Pasadena, Texas | Flood and Drainage Rules

Pasadena, Texas Flood and Drainage Rules: Floor Heights, Permits, Fill and Detention

Pasadena, Texas writes its flood rules into Chapter 9, Article IX of the Code of Ordinances, "Flood Damage Prevention," adopted in full by Ordinance No. 20-186 on January 5, 2021. Much of this article applies to every lot in the city: every development needs a floodplain permit, every building needs an elevation certificate, and every new floor must clear the street and the 500-year flood. This page sets out each rule with its section. The Pasadena overview gives the short version.

The Maps and the Words

Sec. 9-177 says "This article shall apply to all areas within the jurisdiction of the City of Pasadena, Texas." Sec. 9-178 adopts the Federal Emergency Management Agency (FEMA) flood study for Harris County and its maps: volumes 1, 2 and 4 of 12 dated May 2, 2019, volumes 3 and 5 to 12 dated January 6, 2017, "and any revisions thereto." The director of public works is the floodplain administrator (Sec. 9-184) and decides where a boundary falls "where there appears to be a conflict between a mapped boundary and actual field conditions."

A few terms carry the rules. The base flood is "the flood having a one (1) percent chance of being equaled or exceeded in any given year," the 100-year flood. The 500-year flood has a 0.2 percent chance in any year; the code calls its mapped area the "500-year (0.2 percent) (Shaded X)" flood zone. A floodway is "the channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood." Freeboard is "a factor of safety usually expressed in feet above a flood level." The flood insurance study (FIS) is "the official report provided by the Federal Insurance Administration," with the 100-year and 500-year flood heights the rules use.

Where rules overlap, Sec. 9-182 says "whichever imposes the more stringent restrictions shall prevail." And Sec. 9-183 warns that the article "does not imply that land outside the areas of special flood hazards or uses permitted within such areas will be free from flooding or flood damages."

How High the Floor Must Be

Sec. 9-189(1) applies "In all areas of the city," except the coastal high hazard zones, and covers "New construction or substantial improvement of any structure." It requires "the lowest floor, including the basement, garage, mechanical, electrical and HVAC equipment" to be raised to the height in the table. The 500-year flood elevation is read "from the effective FIS using City of Pasadena benchmarks and correcting for latest NAVD leveling," a survey adjustment the City supplies on request.

Source: Pasadena Code of Ordinances on municode, Supplement 33 Update 1, Secs. 9-189 and 9-190.

The street rule is the one that reaches lots outside any mapped zone. A lot whose street centerline sits above the 500-year flood still needs its floor a foot above that centerline. A registered engineer or surveyor certifies the height. Before the "top of form" inspection, when the slab forms are set, Sec. 9-189(13) requires a "building under construction elevation certificate" showing the street centerlines, the base flood elevation, the top of form elevation and a survey of the whole site. Sec. 9-188(9) then requires a finished construction certificate "for each and every building within the City of Pasadena, regardless of its location with respect to the flood hazard boundary."

A commercial or other nonresidential building may instead be floodproofed, made watertight with walls that resist water, below the 500-year flood elevation, with an engineer's or architect's certification (Sec. 9-189(3)). Critical facilities, such as nursing homes and fire stations, are kept out of the 100-year zone.

The Floodplain Development Permit

Sec. 9-179 reads: "A floodplain development permit shall be required to ensure conformance with the provisions of this article regardless of whether the development is within the special flood hazard boundary. A floodplain development permit shall be approved before a building permit application is submitted." Development is "any manmade change to improved or unimproved real estate," including buildings, filling, grading and paving.

Under Sec. 9-186(a), the application includes "two (2) complete sets of engineer sealed plans" with existing and proposed ground levels, the FEMA 100-year and 500-year flood elevations, benchmarks, the centerline elevations of adjacent streets, drainage, fill volume, any detention or mitigation ponds with sealed calculations, and a storm water pollution prevention plan. The Engineering Department's application form lists the same items and says "(City of Pasadena detention rate is 0.55 ac-ft/ac for the total acreage)." It warns that "Approval of this permit does not guarantee approval and/or issuance of a building permit, site plan approval, plat approval or grant a variance," and that "All approved Floodplain Development Permits must be included with the Building Permit Application." Since April 28, 2026, the Planning Department takes "Site Plan and Floodplain Development Permit Applications (combined)" through its online Citizen Self-Service portal.

The administrator weighs factors listed in Sec. 9-186(b), among them "The safety of access to the property in times of flood for ordinary and emergency vehicles." A violation is a misdemeanor with a fine of "not less than five hundred dollars ($500.00) or more than two thousand dollars ($2,000.00) for each violation per day."

Drainage Plans and Lot Grading

Every building permit application carries a drainage plan under Sec. 9-189(11). The plan must not dam or divert the natural flow of water from neighboring land; must carry into the City storm system the water from a five-year storm that used to cross the lot from next door; and must keep "positive drainage on residential lots as originally designed and approved by director from rear to the front." A commercial property, "including residential property used in any form as commercial," must collect all drainage on site, including roof drains, into a storm sewer connected to the City system with reinforced concrete pipe, with "no sheet flow across property lines." The plan must be built before the certificate of occupancy.

Raising a building raises the ground around it. Sec. 9-76(g) allows "a maximum five (5) feet of elevated grade around the structure with a maintainable slope transitioning to natural ground at property line," and the setback sections allow the City to require more distance "to provide adequate drainage." Sec. 9-188(10) adds: "There shall be no adverse flooding impact on any property from any fill placed in the same or nearby watershed."

Fill and Flood Storage

Fill is "any material added above natural grade," and the code says "Any fill placed within the city limits of Pasadena must have a fill permit issued by the city floodplain manager or the designated certified floodplain manager." In the flood zones, Sec. 9-189(8) adds: "Fill placed within the 100-year (one (1) percent) or 500-year (0.2 percent) (Shaded X) flood zones shall be mitigated on a 1:1 basis on the developing site such that no flood storage capacity is lost." Mitigation means digging out an equal volume of storage elsewhere on the site.

For small jobs, the Engineering Department's Residential Fill Permit is limited to an increase of less than 6 inches, is for "placing fill on single residential lot - NOT for Building or Construction," notes that "Fill may not be placed within 5 years on same property," and "Expires 90 days after Approval." Fill for a building pad follows Sec. 9-191: an engineered, compacted design sealed by a Texas engineer and a development permit before any filling.

Detention Ponds

Detention holds stormwater on a site and lets it out slowly. Sec. 9-194.1 says: "For all new development, and redevelopment with greater than fifty (50) percent site improvements, the developer shall use Atlas 14 rainfall data and install detention [pond facilities] at a rate of 0.55 acre feet per acre." Atlas 14 rainfall data is also what the City's permit form asks engineers to use in drainage calculations. "Hydrograph timing cannot be used as a substitution for detention." No construction permit issues until planning and public works staff check the pond design, and ponds must be built before the certificate of occupancy.

An acre-foot is the water that covers one acre one foot deep, so 0.55 acre-feet per acre equals 0.55 feet of water over the site. By VanPlex arithmetic, that is 3,300 cubic feet for a 6,000 square foot site and 23,958 cubic feet for one acre. The code does not set a smaller rate for a single home lot; ask the Engineering Department how it applies the rate to your site before you lay out the buildings.

• Design. A 10-foot maintenance berm all around, 4-to-1 side slopes, a 100-year design with 1 foot of freeboard, and water in and out at one controlled concrete structure (Sec. 9-194.2).
• Placement. Behind the building where possible, at least 15 feet from structures and 10 feet from property lines, with no fence around or in the pond and a 5-foot landscaped screen from the street.
• Sharing. One pond may not serve more than one commercial owner, and "Detention ponds cannot be shared between residential and commercial properties." Multifamily developments count as residential.
• Other agencies. A site next to a Harris County Flood Control District facility "must drain to HCFCD," with HCFCD approval before the City review.
• Upkeep. The owner maintains the pond under a signed maintenance covenant, and each pond is inspected every year (Sec. 9-194.3).

On an apartment site, a dry-bottom pond "may be considered as open space" toward the 35 percent rule if all residents can reach it and the public works director approves (Sec. 9-2).

Floodways, Armand Bayou and Other Limits

• Floodways. "Encroachments are prohibited, including fill, grading, paving, new construction or expansion, substantial improvements and any other development or improvements" (Sec. 9-189(10)).
• Armand Bayou. "There shall be no new development within the 100-year (one (1) percent) flood hazard zone in the Armand Bayou Watershed south of the tidal influenced flow" (Sec. 9-188(8)).
• Manufactured homes. None "within two hundred (200) feet of a designated floodway" (Sec. 9-189(5)).
• Large subdivisions. Base flood elevation data must be generated for proposals of more than 50 lots or 5 acres, whichever is lesser, and soil borings at least 10 feet deep are required (Sec. 9-194).
• Sales. Property in the 100-year (1 percent) flood zone must be disclosed as flood prone for any property sale (Sec. 9-189(9)).

Repairs to an older home meet the full rules when they are a substantial improvement: work whose cost "equals or exceeds fifty (50) percent of the market value of the structure" before construction starts, "as determined from the Harris County Appraisal District." The applicant submits the structure's value and the cost of all labor and materials.

Where the Flood Texts Disagree

• Sec. 9-176 says an enclosure "usable solely for parking or vehicles, building access or storage" outside a basement "is not considered a building's lowest floor," while Sec. 9-189(1) requires "the lowest floor, including the basement, garage," to be elevated. Sec. 9-189 names the garage, so plan the garage slab at the required height and confirm with the floodplain administrator.
• Appendix A, the 1967 subdivision ordinance, defines "Flood plain" to "include all areas thirteen (13) feet or less above the mean sea level," while Article IX uses the FEMA maps adopted in Sec. 9-178. Sec. 9-182 says the more stringent rule prevails.

Where to Go Next

Related on VanPlex: the Pasadena overview, insurance and flood in Texas, and Houston flood rules.

Frequently Asked Questions

Official sources (checked October 2026)