(a) Bridges and
culverts shall be designed and constructed in accordance with the following
criteria:
(1) The structure shall pass flood
flows without loss of stability.
(2) The structure may not create or
constitute a hazard to life or property, or both.
(3) The structure may not materially alter
the natural regimen of the stream.
(4) The structure may not so increase
velocity or direct flow in a manner which results in erosion of stream beds and
banks.
(5) The structure may not
significantly increase water surface elevations.
(6) The structure shall be consistent with
local flood plain management programs.
(b) In determining flood flows and
frequencies for purposes of this subchapter, hydrologic analysis shall be by
methods generally accepted in the engineering profession.
(c) The general criteria for design flows are
as follows:
(1) Rural area-25-year frequency
flood flow.
(2) Suburban
area-50-year frequency flood flow.
(3) Urban area-100-year frequency flood
flow.
(d) The
determination of flood flows for design shall be made with reasonable
consideration of development which may alter the runoff characteristics of the
watershed during the anticipated life of the structure. Specific design
requirements in subsection (c) may be varied to fit the conditions at the site
and the requirements of flood plain management regulations and
ordinances.
(e) The structures shall
pass the 100-year frequency flood with less than a 1.0-foot increase in the
natural unobstructed 100-year water surface elevation, except where the
structure would be located in a floodway which is delineated on a FEMA map, in
which case no increase in the 100-year water surface elevation will be
permitted. Exceptions to this criteria may be approved by the Department if the
applicant prepares a risk assessment which demonstrates, and the Department
finds, that the structure will not significantly increase the flooding threat
to life and property or the environment, and if applicable, is consistent with
municipal floodplain management programs adopted under the National Flood
Insurance Program and a FEMA Flood Insurance Study. This information may be
obtained from the Department of Community Affairs, Floodplain Management
Division, Forum Building, Harrisburg, Pennsylvania 17120.
Notes
The
provisions of this § 105.161 adopted August 11, 1978, effective
8/28/1978, 8 Pa.B. 2229; amended
September 26, 1980, effective 9/27/1980, 10 Pa.B. 3843; amended October 11,
1991, effective 10/12/1991, 21
Pa.B. 4911.
The provisions of this § 105.161 amended under
the Dam Safety and Encroachments Act (32 P. S. §§
693.1-693.27); The Clean Streams
Law (35 P. S. §§
691.1-691.1001); section 7 of the
act of June 14, 1923 (P. L. 704, No. 294) (32 P. S. §
597); sections 514, 1901-A, 1908-A, 1917-A
and 1920-A of The Administrative Code of 1929 (71 P. S. §§
194,
510-1,
510-8,
510-17 and
510-20); and the Flood Plain
Management Act (32 P. S. §§
679.101-679.601).
