Volumes of erosion and deposition in the Yichang-Zhicheng reach from Oct. 2002 to Oct. 2008 were calculated by cross-section method, and they showed significant differences when using different cross-section spacings. To explain it, riverbed form was quantified by using fractal dimensions and comparing the relations between cross-section fractal dimension, thalweg fractal dimension, bed surface fractal dimension, and relative errors of erosion and deposition amounts. Examination at the effect of topographic relief degree on computations of erosion. The deposition shows that the relative computation errors have no clear correlation with river pattern and their root is this relief degree. Relative to cross-section fractal dimension and thalweg fractal dimension, bed surface fractal dimension is a better indicator of the relief degree and has a good linear correlation with the relative errors. In general, a greater relative error corresponds to a greater bed surface fractal dimension, and vice versa.