| 摘要: | 本文提出之都市雨水下水道設計模式，包括雨水下水道管渠及滯洪池兩部份，其中管渠部份之設計模式係將設計雨型之概念融入合理化公式，藉由一場設計雨型之降雨降落在都市雨水下水道之各集水分區上，以合理化公式估算各集水分區之單位流量歷線，做為起始管渠設計之依據，下游管渠之流量歷線則藉由稽延時間（lagging time）予以合成，再做為下游管渠設計之依據。由案例探討得知，當雨型型式為中央式時，管渠中之尖峰流量為最大，後峰式次之，而前峰式最小。雨型之延時為三倍單位降雨時距時，管渠中之尖峰流量已達最大值，延時超過三倍單位降雨時距後，管渠中之尖峰流量已不再增大。 由於國內缺乏雨水下水道之實測流量資料，而僅有淹水深度之資料，以致無法直接驗證融入設計雨型之設計模式其精確度，鑑於SWMM模式於國內曾被驗證許多地區之淹水深度，其可信度可被接受，經以SWMM模式模擬水位之案例予以比較，融入設計雨型之合理化公式較SWMM模式之水位要低，平均差值為5.8%，另再以合理化公式法設計之案例予以比較，融入設計雨型之合理化公式較合理化公式法之流量為高，平均差值在2.0%以下，由此足證融入設計雨型之設計模式其可信度可被接受。 融入設計雨型之合理化公式設計模式，可以解決合理化公式僅能推估尖峰流量而無法提供流量歷線之缺點，其推估之流量歷線除可作為雨水下水道管渠設計之用，同時亦可作為推估滯洪池所需之容量。此外，融入設計雨型之設計模式所需基本資料與合理化公式法相同，於應用上甚為便利，且融入設計雨型之設計模式不僅可應用在僅有幹線之雨水下水道系統，亦可應用在具有幹線與支線之雨水下水道系統。 關於滯洪池設計模式之無因次化，在簡便法、水庫法與逐步法三種方法當中，簡便法係國內規範所規定之方法，其入流量歷線及出流量歷線皆設定為三角形，入流量歷線之基期愈長，滯洪池所需容量愈大。水庫法之入流量歷線則為無因次化之任意形狀，水理模式以無因次化之水文平衡方程式演算，當入流量歷線為無因次化三角形時，由無因次化理論分析得知滯洪池所需容量與三角形之特徵值α(α為尖峰入流量到達時間tp 與基期tb之比值，α= tp / tb)相關，當α值愈大，則滯洪池所需容量愈大。 經以無因次化理論分析簡便法後，當入流量歷線同為無因次化三角形時，簡便法較水庫法所推估之滯洪池容量要大，當α=1/6∼α=5/6，簡便法為水庫法之1.32∼1.02倍。逐步法其水理模式係以水文平衡方程式演算，入流量歷線則由設計雨型推導而得，由於雨型之型式與延時相互影響，導致入流量歷線之形狀不一，因此逐步法無法予以無因次化，惟就逐步法原有模式而言，經由案例之探討得知，設計雨型之尖峰降雨發生時間愈晚，滯洪池所需容量愈大，亦即後峰式有最大之滯洪容量，中央式次之，前峰式最小。當雨型延時超過1小時，滯洪池所增加之容量已不及3%。 本文最後提出複式滯洪池及其設計模式，其構造為在滯洪池內隔間出一小池與大池，並於牆底設置單向式閘門，利用小池於入流量之初期即可排除較多之水量，而達到節省容量之功能，小池之容量係採用水文平衡方程式推估，大池之容量則為小池滿溢過來之總水量，由無因次化理論之探討得知，當入流量歷線為三角形時，複式滯洪池較傳統滯洪池所節省之容量與三角形入流量歷線特徵值α和尖峰流量降低值Q*( Q*為尖峰出流量qp與尖峰入流量ip之比值，Q*=qp/ip)有關，當α值愈大時，所節省之容量愈多，且當Q*值愈大時，所節省之容量亦愈多。另由融入設計雨型之合理化公式法與滯洪池設計模式串聯應用之案例探討得知，當降雨延時為一小時，傳統滯洪池以後峰式所需之滯洪池容量最大，中央式次之，前峰式最小，而複式滯洪池於前峰式時節省47.3%容量，中央式時節省51.0%，後峰式時節省57.5%，此結果與入流量歷線為三角形時之結果一致，亦即當特徵值α愈大時，所節省之容量愈多。由於複式滯洪池較傳統滯洪池所需容量減少甚多，於雨水下水道工程上具有實用價值。 The urban storm sewer design model proposed in this dissertation analyzes conduits and detention ponds. The approach in analyzing conduits is developed from the Rational Formula incorporating design hyetograph. Given a rainfall event of design hyetograph falling in all subcatchment, the unit hydrograph of each subcatchment evaluated by the Rational Formula is applied to design the initial conduit. The downstream discharge hydrograph of conduit is synthesized by the mean of the lagging time to be used in designing the downstream conduit. For a case study, the peak flow in conduit are the largest, the middle and smallest, for the central peak type, the later peak type and the early peak type of rainfall pattern, respectively. It is found that the maximum peak flow in conduit occurs in the case that the duration of the design hyetograph being three times of the unit rainfall interval. Due to the lack of actual discharge measurements, the result calculated by the SWMM model for several regions in Taiwan are employed to verify the confidence of the proposed model. The difference between the water depth, as well as discharge, calculated from the proposed model and that obtained from the SWMM model is insignificant. This model, incorporating the Rational Formula and design hyetograph overcomes the defect of the Rational Formula alone. The Rational Formula provides only the peak flow, while this model provides the complete discharge hydrograph. Not only it can be applied to design the conduit of sewer, but also to design the detention pond. Furthermore, this model, requires the same traditional fundamental data, is convenient to be applied for a system of trunks and branches of sewer conduits. The second part of this dissertation discusses the dimensionless approaches in the model of detention pond sign. Currently three methods, namely, the Simple method, the Reservoir method and the Progress method, are used to evaluate the volume of the detention pond. The Simple method is mandated by the authorities in Taiwan. The triangular hydrograph of inflow and outflow, are assumed in the Simple method. In the Simple method, the longer the base time of inflow hydrograph is, the larger the volume of detention pond is required. As for the Reservoir method, a dimensionless arbitrary shape inflow hydrograph can be applied. The Reservoir method is routed by a set of dimensionless equations based on hydrologic balance. In the case when the shape of inflow hydrograph is triangular, the volume of detention pond is subject to a characteristic value, α (α= tp / tb, tp being the peak reaching time of inflow hydrograph , and tb being the base time.). The larger value of α is, the greater the volume of detention pond is required. Furthermore, the Simple method is analyzed by the dimensionless theorem. For a triangular shape of dimensionless inflow hydrograph, the result shows that the volume of detention pond evaluated by the Simple method is larger than that by the Reservoir method. It is found that when the characteristic value α is between 1/6 to 5/6, the volume of detention pond evaluated by the Simple Method is 1.32 to1.02 times that evaluated by the Reservoir method. Moreover, the Progress method is routed by a set of hydrologic balance equations, and the inflow hydrograph is derived from design hyetograph. So the Progress method cannot be analyzed by the dimensionless theorem. For a case study of the Progress method itself, the result shows that the later the peak rainfall time of design hyetograph is, the greater the volume of detention pond is required. In other words, the volume of detention pond is the largest, the middle and smallest, for the later peak type, the central peak type and the early peak type, respectively. As the duration of design hyetograph exceeds one hour, the increasing volume of detention pond becomes insignificant. The final part of this dissertation proposes the concept and the design approach of a double detention pond. The structure of double detention pond is to add a separate pond within the traditional detention pond and install a set of one-way gates. The puny pond can release water quickly at the early stage during the inflow. The volume of the puny detention pond is evaluated by the equations of hydrologic balance, and the volume of huge detention pond is evaluated by computing the overflowing water from the puny pond. According to dimensionless analysis, for the triangular inflow hydrograph, the volume of double detention pond is subject to the characteristic value α and the peak reducing value Q*( Q*= qp/ip, qp being the peak of outflow hydrograph, ip being the peak of inflow hydrograph). The larger the value of α is, the more the saving volume of double detention pond is. Moreover, the larger the value of Q* is, the more the saving volume of double detention pond is. A case study shows under 1-hr duration of design hyetograph, the volume of traditional detention pond is the largest, the middle and the smallest, evaluated by the later peak type, the central peak type and the early peak type of rainfall pattern, respectively. Furthermore, the saving volume of double detention pond is 47.3%, 51.0% and 57.5%, for the early peak type, the central peak type and the later peak type of rainfall pattern, respectively. Similar result is also identified for the case of a triangular inflow hydrograph. |
