Whenever a member withdraws his or her accumulated normal contributions the matching contributions of the city so released shall be transferred to a reserve account created for the purpose of showing the amount of credits due each city through such operation. Such credits may be used by the city to apply on any charges made against the city but only so much thereof as will insure leaving in such account an amount estimated to be sufficient to again match contributions redeposited by employees returning to service as contemplated in RCW 41.44.190. The board may credit such reserve accounts with interest at such rate as the board deems equitable: PROVIDED, That as to any member city which has elected to and is making contributions in lieu of those required in RCW 41.44.090(1)(a), there shall be no release of the city's matching contributions after the date of its commencement to make such lieu contributions: PROVIDED FURTHER, That any released contributions of any such city which have been credited to its reserve account prior to the date of such commencement, shall be available to it for the purposes hereinabove specified, unless the board shall determine that their immediate use for such purposes would result in a harmful effect upon the assets of the system, in which event the board shall have the right to defer their use for a reasonable time in which to permit it to make adjustments in the current assets of the system to prevent the same.