The said commissioners for the state of Idaho shall have full authority to make full investigations of the Columbia River and its tributaries, including the Snake River, and the drainage thereof, as may be necessary in order to determine the facts as to physical conditions obtaining upon said river, and its tributaries, and of the present and future needs of the state of Idaho and its citizens, to the proper use and benefits of the waters of said river, and its tributaries, and to perform such other duties as may be necessary to sufficiently determine such facts and to secure the necessary information in order that they may properly perform their duties as commissioners of the state of Idaho upon said joint commission.