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|標題:||Development and Application of A Digital Geomorphologic Unit Hydrograph Model|
|關鍵字:||digital geomorphologic unit hydrograph (DGUH)|
|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.|
數值地形單位歷線模式之推導與應用 摘 要 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)。 為評估所建立之理論、模式之妥適性，在應用之前並先探討集水區之數值地形網格劃分對降雨逕流之影響，及分析地文及水文參數在數值地形單位歷線之特性，同時並利用農委會林試所蓮花池3號及畢祿溪11號集水區進行降雨逕流之模擬、分析、比較。由DGUH理論之推導、模式之建立、特性之分析以及實例之模擬，業已獲致若干具體成果。 在地文特性分析中，當集水區於相同降雨強度條件下，若因降雨延時之不同，則配合相同時距網格所產生之DGUH，其集流時間相同，但洪峰流量則與網格長度成線性關係，降雨延時長則洪峰流量大，短則洪峰流量小。而均勻單坡集水區於相同降雨強度條件下，坡度越陡集流時間越短、洪峰流量越大，且當陡坡及緩坡集水區具有相同面積及相同降雨強度條件，將產生相等之逕流總量。 在水文特性分析中，（1）當集水區成為線形條件下，且其降雨延時小於線形集水區面積數時，則產生梯形DGUH歷線；（2）當降雨延時等於線形集水區面積數時，則產生三角形DGUH歷線；（3）在降雨延時遠大於線形集水區面積數之條件下，則產生DGUH之類S歷線。由研究獲知：線形網格集水區於單位降雨延時條件下，與單位面積集水區於線性降雨延時條件下，獲得相同之逕流行為。是以降雨之時間分布與集水區之空間分布，在部分情形下，具有互補之作用。另由理論之推導知系統之輸出函數，為該場降雨與地文轉移函數之乘積，而當時間超過降雨延時與地文轉移函數延時之和減1時（ ）之流出量，即可視為集水區基流之開始。 而蓮花池3號集水區及畢祿溪11號集水區等，於不同糙度係數（n）所推估之數值地形單位歷線，當n值越小，則其集流時間越短、洪峰流量越大；而當n值越大，則集流時間越長、洪峰流量越小。另由網格流出時間及時間、面積等公式知，n值對於峰時、峰量、集流時間等均有影響，且集流時間與n值成正比，而峰量則與n值成反比。經利用DGUH推算兩研究集水區多場降雨之歷線與實測值很接近。 綜上可知，有關數值地形單位歷線之特性，與其他理論所推導之結果相近，而所獲得之DGUH因具有各種物理參數，因此可由不同地文因子如集水區面積(A)、糙度係數(n)、入滲率(f)、坡度(s)值等；或水文因子如降雨強度(i)、漫地流平均水深(h)等為參數，計算集水區之降雨逕流。對於無流量紀錄集水區之水文推估，運用極為方便，未來如再結合頻率分析、雨型分布、降雨延時等方法，其運用性將更寬更廣，因此後續之工作可將此一模式再予精緻化，俾利其應用領域之拓展。
|Appears in Collections:||水土保持學系|
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