| The monitoring and forecasting of soil and water loss is of the most important tasks in soil and water conservation in china.Runoff plot is a commonly used method for soil and water conservation monitoring.The measurement of sediment concentration in runoff collecting bucket(tank)is the key to accurately calculate the amount of soil erosion.Previous studies showed that mixing-sampling measurement method in the runoff sediment monitoring can affect the sediment measurement accuracy because of unevenly mixing and sediment deposition in the sampling process.Besides,runoff and sediment in runoff plot monitoring shaped by different terrain conditions,rainfall conditions and soil types can be distinctive,hindering the construction of runoff plot and lowering the precision of sediment concentration measurement method.Therefore,in this study we propose a simple method to correct the measurement error,through simulating the sediment measurement of mixing-sampling procedure in laboratory experiments to obtain the error correction formula,then contributing to its application to the runoff area monitoring in the whole country.Laboratory experiments were arranged to investigate the error of sediment measurement and build a formula to correct the error through mixing-sampling procedure.The experiments test on purple soil,yellow soil,lou soil and black soil,involving two sediment-laden water volumes of 50 and 100 L,and using 13 sediment concentration levels.The sediment-laden water samples were prepared according to the designed sediment concentration,and the sampling procedures were performed by a professional person.The sediment measurement error was computed from the measured and designed value,and through regression analysis obtaining the error correction formula.The results show that:1)A large error exists in the measurement of sediment concentration by mixing sampling method and the sediment content measured was less than true value.The sediment measuring error changes little with the increase of sediment concentration at the beginning,showing fluctuation within a certain range.The average relative error of purple soil,yellow soil and lou soil is-30%~-40%,and the average relative error of black soil is in-60%~-70%.When reaching to a certain concentration,the relative error occurs a sudden change and reduces to below-20%,with the absolute error still high.But at the super high segment the variance is lower.2)The relationship between sediment concentration measurement error and the volume is negatively correlated.At the low segment of sediment concentration,for purple soil,yellow soil and black soil the measurement results of 100 L sediment-laden water samples is about-7% more than the 50 L sediment-laden water samples,and at the super high segment the value is-3%.The volume exerts little impact on the measurement error of lou soil.3)Based on the analysis of variance and regression analysis,the linear regression equation for the measurement error of four kinds of soil on volume and sediment concentration is obtained: δ= j + aC0+bV.And then the error correction formula between the sediment concentration and the actual sediment concentration is derived:The examine with the experimental results shows that The corrected sediment concentration is closer to the true value.And The error correction formula is helpful for the measurement accuracy.4)To conclude sediment error correction formulas as error correction method through process simulation experiments and apply it to general methods of runoff monitoring,including sample preparation,sampling mixture process and error correction formulas will establish the error correction formula between the sediment concentration and the actual sediment concentration under different working conditions,booming the development of monitoring of runoff areas in china. |
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