(a) The site and the maximum discharge of the side channel spillway, the site, materials and the capacity of the dam were given;
(b) The loss of head by friction in the side channel was included in the coefficient of the velocity distribution;
(c) The full length of the side channel spillway were divided by sections of equal distance and fixed number;
(d) The dimension of the each sections was kept constant and the position of the sections was moved owing to the designing overflow depth.
Under above conditions, these cross sections did not change the elevation of the water surface when a different overflow depth was taken by the change of planning, but the spaces between each sections were changed proportionally to the full length of the new side channel spillway.
Using above results, the author found the most economical overflow depth that cuts to the minimum the total cost of works, such as the banking of the dam body, the compensation of the land covered by H. H. W. L., and cutting and pavement of the side channel spillway.
He also considered on the relations between the overflow depth and the loss of head by friction of the side channel spillways.

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