It shall be unlawful for any person to begin any development or construction which is wholly within, partially within, or in contact with any flood hazard area including but not limited to: filling; grading; construction of new structures; the substantial improvement of buildings or structures, including repair of substantial damage; placement or replacement of manufactured homes, including substantial improvement or repair of substantial damage of manufactured homes; erecting or installing a temporary structure, or alteration of a watercourse, until a permit is obtained from Prince George's County. No such permit shall be issued until the requirements of these regulations have been met. In addition to the permits required in paragraph (a), applicants for permits in non-tidal waters of the State are advised to contact MDE. Unless waived by MDE, pursuant to Code of Maryland Regulations 26.17.04, Construction on Non-tidal Waters and Floodplains, MDE regulates the "100-year frequency floodplain of free-flowing waters," also referred to as non-tidal waters of the State. To determine the 1-percent annual (100-year) frequency floodplain, hydrologic calculations are based on the ultimate development of the watershed, assuming existing zoning. The resulting flood hazard areas delineated using the results of such calculations may be different than the special flood hazard areas. A permit from Prince George's County is still required in addition to any State requirements. A building permit is valid provided the actual start of work is within 180 days of the date of permit issuance. Requests for extensions shall be submitted in writing and justifiable cause demonstrated. For building permits for structures affecting the 1-percent annual (100-year) floodplain, the Floodplain Administrator may grant, in writing, one or more extensions of time, for additional periods not exceeding ninety (90) days each and provided there has been no amendment or revision to the basis for establishing special flood hazard areas and BFEs.