Ray-Shyan Wu

A simulation model for investigating the effects of rice paddy fields on the runoff system

Rice production in Taiwan is likely to decrease because of two major threats: an increase in the industrial demand on water resources and cheaper imported rice resulting from the free trade policy which will be enforced when Taiwan joins the World Trade Organization. A shrinkage in rice paddy acreage raises environmental concerns, especially in relation to water conservation. Besides rice production, the existence of paddy fields promotes groundwater recharge and remediates floods. Unlike rice production, the value of the environmental conservation is difficult to quantify. In this study, the effects of paddy fields on groundwater recharge and flood remediation have been investigated. To assess the long-term significance of these effects, the study team developed a model based on hydrologic equilibrium. This model describes the performance of water recharge and detention. According to a case study, the amount of runoff from a rice paddy field is about 27% of the amount of the precipitation. This percentage is significantly lower than that of the runoff from a dry farming field, which is normally as high as 55% of the precipitation. In this case, the amount of evapotranspiration from a rice paddy field and that from a dry farming field are 56% and 31%, respectively. In this case, the amount of recharge from a rice paddy field, 17%, is higher than that from a dry farming field, which is 14%. Clearly, a significant increase in runoff and a decrease in groundwater recharge can be expected when a rice paddy field is converted to other uses. The second analysis includes an event-based simulation study regarding the effects of rice paddy fields on the flood peak. Attributed to its superior detention capacity, a paddy field typically has a much lower flood peak, about one third of a dry farm field. These positive effects of rice paddy fields on runoff should be considered in making decisions about the reduction of rice cultivation.

Development of a Methodology for Strategic Environmental Assessment: Application to the Assessment of Golf Course Installation Policy in Taiwan

Some countries, including Taiwan, have adopted strategic environmental assessment (SEA) to assess and modify proposed policies, plans, and programs (PPPs) in the planning phase for pursuing sustainable development. However, there were only some sketchy steps focusing on policy assessment in the system of Taiwan. This study aims to develop a methodology for SEA in Taiwan to enhance the effectiveness associated with PPPs. The proposed methodology comprises an SEA procedure involving PPP management and assessment in various phases, a sustainable assessment framework, and an SEA management system. The SEA procedure is devised based on the theoretical considerations by systems thinking and the regulative requirements in Taiwan. The positive and negative impacts on ecology, society, and economy are simultaneously considered in the planning (including policy generation and evaluation), implementation, and control phases of the procedure. This study used the analytic hierarchy process, Delphi technique, and systems analysis to develop a sustainable assessment framework. An SEA management system was built based on geographic information system software to process spatial, attribute, and satellite image data during the assessment procedure. The proposed methodology was applied in the SEA of golf course installation policy in 2001 as a case study, which was the first SEA in Taiwan. Most of the 82 existing golf courses in 2001 were installed on slope lands and caused a serious ecological impact. Assessment results indicated that 15 future golf courses installed on marginal lands (including buffer zones, remedied lands, and wastelands) were acceptable because the comprehensive environmental (ecological, social, and economic) assessment value was better based on environmental characteristics and management regulations of Taiwan. The SEA procedure in the planning phase for this policy was completed but the implementation phase of this policy was not begun because the related legislation procedure could not be arranged due to a few senators’ resistance. A self-review of the control phase was carried out in 2006 using this methodology. Installation permits for 12 courses on slope lands were terminated after 2001 and then 27 future courses could be installed on marginal lands. The assessment value of this policy using the data on ecological, social, and economic conditions from 2006 was higher than that using the data from 2001. The analytical results illustrate that the proposed methodology can be used to effectively and efficiently assist the related authorities for SEA.

Meteorology-hydrology study targets Typhoon Nari and Taipei flood

Typhoon Nari struck Taiwan on 16 September 2001, taking 92 lives. Analysis reveals that the storms heavy rains were due to warmer ocean temperatures, Naris unique track and slow-moving speed, and the terrain of Taiwan. Analysis further suggests that the heavy rains in Nari contained many small raindrops. The typhoon rains overwhelmed existing flood protection capacities downstream of the Chi-Lung River in a part of Taipei that has no regulatory reservoirs, resulting in major flooding. Preliminary findings underscore several key issues for future study, the goal of which will be to improve quantitative precipitation estimation/prediction, hydrologic modeling, and flood prediction.

Eutrophication Modeling in Shihmen Reservoir, Taiwan

Abstract Based on the measured data, including total phosphorus, chlorophyll a, and Secchi disk depth, the Shihmen Reservoir in the state of mesotrophic to eutrophic. A two-dimensional, laterally averaged, finite-difference hydrodynamic, and water quality model was applied to simulate water quality conditions in the reservoir to determine appropriate strategies for the management of water quality. Data collected in the field for a two-year period were utilized to calibrate and verify the model. The model calibration and verification were achieved with water surface elevation, temperature, and water quality constituents such as nutrients, dissolved oxygen, and chlorophyll a. Then the model was used to simulate chlorophyll a concentrations under several scenarios corresponding to various waste load reduction ratios. A 90% reduction of nutrient loadings will upgrade the existing eutrophic/mesotrophic conditions to oligotrophic condition in both 2001 and 2002, exception January in 2001. The modeling effort had yielded valuable information that can be used by decision maker for the evaluation of different management strategies of reduction of nutrients coming from the catchment area.

Simulation model for investigating effect of reservoir operation on water quality

Abstract This paper investigates the effect of reservoir operation on downstream water quality. This is accomplished by the following procedures. An automated channel network extracting system, C-NES, is used to extract channel network from Digital Elevation Model and a distributed rainfall-runoff model is adopted to estimate the streamflows. The relationship between water quality and streamflows is established. Subsequently, a reservoir water quality model, WASP, is employed to predict water quality under several sedimentation conditions and operation policies. Different reservoir operation rules are simulated to address the possibility of maintaining water quality through proper operation. The watershed of Ta-Chi Reservoir in Taiwan is chosen as a case study. The simulation results show that an appropriate operation rule can improve outlet water quality by releasing water from a certain depth in the reservoir. This is because the flow field that influences the bio-chemical reactions is altered. It is suggested that careful consideration of the outlet positions should be included in the future design and operation of a reservoir.

Electro‐kinetic removal of oil from a contaminated soil

Abstract An electro‐kinetic method which combined effects of electrophoresis, electro‐osmosis, electrolysis, and ion exchange, was evaluated for the removal of crude oil from a contaminated soil. A field test was designed to evaluate the removal process and to measure physical and chemical changes which occurred in the soil as a result of electro‐kinetic treatment. A lot of 12m × 5m × 1m was used for the field test and a DC power of 110V was applied. The observations of the test are physical and chemical changes in soil, pH value at electrodes, discoloration of the surface soil, and the oil content in soil. Testing results indicated that the electro‐kinetic treatment induced a hydraulic gradient that helped most of the lighter hydrocarbons in crude oil be removed from the soil within three weeks. The pH values of 2.5 at the anode and 11 at the cathode were measured and indicated that the reduction and oxidation processes occurred as expected.

Modification of generalized watershed loading functions (GWLF) for daily flow simulation

This study modified the generalized watershed loading functions (GWLF) model, and applied the modified model to simulate the water flow of the catchment area of the Lan-Yang River, by entering the current status of land use, hydrological data, and meteorological data into the model. This modified model took soil resistance into consideration when calculating evapotranspiration and added the parameters of moisture content in the unsaturated zone and hydraulic conductivity to calculate percolation. This model also considered the percolation that directly penetrated into the saturated zone. The modifications enabled the GWLF model to simulate the nature of daily stream flows. The results indicated that the modified GWLF model could improve the calculation of percolation and evapotranspiration in the unsaturated zone for the dry season. Because percolation enhanced groundwater flow, we adjusted the underestimations for low-rainfall periods to simulate the daily stream flow. The results showed that the modified GWLF model was appropriate for simulating not only monthly, but also daily stream flows.

Predicting Hardness of Four Groundwater Monitoring Stations in Kaohsiung City of Taiwan Using Seven Types of GM (1, 1) Model

In this study, seven types of first-order and one-variable grey differential equation model (abbreviated as GM (1, 1) model) were used to predict the hardness of four groundwater monitoring stations in Kaohsiung City of Taiwan. The mean absolute percentage error (MAPE) was used to evaluate the predicting performance. The results indicated the minimum MAPE of 4.71 %, 3.15 %, 2.66 %, and 16.63 % could be achieved when predicting hardness of Fonsi, Datung, Shaukang, and Chihsien stations, respectively. According to the results, it revealed that GM (1, 1) was an efficiently early warning tool for providing groundwater quality information to the competent authority.

Assessment of Man-made Ponds on Flood Retention and Water Resources Management

The purpose of this study is to evaluate the applicability of man-made ponds on assisting regional water resources management. The domain of interest is the water supply district of the Shihmen Reservoir, especially the water straitened Taoyuan area in northern Taiwan. To overcome the shortage of irrigation water in the past, numerous man-made ponds were excavated in the Taoyuan area to storage water in wet days. Due to the development of industry and economics in recent years, some farmlands were replaced by buildings and plants and the agricultural purposes of these man-made ponds have no longer existed. However, flooding and drought are still two natural hazards frequently invading this area. The possibility of given new functions to past man-made ponds will be explored in this study. Field investigation will be conducted to identify the drainage area, connecting canals, and the associated farmland sizes for selecting target ponds for further analyses. Hydrological analyses will be conducted to evaluate the capability of using man-made ponds for flood retention. System dynamic simulations will be performed to evaluate the feasibility of man-made ponds on assisting water resources during drought, as well as the possibility of applying natural purification mechanisms to improve the water quality of man-made ponds.