Appropriations for construction or other permanent improvements from the capital improvements fund shall not lapse until the purpose for which the appropriation was made shall have been accomplished or abandoned; provided, any project shall be deemed to have been abandoned if three fiscal years elapse without any expenditure from or encumbrance of the appropriation therefor. Any unappropriated balance in the capital improvements fund may be transferred by the council and used for the payment of outstanding bonded indebtedness of the city.