The engineer, in estimating the benefits to lands, streets, highways, railroad property, rights-of-way, railroad beds, not traversed by the works and improvements, shall not consider what benefits will be derived by such lands after other ditches, improvements, or drainage plans shall be constructed, but only the benefits which will be derived by the construction of the aforesaid works and improvements as they afford drainage or an outlet for drainage, or protection from overflow or damage by water.