(a) new pile-supported structures for nonwater-dependent use shall not extend beyond the footprint of existing, previously authorized pile-supported structures or pile fields, except where no further seaward projection occurs and the area of open water lost due to such extension is replaced, on at least a 1:1 square foot basis, through the removal of existing, previously authorized fill or pile-supported structures or pile fields elsewhere on the project site; as provided in 310 CMR 9.34(2)(b)1., the Department shall waive the on-site replacement requirement if the project conforms to a municipal harbor plan which, as determined by the Secretary in the approval of said plan, specifies alternative replacement requirements which ensure that no net loss of open water will occur for nonwater-dependent purposes, in order to maintain or improve the overall capacity of the state's waterways to accommodate public use in the exercise of water-related rights, as appropriate for the harbor in question;