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Floodplain, who’s in charge, and what does it mean?

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For some reason, of all the “layers” encompassing lands throughout Teton Valley (or anywhere else), floodplain has always been the most difficult for me to understand. Merriam-Webster defines floodplain as “level land that may be submerged by floodwaters, or a plain built up by stream deposition.” To me, floodplain isn’t necessarily always flat, but it isn’t the definition that I struggle with. It more has to do with what it means for those that have floodplains indicated on their property.

Before I go any further here, and with my preface out of the way, I STILL struggle with floodplain. With that—and all articles I have written over the years—take this with a grain of salt. These are my interpretations about complex issues, and I have no authority on these matters. Always do your own research through proper authoritative agencies.

Tayson’s definition of floodplain, and the purpose of having this information:

I don’t think anybody’s really struggling with the definition here, but to expand: Floodplain, as I understand it, is determined through elevation (obviously the low-lying areas are going to accumulate water), hydrology (how water moves), and soil types. For example, in a past article I talked about attending a FEMA open house at the Teton County Courthouse, which detailed how this data is collected and how the County is working with FEMA to update its flood maps. As of this writing, the appeal period for those wishing to contest the proposed maps is closing, paving the way for final approval of the new, more accurate flood zones and associated maps.

The purpose of having this data:

To me, the greatest benefit of having this information is to mitigate risk. In a real-life scenario, I don’t think that Merriam-Webster’s definition works to describe potential areas of risk. Since water moves in precarious ways, we can hope to rely on science and data to give us that clearer picture of areas of risk. This can then be used for landowners to plan new projects or mitigate risk with existing structures. It’s also used by insurance companies—particularly those participating in the National Flood Insurance Program—to assess flood risk and determine insurance requirements. As I understand it, the NFIP is a federal program managed by FEMA that provides flood insurance to property owners, renters, and businesses, and it relies heavily on FEMA’s floodplain maps to assess risk and set insurance rates.

How the data is obtained and displayed:

Again, no expert here, but I do know that the latest information available was provided through LiDAR flyovers to gather contours and terrain, as well as hydrologic and soil studies to model how water moves and flows. Because of the level of technology, these maps can display not only areas of concern but also different levels of risk in certain areas. Historically, my understanding was that the primary defined areas of risk included 100-year and 500-year flood risk areas. I also understand that new efforts are being made to display this risk through percentages as opposed to yearly events, so as not to confuse the intended definition of that risk.

As an example, a property in a 500-year flood risk area does not necessarily mean it will only flood once every 500 years. Describing that same risk as a 0.2% annual chance of flooding conveys the same statistical probability, but in a way that more clearly communicates the level of risk. Similarly, a 100-year flood event area might also be described as having a 1% annual chance of flooding. Because of the advanced technology used to gather this new data, additional flood risk areas can also be defined—but it’s important to remember that these are estimates based on modeling. Obviously, anything can happen.

Who creates the maps?

The maps themselves are generally created through FEMA (Federal Emergency Management Agency) in cooperation with the National Flood Insurance Program (NFIP) and local jurisdictions. FEMA contracts with engineering firms and works with local governments to ensure maps reflect both scientific modeling and local conditions. These are the same maps used for regulating development in flood-prone areas and determining flood insurance requirements.

Can the information be challenged?

As advanced as this data might be, it is broadly used across great areas of landscape. As a result, property owners or developers may have the opportunity to challenge this data through site-specific engineering to determine the exact elevation of a structure relative to the projected floodwaters. This is typically done through an elevation study, which can then be used to produce an Elevation Certificate. While this certificate is often required for determining compliance with building standards or securing flood insurance, it can also be submitted to FEMA to support a request to remove a structure from a mapped high-risk zone.

In some cases, more formal map changes are needed. A Letter of Map Amendment (LOMA) can be requested when a property owner believes their structure or lot was incorrectly included in a flood zone. These are often supported by Elevation Certificates and typically apply to individual lots or structures. For larger-scale changes—such as those affecting an entire development or subdivision—a Letter of Map Revision (LOMR) may be appropriate. These tools can be essential for developers and landowners when building or remodeling near designated floodplains.

What is the County’s role?

In the event that there is development in a floodplain, the County’s policy (as I interpreted during a meeting with the County on the subject) was for structures to be a minimum of one foot above freeboard.

In that meeting, they referred to something called “freeboard,” which, as it turns out, is a nautical term. In boating, freeboard is the distance between the waterline and the edge of the boat—basically the buffer that keeps water from spilling in. In the floodplain world, it’s a similar idea. Freeboard refers to the extra height that structures need to be built above the projected flood level. It gives a bit of wiggle room for things like model inaccuracies or bigger-than-expected storms. In Teton County, that buffer is currently set at one foot above the base flood elevation for any development in a flood zone, though which zone this applies to should be clarified prior to any construction.

Additionally, the representative in the meeting stated that the County does maintain some generic latitude, which might include looking at developable areas on a building site that may not be in the floodplain. There are also considerations when it comes to vegetation removal in instances of development in or around a floodplain, understanding that removing vegetation can also impact these waterways. Because I have not been able to point to any specific area of the code to identify the County’s requirements in addition to those set forth or recommended by FEMA, it is important to remember to consult with industry professionals and engineers, and to work directly with the planning and zoning and/or building departments to understand what’s allowed, and what’s required.

Teton County Idaho’s FEMA Flood Map Updates

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On September 18th, 2024, I attended an open house for a special board with Teton County in conjunction with a FEMA representative for the updated project timeline for new (long-awaited) floodplain maps. Obviously, the information below is my interpretation of that presentation, so always verify information with State, Local and Federal officials.

The purpose of the open house was to review the preliminary floodplain map data released on August 15th. This data was last updated in 1988 with the limited technology at the time. An attempt was made in 2011 to update the mapping with a LIDAR flyover of the county in 2011. However, Teton County GIS coordinator Rob Marin (thanks, Rob) pointed out some deficiencies based on the year and time of year that may have inadvertently resulted in inaccurate and exaggerated flood data. This led to another recent flyover with a greater level of accuracy based on the timing, and newer technology. This new data will lead the way for a 90-day appeal process for those that can provide strong evidence that the new map data is inaccurate. For any objections, it should be noted that a letter of final determination is expected in the Fall of 2025, with final maps taking effect early 2026. The 90 day appeal process is expected to begin in February of 2025 and end in May of 2025. Comments can be provided, and forms are available on site at the Teton County courthouse and online for these appeal processes. This could be something as simple as an incorrect street name, or a more significant appeal such as a formal objection with evidence of inaccuracies. An appeal requires quite a bit of work, and as such, will require some form of significant evidence as to the inaccuracy, usually involving engineering (data based) reports. However, these scenarios will be investigated. These should be provided to Teton County who will pass the comments along to FEMA.

With that out of the way, the meeting was informative as to the new data, how it is mapped, and how it can be beneficial to Teton County. In attendance at the meeting was a representative for FEMA’s Region 10, Marshall Rivers. FEMA’s primary concern is safety, predicting flood risk and preparing for flood events. The last time the flood maps were updated was 1988, and with vast, new technology, FEMA was able to map not only flood information, but ranges of flood risk (as well as a side benefit of 2 foot contour elevations now available from the county). This program for updating the data was in collaboration with local government and the National Flood Insurance Programs (NFIP) in conjunction with FEMA. The federal government is responsible for mapping communities on a continuing basis. The state governments prioritize areas for future mapping studies, and local governments provide local insight and support. They also integrate the data into planning mechanisms and processes.

How are the maps made?

The maps are made using ground survey and LIDAR technology to identify areas of floodplain. The floodplain is generally an area that can be affected by flood or high water. LIDAR is a laser-based aerial tool with extraordinary accuracy that can sense surprisingly small objects. As mentioned above, a byproduct includes two foot contour elevations across almost the entire county. This data can be used by surveyors or land owners for planning and building purposes. There are limitations to these maps which include some uncertainties or uncontrollable circumstances such as log jambs, changing rivers or even land impacted by wildfires. In addition to LIDAR, hydrology and measuring the flow of water is a big consideration in establishing these maps. FEMA worked with Teton County to add study zones with some tasks led by FEMA, and others led by Teton County and other agencies.

Updated Zones and Associated Risks

This new data offers a more granular prediction as to certain areas and their risk levels. Two types of flood hazards were mapped. The moderate flood risk (Yellow, when viewing the map) is intended to show a 0.2% annual chance of flooding (or less impactful areas), and high flood risk which is estimated to be a 1% annual chance of flooding (or more impactful areas). In addition, Floodway (as indicated in these maps in red), indicate areas that could be most impactful, and should be avoided. I was unable to determine the county’s future role in special requirements or restrictions in these areas.

Insurance 

Just because a home is not in one of these identified rest areas, does not mean that there is no risk of flood. Conversely, if your home is removed from these flood areas with the new mapping, it doesn’t necessarily mean that you should cancel your existing flood insurance. According to FEMA, one out of four people who have a claim are not in an area mapped and identified as a high-risk flood area. If your property is added into flood zones in these amended maps, you may be contacted by your lender (and should consider risk insurance, regardless). My understanding is that your flood risk is evaluated by your lender and insurance provider. If homes are built above the base flood elevation of the risk area, this can minimize the added cost, or potentially even the requirement for insurance. You can learn more (and confirm my beliefs) at floodsmart.gov. 

Base Flood Elevation & Development This new data will provide some instant data for what used to require elevation certificates to prove the base flood elevations. Information that may have once required an engineer to evaluate may now be immediately available with the new data. You do need a floodplain development permit whether you are handling infrastructure or building a home, but FEMA does not restrict development in floodplain areas.

OLD DATA (circa 1988)

NEW DATA (as of August 15th, 2024)

Reviewing the Code – A Summary of Considerations when Buying Land in Teton County

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As a quick note prior to diving in, this article applies to the unincorporated areas of Teton County. The City limits of Driggs, Victor and Tetonia have their own Land Use/Development Code. Much of this was covered in Part III of my review of Teton County’s newest (2022) Land Development Code article, but I wanted to take some time to quickly highlight some of the things to watch out for when looking at undeveloped land as an investment and for future development – keeping in mind that these code requirements are obviously subject to change. We seem to be through a good portion of code revisions, and there also seems to be some more solid direction from Teton County with respect to these processes.

Zoning
There are several zoning types in Teton County, Idaho, and it is important to understand that each have their own special requirements for development or splitting property, and each have specific uses. While residential use (building a home) is generally permitted on all parcels and zoning types, it is also important to know that properties that were split illegally such as deed splits without a subdivision process after June 14th, 1999 may not have building rights. Similarly, properties that were split by way of an agricultural split may not have property rights. Much of this information can be verified with Teton County via a “Zoning Verification Request” which does come with a cost (currently $150) but this would generally be less of a concern with any property that is in a platted development. You can read my article on the different zoning types, here.

Flood Hazard
This one is still a bit tricky as FEMA has not completed the draft floodplain Maps. In either case, if a property, be it under the existing floodplain map or the future implemented map, Falls within these areas, the county will require elevation certificates before, during and after the build to make sure that the floor system of the home is above the base flood elevation requirements. Additionally, it should be considered whether flood insurance will be required, regardless of the project elevation upon completion even if the county is satisfied.

Wetland
I just wrote an article on wetland, it can be found, here. For parcels that require a wetland delineation (despite my disagreement with this) the county would prefer that the entire parcel be delineated to provide a holistic overview of the parcel, and to better tie in with Wildlife Analyses, if required.

Natural Resource Overlay (NRO)
Teton County is working on a new draft overlay of Teton County’s natural resources which expands most of the historic wildlife overlays. This one was enough for me to wrap my head around, but basically, if a parcel has an overlay where the site is intended to be improved, a shorthand wildlife analysis is required. This includes maps that show the existing boundaries of the applicable overlay, and some reasonable expertise for a development plan. At the time of this writing, I was told by Teton County that no specific qualifications were needed for this shorthand version of a wildlife analysis, otherwise known as an Abbreviated Wildlife Habitat Analysis (A-WHA). For more in-depth projects such as Land Development, subdividing and so forth, far more extensive analyses may be required which would constitute a full Wildlife Habitat Analysis (WHA). I am linking the policy here, but keep in mind that this is subject to change. Properties that have designated building in the lowest may not require Wildlife Habitat Analyses, even if the NRO layer encompasses all or a portion of the predetermined building envelope.

Hillside Overlay
Certain areas of the Teton Valley are encompassed by a “Hillside Overlay”. Obviously, most of these areas are going to be in areas with steeper terrain, and may have special requirements. In extreme cases, development may not be possible under the current code. This should be considered for accessing parcels in these areas as well as site planning for construction.

Scenic Corridor Overlay
The scenic Corridor overlay encompasses approximately 500 ft from State Highway 31, 32 and 33 as well as Ski Hill Road. Areas that fall within this overlay may have specific height limitations. However, the county code has an amendment in the works to allow variances without a public hearing (which is currently required) if a visual site analysis (what the project may look like from the road) is provided and it is concluded that it is not obtrusive. They are also some additional requirements with respect to design, which could include architectural styles, colors, and so forth. Special landscaping requirements may be implemented as well, which could include berms, trees, screening, etc.

There are several other overlays that, while they may not have any specific impact on one’s ability to improve a parcel, may be considered. Examples include the bear conflict Zone which requires bear proof trash cans, wildlife hazards, and even an understanding of roads that may not be maintained in the winter months, or maintained by the county at all. Other layers and restrictions still exist which obviously include subdivision restrictions, County setbacks and other code requirements including driveway lengths and a variety of other Land Development Code policies.

Wetland: What Does It Mean and How Can It Impact My Property?

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***Article Update: Kent Werlin is the Senior Wetland Scientist with Biota Research and Consulting in Jackson, Wyoming. Kent was kind enough to edit my article and provide updated, more accurate information. My disclaimer stands (do your own research), and see the updated article below:

Wetlands are often confused with floodplains and flood zones. Flood zones are not always wetlands, and wetlands are not necessarily located in floodplains, though there are circumstances where either could be true. Flood zones can occur in areas next to large bodies of water or runoff areas and are often considered higher risk when it comes to flooding. However, any property can flood, not necessarily only properties in a floodplain.

Wetlands are regulated by the U.S. Army Corps of Engineers and Environmental Protection Agency under the Clean Water Act. To be considered a “wetland”, an area must meet all of the following  criteria:

1) Wetland Hydrology: To have wetland hydrology, an area must be at least saturated in the upper 12 inches of the soil profile for a period of 14 days during the growing season in 5 out of every 10 years. Active monitoring of hydrology via the use of shallow groundwater monitoring wells and/or wetland hydrology indicators are utilized by wetland professionals to determine the presence of wetland hydrology. These indicators include the presence of surface water, saturation, geomorphic position, oxidized rhizospheres (root channels), a dominance of wetland vegetation, and others.

2) Wetland (Hydrophytic) Vegetation: roughly a quarter of the plant species in the United States grow in wetland areas. To be a wetland, an area must be dominated by facultative or wetter plant species based on the National Wetland Plant List, which designates plant species as upland, facultative upland, facultative, facultative wetland, or obligate wetland. These are described below:

  • Upland – plant species that occur in non-wetland areas 99% of the time and do not indicate wetland conditions (e.g. sheep fescue, sagebrush, western wheatgrass)
  • Facultative Upland – plant species that occur in upland environments 75% of the time and in wetlands 25% of the time (e.g., orchardgrass)
  • Facultative – plant species that occur in wetland environments 50% of the time and in upland environments 50% of the time (e.g. Kentucky bluegrass, common timothy, and meadow foxtail)
  • Facultative Wetland – plant species that occur wetland environments 75% of the time and in upland environments 25% of the time (e.g. Baltic Rush, reed canarygrass)
  • Obligate Wetland – plant species that occur in wetlands 99% of the time. These species are generally indicative of wet areas. (e.g. beaked sedge, Booth’s willow, hardstem bullrush)

3) Wetland Soils: Wetland soils are often referred to as hydric soils. These soils can generally be analyzed by digging a 20-inch deep hole and looking for hydric soil indicators that indicate a high water table and/or periodic saturation within the upper horizons of the soil profile. These indicators include an abundance of organic soil matter, oxidized iron (rust colored) or manganese (purple) concentrations, and others.

Can you build in Wetland?

Wetland areas do require special permits and approvals. But first, they must be identified as wetland, usually by way of what is referred to as a wetland or aquatic resource delineation performed by a properly trained wetland consultant (such as the co-author of this article, Kent Werlin, the Senior Wetland Scientist with Biota Research and Consulting) and following the wetland delineation protocol approved by the Army Corps. Wetlands in Teton County are subject to both federal and local (county) regulations which differ in their requirements.

If a property in Teton County, Idaho shows indications of wetland presence based on the nationwide National Wetland Inventory (NWI) mapping (can be viewed via the Teton County GIS Mapserver), the county will generally require a delineation before approving subdivision or issuing grading or development permits for the subject property. Under current county regulations (Teton County Land Development Code 2022), the county requires either a 50′ or 100′ development setback on wetlands, depending on the level of analysis conducted. If a site-specific wetland delineation is conducted, the county will place a 50’ development setback on all wetlands delineated by a wetland professional and approved by the Army Corps. If there is no site-specific wetland delineation conducted, then the county falls back on the NWI mapping and requires a 100’ setback on NWI mapped wetlands.

At the federal level, the Army Corps requires a permit application for the placement of fill material (e.g., rock, gravel, concrete, soil, etc.) in jurisdictional wetlands. The Army Corps has a suite of streamlined Nationwide Permits for activities that impact up to 0.5 acres of wetland. If wetland impacts exceed 0.1 acres, then the Army Corps requires a Compensatory Wetland Mitigation Plan that involves the creation of new wetlands or enhancement of existing wetlands to compensate for development-related wetland losses.

A recent supreme court case (EPA v Sackett) decision has put the jurisdictional status of some wetlands at the federal level in question. The Army Corps is in the process of modifying their technical guidance for determining jurisdictional status based on the outcome of this court case and should be issuing guidance in the coming months. While it may be possible to impact wetland areas with the proper permits, it is important to remember the reason that these regulations exist….to protect wildlife, habitat, and waterways, often considered a key cornerstone of Teton Valley’s natural beauty.

END UPDATED ARTICLE – Special thanks to Kent Werlin, biotaresearch.com

Disclaimer: As always, I need to start out this article with a disclaimer. I know enough about many of these topics to be dangerous – which is dangerous. Always seek the advice of appropriate professionals as this information is subject to change as well as my own interpretation. I don’t often go back and update old articles, so I’ll leave this here.

Wetland should not be confused with floodplain. Flood zones are not always wetland, and wetlands are not necessarily in floodplains. Flood zones normally occur in areas next to bodies of water or runoff areas and are often considered higher risk when it comes to flooding. However, any property can flood, not necessarily only properties in a floodplain or a wetland.

How to Identify Wetland

Wetland can occur even in areas not directly adjacent to a body of water and is usually determined by three primary factors:

1) Hydrology: Hydrology indicators can include the presence of surface water or wet soils as determined by evidence or review by a wetland professional utilizing different tools or testing to understand the presence of water.

2) Vegetation: Roughly a quarter of the plant vegetation species in the United States grow in wetland areas. Plant species can be classified in a number of different ways as identified below in order of wet to dry:

  • Obligate Wetland (usually very indicative of wetland areas) ie Sedges (which have triangular, sharp stems) and Willow
  • Facultative Wetland (usually occur in wetlands, but occasionally found in non-wetlands) ie Horsetail, Baltic Rush
  • Facultative (equally likely to occur in wetlands or non-wetlands) Meadow Foxtail, Timothy, Brome, Bluegrass
  • Facultative Upland (usually occur in non-wetlands, but occasionally found in wetlands) ie Potentilla
  • Obligate Upland (almost always occur only in non-wetlands) ie Sheep Fescue

3) Soils: Wetland soils are often referred to as hydric soils. These soils can be analyzed by digging a hole (usually 12-18 in deep) and looking at indications of saturated soils that usually show indications of oxygen depletion. This can be evidenced (essentially) by rust in the soils and the coming and going of water, creating oxidation. Oxidation can be due to iron and is usually identified by orange flecks in the soil or manganese which will reveal itself with a purple color.

Can you build in Wetland?

Wetland areas do require special permits and approvals. But first, they must be identified as wetland, usually by way of what is referred to as a Wetland Delineation performed by a properly trained wetland Consultant.

If a particular property shows indications of wetland, Teton County, Idaho will generally require a Wetland Delineation. They have requirements of 50′ or 100′ setbacks, depending on the delineation findings. If the project looks like it will encroach within 50′ of wetlands as indicated by the Delineation, the county may require a Jurisdictional Determination (JD) from the Army Corps of Engineers. If there are any questions on a project, despite setbacks, the Teton County Planning Staff may still send the information to the Corps for review. A JD is the process of Determining whether areas indicated as wetland are regulated by the U.S. Army Corps of Engineers under section 404 of the Clean Water Act and/or Section 10 of the Rivers and Harbors Act.

If a property is determined to be wetland, with the proper permits it may be possible to impact up to 0.1 acre of wetland for driveway, septic, and a home site. If wetland is mitigated to another area, these improvement areas can be increased to 0.5 acres.

Wetland areas can make tremendous home sites, but it is important to remember the reason that these regulations exist in order to protect wildlife, habitat and waterways, often considered a key cornerstone of Teton Valley’s natural beauty.

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