(a) The commissioners court of a county located below the dam of Lake Livingston with all or part of its area within the 100-year floodplain of the Trinity River basin as described by county maps developed according to Federal Emergency Management Agency requirements may adopt and enforce rules that regulate the future construction of residences and the laying out of residential lots or the development of subdivisions in that portion of the county located in the 100-year floodplain of the Trinity River basin.
(b) Before the commissioners court may adopt and enforce the rules described in Subsection (a) of this section the commissioners court must make a determination that the rules are necessary to protect the health and safety of the public by reducing the damage caused by flooding in the 100-year floodplain.

(c) The rules described in Subsection (a) of this section apply only to development and construction commenced after the effective date of this section for:
(1) the flood-proofing of structures constructed or placed in the floodplain;
(2) the type of structures which may be constructed or placed in the floodplain;
(3) the minimum elevation of structures constructed or placed in the floodplain; and
(4) specification for drainage of residential lots or subdivisions to be laid out in the floodplain.
(d) The commissioners court may not regulate new manufactured or industrialized housing constructed to preemptive state or federal building standards for siting or zoning purposes in any manner that is different from regulation of site-built housing.