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Critical Natural Resource Areas Ordinance Update

The Planning and Development Department is proposing an amendment to the Story County Land Development Regulations (County code) with new protections for critical natural resource areas.

On This Webpage You Can Find:

  • A video and written summaries of the ordinance
  • An interactive map where you can post questions and view the following information:
    • Mapped natural resources
    • Your property
  • The glossary for key-terms in the ordinance can be found here.
  • The full ordinance can also be found here.
  • The DNR's invasive tree species guide can be found here.


Contact Andrea Wagner, Planner


Ordinance Adoption Process and Public Meetings

The Planning and Zoning Commission and the Board of Supervisors will both hold public hearings on the ordinance

The meeting dates are:

Both meetings will also be held in the Public Meeting Room of the Administration Building, 900 6th Street. 


The proposed update to the ordinance will protect Story County’s environmental resources—wetlands, remnant prairie and savanna, steep hillsides, trees, archaeological resources, lakes, streams, and rivers.   

We currently have protections for trees, steep slopes, rivers and streams in our code that apply to all permits and development. However, the ordinance clarifies these requirements to ensure they are applied appropriately and equally. For example:

  • All new lots have to be “properly related to topography” under our current code, but this term is not further defined. The proposed ordinance would define what is considered a steep slope (greater than 15%), maps these areas, and provides standards for building to ensure a site is suitable.
  • In the current code, replanting is required if more than 15% of trees are impacted on a property. The proposed ordinance would allow individual property owners to impact one acre of trees on their property, increasing flexibility while protecting more trees overall.
  • Existing stream buffers would be updated to better account for natural meandering or movement of streams, better protecting development and natural functions.

The standards for wetlands, prairies, savannas, and archaeological resources are proposed to only apply to larger developments: subdivisions of two or more lots and commercial development including conditional use permits. The current code has broad standards for environmental protection that these developments must meet. The proposed ordinance better defines those standards and expectations—when they apply, what impacts are allowed, and what mitigation measures are required.

Without these changes, the County could lose otherwise restorable wetlands, prairie or savanna remnants, and tree stands, as well as constrict natural floodplains that are necessary for carrying floodwaters and recharging our sources of drinking water.

What DOES the Ordinance Do:What DOESN'T the Ordinance Do:
  • Provides standards for evaluating impacts on critical natural resource areas
  • Provides clear, consistent thresholds for when mitigation is required
  • Promotes conservation design
  • Provides a path for preserving and restoring Story County’s natural habitats

  • Affect or regulate agricultural operations
  • Make a parcel “unbuildable” or prevent any development of a property in the County

Watch a Video about the Ordinance and Learn More

Please note the following changes to the ordinance are proposed that are not reflected in the video: 

Steep Slopes

Staff has made the following changes: 

  • For subdivision plats with three or more development lots, conditional use permits, and commercial sites plans, staff’s new proposed standards are less strict for development on slopes between 15%-35%, while development on slopes greater than 35% is still not allowed (with provided utility exceptions). 
    1. The new proposed changes require development in areas with 15%-35% slope to show a proposed development envelope (e.g. where a dwelling is proposed to be located).
    2. If slopes over 15% or area within a buffer measured two (2) feet for every one (1) foot of vertical rise from the toe or summit of a significant slope (>15%) are located in the development envelope, a geotechnical analysis is required to ensure the building site is suitable. 
    3. The existing requirement for an erosion control plan is reiterated. This is already required of all development.  
    4. The limits of disturbance are required to be marked on a site prior to construction. 
  • For all other development (residential permits) on slopes greater than 15% or within a buffer measured two (2) feet for every one (1) foot of vertical rise from the toe or summit of a significant slope (>15%):
    1. The existing requirement for an erosion control plan is reiterated. This is already required of all development.  
    2. A geotechnical analysis is encouraged. 
    3. The limits of disturbance are required to be marked on a site prior to construction. 

Development Definition 

The standards for the other critical natural resources outside of steep slopes, with most of the proposed updates focusing “development” of a significant scale. In the March 1 draft, “development” referred to proposed rezonings, conditional use permits, commercial site plans, and subdivisions of two or more development (buildable) lots. This has been updated to more than two development (buildable) lots, meaning development of two lots is not subject to the stricter standards of commercial and multi-lot residential development.

 Significant Trees

The protections for Significant Trees and Native Woodland Shrubs has been updated to relax standards for commercial and multi-lot residential development. The new proposed standards for commercial and multi-lot development (of more than two lots) reverts back to the existing standard that allows up to 15% of significant trees to be impacted before mitigation is required. However, staff added requirements for mitigation if over five (5) acres of trees are impacted, meaning that mitigation is required if 15% or five (5) acres of significant trees are impacted, whichever is lessMost subdivisions are four lots or fewer, so the five (5) acre threshold would allow over an acre per lot of removal. 

 Other Changes

  • Staff has included examples of qualified professionals who may complete assessments or mitigation plans
  • The Iowa DNR’s invasive species list is now referenced in the ordinance and in the definition of native trees
  • Each section includes a statement that maintenance activities not requiring a permit application are not regulated by the Ordinance, and includes examples of maintenance work
  • Reductions in buffers around wetlands, prairies, and savannas are proposed to be permitted if permanent protection measures such as fences are proposed. A reduction request would require a recommendation by the Story County Conservation Board and could not be more than 50% of the required buffer size. The health or function of the resource could not be impacted.

View the Map of Natural Resources and Leave Questions

View the Full Ordinance and Summaries

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