Improvement of the reservoir shape factor method and evaluation of its changes due to sedimentation

The shape factor is one of the most important physical characteristics of a dam’s reservoir. This factor is equal to the reciprocal of the slope of a line obtained by plotting reservoir depth against reservoir capacity on a log-log paper. The shape factor is used for reservoir classification and sediment distribution. In this study, a new method is proposed for determination of the reservoir shape factor. In this method, the normalized depth-capacity curve is plotted on log-log paper and then the value of shape factor could be derived as the reciprocal of the line slope. In this study, the original depth-capacity data and reservoir sedimentation data of 4 dams in Iran (Dez, Kardeh, Latian and Shahid Abbaspour) and 4 dams in the USA (Cedar Bluff, Kirwin, Nambe Falls, and Theodore Roosevelt) were used. The results showed that reservoir shape factor of all reservoirs decreased 2 to 2.5 for the first or second sedimentation measurements. In addition, the type of reservoirs was changed to type III. Therefore, prediction of reservoir sedimentation by area reduction method should be performed with reservoir type III. The most important advantage of the proposed method is the capability of plotting and comparing the normalized depth-capacity data of several reservoirs (or several sedimentation measurements of a single reservoir) on individual log-log paper. While in the old method, the depth-capacity data of each reservoir should be plotted on a separate log-log paper.