伊都キャンパス内5号調整池における水環境特性の定量化

概要

論文の詳細を見る
The water quality of the no. 5 regulation pond at the Ito campus of Kyushu University has deteriorated because of the overloading of organic matter including a large amount of humic substancederived from the deforested wood chip. The reservoir has water quality problems, such as generation of anoxic water mass, decrease in transparency, and deposition of colloidal sediment. Therefore,analysis of the dynamic changes in water quality is important for the maintenance and improvement of the no. 5 regulation pond. In this study, the characteristics of the water area were quantitatively estimated on the basis of the 3 research subjects as the first step for analyzing the dynamic changes in water environment by using the water quality prediction model. These subjects included modeling the vertical turbulent diffusion coefficient, estimation of inflow loading of organic matter, and the evaluation of the effects of the bottom sediment on water quality. First, the temporal and vertical profiles of water temperature were measured in summer, and then, the vertical turbulent diffusion coefficients of the stratified water body were calculated by using a vertical one-dimensional diffusion equation based on the observation data. The model equation for the coefficient could be represented by the stratification function using the local Richardson number, and its validity was assessed on the basis of the relations between the calculated results and observed values. Second, inflow loading for 3 water quality parameters?dissolved organic carbon, total nitrogen, and total phosphorus?was measured at 2 box culverts through which water containing a large amount of organic matter, including humus, from the drainage basin mainly flowed into the no. 5 regulation pond. These measurements were used to derive the accurate L-Q equations for each water quality parameter in both types of drainage. Further, the characteristics of inflow loading were found to differ according to the water quality parameters and the location of the box culverts. Finally, the measurements for the physico-chemical characteristics of the bottom sediment showed that the concentration of total phosphorus was relatively high and that concentrations of total nitrogen and hydrosulphide were low. In addition, the oxygen transfer coefficient was calculated by using the Hosoi’s model based on the physical properties of the sediment, such as specific gravity, representational grain size, water content ratio and ignition loss, and the representative value s of oxygen consumption could be estimated for summer and autumn.九州大学伊都キャンパス内の5号調整池では、夏季に貧酸素化・無酸素化が発生するなど、顕著な有機汚濁現象が見られる。水環境学的アプローチによるモデル解析を通じて、このような水域の水質環境を論じる場合、そのダイナミクスと直接的に関わる鉛直渦動拡散係数のモデル化、有機汚濁物質の流入負荷量の算定、および底質が水質環境に及ぼす影響の定量的評価が具体的な課題となる。本研究では、5号調整池を対象とした水質予測モデルによる水環境動態の解析精度の向上に資するべく、現地観測に基づいて上記3つの課題を検討し、鉛直渦動拡散係数、流入負荷量、底質環境の3つの視点から対象池の水環境特性の定量化を行った。水質の鉛直分布に関する集中観測を実施し、現地観測で得られた水温鉛直分布と日射量のデータにより、鉛直1次元拡散方程式を用いて鉛直渦動拡散係数を逆推定した。さらにその鉛直分布を局所リチャードソン数による成層化関数でモデル化したところ、5号調整池に対応した鉛直渦動拡散係数の良好な評価式を得た。5号調整池に流入する2つのボックスカルバートを対象に、DOC、TN、TPを指標とする有機汚濁物質の流入特性をL-Q式ならびにC-Q式で評価した。その結果、両ボックスカルバートで3つ水質項目に関する良好なL-Q式が得られた。また、ボックスカルバートと水質項目よる有機汚濁物質の流入特性の違いをL-Q式およびC-Q式より見出せた。さらに、PAC剤による汚濁処理施設のDOC負荷量の低減に対する有効性が示された。5号調整池の底質調査の結果、ヘドロの堆積を確認できたとともに、底質中のリン含有量が相対的に大きい結果を得た。また、細井ら(1992)の酸素消費予測モデルを用いて、底質調査から得られた物理的特性値を基に、底質の酸素消費速度を算定した。さらに、5号調整池の夏季ならびに秋季の代表的な酸素移動係数を推定した。
2010-10-29

伊都キャンパス内5号調整池における水環境特性の定量化

スポンサーリンク

概要

著者

関連論文

スポンサーリンク