CITY OF HOUSTON DESIGN MANUAL
Department of Public Works & Engineering Stormwater Design Requirements
9-17
3. Relationship of Structures to Street: All structures shall be above the maximum
ponding elevation anticipated resulting from the extreme event analysis
a. Barring conditions listed in 9.05.D.3.a and b, the maximum ponding
elevation for the 100-year event at any point along the street shall not be
higher than the natural ground elevation at the R.O.W. line.
b. For City CIP Projects, the maximum ponding elevations shall be no higher
than 12 inches below the finished slab elevations, or, if the finished slab
elevations are less than 12-inches above the natural ground
elevations
at
the R.O.W., the ponding elevations shall be no higher than the natural
ground elevations at the R.O.W. In instances where the maximum ponding
elevation for the 100-year event is not within the natural ground elevation
at the R.O.W. line, the engineer will add a note on the drawings indicating
the rainfall frequency event is designed to be conveyed within the R.O.W.
c. For Development or Redevelopment by private entities, the post- project
maximum WSE shall be no higher than the pre- project maximum WSE in
surrounding areas, and proposed finished slab elevation shall be above the
post-project maximum WSE. The Maximum Ponding Elevation is
determined from the physical characteristics of an area, and may change
as a result of the proposed Development. Where existing topographic
conditions, project location within a special flood hazard area, and/or
other site conditions preclude achieving this objective, the City will
consider waiver of this requirement upon submittal of documentation and
analysis prepared, signed, and sealed by a professional engineer,
registered in the State of Texas. Analysis shall demonstrate that structural
flooding will not occur and will identify the rainfall frequency event that
will be conveyed within the R.O.W. The limiting parameter will depend
on project-specific conditions, and the most restrictive condition (the
lowest ponded water elevation) shall govern.
4. Design Considerations:
Streets shall be designed so that consecutive high points in the street will provide for a
gravity flow of drainage to the ultimate outlet. If a detention facility is designed to
mitigate peak flows from the extreme event, the overland flow path shall carry the
extreme event sheet flow to the detention facility. If the extreme event sheet flow must
enter a receiving channel, the overland flow path shall carry the extreme event sheet
flow to the channel. In the event that there is no overland flow path, or the overland
flow path is insufficient to carry all of the extreme event sheet flow, the inlets and
storm sewer at the downstream end of the overland flow path shall be sized to carry
the extreme event sheet flow from the end of the overland flow path into the detention
facility or receiving channel.
a. The maximum depth of ponding at high points shall be 6-inches above top