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Show 24 So also is the decision on the necessity for a given improve- ment of navigable capacity, and the character and extent of it.83 Likewise as to whether a structure constitutes a hin- drance.84 And the courts may not assume, contrary to a statu- tory declaration, that Congress has no purpose to aid naviga- tion, or that its real intention is to use the stored waters for other purposes so as to defeat a declared primary navigation purpose.85 Nor is the exercise of commerce authority invalidated where Congress elects thereby to serve purposes in addition to navi- gation, even if such other purposes would not alone justify an exercise of congressional power.86 Also, there is no con- stitutional barrier to exercise by Congress of its commerce power to authorize issuance of a license for nonfederal con- struction of a dam for power only in waters under its juris- diction.87 Correspondingly, since there is no "constitutional necessity for viewing each reservoir project in isolation from a comprehensive plan covering the entire basin of a particular river," the decision upon the wisdom, need, and effectiveness of a particular project-such as its flood-control value in a com- prehensive plan-is for Congress.88 In the words of the Deni- son Dam opinion:89 To say that no one of those projects could be constitu- tionally authorized because its separate effect on floods in the Mississippi would be too conjectural would be to deny the actual or potential aggregate benefits of the in- tegrated system as a whole. That reveals the necessity, from the constitutional viewpoint, of leaving to Congress the decision as to what watersheds should be controlled (and what methods should be employed) in order to pro- "Scranton v. Wheeler, 179 U. S. 141,162-163 (1900). 84 United States v. Appalachian Electric Power Co., 311 U. S. 377, 424 (1940), reh. den., 312 U. S. 712 (1941). 85 Arizona v. California, 283 U. S. 423, 456-457 (1931). 84 283 U. S. at 456. 87 United States v. Appalachian Electric Power Co., 311 U. S. 377, 426 (1940), reh. den., 312 U. S. 712 (1941). 88 Oklahoma v. AtMnson, 313 U. S. 508, 525-527 (1941). " 313 U. S. at 527-528. |