The board on construction of the improvement may advance that portion to be collected by special assessment, the amount so advanced to be replaced as the first special assessments are collected. The board may in lieu of making advancements, issue warrants to be known as “Drainage Warrants”, the warrants to bear interest at a rate not exceeding that permitted by chapter 74A payable annually from the date of issue and to be paid out of the special assessments levied, when they are collected.