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Error Analysis of Gullies' Measurement with Different Methods

The authors mainly study the error of the gullies' volume when they are measured with tapes,since it's a very traditional method to measure gullies' volume and area with tapes in the research of gully erosion.The error is mainly caused by limited precision of tapes and mechanism of measurement.The error caused by limited precision of tapes can be calculated with error transfer formula,and it was found that this kind of error does not depend on the distance between two neighbouring cross sections,but only relate to the tapes we used.The ratio of the error to gullies' volume is less than 2%,which is the same for different gullies.The system error caused by mechanism of measurement is comprised of two parts.One is due to the nonidentity of cross sections,which has maximum value of 2%;the other one is caused by irregularity of cross sections.In order to minimize the system error caused by the nonidentity of cross sections,it's important to decrease the distance between two neighbouring cross sections,which was about 10 meters in our outdoor measurement.Additionally,we also compare the gullies' volume measured with tapes and GPS.It's found that the error of single measurement is about 10%,and that the annual variations of gullies' volume measured with tapes and GPS are almost the same.Therefore,it's an effective method to measure annual variation of gullies' volume with tapes.