Is Your Property in a Floodplain?
What Central Texas Developers Need to Know Before You Build
Every few years, Central Texas reminds everyone why we take drainage seriously. Our rainfall doesn't come evenly across the calendar — it tends to arrive in two heavy stretches, one in late spring and another in the fall. By September and October, the ground is often already wet, the creeks are already up, and a single slow-moving storm can turn a quiet draw into a fast-moving hazard. The tragic Hill Country flooding in July 2025 was a hard reminder that flood risk here is real, and it's why so many developers, lenders, and cities are looking harder at floodplains than they were a few years ago.
So if you're buying land or planning a project anywhere near a creek, river, or low-lying area, one of the first questions worth answering is a simple one: is any part of this property in a floodplain? The answer changes what you can build, where you can build it, how much it costs, and how long your permitting takes. Here's what that actually means in practice, and how we help clients work through it.
What "floodplain" really mean
When people say a property is "in the floodplain," they're usually talking about a Special Flood Hazard Area shown on FEMA's Flood Insurance Rate Maps (FIRMs). That's the land expected to be inundated by the base flood — the flood that has a 1% chance of happening in any given year. You'll often hear it called the "100-year floodplain," which is a little misleading. It doesn't mean a flood happens once a century. It means there's roughly a 1-in-100 chance every single year, which over the life of a 30-year mortgage adds up to about a 1-in-4 chance. Central Texas has seen "100-year" events land back-to-back.
Within that mapped area, two zones matter most:
Thefloodplain — the shallower, slower storage area outside the floodway but still inside the 1%-chance floodplain.
The floodway — the channel and the land immediately beside it that carries the bulk of the moving water. This is the most restricted ground on your site.
FEMA maps also give you a Base Flood Elevation (BFE)in many areas — the water-surface elevation the base flood is expected to reach. Almost every rule that follows comes back to that number.
The map is a starting point, not the final word
Here's something a lot of buyers don't realize: the FEMA maps are regional, they're often years old, and they were never drawn to the resolution of your individual parcel. A property can sit right on the line, or the mapped floodplain can be based on modeling that predates recent development upstream. That cuts both ways. Sometimes a site that looks "clear" on the map actually carries real risk, and sometimes a site that looks encumbered can be shown — through proper engineering — to be higher and drier than the map suggests.
That's why the map is where we start, not where we stop. A lot of the time the effective FEMA study is sound, and the right move is simply to engineer the site around it — respecting the mapped floodway and base flood elevation and laying the project out to work within those limits instead of fighting them. Other times the mapping is dated, too coarse for your parcel, or clearly doesn't match what's on the ground, and it's worth running our own numbers. When that's warranted, we build a detailed hydraulic model in HEC-RAS — the same tool behind the FEMA and TxDOT studies — to show how water actually moves through your reach of the creek under design storm conditions. A big part of the job is knowing which of those two paths your project actually needs, so you're not paying for a study you don't require.
If you're in the floodplain, you'll need a floodplain development permit
Any development inside a mapped Special Flood Hazard Area in the City of Waco — and in McLennan County and the surrounding communities — requires a floodplain development permit before work begins. And "development" is broader than most people expect. It's not just buildings. Clearing, grading, placing fill, excavation, and altering a watercourse all count.
Depending on what you're proposing, the community will typically want to see some combination of:
A site plan showing the work relative to the mapped floodplain and floodway
Proposed finished-floor elevations for any structures
An Elevation Certificate prepared by a surveyor or engineer
For anything in or affecting the floodway, a no-rise certification backed by engineering analysis
For non-residential buildings, an elevation-or-floodproofing plan
Skipping this step is not a corner worth cutting. Building in a regulated floodplain without a permit can stop your project cold, jeopardize your certificate of occupancy, create serious flood-insurance problems for you and future owners, and — most importantly — put people and property in harm's way.
The "no-rise" rule is the one that trips people up
If any part of your work touches the floodplain, you generally have to prove it causes no rise in the base flood elevation — zero increase, or in some cases a very small permitted amount. The logic is straightforward: the floodway is the part of the corridor doing the heavy lifting of moving water downstream. Fill it in or squeeze it, and you push that water somewhere else — usually onto your neighbor.
Demonstrating no-rise isn't a checkbox. It's a hydraulic modeling exercise, comparing existing and proposed conditions and documenting that your project doesn't raise the water surface. This is exactly the kind of analysis that needs to be done — and sealed — by a licensed engineer before the city will sign off. Get it right and the permit moves. Guess at it, and you're looking at redesigns and delays.
Freeboard, fill, and finished-floor elevation
Even outside the floodway, building in the floodplain usually means elevating. Most Central Texas communities require your lowest finished floor to sit a set distance above the BFE — an extra margin called freeboard, commonly one to two feet depending on the jurisdiction. That margin exists because the maps aren't perfect and storms don't read the rules. Confirm the current standard for your specific city or county, because these requirements have been tightening.
If your plan involves placing fill to raise a building pad, expect questions about compensatory storage — replacing the floodplain volume you're filling so you're not simply displacing floodwater onto adjacent properties. How strictly that's applied varies by community, and it's another reason to model before you commit to a grading plan.
Sometimes the map can be changed — legitimately
If a proper study shows that your property (or part of it) actually sits above the base flood, or if you're raising the site with engineered fill, FEMA has a formal process to update the maps: a Conditional Letter of Map Revision (CLOMR) before construction and a Letter of Map Revision (LOMR) after. A successful LOMR can remove a structure from the Special Flood Hazard Area, which can eliminate the mandatory flood-insurance requirement and meaningfully change the economics of a deal.
This is a real, legitimate tool — but it's an engineering-and-paperwork process with FEMA, not a shortcut, and it needs to be scoped early. Done at the right time, it can save a project. Discovered too late, it just adds months.
Why this belongs at the front of your due diligence
The theme running through all of this is the same one we come back to again and again: the cheapest time to deal with the floodplain is before you close on the property. Once you own it, the constraints are yours. Before you own it, they're a negotiating point — or a reason to walk.
We regularly help clients answer these questions during due diligence: Is the site actually encumbered, or does it just look that way on the map? How much developable area do you really have once the floodway and setbacks come off? What will the elevation and permitting requirements do to your pad costs and your schedule? Is a map revision worth pursuing? Getting straight answers up front is a lot cheaper than discovering them halfway through design.
Talk to an engineer before you commit
Floodplain work is one of the areas where having the licensed engineer involved from day one makes the biggest difference. At Merritt Engineering, we help clients with these issues as a licensed Professional Engineer and Certified Floodplain Manager. If you're evaluating a property near a creek or river in Waco, McLennan County, or anywhere in Central Texas, I'm glad to look at the mapping with you and tell you honestly what you're working with.
Thinking about a site that might touch the floodplain? Reach out and let's pull up the maps together before you make the call.
Related reading:
What Is a Drainage Study and When Does Your Project Need One? ·
Do I Need Stormwater Detention for My Development in Waco? ·
Why Your Civil Engineer Should Be the First Call on Any Land Development Project