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|標題:||Development and Application of A Digital Geomorphologic Unit Hydrograph Model
|關鍵字:||digital geomorphologic unit hydrograph (DGUH);數值地形單位歷線;rainfall-runoff;peak discharge;concentration time;rainfall duration;降雨逕流;洪峰流量;集流時間;降雨延時||出版社:||水土保持學系||摘要:||
Development and Application of A Digital Geomorphologic Unit Hydrograph Model
Taiwan region is characterized by steep mountains and torrential streams. The precipitation is unevenly distributed in both space and time. Therefore the natural environmental constraints have made the planning, development, utilization, management and conservation of water resources tough and very difficult. For improved water resources planning and its related engineering, a powerful hydro-geological analysis tool is important and necessary.
Investigations of relationship between rainfall and runoff in watersheds is an important component in hydrological analysis. There have been many linear and non-linear rainfall-runoff hydrological models developed since 1932. However, most of them are often too complicated, physical meaningless or too many assumptions. This study is conducted to develop a digital geomorphologic unit hydrograph (DGUH), which was derived, based on the theory of one dimensional hillside-rampant-flow, firstly with the geomorphologic and hydrological characteristics considered separately and then the in-site terrain and rainfall data were integrated to become a model of more theoretical and physical soundness.
To verify the model, firstly the influence of the size of computational grid on the rainfall-runoff relationship was studied. Secondly the meaningfulness of physiographic and hydrological parameters in the DGUH model was analyzed. In this study, the data of Lien-Hua-Chi (LHC) #3 watershed and Pi-Lu-Chi (PLC) #11 watershed of the Taiwan Forestry Research Institute in central Taiwan were retrieved and fed into the model. It was found that the DGUH model was sound, rational, and consistent through a series of theoretical deduction, model establishment, characteristic analysis and verification tests.
In the geomorphologic analysis, the concentration time in the DGUH model under a given rainfall intensity is the same for a selected time interval with different rainfall durations. However, the peak discharge is linearly proportional to the grid size. It was also found that the longer the rainfall duration is, the larger the peak discharge and vice versa. On an uniform slope under a given rainfall intensity, it had found that the steeper the slope is, the shorter the concentration time, and the larger the peak discharge. However, the total runoff was the same if the area of watershed kept the same no matter whether the slope was steep or gentle.
In the hydrological analysis, the DGUH model became trapezoid in shape under a linear watershed condition if the value of rainfall duration is less than that of the watershed area. However, the model became triangular if the value of rainfall duration is the same as that of the watershed area. If the value of rainfall duration was far more than that of the watershed area, then the DGUH hydrograph was S-like in shape. Therefore, both the linear grid watershed with unit rainfall duration and the linear rainfall duration with unit watershed area would result in the same runoff features. Under certain conditions the time distribution of rainfall and space distribution of watershed would compensate each other. In addition, the system output function would theoretically be the multiplication of rainfall and geological transit function. The discharge is considered as the start of watershed base-flow when the time interval is greater than rainfall duration plus duration of geological transit minus one, i.e., ( ).
The results of data analysis of LHC #3 and PLC #11, indicated that the smaller the n (roughness coefficient) value is, the shorter the concentration time, and the larger the peak discharge, and vice versa. The n values would affect peak time, peak discharge, concentration time and others if the formulas of grid output time, duration and area were applied. In addition, the concentration time is directly proportional to n value, while the peak discharge is inversely proportional to it. If the hydrographs were estimated from the DGUH models with rainfalls of the two study watersheds, it was found that the DGUH models fitted the real data reasonably well.
In conclusion, the DGUH model developed in this paper serves as good as the models developed by other researchers. However, the advantage of DGUH model is that the parameters needed for calculation are easy to obtain. For example, the calculation of runoff of DGUH could be achieved by obtaining geological factors such as watershed area (A), roughness coefficient (n), infiltration rate (f), slopes (s), etc, or hydrological factors such as rainfall intensity (i), average depth (h), etc. For estimating stream flow hydrographs in a watershed without discharge records, it is straightforward to using DGUH model. If combined with frequency analysis, storm hyetographs, rainfall duration, the applications of DGUH model would be even more powerful and wider. Therefore, it is suggested that further studies focus on the revision of the model to expand its application.
台灣地區之河川因坡陡流急，加上降雨時空不均，以致在水資源之開發、利用、保育及管理工作上極難全然掌握，為使水資源及相關工程之規劃及設計能更迅速精確，實有必要建立一水文分析工具以資應用。而在水文分析上，對於發生在集水區降雨與逕流間關係之探討十分重要，但由降雨到逕流之水文歷程係一複雜多變之過程，實難於掌握。自1932年Sherman創擬單位歷線以來，其後繼學者又發展了各種線性及非線性之降雨逕流模式，惟其理論複雜、具有過多假設或物理意義不甚嚴謹，致應用困難。本研究爰以一維坡地漫地流理論為基礎，推導一將地文及水文特性分離，並將現地數值地形資料及降雨分別處理後，再整合成一具有理論基礎及物理意義之數值地形單位歷線模式(Digital Geomorphologic Unit Hydrograph，簡寫 DGUH)。
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