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The investigation of watershed time of concentration equations and kinematic-wave based geomorphic instantaneous unit hydrograph
|Authors: ||Nai-Chin Chen|
|Contributors: ||NTOU:Department of Harbor and River Engineering|
Time of concentration;KW-GIUH;channel width;channel roughness;rainfall intensity
|Issue Date: ||2011-06-30T07:32:12Z
|Abstract: ||本研究首先針對台灣地區經常使用之集流時間公式，經由水力學的觀點，以數值試驗方式探討此集流時間公式之合適性。研究中發現，角屋公式較能提供合理的集流時間推估值，Kirpich公式與Rziha公式有低估集流時間之情形，而水土保持技術規範(1996)中所列之公式則有高估集流時間之情形。研究中同時應用運動波理論，配合V型漫地流模型，分析集水區之集流時間值。研究結果顯示，由於此V型運動波集流時間公式已考慮集水區中之糙度、降雨強度與幾何因子，且將集水區分為渠流與漫地流不同的逕流機制，因此所推求之集流時間值與相關係數分析方式所推求者最為接近。 有鑑於早期運動波－地貌瞬時單位歷線模式之架構，其河寬與糙度係數之推求方式，未能適切反應其空間變異特性；且模式往往無法合理反應高強度且不均勻降雨事件之逕流情形。因此本研究將原模式中河寬線性遞減之假設，修正為河寬與上游集水面積之指數關係；且藉由渠流坡度之指數關係，以推求糙度係數由上游往下游之遞減情形。研究中並改變推求瞬時單位歷線過程中，降雨強度值之輸入方式。研究結果顯示，上述之模式修正方式，能獲得較佳的模擬結果。|
The objective of this study is to investigate the adequacy of the time of concentration (Tc) equations frequently applied in Taiwan. Series numerical tests were used to investigate the applicability of the Tc equations from the hydraulic viewpoint. The results show that the Kadoya equation can, in general, provide a reasonable estimation for the time of concentration. However, the Kirpich equation and the Rziha equation always give a lower estimate, and the Soil Conservation Handbook equation (1996) usually yields a higher estimate. The V-shaped kinematic wave Tc equation is also applied in this study for analysis. The results indicate that the V-shaped kinematic wave Tc equation can adequately account for the watershed hydrologic and geomorphic conditions, because the runoff process has contained the overland-flow state and the channel-flow state, and the equation includes the factors of watershed geometry, roughness condition, and rainfall intensity. Therefore, the time of concentration obtained by the V-KW equation was closer to that obtained by the correlation analysis. Since channel width and channel roughness used in the KW-GIUH model (Lee and Yen, 1997) couldn’t adequately reflect watershed characteristics, and the model couldn’t well simulate runoff resulting from concentrated heavy rainstorms, the assumptions adopted in the KW-GIUH model were examined. A linear variation of the channel width from upstream to downstream adopted in previous model was changed to a power function of the watershed contributing area. Since the bed load diameter of the channel was usually decrease from upstream to downstream, variation of the channel roughness coefficient was set to relate to the local slope of the channel reach. The way of choosing the temporal rainfall intensity to generate the IUH was revised based on the concept of the watershed time of concentration. The rainfall-runoff simulation results from the revised KW-GIUH model showed better simulations than the original model.
|Appears in Collections:||[河海工程學系] 博碩士論文|
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