21. If at any time after the completion of a specified work or a protective work, not being a work vested in the Board, the Board gives notice to the promoter informing it that the state of maintenance of the work appears to be such that the work is causing or likely to cause detriment, the promoter shall, on receipt of such notice, take such steps as may be reasonably necessary to put the work in such state of maintenance as not to cause such detriment.