The plenary federal power over commerce must be able to develop with the needs of that commerce which is the reason for its existence. It cannot properly be said that the federal power over navigation is enlarged by the improvements to the waterways. It is merely that improvements make applicable to certain waterways the existing power over commerce. Nor is it necessary for navigability that the use should be continuous. The character of the region, its products and the difficulties or dangers of the navigation influence the regularity and extent of the use.
Small traffic compared to the available commerce of the region is sufficient.
Even absence of use over long periods of years, because of changed conditions, the coming of the railroad or improved highways does not affect the navigability of rivers in the constitutional sense. It is well recognized too that the navigability may be of a substantial part only of the waterway in question. Of course, these evidences of nonnavigability in whole or in part are to be appraised in totality to determine the effect of all. The evidence of actual use of the Radford-Wiley's Falls section for commerce and for private convenience, when taken in connection with its physical condition make it quite plain that by reasonable improvement the reach would be navigable for the type of boats employed on the less obstructed sections. Indeed the evidence detailed above is strikingly similar to that relied upon by this Court in United States v. Utah to establish the navigability of the Colorado from Cataract Canyon to the Utah-Arizona boundary line.