Abstract The need for integrated reservoir system operation become more intense as the demands from the system increase. A deterministic, three-dimensional discrete incremental dynamic programming approach is presented to derive reservoirs system operational planning strategies. The developed H3DP model optimizes the monthly operation of the Hwachon and Soyang Projects on the North Han river and Chungju Main Project on the South Han river. By using the H3DP model, Hwachon project was reevaluated as a component of the upstream multipurpose storage reservoirs in the basin based on 1993 hydrology. This case study demonstrates the practical use of the developed model for the basin multi-reservoir system operation in an integrated, multipurpose fashion.

비점원오염은 하천 및 지하수 수질오염에 많은 기여를 하고 있는 것으로 나타나고 있는 반면에 우리나라에서는 비점원오염에 관한 연구는 상대적으로 미약한 것으로 지적되고 있다. 본 기사에서는 비점원오염에 대한 이해를 증진하고 현장실험연구를 활성화하는 데 기여하기 위하여 미국 등의 선진국에서 실행하고 있는 현장실험방법을 경지단위의 연구, 유역단위의 연구, 그리고 지하수 수질에 관한 연구로 구분하여 고찰하였다. 비점원오염에 관한 현장연구방법, 연구시 중요사항, 고려하여야 할 사항 등에 관한 자료는 'Gale, J.A., D. E. Line, D. L. Osmond, S. W. Coffey, J. Spooner, J. A. Arnold, T. J. Hoban, and R. C. Winverley. 1993. Evaluation of the Experimental Rural Clean Water Project, NCSU Water Quality Group, Biological and Agricultural Engineer-ing Department, North Carolina State University, Raleigh, NC, EPA-841-R-93-005'에 자세히 기술되어 있다.

Abstract This paper presents a heuristic method for optimal design of water distribution system with multiple sources and potential links. In multiple source pipe network, supply rate at each source node affects the total cost of the system because supply rates are not uniquely determined. The Linear Minimum Cost Flow (LMCF) model may be used to a large scale pipe network with multiple sources to determine supply rate at each source node. In this study the heuristic method based on the LMCF is suggested to determine supply rate at each source node and then to optimize the given layout. The heuristic method in turn perturbs links in the longest path of the network to obtain the supply rates which make the optimal design of the pipe network. Once the best tree network is obtained, the frequency count of reconnecting links by considering link failure is in turn applied to form loop to enhance the reliability of the best tree network. A sample pipe network is employed to test the proposed method. The results show that the proposed method can yield a lower cost design than the LMCF alone and that the proposed method can be efficiently used to design irrigation systems or rural water distribution systems.

Abstract [] The prediction of changes in the tidal regime due to the sea dike closure in the Saemankum area was performed using the nonlinear finite element model, TIDE. Based upon an overall comparison of calibrated model results with available field data, the TIDE model behaves well and is good representation of the hydrodynamic of the Saemankum tidal project area. It is shown that the TIDE model does an excellent job of computing the changes of tidal characteristics resulting in sea dike closure in an estuary area.

Abstract A series of permeability tests was performed on the mixtures with specific mixing rates of sand and bentonite using modified rigid-wall permeameter. Sand-bentonite mixtures were permeated by organics, ethanol and TCE. Permeability of bentonite with several mixing rates had a tendency to decrease up to initial one pore volume and permeability was thereafter converged to a constant value. When sand-bentonite mixtures was permeated by water, permeability was decreased at the beginning but it was thereafter converged to a constant. Among several mixing rates, permeability was greatly decreased at 15% of mixing rate. When sand-bentonite mixtures with 15% mixing rate was permeated by ethanol, permeability was about 10 times larger value than permeability of water. Peameability was shown greater values when permeated by TCE (TrichloroEthylene) followed by ethanol. Suitable mixing rate of sand-bentonite for a liner of waste landfills was detected.

Abstract A series of permeability tests was performed on the mixtures with specific mixing rates of sand and bentonite using modified rigid-wall permeameter. Sand-bentonite mixtures were permeated by organics, ethanol and TCE. Permeability of bentonite with several mixing rates had a tendency to decrease up to initial one pore volume and permeability was thereafter converged to a constant value. When sand-bentonite mixtures was permeated by water, permeability was decreased at the beginning but it was thereafter converged to a constant. Among several mixing rates, permeability was greatly decreased at 15% of mixing rate. When sand-bentonite mixtures with 15% mixing rate was permeated by ethanol, permeability was about 10 times larger value than permeability of water. Peameability was shown greater values when permeated by TCE (TrichloroEthylene) followed by ethanol. Suitable mixing rate of sand-bentonite for a liner of waste landfills was detected.

Permeable polymer concrete can be applied to roads, sidewalks, river embankment, drain pipes, conduits, retaining walls, yards, parking lots, plazas, interlocking blocks, etc.. This study was to explore a possibility of using stone dust and heavy calcium carbonate as fillers for the permeable polymer concrete. Different mixing pro-portions were tried to find an optimum mixing proportion of the permeable polymer concrete. The tests were carried out at 20 f 1 t and 60 ${\pm}$ 2% relative humidity. At 7 days of curing, compressive, flexural and splitting tensile strengths and water permeability ranged between 209~246kgf/cm$^2$, 101 ~ l2lkgf/cm$^2$, 36~52kgf/cm$^2$ and 3.076 ~ 4.390L/cm$^3\;^2$/hr, respectively. It was concluded that the stone dust and heavy calcium carbonate could be used in the permeable polymer concrete.

Abstract Over 4.1 billion tons of non-hazardous solid wastes are generated in the United States annually. This equals to about 16 tons of wastes per person, per year. Disposal of the wastes is a national concern due to many factors such as environmental issues, costs, and public views. South Carolina, like many other states, had a home of many military bases which were ordered to be closed. The contaminated soil was vitrified and tested for suitability in the asphalt mixes. For mix design purposes, a total of 75 specimens were made and tested. For moisture susceptibility testing, a total of 32 samples were made and tested. The results indicate that the mixtures made with sample B produced dry and wet that were comparable with the controlled mixture. At this point and with in this limited study, use of 5% of sample B in asphalt mixture is recommended in several applications such as parking lots, walking paths and drive ways.

The interface system, GIS-AGNPS was to be validated with field data from six tested small watersheds ranging from 0.7 to 4.7$km^2$ in size which have steep topography and complex landuses. The model validation involved the calibration of input parameters and component modifications, in efforts to develop a model applicable to general uses for identifying and controlling nonpoint source pollution loads from agricultural watersheds. The simulated direct runoff from AGNPS was in good agreement with the field data for the averaged antecedent moisture conditions or AMC- II. The results differed, however, from the observed for AMC- I or III. A simple empirical relationship was proposed to estimate the curve number for AMC- I or m from AMC- II, which was found to result in simulated runoff close to the observed. The peak runoff relationship at AGNPS was also modified to reflect the watershed conditions and tested satisfactorily with the field data. The simulated sediment yields from the watersheds were fair as compared to the observed. Nutrient loads simulated from the model were different from the observed data. It appeared that the model was incapable of adequate depicting nutrient transport processes at paddy field and other landuses of the tested watersheds. Some modifications may be needed for the accurate representing the processes at paddy field.

The application of nutrients and pesticides to agricultural lands has been reported to contribute to groundwater contamination, which can be explained by preferential flow in lieu of convective-dispersive flow. An one-dimensional numerical model depicting preferential water and solute movement was modified to describe multi-layer flows. The model is based on a piecewise linear conductivity function. By combining conservation of mass and Darcy's law and using the method of characteristics a solution is obtained for water flow in which water moves at distinct velocities in different flow regions instead of an average velocity for the whole profile. The model allows transfer ofqr solutes between pore groups. The transfer is characterized by assuming mixing coefficients. The model was applied to undisturbed soil columns and an experiment site with structured sandy clay loam soil. Chloride, bromide, and 2, 4-D were used as tracers. Simulated solutes concentrations were in good agreement with the soil column data and field data in which preferential flow of solute is significant. The proposed model is capable of describing preferential solute transport under laboratory and field conditions.

Abstract A field experiment of wetland system was performed from August 1996 to August 1997 to treat the domestic wastewater in Chon-Ahn, Korea. The wetland was a subsurface flow type and was consisted of sand and reeds. The theoretical retention time was 2.33 days and the flow was continuous. The performance of BOD, COD, SS, and T-P removal was satisfactory and consistent. The effluent concentrations of BOD and SS met the effluent water quality standards set in Korea for the treatment plant size of interest. However, the performance of T-N was not satisfactory and average removal rate was about 12%. Further research is recommended to reduce nutrients in the effluent. The variation of removal rates with flow distance showed that treatment zone of the first few meters from inlet were more active in reducing concentrations, and removal rates increased gradually thereafter. It implies that series of moderate size of treatment basins might perform better than a long treatment basin. The hydraulic loading rates affected the performance of BOD and COD, but SS was less affected. The effects of pollutant loading rates was not significant for the normal range of domestic wastewater treatment. The effluent concentrations of BOD, COD, and SS did not show much fluctuation while input loading rates varied significantly, which implies that buffer capacity of the wetland system can keep the effluent quality quite stable for normal situation. Overall, the results of the experimental wetland system was encouraging, and it can be considered as one of the practical alternatives for rural domestic wastewater treatment in Korea.

Abstract Best management practices (BMPs) have been applied for erosion control and soil conservation worldwide for many years. BMPs have been expected to result in water quality improvements in rural areas in addition to functioning in soil and water conservation and erosion control capacities. In recent years, interest in control of nonpoint source (NPS) pollution from agricultural areas has resulted in studies of the effectiveness of BMPs for reduction of NPS pollution. In this paper, the physical characteristics and functions of several frequently applied BMPs are reviewed. The effectiveness of these BMPs in reducing nutrients in agricultural runoff is evaluated on the basis of available field studies. Combining several complimentary BMPs into a Best Management System (BMS) typically results in effective reduction of nutrients in run-off from agricultural areas. However, even with implementation of a well designed BMS, it may take more than 10 years to achieve measureable reductions in nutrient concentrations in receiving waters. Thus, BMPs and BMSs should not be considered a quick solution for water quality problems.

This study aims at the development of a mathematical approach for the optimal water allocation in the river basin where available water is not in sufficient. Its optimal allocation model is determined from the comparison and analysis of mathematical programming techniques such as transportation programming and dynamic programming models at its optimal allocation models. The water allocation system used in this study is designed to be the optimal water allocation which can satisfy the water deficit in each district through inter-basin water transfer between Kumho river basin which is a tributary catchment of Nakdong river basin, and the adjacent Hyungsan river basin, Milyang river basin and Nakdong upstream river basin. A general rule of water allocation is obtained for each district in the basins as the result of analysis of the optimal water allocation in the water allocation system. Also a comparison of the developed models proves that there is no big difference between the models Therefore transportation programming model indicates most adequate to the complex water allocation system in terms of its characteristics It can be seen, however, that dynamic programming model shows water allocation effect which produces greater net benefit more or less.

For the efficient operation and maintenance( 0 & M), irrigation facilities were graded on the basis of their indices related to the 0 & M condition and the characteristics of reservoirs managed by Farmland Improvement Association(FIA) were examined. The results obtained are summarized as follows : 1. Characteristics of reservoirs include effective storage capacity, irrigation area, basin area, height and length of bank. Each characteristic is scored by the principle component analysis method. Variables which compose one index are categorized on the basis of their unit and each variable is scored so that the score of each unit sums to 100 for each index. 2. The Optimum MAnagement System of Irrigation Facilities(OMASIF) for Pyoungtaek area was developed by connecting general data of the irrigation facilities to image data. The database system is divided into three tables; LookUp Table, Facility Table, and Image Table. Image Table is again divided into five sub-tables, Image Table, Construction Cost Table, Acreage Table, 0 & M Cost Table, and Specification Table. 3. The evaluating criteria for the 0 & M of irrigation facilities can be established using the OMASIF. Irrigation facilities evaluated as poor state by the criteria should be repaired.

Abstract Agriculture causes 60% of the total nitrogen emissions and 40~50% of the total P emissions to the surface waters in the Netherlands. These high emissions are mainly caused by the large amounts of fertilisers used on Dutch farms. On average, 39kg P/ha and 340kg N/ha are given in excess to the uptake by the crop. The Netherlands follows a strategy of gradual reduction of the nutrient applications to crops. The first two phases were aimed at stabilisation and a gradual reduction of the use of organic manure. The goal of the third phase is to accomplish equilibrium fertilisation in the year 2000. This means that the amount of fertiliser given may not exceed the crop uptake, considering an acceptable loss to the environment. The losses are based upon acceptable emissions, mainly to surface waters. With the average excess rainfall in the Netherlands, the water quality standards are met with a loss of 0.4kg P/ha and 6kg N/ha, much lower than the present excesses of minerals. The challenge for the future is to close the gap between environmentally acceptable and present losses. Equilibrium fertilisation will not solve all problems at short notice. Therefore, additional techniques to reduce nutrient losses are in development. Examples are restoration of buffer strips and wetlands, lowering of groundwater levels, dosing of ferric and aluminium compounds in the soils and several additional measures in eutrophied lakes.

The technique of the calculation for probabilistic functions used in the reliability analysis of agricultural structures is proposed in this paper for adapting the standardization method using a numerical intergration. The proposed standardization method deals with the structures whose deviations of material properties and loads are large such that the deviation range from 20% to 70%. The results computed by the proposed method are compared with those obtained by the Monte Carlo Simulation. Deterministic values such as deflection, stress, obtained by conventional structural analysis can be directly changed to probabilistic distributions by the proposed method.

DO concentration in the aquatic system is important for the water quality management perspective. Water quality model uses available reaeration coefficient (K2) estimation equations in calculating DO, however, they might include inevitable uncertainty that the model output can be less reliable. In this study, the calibrated QUAL2E model for the Passaic River in New Jersey, U.S., was used to examine the effect of K2 estimation equation on the output DO concentration of the river. The model was run with six commonly used equations separately with all the other conditions remained same. The result showed that the output DO concentration profiles varied widely with different equations, and maximum difference was 4.96 mg/L for the same location which is unacceptably large. It implies that the development of reliable equation is required for proper water quality management. The unreliable model output can lead to a wrong decision in water quality management such as unnecessarily high or too low treatment of wastewater, which will cause serious effect on the community economically and socially in either case. Generating more reliable model output with slight investment to develop a site specific K$_2$ equation can improve the decision making process significantly and is highly recommended.

A CELTHYM(CEll-based Long-term HYdrologic Model), a pre-processor and a post-processor that can he integrated with geographic information system(GIS) were developed to predict the stream flow of a small agricultural watershed. Three kinds of routines, that are watershed boundary extraction routine(WBER), curve number calculation routine(CNR) and maximum available soil moisture calculation routine(MASR) composed pre-processor that was nicely interfaced with CELTRYM and GIS. Two kinds of routines, grapher and map composer composed post-processor that was well adapted CELTHYM output to chart making and GIS map making. The developed pre-post processor was useful for the GIS integration and spatial comprehension of the CELTHYM output.

This study was initiated to build runoff plots, install soil and water quality monitoring systems and collect background data from the plots and neighboring soils as the 1st year study of a 5 year project to assess soil quality and develop the management practices for environmentally sound agriculture in mountainous soils. Eleven $3{\times}15m$ runoff plots and monitoring systems were installed at a field of National Alpine Agricultural Experiment Station to monitor soil quality and discharge of nonpoint source pollutants. Corn and potato were cultivated under different fertilizer, tillage and residue cover treatments. The soil has a single-layered cluster structure that has a relatively good hydrologic properties and can adsorb a large amount of nutrient. Concentrations of T-N, $NH_4$-N, and $NO_3$-N of surface soil sampled in the winter were relatively high. Runoff quality in the winter and thawing season in the spring was largely dependent on surface freezing, snow accumulation, temperature, surface thawing depth and so on. Runoff during the thawing season caused serious soil erosion but runoff quality during the winter was relatively good. Serious wind erosion from unprotected fields after the fall harvest were obserbed and best management practices to reduce the erosion need to be developed.

Pile load test is good for estimating pile bearing capacity, but using this method is limited by time and cost required. Dynamic and static method is more convenient and economical, but confidence of estimated value by dynamic and static method are lower than that of pile load test. After being compared pile bearing capacity data obtained from pile load test with those of other two methods, the results from this study were summarised as follows. For allowable bearing capacity values greater than 175t per pile, bearing capacity acquired from static method was higher than that acquired from pile load test, whereas bearing capacity acquired from pile load test was higher than that acquired from static method for values under 175 per pile. It was that variance of bearing capacity was large when bearing capacity obtained by dynamic method was higher than 250t. Also bearing capacity based on dynamic method was higher than that based on pile load test. Allowable bearing capacity get from dynamic method suggested that carefull precautions are necessary in application for allowable bearing capacity values higher than 2S0ton per pile.

This study was performed to evaluate the drain runoff characteristics from one paddy field, and to provide the basic data required for the determination of flood discharge and unit drainage water for drainage improvement and farmland consolidation. For this purpose, under the assumption that drain discharge from paddy field was similar to outflow of reservoir, runoff model based on storage equation was applied to the experimental field, and simulated results were compared to the measured discharge at weir point. To estimate effective storage volume of paddy field with water depth, 4 regression formula were examined such as linear, exponential, power, and combined. From the observed runoff characteristics, it was shown to be 3.3~16.3${\ell}$/sec in weir discharge, 57.2~98% in runoff ratio, and relative error of simulated result was 3.0~39.4%, 8.5 ~56.0 % for peak flow and runoff ratio, respectively. Curve number by SCS method was calculated as mean value of 96.4 using measured rainfall and runoff data, it was considered relatively high because paddy field has generally flooding depth contrary to the upland watershed area.