摘要
坡面径流含沙量和流量是研究坡面土壤侵蚀规律的重要参数，也是水土流失动态监测网络的基础数据。坡地径流全过程含沙量和径流量的连续、快速、准确和动态监测，为研究土壤侵蚀动态力学过程提供重要的参数，同时使水土流失动态监测网络向自动化和智能化过渡。
目前，径流含沙量均采用烘干称重法。这种方法的测量结果受采样随机性影响很大，同时烘干时间长，耗费人力物力多。坡面径流小区的流量都靠集流桶采集后人工读取，再概略地换算成均值流量，测量不但劳动强度大，人为误差大，无法得到流量动态过程。研究自动坡面径流含沙量与流量测量系统，不仅有重要科研价值而且有广泛实际意义。
本研究利用γ射线衰减原理测量含沙量、采用水位随时间的变化测定流量。研制了集坡面径流含沙量与流量动态测量于一体的机电一体化在线自动测控系统。具体研究内容和结果如下：
1．用理论和室内实验研究了γ射线测量含沙量的可行性。利用γ射线透射衰减规律，推算了γ射线透射水沙两相物质下计算含沙量的理论计算公式。大量室内试验表明，γ射线强度值与标准含沙量线性相关，相关系数值达0.97以上。从而理论和实验证明了γ射线透射法测量含沙量完全可行，且测量结果具有很高的精度和可靠性。
2．选择合理的放射源强度，避免土壤种类对测量精度的影响。从试验数据显示，在不同γ射线能量下，不同土壤类型的质量吸收系数不同。但在一定的源强能区内，不同类型土壤的质量吸收系数相差很小，可以认为是一个常数。对两种土壤的实测数据的统计检验表明，含沙量与γ射线强度值的线性关系不受土壤类型、采样时间的影响。
3.结合核技术、电子技术、机械工程技术和计算机技术，研制了一
套机电一体化的径流含沙量与流量的测控系统，实现了控制条件下径流
自动采样、含沙量与径流流量自动测量、数据自动采集、结果在线显示
和数据统计分析等功能。
4.综合分析了影响系统测量精度的因素，提出了减少误差，提高测
量精度和灵敏度的措施和解决途径。考虑了各种测量影响因素相互制约
下选择最佳组合的方法。
5.为了提高小径流条件下系统对含沙量动态变化反应灵敏度，研究
矫正侧量结果的理论与相应计算公式。
本项研究实现了坡面径流含沙量与流量在线动态测量方法的试验研
究，开发了测量样机，并在实际应用中充分验证了本系统的准确性和可
靠性。
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 between
sediment 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.
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