Delta progradation, reservoir infill, and deposit removal in idealized and field reservoirs

本論文的主要目標在研究理想水庫中三角洲的發展，水庫淤積過程，水力抽取排砂之方法。本研究以數學理論、數值計算、實驗模型與野外調查測量來闡明三角洲的發展。基於艾克納方程式，利用鏡像方程式安息角的特殊解，推導出可以應用於任意岸線形狀的三角洲前進方程式。這個方程式將應用於數值計算二維三角洲的演化過程，以帶有解析解的在水平底床上發展的逕向對稱三角洲做一個例子，來驗證數值模型的正確性，之後更進一步模擬一個點源供砂在堅硬傾斜底床與固定水位的三角洲發展。我們還進行了小尺度的實驗室三角洲模型試驗，與數值模型進行比較。此實驗為在一個堅硬的傾斜底床上，以點源供砂的方式，來研究三角洲在固定水位的水庫中發展的過程，並佐以雷射掃描的方法來測量三角洲的形狀體積與建立三維的數位高程模型，實驗三角洲上的沼澤區域周長與面積被用來與位於加拿大薩克其萬省莫西河的莫西三角洲比較，數位高程模型可用於分析通過岸線的輸砂量分布。我們選擇了霧社水庫來研究現地的水庫三角洲發展，並進行了四次縱剖面的測量，及收集了歷年的霧社水庫泥砂淤積資料。我們根據擴散方程式，推導出水庫淤積的自相似方程式的解析解，以有限體積法之數值計算來進行比較，並用以模擬現地水庫。為了延長水庫使用壽命，水力抽砂為一項可利用在不需將水庫儲水排光的情況下將泥砂排出水庫的方式。水力抽砂是將水庫底床泥砂以水砂混合的泥漿抽出，並將其輸送到水庫外。此方法的效率高度依賴著泥漿中的泥砂濃度，而泥沙濃度又決定於底床泥砂的壓密程度。為了探討泥砂壓密程度與水力抽砂的濃度關係，我們進行了一系列的小尺度實驗，並利用即時密度計來測量抽砂過程中的泥砂濃度的變化過程，最後利用非黏性選擇抽砂理論來比較實驗結果。最後，我們在地工離心機上進行實驗，期待開創新型的水力抽砂研究方法。The aim of this thesis is to present the curved delta progradation, longitudinal reservoir infill, and hydrosuction removal deposits in idealized reservoir. The mathematical theory, numerical computation, laboratory experiments, and field observations are used to illustrate the delta progradation. Based on the Exner equation expoliting the special properties of solutions to the eikonal euation with the finite angle of repose, we derive a formula for delta front progradation rate applicable to arbitrary shoreline shape. Applying this delta front progradation rate formula, numerical computation results for two-dimensional delta are illustrated as the applications. In a case of the radially symmetrical delta prograding over a horizontal plane, an analytical solution is obtained and comfirms the numerical computation results. An exploring numerical case is to model the delta supplied by a point sediment source prograding over an inclined rigid basement into a basin with a constant standing water level. To compare with the numerical computation results, a small-scale laboratory experiment was conducted. The delta fed by a point sediment source upstrem develops over an inclined rigid basement entering a body of standing water with a constant level. The delta deposits are surveyed during experiments by video imaging of a scanned laser sheet. Through the imaging measurements of the entire delta deposits, a series of formation evolution and DTM are acquired. The characteristics of experimental delta including the perimeter and area of marsh and topset are used to compare to the field landscape of Mossy delta where is in the Mossy River, Saskatchewan, Canada. The DTM results are analyzed to obtain the sediment flux through the shoreline and distribution over foreset. Wushe Reservoir is selected for the field case study site of delta progradation. We surveyed the long-profile including the topset upstream and reservoir bathymetry for four times and collect the sedimentation measurements over past decades. We then derive a simplified theory from the Exner equation to obtain three analytical self-similar solutions for the longitudinal reservoir infill. The numerical computation of finite volume method is applied to compare with analytical self-similar solutions. The simplified numerical computation is used to simulate the field reservoir. To remove the sediment deposits in the reservoir and extend the life of the reservior, the hydrosuction sediment removal which is used to draw water and sediment into pipeline and convey the slurry out of reservoir is an option without empty the entire reservoir. The sediment concentration of the slurry depneds largely on the degree of the sediment consolidation of the bottom deposits. To investigate the influence by degree of sediment consolidation, a series of laboratory experiments were conducted using a small-scale suction pipe equiped with an online densimeter to measure the time evolution of the outflow sediment concentration. An inviscid selective withdrawal theory is applied to compare to the experiment results. Finally, the exploring experiment for hydroscution sediment removal on geotechnical centrifuge provides possiblies for future researches