For the purpose of compiling the data to be presented to the court as set forth in the preceding sections, the board of commissioners of said drainage district may employ one or more competent engineers, surveyors and other helpers, and such legal assistance as may be necessary, with full power to bind said district for the compensation of such assistants or employees employed: provided, however, that all maps, profiles, surveys, plans, specifications or other data heretofore made or property acquired under laws heretofore enacted on the subject may be purchased and used under the provisions of this chapter.