1) and 22% (St. 2). As a result of factor analysis, the Shannon-Weaver index (H') was high for low water temperature, and it tended to lower for high flow velocity and low flow velocity. In this study, it appears that certain aquatic insects were swept downstream due to the effects of the high river flow.
An alternative approach to the inverse problems encountered prior to the computations of saturated-unsaturated groundwater flow is addressed. The soil hydraulic properties (i.e., the relative hydraulic conductivity K_r and the volumetric water content θ) which are the a priori unknown parameters in the Richards equation governing the flow are interpolated by an assembly of the piecewise cubic spline functions expressed in terms of the pressure head. This free-form parameterization approach provides high flexibility and degrees of freedom in identifying the functional form of the parameters, compared with the conventional approaches in that the functions are of specific shape as in the van Genuchten model of a fixed functional form. In addition, the approach is field-oriented in a point that the solution of the inverse problem can be achieved having only recourse to the observed time-series data of pressure head which are relatively easily in situ available. To find the shapes of such spline functions best expressing head-dependency of the soil hydraulic properties, a simulation-optimization algorithm with the aid of the Levenberg-Marquardt method is developed which serves to iteratively solve an optimization problem of minimizing errors between the observed (or measured) and computed values of the pressure head, in combination with the embedded simulation module for solving forward problems. Validity of the approach is examined with its application to different two soil types which are characterized by less and more sensitive changes of the relative hydraulic conductivity near saturation, respectively. The results show that the approach developed could be a viable alternative to the conventional fixed functional form approaches.
In Japan, more and more paddy fields, left fallow mainly by nationwide rice production control policy, have recently been changed to upland crop fields or artificial wetlands. Since such change or diversification of land use probably has an impact on the water quality environment of the whole neighborhood, it must strategically be implemented in the context of land use arrangement for environmentally sound watershed management. Of great importance is then to make effective use of self-purification functions fulfilled by paddy fields or wetlands. The present study is associated with development of a simulation-optimization model for designing an optimal land use on a watershed scale. The model is composed of a hydro-environmental subsurface watershed simulation model, represented by coupled 3-D Richards and advection-dispersion equations, and a GA (Genetic Algorithm)-aided optimization part. An optimization problem is formulated which, with the most use of self-purification, minimizes the objective function expressed in terms of a weighted total of discharged nutrient from a watershed and residual nutrient within the watershed, taking the location of paddy fields in fallow, changed to upland crop fields or wetlands, as a decision variable. An example problem for a small watershed of an irrigation tank is solved that requires deciding the optimal locations of paddy fields that can be changed to other land use categories. The results show that the model developed could be a powerful tool for making tactics to combat the environmental impact resulting from land use diversification.
This research was done to study the relationship the effect of method fertilization and rainfall intensity to the losses of nutrients in surface runoff. The results of this experiment showed that nutrients concentration in runoff of the parameters analyses that were significantly higher than that of original water. Ratios of contents of the most nutrients (T-N, NH_4-N, NO_3-N, T-P, PO_4-P) in runoff from broadcasting per subsurface of 1cm depth fertilizer application are more than 1.0, leaching of nutrients content was high when rainfall high and on the first time after rain event nutrients content also losses most high in runoff. Nutrient losses in runoff depend on dissolution of granular fertilizer in runoff. Fertilization can rapidly increase the nutrient concentration in runoff, which varies with the methods of fertilization and forms and elements of the nutrients. The concentration of nutrients in runoff was mostly related to the nutrient content of the very shallow surface soil. Data collected in this study may be useful as estimates of maximum losses from runoff under similar farming practices. Such determine the loss potential of fertilizers under high rainfall conditions.
Mohr's envelopes, which describe the shear strength of materials, are shown for structural designs, particularly the stability analyses of rockfill dams. Firstly, an effective method which has passed into oblivion is followed by a complete verification. This method provides a general analytic solution for Mohr's envelopes and is applicable to arbitrary functions which describe the results of triaxial tests. Then, the method is applied to a particular empirical criterion for rockfill materials which has been recommended over a long period of time. Suitable results are obtained from the application of such a method to a set of triaxial data for a particular rockfill material.
This paper examines the applicability of high-resolution multispectral satellite imagery in hydrological and agricultural areas. The applicability was investigated via three QuickBird multispectral images of Osaka, which were acquired during summer and winter 2005-2006. In a supervised classification, shadows of ground obstacles were occasionally misclassified as surface water. This problem could be avoided using summer images and a filter. Vegetations were easily separated from non-vegetation, but separation of agricultural crops from forests was somewhat difficult. NDVI from QuickBird image well described the vegetation conditions in small plot-size fields in Japan. Thus, high-resolution NDVI should be a valuable source for agricultural land and water managements. A sensitivity analysis indicated that atmospheric correction is recommended if absolute value of NDVI is important, although atmospherically uncorrected NDVI is sufficient for relative analysis within a single image.
Author's last experiments revealed that the maximum allowable salinity concentration of irrigation water for the rice plants under permanently flooded conditions was 1800μS/cm in terms of EC (electrical conductivity). They also demonstrated that the rice plants grew healthy at any stage of their growth when the number of stems in each of the brunches was limited to 20. The present research was carried out to investigate if the above mentioned maximum allowable salinity concentration level for intermittent irrigation during the irrigation season would be suitable. Our experiments were carried out by growing rice plants in pots inside a green house from 2004 to 2005. The percolation rate for the second year was set at 5 mm/d in particular. During the period from transplanting time to the end of heading time, the average daily maximum temperatures inside the green house reached 40 degrees Celsius, with evaporation per pot at approximately 4mm/d, and the surface water salinity concentration increased on average to 1.7 times that of the supply water. Under these conditions, damage was observed only during the tilling peak stage. However, the damage was limited to brown discoloration on the first-growth blades in a very small minority. No more damage was observed on the plants at any subsequent developmental stages. Compared to the rice plants supplied with ground water (fresh water), the period required for the plants under control to tiller into 20 stems and to head fully was delayed by only one or two days. The transpiration of the rice plants under control was 4.3 mm/d, which equaled to that of the rice plants supplied with fresh water. The yield survey revealed that the percentage of the ripened grains from the rice plants supplied with fresh water fell by 3% due to the stringent growth conditions caused by the 5 mm/d percolation rate in the year 2005. No significant damage was detected on the rice plants supplied with the salt water through the entire irrigation period. Consequently, suitability of the irrigation water at 1,800μS/cm salinity concentration was verified.