圖書典藏及影音數位平台

調查烏溪可利用之公有河川高灘地進行現地處理淨化水質可行性分析，期能提高河川自淨作用達成水質改善效果，並可提供多元供水方案以穩定區域供水能力外，另可落實水岸環境改善，提升生態效益與環境營造等多重功效。

This project evaluated the feasibility of using on-site treatment facilities to clarify the river water and replenish the regional water supply. Based on the hydrological analysis of the Wu River basin, we have drafted an algorithm to select the proper sites to install on-site treatment facilities. Summarizing the worldwide examples, the proper process has been selected. Using water quality model, the benefits of clarification has been evaluated. Finally we have proposed a planning of the construction works, the required budget, the evaluation of the influence on the embankment and flood relief, and the water supply scheme to the potential users. The details are described in the following paragraphs below. 1. Background Wu River basin is composed of the main stream of Wu River, Fa-Zi River, Da-Li River, Mao-Luo River, Bei-Gang River and Mei River. Most of the river banks in this basin are used in agriculture. Along the stream of this basin, the orchards and rice paddies are frequently seen on the river bank, where orchards are more common at the upstream and rice paddies are more common at the downstream. According to the monitoring data of Environmental Protection Agency (EPA) Taiwan, 20~49% of the Wu River basin is the unpolluted/slightly polluted level. 37~59% is the moderately polluted. A main reason could be the rainwater run off would bring lots of suspended solids (gravels and clays) into the main stream. On the other hand, the side streams pass through the urban area and may be polluted by the domestic and industrial wastewater. Wu River is the main stream in the central Taiwan. The annual flow rate is 3.72 billion m3. However, only 17% of the water flow has been used as resource. As the water requirement of Changhua Coastal Industrial Park increases gradually, Central Region Water Resource Office has considered a series of schemes, including taking the Wu River water through the Fu-Ma irrigation channel to the Changhua Coastal Industrial Park, as well as establishing the seawater desalination plant. In this project, we consider the scheme that applies on-site treatments to improve the Wu River water quality to elevate the percentage of available water resource. This project summarized ten examples in Japan, United States of America and Germany regarding the river clarification using on-site treatments. The performances of 17 gravel contact treatments and 37 constructed wetlands in Taiwan were also surveyed. Overall speaking, gravel contact treatments perform better than constructed wetlands in water clarification. Constructed wetlands, on the other hand, provide ecological habitats and benefiting the biodiversity in this region. The area of constructed wetlands in Taiwan ranges from 0.35 to 40 hectares, while the treatment capacities range from 350 to 30,000 CMD per site. On the other hand, the area of gravel contact sites in Taiwan ranges from 0.05 to 2 hectares, while the treatment capacities range from 160 to 50,000 CMD per site. Considering a variety of criteria, including the environment, water quality, the target of water quality improvement, economy, the requirement of maintenance, the constructed wetland may be applicable as the basis of on-site treatment facility on the river banks to clarify the water quality. If one would like to set the scheme target not only as the water quality improvement but also the water supply, the constructed wetlands should be further connected with the gravel contact treatment to further elevate the water quality to ensure the supplying stability. 2. Water Quality of Wu-River Basin and the Site Selection of High River Bank The monitoring data show that at the Da-Du bridge station, the pollution is the most serious, where the pollution mainly comes from the domestic and industrial polluted plumes in Da-Li River, one of the branches. At the high flow period, the dilution significantly mitigates the pollution. Only the suspended solids in Mao-Luo River increase due to the strong flushing. Based on the monitoring data, this project used the water quality model, WASP (Water Quality Analysis Simulation Program), to simulate the water quality variation under a variety of flow rate. The results show that when the flow rate is 4.78 CMS lower than the current status, the water quality variation is not significant. For the most quality items, the increase is generally less than 6.0% at the high flow period. In the low flow period, the variations become significant, ranged from 6.0~17.0%. According to the literature, site survey and the one-dimensional hydrological analysis, 23 potential sites of high river bank have been selected. The total area is 384.4 hectares. Among the 23 sites, 5 proper sites have been further identified regarding the surface integrity, flooding frequency and the flushing/movement of river courses, to ensure that these sites will not easily subject to the flood destruction. The five sites are H14, H18 and H17 at Wu River, H23 at Fa-Zi River, and H7 at Da-Li River, respectively. Although the safe sites are selected, it is impossible to completely avoid the flood destruction when setting on-site treatment facilities on the high-river bank. To evaluate the possible destruction, the simulation considered the three scenarios: floods at the 10-year return period, 20-year return period and 100-year return period, respectively, to conduct the two-dimensional hydrological analysis. The results show that under the flood of 20-year return period, the flushing speed in the submerged region is less than 2 m/s and may not cause strong destruction. For the maintenance strategies, the main point would be reducing the flush raised from the facility hardware. For example, to prevent the damage on the river embankment, the on-site treatment facilities should be kept a certain distance (say, 10 m, depending on the pond depth) from the embankment. On the other hand, the house for the controlling facilities and the blower should be set inside the embankment to be away from the possible flooding. To ensure the safety of the facility itself and the river embankment, as well as to reduce the restoration cost, only the required treatment units are planned in the site. The other entertainment and landscape facilities, however, are excluded in this plan. 3. The Benefits and the Capability If the 23 river banks (384.4 hectares totally) have been all selected to set on-site treatment, the facilities may help clean the wastewater from the channels and ditches nearby so that the point and non-point water pollution can be reduced. On the other hand, the river water may be drawn to flow into the facilities for further clarification. In summary, the possible BOD reduction is 9,737 kg/day and NH3-N reduction is 1,069 kg/day. The WASP simulation further confirms the previous evaluation, where the benefit would be more significant at the low-flow period. The reducing magnitude of a variety of pollutant items ranges from 2.6 to 29.9% at the low-flow period and ranges from 0.4 to 6.6% at the high-flow period. The sites H7, H14 and H18 are selected as the possible sites for further demonstration. The main function of H17 is to clarify the water from Da-Li River by using constructed wetlands (capacity 1,200 CMD; construction cost NT$24 million; annual O&M cost NT$2.48 million; restoration cost NT$1.64 million). It takes NT$8.49 to clarify one cubic meter of river water. H14 and H18 are functioned both as river clarification and as water supply, where the water is drawn from Wu River. The treatment facilities are constructed wetland plus the gravel contact treatment. For H14, the capacity is 4,000 CMD, the construction cost is NT$130 million, annual O&M cost is NT$5.25 million, and the restoration cost is NT$6.55 million. For H18, the capacity is 30,000 CMD, the construction cost is NT$750 million, annual O&M cost is NT$27 million, and the restoration cost is NT$38 million. In H14 and H18, it takes NT$8.34 and NT$6.06, respectively, to treat one cubic meter of water for supply. Regarding the water supply, to install the constructed wetland and the gravel contact treatment on the site H18, it may possible provide 30,000 CMD water to supply Changhua Coastal Industrial Park. The possible schemes include: (1) setting a pipe to convey the water from H18 to the industrial park (piping cost NT$7.24/m3); (2) setting a pipe to convey the water from H18 to the downstream of Yu-Pu water gate, and to mix the water from Fu-Ma channel (piping cost NT$5.73/m3); (3) setting a short pipe to convey the water mixed with the water in Fu-Ma channel, and then to convey to the Changhua Costal Industrial park (on the basis of original plan). The third scheme only cost NT$0.69/m3 for piping but the quality of clarified water may be deteriorated by the water from the irrigation channels. Thus the second scheme would be the most suggested one for further promotion. It is suggested that the river management authority may take responsibility to construct the facility if the main function is river clarification. The maintenance may be conducted by the river management authority itself or the local government. It is also possible to assign NGO (non-government organizations) to help the maintenance. On the other hand, if the main function is water supply, the water resource authority (like Central Region Water Resource Office) may initiate the construction. The user should take in charge of the following maintenance. It is concluded that setting on-site treatment facilities on the high river bank along the Wu River basin surely benefits the river water clarification. If the purpose is “water supply”, the stability of supplying amount and quality should be further evaluated. H7, overall speaking, may be a proper site for demonstration and pilot testing.