DESIGN CRITERIA FOR CONSTRUCTION OR MODIFICATION
§ 105.161. Hydraulic capacity.
(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.
Authority 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).
Source The provisions of this § 105.161 adopted August 11, 1978, effective August 28, 1978, 8 Pa.B. 2229; amended September 26, 1980, effective September 27, 1980, 10 Pa.B. 3843; amended October 11, 1991, effective October 12, 1991, 21 Pa.B. 4911. Immediately preceding text appears at serial page (117699).
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