A finite element model of transient groundwater flow is coupled with genetic algorithm to solve the problem of determining an optimal aquifer yield. The model is applied to a shallow depleted leaky phreatic aquifer of Comilla region, Bangladesh. The amount of leakage is also predicted by this model. The whole study area is sub-divided into six small regions to get distributed optimal discharge and leakage for a droughty period. The model suggests that the present pattern of discharge ranges from 31.6 to 131.0 mm in different sub-areas, and that the optimal pattern of discharge ranges between 44.8 mm and 113.1 mm. Only 9.2 percent of overall cut-off of water withdrawal from the present level of utilization with some modified water use pattern from each sub-area could effectively solve the problem of water levels going below the suction limits which make suction lift pumps inoperative. According to the model, the amount of leakage of six months in different sub-areas ranges from (+) 30.6 to (-) 37.6 mm which has very significant role in controlling the discharge pattern. The estimated irrigation water requirement from the upper leaky phreatic aquifer is 207.2 mm, while the present level of discharge, obtained by the model, is 406.6 mm. This indicates that 96.2 percent higher water is being withdrawn from the upper aquifer with serious water management problems. The results show that the methodology employed is very effective and efficient to obtain global optimal solution to the problem.

View full abstract

Soil losses were measured from ridge models for Kuroboku soil simulating crop row with and without cabbage under simulated rainfall. Our observations suggested that soil losses from the ridges were mainly caused bysplash erosion due to direct impacts of raindrops on the soil surface. The soil loss rate increased proportionallyto the approximate square to the rainfall intensity and to the side-slope steepness. The soil loss decreased with the cabbage growth. The effect of the cabbage plant on the soil erosion rate could be described as a linear function ofcanopy cover ratio. Furthermore, observed ridge erosion dataon the field plots with natural rainfall indicated thevalidity of the linear function.

View full abstract

The flow pattern and the coefficient of discharges were examined experimentally in the hybrid-type fishway (width B=0.8m, slope I=1/10) consisted of a recutangular notch (b=0.2m) at the center wall and a triangular type weir at the either wall (1: 7). As regards to the flow pattern, when the value of L/PL (L=horizontal distance until the drop point of nappe, PL=horizontal pool length) becomes more than about 0.3, the central flow formed stream type in the case of PL/B=0.46. Regarding the pool type flow, the coefficient of discharge (C) in the case of flow over only on the notch tends to increase linearly in comparison with C=0.6 by the effect of approaching velocity, when the value of L/PL becomes above 0.3. On the other hand, the the flow over on the triangular type weir of the pool-type flow tends to be approximate to flow over a triangle weir and the experimental equation can be obtained in the pool type flow.

View full abstract

A flow regime was examined experimentally in the Hybrid-type fishway (width B=0.8m, slope I=1/10) consisted of a recutangular notch (b=0.2m) at the center wall and a triangular type weir at the either wall (1: 7). Hydraulic characteristics in the pool of the fishway were understood by three-dimensional distribution and two-dimensional distribution of velocity in the case of both a pool-type flow and a stream-type flow. Especially, as regardsto the flow regime in the stream-type, at the center traverse section, the quasi-smooth flow which was occurred by linearly flow from the notch and the rotate flow to upstream direction at the down stream of the notch were formed.On the other hands, over flow on the triangular type weir formed the drop flow, the characteristics of this flow type was shown. There, if it was supposed that a value of the application critical velocity was 2m/s-3m/s, and the Froude's similarity was applied at 1/5 contraction scale, it was considered that the maximum discharge of the practical fish way would be 3.0m³/s in the case of PL/B=0.46 (PL=horizontal pool length) which formed the stream-type flow.

View full abstract

This paper aims at analyzing the effect of the farm land consolidation project by using the statistical method. The findings are as follows. Firstly, the land productivity hardly changes, but the labor productivity improves drastically due to the project. As for the capital productivity, the conditions of the productivity change vary in the management scale. Secondly, by the cost-benefit analysis in the project complete area, it is found out that average annual internal rate of return is higher than 4 percent, in spite of being left many small scale farmers in the project area. However, this rate does not reach the rate that presumed at the time of the plan. Thirdly, the important points to improve the cost reduction effect of the project are to accumulate the land on farmers who hope for the scale expansion, to prevent the excessive investment of the agricultural machine, to give priority to the wet or less inclined area, and to constructhe waterway with pipeline system.

View full abstract

The phenomenon of hydraulic fracturing is considered as one of the causes of leakage in fill-type dams. In recent years, it has been found that an estimate of the fracture toughness of a given type of soil could be used as an indicator of the soil's resistance to hydraulic fracturing. One of the problems encountered in its estimation is the assumption that fracture toughness has been theoretically defined for samples of infinite sizes. In this study, laboratory tests were conducted to determine the fracture toughness of samples (of the same size) prepared with initial cracks of various lengths. The main objective was to investigate the effect of the initial crack lengths on fracture toughness. The stress distributions around the crack tips in the laboratory test samples were estimated by the FEM analysis and also by a theoretical equation. The results were compared reasonably well with those of laboratory tests to determine the appropriate length of the initial crack for test specimens.

View full abstract

It is often difficult and requires a lot of data to generate interface element of zero or very thin thickness. In this paper a method, which automatically determine joint/interface element positions, based on material properties of elements is presented. By recording elements around nodal points in a special way, additional nodal points and interface positions are correctly determined. Additional data required is very small. The method is applicable to all one-dimensional and two-dimensional element types and can easily be incorporated into available automatic meshing programs with minor modifications. To check the validity of the method, it was used to generate interface elements of several complicated domains such as in composite materials or geosynthetic reinforced soils successfully.

View full abstract

Crop water requirements (CWR) in the Gezira scheme is estimated by multiplying the long-term average Penmanevaporation (E₀) by the relevant crop factors developed by Adam and Farbrother. The weather data of the period 1966-1993 are collected and used to calculate the monthly E₀ and the CWR. The trend of climate changes is studied with respect to E₀ values. The CWR of the old wheat cultivars are estimated using the average E₀ values of the period 1984-1993 and compared with the actual requirements of the recent cultivars. Results show that the recent climate changes are towards higher E₀ values during July, August and September mainly due to higher vapor pressure deficit resulted from the recent droughts in Africa. The use of the average E₀ of the whole record in the estimation of the total CWR of the Gezira scheme may underestimate the total CWR by 4%(about 210 millions of cubic meters per season) compared with the average E₀ during the period 1984-1993. A good fitting is obtained that relates the monthly E₀ values to the probability of exceedence with coefficients of determination ranging between 0.94 and 0.99. The CWR of the old wheat cultivars is by far different from the actual requirements of the recent ones and hence their crop factors should not be.used to predict the CWR of the recent wheat cultivars in the Gezira scheme.

View full abstract

To clarify the phenomena of resuspension and transport of the bottom sediment in shallow sea area, it is necessary to understand the shear stress acting on the tidal flat surface under the condition that wave and current coexist quantitatively and qualitatively. The purpose of this study is to analyze the shear stress near the bottom wave boundary layer under wave-current coexistent conditions, and clarify the characteristics of shear stress theoretically. Firstly, the velocity distributions and the bottom shear stress under combined wave and current conditions are obtained analytically by using a three-layer time invariant eddy viscosity model for currents and a two-layer time invariant eddy viscosity model for waves. Secondly, the theoretical results of velocity distributions and bottom shear stress are in fairly good agreement with experimental ones. Thus, it is confirmed that the present theoretical analyses are reasonable. Furthermore, on the basis of the theoretical results for shear stress, the relationships between shear stress profiles near the bottom wave boundary layer under combined wave-current conditions or a maximum bottom shear stress and physical parameters in the combined flows are clarified.

View full abstract

We used a model of a stratified paddy field (plow layer, plowsole and subsoil) with the gravel under the plowsole that exist in volcanic ash areas beside flood plains. These models were planted with rice and were fertilized. The models were used to investigate the removal of soluble ions in percolation water under different percolation patterns; the open system percolation and the closed system percolation.
The results are as follows.
In the case of high drainage levels, plow layer, plowsole and subsoil became the closed system percolation and were made into reduction layers. But in the case of low drainage levels, only subsoil became the open system percolation and were made into a oxidation layer. Concentrations of nitrate ion, nitrous ion, iron ion, manganese ion and dissolved oxygen in water of the closed system percolation increased more than those in the open system percolation. Potassium ion concentrations in plow layer and plowsole increased during the 50 days from the start of examination as compared with its concentration in the subsoil. Concentration of the total nitrogen in drainage was higher than those in inundation during 60 days as well as total phosphorus during 30 days. After these periods, the two concentrations were nearly equal.

View full abstract

Unevenness of number of passages of a bulldozer causes unevenness of growth and differential settlement in a field lot. And, we chased a movement of bulldozer in the paddy field consolidation. We recorded a precision run track using the installation which can record run of bulldozer in personal computer automatically. Incidentally this run track record can contain a height in addition to position coordinate, too. As a result, we recorded a moving trace of bulldozer that operate cutting and banking process. We computes operation area of bulldozer of a pixel which divided a paddy field into a mesh as unit, we analyzed an bulldozer's operation record and change in height of every a pixel.
Main results obtained are as follows:
1. There is unevenness of number of passages of a bulldozer in a field lot.
2. A bulldozer isn't working in the same spot repeatedly at same time.
3. Even if laser level bulldozer is used, it is completed in the fixed height through the process of trial and error.

View full abstract

This paper presents a numerical program uniting 1) a finite element program for the saturated-unsaturated seepage analysis and 2) the Rigid Body-Spring Model program for the slope stability analysis. The programhas employed an uncoupled treatment, considering the reduction of the shear strength due to the rain infiltration as the changes of the shear strength parameters with the matric suction. It can predict the change of the safety factor of slopes with considering the reduction of the shear strength due to the rain infiltration for unsaturated zones, and also with carrying out the effective stress analysis for saturated zones. According to the analysis for a model slope, the slope has possibility of collapse due to the reduction of the shear strength near the surface of the slope, even though the ground water table does not develope yet. Also, the greater magnitude of the rain intensity reduces thesafety factor of the slope swiftly.

View full abstract

Drift type buoy equipped with differential GPS (DGPS) was developed as a new observation system for current and water quality in the estuary. The drift type buoy with DGPS will make the current observation such as current direction or velocity and water quality such as turbidity and salinity concentration easy and accurate. This paper reports on the characteristics of the system and its tested results observed in an estuary in the Ariake Sea. Through the observations twice, the system was shown to be useful as a current observation method in an estuary.
The system has the following characteristics.
(1) It is possible to grasp a current direction and velocity in outer layer by the locus of flow of the drift type buoy with DGPS.
(2) The system is useful for the flow elucidation in the fields where two kinds of flows like salt water and fresh water exist.
(3) The system installs two salt concentration sensors and a turbidity sensor, although it is easy to change the sensors to other sensors according to the objectives.
(4) The system is expected to improve the dangerous observation work like in flood.

View full abstract

This study presents an evaluating method of soil moisture tension (pF) prior to irrigation for obtaining maximum yields. Seven crops are grown under three different points of starting irrigation, which are the initial wilting, medium and optimum points. Ratios of consumptive use (CU) to pan evaporation (Epan) per day are computed for test spots obtaining maximum yields under the three. CU/Epan ratios decrease with increase of pF values, each of whichis the last pF of 24 hours for determining CU per day. Two patterns appear on the decrease of CU/Epan. One pattern is that decrease is gentle up to a marginal pF, and then sharp. Four crops show this pattern. The marginal pF values of four crops are verified and recommended for the pF values of starting irrigation to obtain maximum yields, by applying the relationships of CU with yields and real data. Another pattern is that decrease is gradual up to a marginal pF, and then little. Three crops show this pattern, which show small yield reduction under the dry. The marginal pF values of three crops are too low to be applied. It is therefore recommended that pF values of starting irrigation are decided in considering availability of labor and water resource.

View full abstract

The Disdrometer is an instrument for measuring raindrop size distributions continuously and automatically. The instrument transforms the vertical momentum of an raindrop impact into an electric pulse, whose amplitude is a factor in a function of the drop diameter. But the instrument is not able to sense raindrops below 0.3 mm diameter and to measure completely to 1 mm diameter. Raindrop size distribution below 1 mm diameter were estimated by the exponential equation, based on Seino's observed data. In this research, raindrop size distribution and kinetic energy of rainfall were measured at Tsukuba for 2 years and Ishigaki Island for 1 year, and compared to the energy-rainfall intensity equations.
Results:
1) The rainfall intensity measured by the Disdrometer at Tsukuba were less than those measured by ordinary equipment, as those intensity increased. The reason depends on defect of the instrument as mentioned above. On the other hand the rainfall intensity by the Disdrometer at Ishigaki were no less than those by ordinary equipment.
The influence by defect of the instrument was little under wide ditribution of raindrop size.
2) Measured kinetic energy vs. rainfall intensity data were distributed between the upper limit equation by Wischmeier and the lower equation by Mihara.
3) On regional characteristics of Ishigaki, there were large size raindrops below 30 mm/h rainfall intensity and the distribution of raindrop size was wide from 1 mm to 5 mm in diameter, but in Tsukuba the distribution of raindrop size concentrated between 1 mm and 2 mm.

View full abstract

The Toyosawa River, Iwate Prefecture, is one of medium-sized alluvial fan rivers in Japan. There are many rivers with similar size in the Tohoku Area, such as the Shizukuishi River, the Sagae River and etc. These rivers were in almost natural states until the end of the Second World War. Dykes and river bank protections have been gradually constructed and those rivers have changed into compound cross section channels with high water channels. Comparative investigations of many aerophotos taken at interval of nearly ten years from around 1947 make clear not only the above artificial changes but also the natural changes of river channels caused by flood in the Toyosawa River. Natural river changes occur with river bank erosions and disasters. Their locations have close relations to the main courses of flood and colliding banks in each period estimated the formations of alternate bars. The actual states of bank erosions and disasters are checked precisely by field surveys. Through these studies, we will be able to predict the locations of colliding banks more accurately and to prevent bank disasters.

View full abstract

In the landcover classification of the Naze area, Amamioshima, using Landsat-TM and Spot-XS images, forest, urban and coral areas are categorized using core clusters based on sampling data covered by a single image for the whole projected area. However, there have been some problems with the classification accuracy of farmland due to the complex topography of the area.
The purpose of this study was to examine whether national land numerical information is useful for improvement of classification accuracy. We made a core cluster based on a clustering algorithm as supervised data for each mesh sampling, since 1/2 regional mesh data have 8 land use planning categories, such as forest, farmland and urban areas, in each mesh. By using these core clusters for the whole area, landcover classification accuracy was improved for farmland. The effective use of known information, such as national land numerical information, for object area pixels makes it possible to improve landcover classification accuracy.

View full abstract

An in-situ permeability test of soil using a pressure infiltrometer method is introduced and its applicability is examined. The pressure infiltrometer method involves a measurement of a steady-state infiltration rate required to maintain a steady depth of water within a single ring inserted a small distance into the soil. An equation to determine a field-saturated hydraulic conductivity is derived based on an infiltration theory. An apparatus as well as a procedure to measure the steady-state infiltration rate is quite simple. Firstly theoretical aspects of the pressure infiltrometer method are discussed. Two special features of the pressure infiltrometer method, a theoretical treatment of threedimensional water flow out of the ring and a simple assumption of an exponential relationship between unsaturated permeability and pressure head of soil, are established. Then soil data published in the literatures are analyzed and numerical calculations to simulate a constant-head infiltration into soil are conducted to show the assumption of the exponential relationship affects significantly an accurate determination of the field-saturated hydraulic conductivity. It's also shown that values of soil parameter which has been recommended for the exponential relationship of unsaturated soil properties are something higher than real values of soils.

View full abstract

Water resources on small islands depend greaty on coastal groundwater. For the purpose of monitoring and predicting groundwater quality, it is important to analyse seawater intrusion and dispersion processes in these coastal aquifers. This paper describes a numerical method which evaluates the salt concentration distribution in coastal groundwater in response to the tide. Numerical solutions obtained by the numerical method were compared with numerical solutions obtained previously by the finite element method. Tidal effects on the mixing zone between freshwater and seawater were numerically investigated for a two-layered aquifer with different permeability coefficients. The numerical results can explain the behavior of the mixing zone in response to tidal change which was observed under the field condition. It is concluded that this numerical method is a practical one for analysing seawater intrusion and dispersion in coastal aquifers.

View full abstract

The objective of this study is whether or not it is possible to use melting slag from municipal solid waste (MSW slag) as fine aggregate for reinforced concrete products. In this paper, MSW slag made by the coke-bed melting processes was examined. Reinforced concrete products (gutters for roadsides (JIS A 5345) and bench flumes (JIS A 5318)) having a MSW slag replacement rate of 0, 30, 50 and also 70%(by weight ratio) to the fine aggregatewere experimentally produced. As a result, the following results have been clarified:(1) The strength of concrete with MSW slag aggregate was equal to that of the crushed sand concrete.(2) In a high replacement ratio of slag, the freezethaw resistance of concrete with MSW slag aggregate was reduced due to the high amount of bleeding. It is proposed that MSW slag should be used with crushed sand at a replacement ratio of 50% or less.

View full abstract