Rivers are one of the most essential sources of sand and gravel supply for civil works. However, undesirable effects of irregular in-stream mining have been reported on natural sources, environment and infrastructures close to rivers. Therefore, it is necessary to find the effects of mining on rivers in more details. This research concentrates on mining-pit migration phenomenon and its effects on the channel bed. This paper reports an experimental study on the migration of rectangular mining pits and variation of longitudinal profile in the channel bed composed of rather uniform sediments. Different values of widths and lengths were used for pit while pit depths and flow variables were kept constant. The results show that the migration speed changes with the length/width ratio of the pit. The migration speed in convection period is higher than that in diffusion period. In addition, by increasing the length or width, filling rate of pit increases, where the effect of width is more important than the effect of the length. Also is reported in this paper a field study on the changes of three pits excavated at different locations of a river. Some similarities between the pit migration in the straight reach of the river and that of the experimental work is realized and presented. Rivers, one of the most essential sources of sand and gravel supply for civil works. However, undesirable effects of irregular in-stream mining have been reported on natural sources, environment and infrastructures close to rivers. Therefore, it is necessary to find the effects This research concentrates on mining-pit migration phenomenon and its effects on the channel bed. This paper reports an experimental study on the migration of rectangular mining pits and variation of longitudinal profile in the channel bed composed of rather uniform sediments. Different values ​​of widths and lengths were used for pit while pit depths and flow variables were kept constant. The results show that the migration speed changes with the length / width ratio of the pit. The migration speed in convection period is higher than that in diffusion period. In addition, by increasing the length or width, filling rate of pit increases, where the effect of width is more impor tant than the effect of the length. Also is reported in this paper a field study on the changes of three pits excavated at different locations of a river. Some similarities between the pit migration in the straight reach of the river and that of the experimental work is realized and presented.