(a) The Department of Natural Resources shall define 100-year floodplains within the State of Illinois on a township by township basis and may issue permits for any construction within such 100-year floodplains on or after the effective date of this amendatory Act of 1971. The Department shall publish and distribute suitable reports, together with mapping and hydrologic exhibits pertaining to 100-year floodplains defined and established under this Act. In defining applicable 100-year floodplains, the Department shall cooperate with, and shall consider planning and zoning requirements of, regional planning agencies created by statute, counties, municipalities and other units of government. A period of thirty days shall be allowed for any agency to submit written comments to the Department regarding any proposed 100-year floodplain area. If such agency fails to return comments to the Department within the specified time period the Department may proceed with the publication and institution of the 100-year floodplain permit procedure. The Department is charged with the planning, development, and evaluation of the most economic combination of retention storage, channel improvement, and floodplain preservation in defining and establishing 100-year floodplain areas. All construction undertaken on a defined 100-year floodplain subsequent to the effective date of this amendatory Act, without benefit of a permit from the Department of Natural Resources, shall be unlawful and the Department, may in its discretion, proceed to obtain injunctive relief for abatement or removal of such unlawful construction. The Department, in its discretion, may make such investigations and conduct such hearings as may be necessary to the performance of its duties under this amendatory Act of 1971. Activity of the Department under this Section shall be limited to townships related to projects of the Department authorized by the General Assembly. The report of the Department shall be considered a final administrative decision and subject to judicial review in accordance with the provision of the Administrative Review Law.
     (b) For the purposes of this Section, including for the purposes of granting permit and license applications filed or pending prior to the effective date of this amendatory Act of the 96th General Assembly, “100-year floodplain” means the lowland and relatively flat areas adjoining inland and coastal waters, including flood-prone areas of offshore islands, that are inundated by a flood that has a 1% or greater chance of recurring in any given year or a flood of a magnitude equalled or exceeded once in 100 years on the average over a significantly long period. For the purposes of this Section, an area shall be deemed by operation of law not to be within the 100-year floodplain if the area lies within an area protected by a federal levee and is located in a flood prevention district established in accordance with the Flood Prevention District Act; provided, however, that an area that lies within a flood prevention district established in accordance with the Flood Prevention District Act shall be deemed by operation of law to be within the 100-year floodplain if, according to the currently adopted federal flood insurance rate map, the area is subject to inundation by a 100-year flood from bodies of water other than the Mississippi River.