The district board may also include in its estimate prepared pursuant to Section 49140 an unappropriated reserve to cover expenditures that have not been provided for, or that have been insufficiently provided for, or for unforeseen requirements.

The money in any unappropriated reserve fund so established may be made available for appropriation by a four-fifths vote of the members of the district board at any regular or special meeting of which all members have had reasonable notice.

In addition, the district board may further provide, by resolution, for transfers or revisions of unencumbered funds within the general district expenditures provided for during any fiscal year where, in the opinion of the district board, the transfer or revision is necessary for purposes of the district.