Construction in the Floodplain

What is a floodplain?

A floodplain is the area adjacent to a river, creek, lake, stream, or other open waterway that is subject to flooding when there is a significant rain. Floodplains can be entirely within the waterway.

How do I find out if my lot is in the floodplain?

You can request this information from the County Engineer's Office. All floodplain information is handled in "writing", so you must mail, email, fax, or deliver requests to the department directly. We must do this work with written documents because it is very easy to confuse or misunderstand locations or directions. It's important for us and for you to get the data correct. Send a copy of your lot, a deed, or a legal description along with a map indicating the location of the proposed improvements.

What is a 100-year floodplain? A 25-year floodplain?

If your property is in the 100-year floodplain, there is a 1-in-100 chance in any given year that your property will flood. If it is in the 25-year floodplain, there is a 1-in-25 chance in any given year that your property will flood. The statistical chance of flooding is not changed by any one flooding event; but repeated flooding may result in the floodplain being recalculated.

A 100-year floodplain is always wider than a 25-year floodplain, and the 25-year floodplain is contained within the 100-year floodplain.

Why do floodplain maps change?

Comal County works with the Federal Emergency Management Agency (FEMA) to update floodplain maps to show the areas that will flood during the 100-year flood in support of the National Flood Insurance Program.

The changes in floodplain maps reflect changes in land use (such as increased building activity), changes in the waterways, and flood control improvements (such as detention ponds or other flood control measures).

As more lots are covered with more buildings and parking lots, the peak discharges of water that flows into creeks and lakes increase because there is less vegetation to absorb the water when it rains and runoff velocities are generally increased. This is one reason why buildings that were not originally built in a floodplain can, after time be in the100-year floodplain.

If the County or private property owners install flood controls or detention ponds, the peak discharges going to creeks and lakes can be reduced. Certain flood control measures have caused the 25-year or 100-year floodplain to be removed from some lots.

Can I build on a lot in the 100-year floodplain? The 25-year floodplain?

If you wish to build a home or place a manufactured home in the 100-year floodplain, you must file a permit application. You must also file a plot plan and submit building plans that shows compliance with all floodplain regulations as well as other County standards. When your site plan and building permit applications are approved, you can request a pre-construction conference and then begin constructing the improvements and requesting inspections, if required. All construction that is allowed in floodplain areas must have the lowest floor elevation at or above the 100-year floodplain elevation.

If you have a multi-family or commercial project, you may build in the 100-year floodplain only if your lot complies with all floodplain standards.

Building construction is prohibited for projects that will not comply with all standards for construction in the 100-year floodplain.

Are there special requirements in the floodplain?

Yes. Structures are generally required to be elevated above the base flood elevation and an engineering evaluations is required to determine no adverse impact to upstream properties.

If I build an addition or deck outside my building, do I need to raise my existing building one foot above the 100-year floodplain?

The addition or new deck must comply with all floodplain standards. If the value of the addition and remodeling of the home or business exceeds 50% of the value of the existing home or business, the existing structure(s) must be elevated one foot above the 100-year floodplain or flood-proofed according to the County's floodplain standards.

What is the penalty if I don't secure all my approvals?

• You would not be able to occupy or use your building or parking lot until you received all required permits and passed inspections.
• You could be fined.
• The county may require the removal of the improvements constructed without permits and inspections.

Who can I see if I need additional information?

The Comal County Engineer's Office can help you, your architect or engineer obtain additional information about requirements for building in the floodplain.