In all cases where rights-of-way and easements have been or may be hereinafter acquired, either by purchase or condemnation, for the laying of any conduit, supply pipes, electric poles, wires or mains, or gas mains or other appliances or works for supplying water, electricity, and gas as contemplated in this chapter, such rights of way and easements shall be paramount, and neither the said City of Austin, the County of Mower, or other county or municipal body or corporation, nor other corporation or person, shall enter thereon, use and occupy the same for any purpose other than said purpose for which said right-of-way or easement was or may be acquired as aforesaid, except with the consent in writing of said board, and upon such terms and in such manner as may be agreed upon. The board is hereby authorized to make and enter into any agreement in that behalf which it may deem necessary and expedient.