An Automatically Controlled Systme For Measurement Of Sediment And Discharge Rate Of Runoff And Its Applications

Sediment concentration and flow discharge rate in runoff are the important parameters in investigation of soil erosion on hill-slope, and are the basic, required data of dynamic monitoring network for water loss and soil erosion. The real-time, fast, and accurate measurements of sediment and flow rate can help to understand the dynamic soil erosion processes and to automate the monitoring practice of water loss and soil erosion.Volumetric or oven-dry method has long been the standard method for determining sediment concentration. The accuracy of the measurements, to a great extend depends on sampling processes. The method is known as a time consuming, labor and resources demanding technique. The standard way for runoff measurement has been that to collect runoff in a container and the discharge rate is determined as a time-averaged value as estimated from the collected runoff. This method not only needs intensive labor input, but also can not record the dynamical fluctuation of the flow rate. Therefore the development of a system for measurements of sediment and runoff rate is of great importance.This research was conducted to use Gamma ray attenuation method to measure sediment concentration and to use water level change rate to determine flow rate. An integrated and automatically controlled system was developed for the purposes. The following details the outcome of this study.1.The feasibility of Y ray to determine sediment concentration was studied theoretically and experimentally. With the theory of Y ray attenuation, the theoretical algorithm of sediment concentration was derived. Laboratory experiments showed very good linear correlation betweensediment concentration and gamma ray readings with determination coefficient great than 0.97. Both theory and experiments indicated the feasibility of using y ray method to measure sediment concentration The measured results were very accurate and reliable.2.To avoid the influence of soil types on measurement accuracy , the energy level of r ray should be reasonably chosen. The experimental data showed that the mass absorption coefficients varies with soil type under different Y ray energies. However, under a certain energy level, the mass absorption coefficients for different soils are practically the same. Statistic analysis of experimental data of two soils showed that the linear relationship between sediment concentration and Y ray reading was not influenced by soil types and sampling-periods.3 .A prototype system was developed to measure sediment concentration and flow rate, with the integration of nuclear technique, electronics technique, mechanical engineering technique and computer application knowledge. And this system has the functions such as automated and controlled sampling, sediment concentration measuring, automated flow rate measuring and data acquisition, analysis and management.4.The factors influencing measurement accuracy were investigated. Measures and approaches were taken to reduce error and to improve measurement accuracy and sensibility. In considering the interaction of various factors the optimal combination of parameters was selected.5.To improve the sensibility of the system to dynamic sediment change at low flow rate and high measurement frequency, theoretical analysis was made to formulate algorithm for measurement corrections.This makes dynamic measurement of sediment concentration and flow rate of runoff possible, with appropriate equipment. Its accuracy and reliability were validated by laboratory experiments and practical applications.