There is authorized an expenditure as required, from any appropriations heretofore or hereafter made for flood control, rivers and harbors, and related purposes by the United States, for the establishment, operation, and maintenance by the Secretary of Commerce of a network of recording and nonrecording precipitation stations, known as the Hydroclimatic Network, whenever in the opinion of the Chief of Engineers and the Secretary of Commerce such service is advisable in connection with either preliminary examinations and surveys or works of improvement authorized by the law for flood control, rivers and harbors, and related purposes, and the Secretary of the Army upon the recommendation of the Chief of Engineers is authorized to allot the Secretary of Commerce funds for said expenditure.