Raingauge Network Design Using Geostatistics
Date Issued
2006
Date
2006
Author(s)
Lin, Yun-Ching
DOI
zh-TW
Abstract
Rainfall data is one of the essential data in hydrological analysis and engineering design including water budget analysis, frequency analysis and stormwater drainage design. Direct measurement of rainfall can only be achieved by raingauges and raingauge networks are often installed to provide temporal and spatial variations of rainfall. However, even though raingauges are capable of measuring rainfall rate in real-time and at very fine resolution in time, the spatial variation of rainfall is still difficult to be characterized without a raingauge network of enough density in space. In addition, selection of raingauge locations is affected by many factors such as accessibility, easiness of maintenance, topographical aspects, etc. Furthermore, the density of a raingauge network is dependent on the time resolution (or scale) of the desired rainfall measurements. For example, for the purpose of water resources planning, observation of monthly or annual rainfall is desired; however, for flood mitigation and forecasting, hourly rainfall must be measured. Hourly rainfall exhibits higher spatial variability and thus, as compared to monthly or annual rainfall, a network of higher density is needed. Therefore, a methodology for raingauge network design and performance evaluation of an existing raingauge network is important in that it can help to understand its capability and the quality of the data it provides.
In this study, a geostatistical approach for raingauge network design and evaluation was proposed and a network of 27 raingauges in lower Danshuei River watershed was chosen for evaluation. It first defines the “acceptable precision” for rainfall estimation at ungauged sites using rainfall measurements of the existing raingauges and the ordinary kriging. The rainfall estimates at ungauged sites are considered acceptable if the probability αA that the estimate falls within one standard deviation of the true value exceeds a specified level α, say 0.8 or 0.9. By adopting such a criterion, both the ungauged locations and the area percentage pA within the study area satisfying this criterion can be obtained. A sequential algorithm is also developed to find raingauges that provide only
redundant information and can be eliminated or moved. Relocation of such raingauges can also be suggested using a contour map of αA and the area percentage of pA corresponding to the altered network. It was found that, among the four major storm types in Taiwan, hourly rainfall of Mei-Yu exhibited the highest spatial variability and therefore raingauge network evaluation was conducted based on hourly rainfall of Mei-Yu. It was concluded that at α = 0.8, 8 existing raingauges are redundant and only 19 raingauges are needed to achieve pA=0.5379. After relocating the 27 raingauges, the altered network can achieve pA=0.8791.
Subjects
區域化變數理論
站網評估
空間變異
Theory of Regionalized Variables
Raingauge Network Analysis
Spatial Variation
Type
thesis
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