THE ROLE OF PERIMETER SHAPE IN ESTIMATING ANNUAL RUNOFF FROM SMALL SIERRA NEVADA BASINS

Perimeter shape of drainage basins is evaluated as a control of annual runoff depth from small Sierra Nevada basins underlain by granitic rocks. In contrast to three perimeter shape ratios, none of which contributes a statistical explanation of annual runoff depth, three terms of a Fourier expansion of the basin perimeter substantially improve the estimating model. When added to annual precipitation, the first, third, and seventh Fourier amplitudes increase statistical explanation by 15 percent and prediction accuracy by 10 percent. These improvements are much greater than corresponding gains atributable to other morphological variables. [Key words: basin runoff, basin shape, Sierra Nevada.]