Application of Real-Time Runoff Model in Mountain Areas Integrated into Disaster Contingency Platform (II)

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Project title

Code/計畫編號

MOST103-2625-M019-002

Translated Name/計畫中文名

即時測預報與多層級應變作為之分析與連結-以易受坡地與洪氾災害之高屏地區為例-子計畫:即時山區逕流模式於災防應變資訊平台之整合應用(II)

Project Coordinator/計畫主持人

Kwan-Tun Lee

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Harbor and River Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=8323635

Year

2014

Start date/計畫起

01-08-2014

Expected Completion/計畫迄

01-07-2015

Bugetid/研究經費

840千元

ResearchField/研究領域

防災工程;土木水利工程

一般洪水預報系統所需之降雨逕流演算模式，可區分為集塊式模擬模式與分佈式模擬模式。集塊式模式係以傳統單位歷線法或簡化的水文概念化模型為基礎，藉以推求集水區出口處之流量歷線。而分佈式演算乃是透過水動力學方程式，以模擬逕流於集水區內之運移情形，故可求得集水區內任一點位置之水深與流量歷線。無論選用上述任一逕流演算方式進行模擬，皆須配合數值高程模式求取模式所需之地文參數。本計畫第二年度之研究方向則為探討不同流向判定機制，對於集水區邊界擷取、地文特性之認定以及逕流模擬結果之影響。由於一般水文逕流模式需明確劃分集水區範圍及判釋河川格點，通常會採用D8流向判定方式進行演算，該法以格點八方位最陡坡降為單一排水方向。然而，過去文獻中已有學者指出單一流向判定法（single flow direction method, SFD）無法描述水流於地表傳遞過程中之擴散特性。有鑑於此，諸多研究學者相繼提出各種流向判定法則，期能透過多出流點機制之考量以彌補其闕漏。本計畫第二年度之研究工作乃是釐清各種流向判定法之計算方式，藉以評估不同判定方法應用於地文參數擷取與逕流模擬演算所存在之不確定性。此外，考量全二維逕流模擬機制已廣泛為水力計算領域所利用，研究中亦一併探討以十字型匯流方式為基礎的D4流向判定法。本年度計畫一共建置五種不同流向判定機制為基礎之數值高程模式（包括：D8 scheme, MD8 scheme, D-infinity scheme, MD-infinity scheme, and D4 scheme），用以劃分集水區邊界、擷取河川網路及探討逕流排水路徑，並且已將其應用至真實集水區中，以分析判釋結果之差異性。此外，研究中藉由一簡易特性指標之建立，設法量化不同流向判定法對於水流擴散特性之描述，進而詮釋前人文獻中，僅以文字敘述方式指出多流向判定法(multiple flow direction method, MFD)適用於水流擴散過程之模擬。本研究成果將能提供模式開發者，瞭解不同流向判定方法應用於逕流演算模式之影響性，並慎選合適之流向判定方式。 The real-time flood forecasting system can be categorized into two types of model for simulations, the lumped runoff model and distributed runoff model. The lumped runoff model is developed to estimate flow hydrographs at a designated location by using a conceptual assumption as well as the conventional method of unit hydrograph. The distributed runoff model is then capable of imitating the phenomenon of flood transportation by employing hydrodynamic equations and deriving the discharge as well as water depth of any location. The application of digital elevation model is required to obtain the geomorphological parameters providing for any of the aforementioned models. The second-year project (2014-2015) aims to realize the influence of different flow-direction algorithms adopted in the DEM on the extraction of watershed boundary, calculation of geomorphological properties and the simulation result of runoff model. By virtue of the competence to clearly delineate the watershed boundary and extract consecutive stream network, the D8 algorithm, assigning the single flow direction to the steepest descent of eight adjacent cells, is most widely used method for hydrological simulations. However, several previous studies have indicated that the single flow direction (SFD) method is incapable of describing the diffusive feature of surface runoff transportation. For this reason, a variety of multiple flow direction (MFD) methods were subsequently proposed to eliminate the deficiency. In this study, the five most widely used methods, the D8, D-infinity, MD-infinity, D4, and MD8 algorithms, for flow-direction determination are implemented to investigate watershed extent, water mass contribution, stream network, and the track of the longest water course. Distinctions of these properties should affect subsequent applications of hydrological analyses, such as the time of concentration calculation and peak discharge estimation. Moreover, a simple index is developed to rank the effects of flow dispersion and flow concentration among the different flow-direction algorithms. The research findings obtained in this study can facilitate to understand the impact of various flow-direction algorithms on the hydrological applications and can provide valuable information for selecting the adequate algorithm used in the runoff simulation models.

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Application of Real-Time Runoff Model in Mountain Areas Integrated into Disaster Contingency Platform (II)

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