从泥沙运动、河型形成、水力几何形态和河床调整过程等方面对砂质与砾石河床进行系统的比较研究，以大样本为基础建立适用于砂质与砾石河床的河型统一判别关系，揭示包括砂质与砾石河床在内的冲积河流非线性行为，建立非线性水力几何形态关系并定量表达其中的临界现象，开辟河流地貌研究的新领域，对水库修建后砾石河床调整趋势预测有重要意义

Sand- and gravel-bed rivers are two basic types of alluvial rivers. Although they obey the same physical laws, the formation and process of these two types of rivers are different, due to the difference in sediment movement and boundary material composition. Some existing discriminating relationships for channel patterns that were established based on sand-bed rivers are not applicable to gravel-bed rivers, and vice versa. The research on the two types of rivers is along different lines, thus the results obtained can hardly be unified. At present, there is no common criterion that can be used for channel pattern discrimination of both sand- and gravel-bed rivers. The long used Leoplod-Wolman relationship cannot well discriminate channel patterns of rivers including the two types, and many researchers have tried to modify this relationship, but so far success has not been achieved yet. However, many data have been cumulated in the past 20 years, which prepared some conditions for solving such a difficult issue..Through collecting data from rivers in China and abroad, we have set up a database including more than 200 alluvial rivers. On this basis, a systematical comparison has been made on sand- and gravel-bed rivers, including channel geometry, channel patters and the ways they respond to changing runoff and sediment load. Through the generalization macro-scopic geographical and geomorphic phenomena and the elucidation of hiding physical mechanisms, better understanding has been made of the laws governing channel process of sand- and gravel-bed rivers, and some unified relationships established for channel pattern discrimination for them. Thus, substantial progress has been made towards solving the difficult problem of establishing unified theory for channel patterns of sand- and gravel-bed rivers..The main results include: (1) A preliminary relationship has been established for discriminating channel patterns of sand- and gravel-bed rivers; (2) Systematic comparison has been made of hydraulic geometry of sand-and gravel-bed rivers and hydraulic-geometry based methods have been proposed for discriminating channel patterns of sand- and gravel-bed rivers; (3) Some statistical relationship between channel pattern frequency and bed material grainsize has been established, i.e., the frequency of meandering channel decreases with the increase in bed material grainsize, but the frequency of braided channel decreases. (4) The Leopold-Wolman relationship has been modified and a new discriminating relationship has been proposed for braiding threshold, based on channel width-slope relationship..