San Jacinto Flood Planning Group’s Proposed Minimum Floodplain Management Practices

11/11/25 – The San Jacinto Regional Flood Planning Group will consider adopting a set of proposed minimum floodplain management practices for the entire river basin at its meeting on November 13. The standards are part of a requirement by the Texas Water Development Board for the 2028 update of the state’s next flood plan.

The recommendations start on page 22 of the technical document. However, the document is 634 pages long and 214 megabytes in size. So, I’ve extracted them for easy reference.

They are targeted to floodplain managers in cities and counties in the San Jacinto River Basin. But they affect everyone from developers, homebuilders, and home buyers to home owners, insurers and first responders. So, I will add some explanatory comments below the proposed regs for those who may not understand their logic or language.

Proposed Minimum Floodplain Management Practices

Participation in the National Flood Insurance Program (NFIP)

• All regulatory entities to implement ordinances that meet minimum requirements per the NFIP
• All regulatory entities to remain active NFIP participants in good standing
• All regulatory entities to participate in the Community Rating System (CRS) Program to reduce flood insurance rate premiums across the region.

Development of “No Adverse Impact” Policies

• All regulatory entities to define a no adverse impact policy.
• The no adverse impact policy should be focused on preventing negative impacts. Evaluation of impacts should be completed using best available hydrologic and hydraulic modeling, where appropriate.

Establish Minimum Finished Floor Elevations

• All new habitable structures shall have a finished floor elevation established at or above or waterproofed to the FEMA effective 0.2% Annual Chance of Exceedance (ACE) flood elevation as shown on effective FIRMs except in areas designated as coastal flood zones.
• Where regulatory mapping has been updated using Atlas 14 or newer rainfall data, all new habitable structures shall have a finished floor elevation established at or above or waterproofed to the FEMA effective 1.0% ACE flood elevation as shown on effective FIRMs except in areas designated as coastal flood zones.
• In areas designated as coastal flood zones, all new habitable structures shall have a finished floor elevation established at or above or waterproofed to the FEMA effective 1.0% ACE flood elevation as shown on effective FIRMS plus 1 foot of freeboard.
• All new critical facilities shall have a finished floor elevation established at or above or waterproofed to the FEMA effective 0.2% ACE flood elevation as shown on effective FIRMs plus 2 feet of freeboard except in areas designated as coastal flood zones.
• Where regulatory mapping has been updated using Atlas 14 or newer rainfall data, all new critical facilities shall have a finished floor elevation established at or above or waterproofed to the FEMA effective 1.0% ACE flood elevation as shown on effective FIRMs plus 2 feet of freeboard except in areas designated as coastal flood zones.
• In areas designated as coastal flood zones, all new critical facilities shall have a finished floor elevation established at or above or waterproofed to the FEMA effective 1.0%ACE flood elevation as shown on effective FIRMS plus 2 feet of freeboard.

Encourage Use of Best Available Data

• Utilize the latest rainfall data, NOAA Atlas 14 or newer rainfall data, when conducting new analyses, designing drainage infrastructure, or developing regulations and criteria.

Compensatory Storage Requirements in the 1.0% ACE Floodplain

• Any reduction in floodplain storage or conveyance capacity within the 1.0% ACE regulatory floodplain must be offset with a hydraulically equivalent (one-to-one) volume of mitigation sufficient to offset the reduction, except in areas identified as coastal flood zones.
• A full hydrologic and hydraulic analysis should be performed to demonstrate that floodplain fill mitigation provided is sufficient.

Compensatory Storage Requirements in the 0.2/% ACE Floodplain

• Any reduction in floodplain storage or conveyance capacity within the 0.2% ACE regulatory floodplain must be offset with a hydraulically equivalent (one-to-one) volume of mitigation sufficient to offset the reduction, except in areas identified as coastal flood zones.
• A full hydrologic and hydraulic analysis should be performed to demonstrate that floodplain fill mitigation provided is sufficient.

Development of Detailed Hydrologic and Hydraulic Analysis Criteria/Requirements

• All regulatory entities to develop hydrologic and hydraulic modeling criteria or requirements.
• All regulatory entities to identify features of a proposed development that would warrant a full hydrologic and hydraulic analysis.

Incentivizing the Preservation of the Floodplain

• All regulatory entities to explore and develop systems for incentivizing the preservation of the floodplain directly within the regulatory floodplain or within 100 feet of the banks of unstudied streams.

Nature-Based Solutions

• All regulatory entities to adopt criteria for design of nature-based solutions for drainage infrastructure and stormwater quality management. TWDB’s nature-based solutions guidance manual should be referenced when adopting criteria.
• All regulatory entities to establish criteria that would require new construction to incorporate, or minimally consider, nature-based solutions in design of drainage infrastructure and mitigation.

Operations and Maintenance

• All flood-related authorities who own and operate drainage infrastructure to create a maintenance plan for those assets to manage and reduce future replacement costs.
• All flood-related authorities who own and operate drainage infrastructure to develop and maintain an asset management plan, including GIS dataset of assets, to support maintenance of infrastructure. Datasets to leverage infrastructure toolkit that has been prepared by the TWDB to improve the assessment of drainage infrastructure condition and functionality.

Property Acquisition Program

• All regulatory entities to develop property acquisition program for repetitive loss structures.

Flood Warning System

• All regulatory entities to develop flood warning system for public awareness.

Hazard Mitigation Plan

• All regulatory entities to develop a Hazard Mitigation Plan to help prepare for, respond to, and recover from flood events and maximize funding eligibility for disaster recovery funding.

Explaining the Proposed Minimum Floodplain Regulations

If you’re scratching your head about anything above, the following explanations may help.

NFIP and CRS

The National Flood Insurance Program’s Community Rating System (CRS) encourages counties and municipalities to go beyond minimum floodplain management requirements in exchange for discounts on flood insurance premiums for their residents.

CRS rewards local governments that implement regulations which:

1. Reduce flood losses
2. Encourage accurate insurance rating
3. Promote awareness of flood risk

Depending on the strength of a community’s practices, it could earn its residents anywhere from 0% to 45% discounts on their flood insurance premiums. Currently, Houston and Harris County earn 25% discounts. Montgomery County earns 15%.

So encourage your elected officials. This recommendation hits you in the pocketbook.

No Adverse Impact

Chapter 11.086 of the Texas Water Code says “No person may divert or impound the natural flow of surface waters in this state, or permit a diversion or impounding by him to continue, in a manner that damages the property of another by the overflow of the water diverted or impounded.”

The San Jacinto Flood Groups recommendation encourages local governments to adopt policies and best practices that prevent such adverse impacts.

Finished Floor Elevations

These recommendations encourage cities and counties to establish minimum heights above expected flood levels for buildings. “Finished floor” refers to living space. Sometimes people park cars under the first finished floor. This recommendation does not count garages below living space.

Together these recommendations say that if an area has adopted Atlas 14 (the latest rainfall probability statistics) and flood maps have been updated, the first finished floor can be set at or above the 100-year (1%) flood level. Otherwise, the first finished floor should be elevated at or above the 500-year (.02%) flood level.

Critical facilities, such as hospitals, fire stations, police stations and evacuation centers should always be at least 2 feet above the 500-year flood elevation.

Compensatory Storage Requirements

This recommendation is the same as “no net fill” requirements already in effect for many 100-year floodplains in the region. It has the effect of saying, “You can’t bring dirt into the floodplain, but you can move it around.” For instance, to elevate homes, builders would have to use the dirt excavated from a detention basin. It’s designed to prevent constriction of the floodplain, which could raise flood heights.

Hydrologic and Hydraulic (H&H) Analyses

H&H Studies define where and how flooding occurs, including how fast runoff occurs, how fast it will move and where it will go. They replace flood maps based on outdated or incomplete data. They incorporate Atlas 14 rainfall data and account for new development, impervious cover, and drainage changes, including recent channel improvements or detention basins.

They enable updated floodplain mapping and help build regional consistency in data and methodology. That in turn helps improve local floodplain regulations and insurance accuracy.

Floodplain Preservation and Nature-Based Solutions

The farther homes are from floodplains, the safer they are. Preventing flood damage is vastly cheaper than correcting damage afterwards, often by a factor of 5 to 10 times or more.

Floodplain preservation provides permanent benefits including economic continuity, insurance savings, environmental benefits, and recreational benefits. It also avoids post-flood recovery costs including infrastructure repair, housing assistance, insurance claims, business disruption, and environmental cleanup.

O&M, Property Acquisition, Flood-Warning System, and Hazard Mitigation Plan

The last four floodplain management recommendations emphasize preparation.

• Regular maintenance, for instance, can keep channels from becoming clogged with sediment.
• Buyouts in areas that flood repeatedly prevent future damage and mitigation costs.
• Flood warning systems can tell people when to evacuate or streets to avoid in a flood.
• A hazard mitigation plan helps identify natural hazards, assess risks and vulnerabilities, and outline long-term strategies to deal with them.

As common-sense as these ideas are, it’s amazing that many areas still have not adopted them. That may be why Texas has more people living in floodplains than the populations of 30 states.

Posted by Bob Rehak on 11/11/25

2996 Days since Hurricane Harvey

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