1. Protections for Critical Natural Resource Areas. When property is developed, it shall be done so that the development is designed and arranged to protect critical natural resource areas. The purpose of these standards is to further the goals of the Cornerstone to Capstone (C2C) Plan and the Countywide Watershed Assessment by providing protections for areas that are environmentally or culturally significant. It is also to achieve the purpose of the Story County Land Development regulations to balance land use rights of individual landowners and the economic, social, and environmental concerns of the public. Critical natural resource areas include wetlands, watercourses and waterbodies, steep slopes, significant trees, archaeological resources, and remnant prairies and savannas. These areas are mapped as Natural Resource Areas on the C2C Plan Future Land Use Map. However, not all critical natural resource areas are mapped and individual developments will need to consider site specific characteristics. Disturbance shall be minimized and/or mitigated where avoidance is not possible.
(Ord. 317 – Apr. 24 Supp.)
A. General Requirements. The following standards apply to all critical natural resource areas that are not otherwise exempt.
(1) Impact. Impact to critical areas is permitted only in accordance with the provisions of this chapter. Protected areas shall be denoted on the site plan or subdivision plat, if applicable, and shall be marked on the site prior to any construction activities, including any ground disturbance or vegetation removal. Markings shall consist of lath or another marking at maximum intervals of every 50 feet along the edge of the critical natural resource area. A greater interval may be required as necessary to provide visibility between the markings. Fencing or a buffer from the edge of a resource may be required for extremely critical resources. During the construction stage of development, the applicant shall not clean equipment or material or store or dispose of waste such as paints, oils, solvents, asphalt, concrete, motor oil, or other harmful material in the critical natural resource area.
(2) Mitigation Plan. In all cases where mitigation is permitted and required due to exceeding allowed thresholds for disturbance, a mitigation plan shall be developed and implemented in accordance to the following standards. These requirements shall not supplant regulatory mitigation required through the U.S. Army Corps of Engineers or other regulatory agency or governmental body. If the provisions under this chapter of the Story County Land Development Regulations are in excess of another governmental entity or body’s standards, then the County provisions shall still apply.
a. Qualified Professional. All mitigation plans shall be developed and implemented by a qualified professional as defined in Chapter 85.08.
b. Responsible Party. The party responsible for maintenance and their contact information, if different from the property owner or permit applicant, shall be included.
c. Methods of Mitigation. Required mitigation may be accomplished through preservation and enhancement of off-site critical natural resource areas, reconstruction of critical natural resource areas, or a combination thereof.
d. Location. All mitigation shall occur within Story County unless the applicant can demonstrate that mitigation in accordance to this section is not feasible within the County or otherwise permitted by a specific resource subsection.
e. Standards for Permanent Protection. Areas preserved, reconstructed, or created to meet mitigation requirements shall be permanently protected from development through a conservation easement, deed restriction, or donated to a public agency for protection. They shall also be placed in an outlot in the case a subdivision plat is proposed.
i. Conservation easements shall be held by an accepted third party land conservation organization (e.g. Iowa Natural Heritage Foundation, The Nature Conservancy) or Story County Conservation.
ii. Land donations to public agencies would include entities such as the Story County Conservation Board, Iowa Department of Natural Resources, U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, etc. If donation to a public agency is infeasible, land donations to conservation non-profits may be permissible.
iii. A long-term management plan, with provisions for monitoring and reporting to the County, and a process for addressing necessary changes due to failure of plans shall also be provided within the mitigation plan.
iv. Suitable remedial action by the responsible party will be required if all or part of a reconstructed critical area fails to become established in the timeframe indicated in the plan.
f. Approval. Mitigation plans shall be approved by the Board of Supervisors after a recommendation from the Story County Conservation Board.
i. If the Board of Supervisors does not approve the mitigation plan, then no permit or other approval may be granted for a development project.
(3) Conservation Easements. To provide balance between development and protecting critical natural resource areas, conservation easements or other permanent protections may be required over critical natural resource areas and their applicable buffers as a condition on rezonings, subdivisions of two or more development lots, conditional use permits, and commercial site plans. Requiring a conservation easement as a condition will be determined by the Board of Supervisors after the Story County Conservation Board makes a recommendation on whether they support the easement.
(4) Stream Easements. Easements shall be required for watercourses and waterbodies included in subdivisions of two or more development lots and the easement shall include provisions for maintenance and upkeep due to potential erosion issues.
(5) Violation. If a responsible party fails or refuses to meet the requirements of the approved mitigation plan or any provision of this ordinance, the County shall notify the party responsible for implementation and maintenance of the mitigation plan in writing following the procedure for Notice of Violations in Chapter 93 of the Story County Land Development Regulations. Depending on the severity of the violation, the permitted timeframe to submit a compliance schedule may be reduced. If the violator does not correct/abate the violation or provide an acceptable schedule to correct/abate the violation, or does not comply with the schedule, a citation for a County infraction may be issued in accordance with Chapter 93 of the Story County Land Development Regulations.
B. Requirements for Significant Trees and Native Woodland Shrubs. Native trees and shrubs provide wildlife corridors and habitat for Story County’s wildlife species. They also provide water quality benefits, supply oxygen, and store atmospheric carbon.
(1) Applicability. The provisions within this section apply to all zoning and grading permits, conditional use permits, commercial site plans, and subdivisions of more than two (2) development lots. These shall be hereinafter referred to as “development.” The provisions do not apply to general tree/shrub management, i.e. thinning of trees or removal of invasive or dead/dying trees not associated with or intended to facilitate development.
(2) Identification. Significant trees are native, deciduous trees with a caliper greater than four (4) inches, measured four (4) feet off the ground, or a native coniferous tree taller than fifteen (15) feet. Significant native shrubs have a basal diameter of three (3) inches. Significant trees and native shrubs that meet one or more of the following removal criteria shall be exempt from the requirements of this subsection:
a. Tree stands that are low quality replantings. These shall be identified through historic aerial imagery taken between the 1930s and 1980 to determine cropping history and locations of old-growth stands. Stands planted post-1980 may be considered low quality plantings.
b. Dead, dying or naturally fallen trees, or trees found to be a threat to public health, safety or welfare;
c. Trees that are determined to substantially obstruct clear visibility at driveways and intersections; or
d. Tree or shrub species identified as invasive species by the Iowa Department of Natural Resources.
(3) Impact. Impact to significant trees and/or shrubs shall be avoided where possible, and the burden of persuasion as to why impact is unavoidable will at all times be on the applicant. Mitigation for impact to significant trees or shrubs shall be required in Natural Resource Areas, as mapped on the C2C Plan Future Land Use Map. Cut or fill over a four-inch depth or compaction within the drip line of any significant tree shall be considered impact. The following mitigation standards shall be required in addition to those general standards in Chapter 88.05(1)(A).
(Ord. 317 – Apr. 24 Supp.)
a. Zoning and grading permits for parcels intended for residential development, or for subdivision lots created before the adoption of this ordinance, may impact up to one (1) acre of significant trees and/or shrubs without mitigation. Impacts over one (1) acre shall require mitigation.
b. Commercial site plans, conditional use permits, or subdivision plats of more than two (2) development lots may impact up to 15% or five (5) acres, whichever is less, of the wooded acres on a development site (including across multiple parcels or phases of development). Impacts over 15% or five (5) acres, whichever is less, shall require mitigation.
c. Prior to impact, a replacement plan or mitigation plan shall be submitted as part of a development application.
i. For zoning and grading permits, a replacement plan may be approved by the Planning and Development Director in lieu of a mitigation plan approved by the Board of Supervisors. The replacement plan shall outline why the impact is unavoidable and include a site plan showing where trees are being replanted and the number and species.
ii. For subdivisions creating more than two development lots, conditional use permits, and commercial site plans, a mitigation plan shall be completed by a qualified professional and shall include additional information regarding the long-term management of the wooded area(s), including outlining when it may be necessary to remove native trees or shrubs due to overgrowth and for the overall health of the wooded area(s). When the removal of native, significant trees and/or shrubs is deemed appropriate by a qualified professional for the overall health of the wooded area(s), such removal shall not count towards replacement ratios. A qualified professional may be a professional in natural resource science or management, or forestry.
d. The replacement or mitigation plan shall also meet and or/address the following standards:
i. Replacement trees shall be planted either on the development site or in an alternative planting site within Story County when infeasible. Allowable alternative planting sites are the following: County-owned parks or preserves; eligible areas undergoing riparian buffer improvements; privately owned land under a conservation easement or in a land trust, with permission of the property owner. Planting areas shall be appropriate locations for native trees based on where old growth forests currently, or historically, are located, and shall not cause detriment to other critical natural resource areas and shall be appropriate for the tree or shrub species involved.
ii. For zoning and grading permits requiring mitigation, a significant tree or shrub that is impacted shall be replaced at a ratio of 1:1, and a 20% mortality buffer shall be added to the total number of replacement trees or shrubs (e.g. if thirty (30) trees are the minimum needed for the replacement ratio, then at least thirty-six (36) shall be planted). Replacement costs shall be at the applicant’s expense.
iii. For commercial site plans, conditional use permits, or subdivisions of more than two development lots, significant trees or shrubs shall be replaced at a minimum ratio of 1:1. A greater ratio, up to 6:1, may be required if recommended by a qualified professional based on species and size. A 20% mortality buffer shall be added to the total number of replacement trees or shrubs (e.g. if thirty (30) trees are the minimum needed for the replacement ratio, then at least thirty-six (36) shall be planted). Replacement costs shall be at the applicant’s expense.
iv. Replacement trees and/or shrubs shall meet the following minimum size requirements and shall be primarily native species in order to restore and enhance the site as nearly as practicable to its pre-settlement character. Coniferous trees shall not be permitted as replacement trees.
Deciduous Trees—one and one-half inch (1.5 inch) caliper
Native Shrubs—five gallon pot size
C. Requirements for Wetlands. Wetlands provide wildlife habitat, downstream water quality protection, and natural flood/stormwater attenuation.
(1) Applicability. The provisions within this section shall be applicable to all proposed rezonings, conditional use permits, commercial site plans, and subdivisions of more than two (2) development lots. These shall be hereinafter referred to as “development.” Zoning permits and grading permits on subdivision lots established before the adoption of this ordinance, or on unplatted parcels or tracts, are exempt. The provisions do not apply to general management, i.e. mowing of vegetation.
(2) Identification. When an application for development is submitted, the following identifying features and sources shall be referenced to identify wetlands. Applicants are encouraged to consult these sources prior to making a submittal.
a. Wetlands identified on the Story County Countywide Watershed Assessment maps and/or U.S. Fish and Wildlife Service National Wetland Inventory.
b. Hydric soils identified on the Story County Soil Survey maps.
c. Depressions and evidence of ponding on U.S. Geological Survey Topographic Maps and aerial imagery.
d. Soil borings provided by a registered soil engineer and/or a survey of plant material completed by a botanist, landscape architect, engineer, or other qualified professional.
(3) Wetland Delineation Required. When development is proposed within one hundred and fifty (150) feet of an identified wetland, a qualified wetland specialist shall be hired to provide wetland delineation. The delineation shall use the methods in the U.S. Army Corps of Engineers Wetland Delineation Manual and Regional Supplement. If the delineation occurs outside of the normal growing season, the applicant may be required to amend the delineation with information on plant species during the growing season, if vegetation may impact the wetland classification. The delineation shall be completed at the applicant’s expense.
a. Wetland Classification. The delineation shall classify the wetland based on the following types. When the areas of any wetland are hydrologically connected and/or have contiguous buffers, the connected areas shall be added together to determine the wetland's size for wetland classification purposes. Vegetation classes identified during the delineation shall adhere to those adopted by the U.S. Army Corps of Engineers in the National Wetland Plant List Indicator Rating Definitions and current National Wetland Plant List.
Class 1 Wetlands.
i. Wetlands that are used by species listed by the federal or state government as endangered or threatened, or which have an outstanding natural habitat for those species; or
ii. Wetlands which have forty to sixty percent open waters in dispersed patches with two or more wetland vegetation classes; or
iii. Wetlands which are equal to or greater than ten (10) acres in size and have three or more wetland vegetation classes, one of which is an aquatic bed wetland; or
iv. Wetlands with plant associations of infrequent occurrence according to the Iowa Coefficient of Conservatism (a Coefficient score greater than or equal to seven).
Class 2 Wetlands.
i. Wetlands which are greater than one acre in size; or
ii. Wetlands which are equal to or less than one acre in size, and have three or more wetland vegetation classes; or
iii. Wetlands which are equal to or less than one acre in size and with a forested wetland vegetation class.
Class 3 Wetlands.
i. Wetlands which are equal to or less than one acre in size and have two or fewer wetland vegetation classes.
b. Restoration Recommendations. The delineation shall also include recommendations to improve the wetland’s function, including removal of invasive species and drain tiles, reseeding and planting, ongoing maintenance recommendations, and restoring the vegetative buffer around the wetland area.
(4) Implementation. After a delineation is completed and the wetland(s) is classified in accordance with the wetland classification section, the proposed development shall comply with the following:
a. Buffering. The following buffers are required around the delineated area:
i. Class 1 Wetlands: One hundred (100) feet.
ii. Class 2 Wetlands: Seventy-five (75) feet.
iii. Class 3 Wetlands: Fifty (50) feet.
b. Activities Allowed. Only the following activities are allowed in buffer areas:
i. Minor land-disturbing activities for erosion control or revegetation.
ii. Fencing.
iii. Utilities.
iv. Unpaved trails and paths.
c. Buffer Averaging. Buffers may be averaged so that the total area of the buffer is not reduced, and the width of the buffer at any one point is not decreased by more than fifty (50) percent of the required buffer width, if the following is demonstrated by the wetland delineation:
i. The wetland is less than one (1) acre in area; and
ii. Does not contain species listed by the federal or state government as endangered or threatened, or critical or outstanding natural habitat for those species; and
iii. Does not contain diverse plant associations of infrequent occurrence or of regional significance; and
iv. Buffer averaging will improve the buffer function, wetland protection, and/or enhance the vegetative cover; and
v. The area being removed from the buffer does not contain other critical natural resource areas or act as a buffer for those areas, such as native trees or prairie remnants.
d. Buffer Reduction. The Story County Conservation Board may make recommendations to the Board of Supervisors regarding reductions in required buffer sizes. The Board of Supervisors may approve plans where the required buffer is reduced in size by no more than (50) percent of the required buffer width when sufficient protective measures are in place to identify and protect a wetland(s) from impacts, such as fencing installed by a developer. This shall not apply in conjunction with buffer averaging. The reduction in buffer size may not result in any impacts, as determined by a qualified wetland specialist, to:
i. Species listed by the federal or state government as endangered or threatened, or critical or outstanding natural habitat for those species; or
ii. Diverse plant associations of infrequent occurrence or of regional significance; or
iii. The function or health of the wetland, including ensuring a sufficient vegetated area around the wetland is maintained to filter pollutants or slow surface runoff; and
iv. The area being removed shall not contain other critical natural resource areas or act as a buffer for those areas, such as native trees or prairie remnants.
(5) Impact. To meet the goal of no net-loss of wetlands in Story County, impact to delineated wetlands, including, but not limited to, grading and earth disturbance, construction, vegetation removal, and vehicle or heavy machinery movement, shall be limited to the following when permitted based on the wetland class: management activities necessary for restoration and maintenance of the wetland; infrastructure necessary for access to a property, such as drive entrances and access roads; and rural water lines, gas lines, or other public utilities. These impacts shall be the minimum necessary to accomplish the needs of the infrastructure project or utility installation. Wetlands shall not be used for stormwater retention or detention basins. If impacts are permitted, the applicant shall provide a written statement from the U.S. Army Corps of Engineers stating that development fully complies with all applicable federal wetland regulation as established in the Clean Water Act.
a. Class 1 Wetlands. Shall not be impacted for any purpose other than public infrastructure projects.
b. Class 2 and Class 3 Wetlands. Impact shall only be allowed when the impacts are strictly for the infrastructure and utility installation listed in 88.05(1)(C)(5). The applicant shall demonstrate that avoiding and minimizing the impact to a wetland is unreasonable and that siting said infrastructure in other locations is infeasible.
(6) Compensatory Mitigation. Compensatory mitigation is required for any delineated wetland impact that equals or exceeds one tenth (0.10) of an acre. The following mitigation standards shall be required in addition to those general standards in Chapter 88.05(1)(A):
a. Mitigation areas for wetlands shall be located in the same HUC-12 subwatershed as the original wetland. If that is shown to be infeasible, then the same HUC-10 could be used upon extenuating circumstances and with approval as part of the mitigation plan.
b. For mitigation areas preserving existing wetlands off-site, wetlands shall be preserved at a ratio of 1:1. For mitigation areas reconstructing or creating wetlands, wetlands shall be replaced at a ratio of 2:1. For mitigation areas restoring previously drained or impacted wetlands, wetlands shall be restored at a ratio of 2:1.
c. Story County Conservation shall approve of all seeds used in the mitigation area prior to planting. No invasive or foreign species shall be planted in the mitigation area.
(7) Restoration. Restoration to improve the wetland’s function, including removal of invasive species and drain tiles, reseeding and planting, restoring the vegetative buffer around the wetland area, and placing the area in a conservation easement that includes provisions for ongoing maintenance, may be required as a condition of the applicable permit for the development. When the wetland in question is a farmed wetland and commercial or residential development is proposed, restoration of the farmed wetland shall be required.
D. Requirements for Watercourses and Waterbodies. Watercourses and waterbodies are areas that store and/or convey surface water, including but not limited to rivers, streams, creeks, drainageways, ponds, and lakes. These areas provide floodwater conveyance and storage, and their riparian areas improve water quality. Additionally, they provide habitat and recreational opportunities. The requirements of this section shall be in addition to the applicant’s obligation to satisfy all other applicable local, state, or federal regulations and permits.
(1) Applicability. The provisions within this section apply to all zoning and grading permits, conditional use permits, commercial site plans, and subdivisions with two (2) or more development lots. These shall be hereinafter referred to as “development.”
(2) Identification. The existence of watercourses and waterbodies shall be identified or ruled out in accordance with the following procedures:
a. Use of Story County Countywide Watershed Assessment maps, critical resource area maps, or FEMA Flood Insurance Rate Maps (FIRMs) may be used to identify or rule out the existence of watercourses and waterbodies.
(3) Implementation. If watercourses or waterbodies are located on the site, the proposed use and development shall comply with the following:
a. Buffering. An undisturbed buffer shall be provided in accordance to the following requirements:
i. Rivers and streams within the Special Flood Hazard Area (SFHA) for which no floodway is identified on the effective Flood Insurance Rate Map (FIRM) shall require a minimum 50-foot undisturbed buffer on each side of the stream’s belt width, which is the stream flows measured between the outsides of opposing meander bends. (See Figure 2)
ii. Rivers and streams within the SFHA for which floodway is identified on effective FIRM maps shall require a minimum 75-foot undisturbed buffer on each side of the floodway boundary, measured from the edge of the floodway boundary, or the belt width as described for streams with no floodway, whichever creates the largest stream buffer.
iii. Other mapped watercourses and surface waterbodies not within the SFHA shall have an undisturbed buffer 50 feet in width, measured from the edge of the watercourse or surface waterbody.
iv. The buffer size shall be required to be increased to cover the entirety of a riverine wetland, including a buffer in accordance with Section 88.05(1)(C)(4), wetland buffers by class.
Figure 2
b. Permitted Uses. The following uses are permitted in a required buffer zone or easement area:
i. Agricultural uses, such as grazing and fencing
ii. Legal, nonconforming uses
iii. Minor land-disturbing activities for erosion control and bank stabilization, desilting of waterbodies, or revegetation
iv. A perpendicular stream crossing by a driveway, street, or utility lines
v. A street or driveway where buffer intrusion is the only option to provide access to a property
vi. Paved and unpaved trails and paths for use
vii. Public water supply intake or public wastewater outfall structures
viii. Public access facilities that must be on the water, including boat ramps, docks, foot trails leading directly to the stream or watercourse, fishing platforms, and overlooks
ix. Utility lines and easements running parallel with the stream, except that all easements (permanent and construction) and clearing and grading shall recognize the sensitivity of the streams and use Best Management Practices (BMPs) to limit and repair the disturbance within the buffer area. This includes such impervious cover as necessary for the operation and maintenance of the utility, including but not limited to manholes, vents, and valve structures.
(4) Impact. Development shall be designed to avoid and minimize impact to all streams and watercourses. Development in the floodplain is discouraged. Watercourse alterations or relocations (channel changes and modifications) or any proposed development in the floodplain shall be in accordance with Chapter 80 Floodplain Management Program of the Story County Code of Ordinances or other State or Federal requirements. Only the following types of development shall be permitted to encroach on a required buffer: management activities necessary for restoration and maintenance of the stream or watercourse; infrastructure necessary for access to a property, such as drive entrances and access roads; and rural water lines, gas lines, or other public utilities. These impacts shall be the minimum necessary to accomplish the needs of the infrastructure project or utility installation.
(5) Restoration. Restoration to improve riparian buffer areas along watercourses and waterbodies, including removal of invasive species and drain tiles, reseeding and planting, restoring the riparian buffer, and placing the area in a conservation easement that includes provisions for ongoing maintenance, may be required as a condition of a rezoning, conditional use permit, commercial site plan, and/or subdivision with more than two development lots.
E. Requirements for Prairie Remnants and Savanna Remnants. Prairie remnants are characterized by areas containing an association of native grasses, sedges, and forbs. Savanna remnants are characterized by a mixed association of native trees and shrubs in grassland and forbs. The native trees are open grown and are frequently oaks and hickories. Prairie remnants and savanna remnants provide habitat to Story County’s wildlife species and pollinators, reduce soil erosion, and improve water quality through infiltration. Determination of prairie remnants and savanna remnants shall be made by a qualified professional.
(1) Applicability. The provisions within this section shall be applicable to all proposed rezonings, conditional use permits, commercial site plans, and subdivisions with more than two (2) development lots. These shall be hereinafter referred to as “development.” Zoning permits and grading permits on subdivision lots established before the adoption of this ordinance, or on unplatted parcels or tracts, are exempt. The provisions do not apply to general tree/shrub management, i.e. thinning of trees or removal of invasive or dead/dying trees not associated with or intended to facilitate development.
(2) Identification. When an application for development is received, identification of prairie remnants and/or savanna remnants shall be made in accordance with the following procedures:
a. Review of critical natural areas mapping.
b. Use of historic aerial photographs to determine cropping history of the property. Unplowed or uncropped prairies and savannas shall be considered remnants.
c. If the above procedures do not definitively rule out a prairie remnant or savanna remnant, a qualified professional shall complete an on-site assessment during the prairie growing season, between June 15th and August 15th. A prairie remnant and savanna remnant may only be identified by the flora present, not soil type. For savanna remnants, large (greater than eighteen (18) inches diameter breast height), open grown, native trees, such as Oak or Hickory, must be present.
(3) Prairie Remnant and/or Savanna Remnant Delineation Required. If development is proposed within one hundred fifty (150) feet of a prairie remnant and/or savanna remnant, the full extent of the remnant shall be delineated by a qualified professional such as a biologist or ecologist. The delineation shall be completed at the applicant’s expense.
a. Restoration Recommendations. The delineation shall also include recommendations to improve the prairie remnant and/or savanna remnant, including removal of invasive species, reseeding and planting, ongoing maintenance recommendations, and restoring and/or creating a vegetative buffer around the remnant.
(4) Implementation. After delineation of a prairie remnant and/or savanna remnant, the proposed use or development shall comply with the following standards:
a. Buffering. A one-hundred (100) foot vegetated buffer is required around all delineated prairie remnant and savanna remnant, following the delineation’s restoration recommendations.
b. Buffer Reduction. The Story County Conservation Board may make recommendations to the Board of Supervisors regarding reductions in required buffer sizes. The Board of Supervisors may approve plans where the required buffer is reduced in size by no more than (50) percent of the required buffer width when sufficient protective measures are in place to identify and protect a prairie remnant and/or savanna remnant from impacts, such as fencing or subdrains installed by a developer. The reduction in buffer size may not result in any impacts to:
i. Species listed by the federal or state government as endangered or threatened, or critical or outstanding natural habitat for those species; or
ii. Diverse plant associations of infrequent occurrence or of regional significance; or
iii. The function or health of the prairie remnant and/or savanna remnant, including ensuring a sufficient vegetated area around the prairie remnant and/or savanna remnant to filter pollutants or slow surface runoff; and
iv. The area being removed shall not contain other critical natural resource areas or act as a buffer for those areas, such as native trees or wetlands.
(5) Impact. Impact to delineated prairie remnant and savanna remnant, including, but not limited to, grading and earth disturbance, construction, vegetation removal, and vehicle or heavy machinery movement, shall be limited to the following: management activities necessary for restoration and maintenance of the remnant; and rural water lines, gas lines, or other public utilities. These impacts shall be the minimum disturbance necessary to accomplish the needs of the infrastructure project or utility installation. Trenchless construction methods may be required.
(6) Mitigation. The following mitigation standards shall be required in addition to those general standards in Chapter 88.05(1)(A).
a. In cases where delineated prairie remnant and/or savanna remnant exists on the site and impact to the prairie remnant and/or savanna remnant is allowed as outlined in 88.05(1)(E)(5), the following mitigation procedures shall be required. In all instances, impacted prairie shall be mitigated with prairie, and impacted savanna shall be mitigated with savanna:
i. For mitigation areas preserving existing prairie and/or savanna off-site, prairies and/or savannas shall be preserved at a ratio of 1:1. For mitigation areas reconstructing or creating prairie and/or savanna, prairie and/or savanna shall be replaced at a ratio of 2:1.
ii. Story County Conservation shall approve of all seeds, plugs, and species used in the mitigation area prior to planting. The seed mix shall be equivalent to the Natural Resources Conservation Service CP42 pollinator mix or another Story County Conservation approved planting plan, with local ecotype seed only, and a ratio of 10 grass seeds to 30 forb seeds per square foot.
(7) Restoration. Restoration to improve the prairie remnant and/or savanna remnant, including removal of invasive species, reseeding and planting, restoring the vegetative buffer around the remnant, and placing the area in a conservation easement that includes provisions for ongoing maintenance, may be required as a condition of the applicable permit or rezoning for the development.
F. Requirements for Archaeological Resources. Those areas containing significant sites of archaeological resources, such as Native American mounds and burial sites, which contain material remains of past human life or of archaeological interest. The requirements of this section shall be in addition to the applicant’s obligation to satisfy all other applicable local, state, or federal regulations and permits.
(1) Applicability. The provisions within this section shall be applicable to all proposed commercial and industrial development and site plans, subdivisions with more than two (2) development lots, rezonings, and conditional use permits within six-hundred fifty (650) feet of a stream.
(2) Identification. An archaeological assessment shall be conducted for the entire property to determine whether burial sites and Native American mounds exist on site, in accordance to the following procedures:
a. The applicant shall conduct a search of the Iowa Site File for archaeological sites recorded within a one-mile radius of the proposed development through the University of Iowa Office of the State Archaeologist (OSA). The applicant shall indicate in their request to the OSA that the search is required to comply with the Story County Land Development Regulations Chapter 88.05 Environmental and Natural Resource Standards. The OSA report will identify and evaluate known surveys and archaeological resources and include recommendations for further archaeological investigations.
b. If OSA does not recommend an archaeological survey, written notice as such from the OSA will suffice for completing this requirement.
c. If OSA recommends an archaeological survey, the applicant shall engage a qualified consultant from the Association of Iowa Archaeologists (AIA) Consultants List to complete the survey.
d. The consultant shall provide an electronic report of the survey to the Planning and Development Director and OSA. OSA may review the report to determine its adequacy using standard AIA guidelines. The report shall include recommendations regarding further archaeological investigations and appropriate research questions to assist in the event of mitigation.
(3) Implementation. If burial sites and/or Native American mounds are found on site, the applicant shall proceed in accordance with the following:
a. Buffering. A buffer zone shall be established that measures one hundred (100) feet, or as requested by Native American Nations (or other appropriate descendent communities) around the burial site and/or Native American mounds.
(4) Impact. The critical area and its buffer area shall be left undisturbed except for non-invasive/non-ground-disturbing management practices.
(5) Mitigation. The following mitigation standards shall be required in addition to those general standards in Chapter 88.05(1)(A).
a. Disturbance to the buffer area and/or reduction in buffer size shall only be permitted after recommendation from OSA, which may include consultation between Native American Nations (or other appropriate descendent communities), OSA, the State Historic Preservation Office, the Planning and Development Director, and funding agencies involved to determine mitigation measures.
b. A programmatic agreement or memorandum of understanding or agreement (MOA) or other appropriate protection measures may be developed as part of the recommendation.
2. Common Open Space Requirement. In all major subdivisions of 10 development lots or more there shall be a minimum of 15 percent of the subdivision dedicated or reserved as common open space, as defined in Section 85.08, Definitions.
A. Common open space shall be clearly designated on plans and shall not include:
(1) Areas reserved for the exclusive use or benefit of an individual tenant or owner.
(2) Dedicated streets, alleys, and other public rights-of-way.
(3) Vehicular drives, parking, loading, and storage areas.
B. Suitable provisions for maintenance and upkeep of common open space shall be provided through a homeowners association, deed covenants, or through other similar provisions as approved by the Board of Supervisors.
3. Construction Site Erosion and Sediment Control. Sedimentation and erosion pollute water, degrade land, cause the loss of native vegetation and habitats, and impair drainage. Development activities cause land to become susceptible to erosion and sedimentation by wind and water. The following requirements shall apply to development and land disturbance activities in Story County to mitigate the impacts of erosion and sedimentation, protect public and private property, and to protect natural resources and preserve their functions.
A. All development shall submit the following information in addition to other applicable development permit applications or, if no development permits are applicable, a grading permit and the following information. Any development that disturbs one or more acres is required to also obtain a National Pollutant Discharge Elimination System (NPDES) Permit from the Iowa Department of Natural Resources. The Stormwater Pollution Prevention Plan (SWPPP) shall be submitted to the Planning and Development Department as part of a permit or development application submittal.
(1) A site plan showing the area to be disturbed, any slopes, watercourses, floodplain, other features prone to erosion, and the location of Erosion and Sediment Control Best Management Practices (BMPs) selected to meet the requirements of this Chapter;
(2) Other information necessary to illustrate conformance with the Erosion and Sediment Control Requirements in this Chapter including a construction/grading schedule and schedule for the installation of erosion and sediment control BMPs. For example, a schedule of when grading will occur and when temporary erosion control BMPs will be installed or a schedule of staging activities.
(3) The party responsible for maintenance and their contact information if different from the property owner or permit applicant.
B. Erosion and Sediment Control Requirements.
(1) General Requirements. The following requirements apply to all developments required to submit information on Erosion and Sediment Control in accordance with this Chapter.
a. Erosion and sediment control BMPs shall be installed following the Iowa Statewide Urban Design and Specifications (SUDAS) Design Manual and Standards Manual or other professionally accepted design criteria.
b. Maintenance of erosion and sediment control BMPs shall occur to keep the BMPs functioning in an effective manner.
c. Minimize Disturbed Area.
i. The area of land to be disturbed shall be minimized and staging shall be used to minimize the area disturbed at a given time, as practical. The limits of the development including staging and equipment storage areas shall be delineated/flagged/fenced on the site to protect areas that are not proposed to be disturbed.
ii. Natural plant covering shall be retained and protected to the maximum extent practicable and as consistent with developing the site.
d. Stabilize Disturbed Areas.
i. Final stabilization of disturbed areas shall, at a minimum, be initiated immediately whenever any clearing, grading, excavating or other earth disturbing activities have permanently ceased on any portion of the site. If final stabilization cannot occur due to the time of year or weather conditions based on SUDAS specifications for a practice, temporary stabilization shall be immediately initiated until such time final stabilization may be completed. final stabilization BMPs may include seeding and sodding.
ii. Temporary stabilization shall, at a minimum, be initiated on all disturbed areas, including stockpiles, whenever any clearing, grading, excavating or other earth disturbing activities have temporarily ceased on any portion of the site and will not resume for a period exceeding 14 calendar days. Temporary erosion control stabilization BMPs may include temporary seeding, geotextiles, mulches, vegetative filter strips.
(2) Requirements for Sites with Sensitive Features. The following requirements apply to all developments required to submit information on Erosion and Sediment Control in accordance with this Chapter where watercourses, floodplain, slopes, or other features prone to erosion are proposed to be disturbed or where work may affect adjacent properties.
a. Development in the floodplain is discouraged. Any proposed development in the floodplain shall be done in accordance with the adopted Floodplain Management Ordinance (codified in Chapter 80 of this Code of Ordinances) or other State or Federal requirements.
b. Perimeter sediment control BMPs shall be in place prior to disturbing activities when the disturbed areas are above or on a slope to site borders, watercourse, or environmentally sensitive areas. Perimeter sediment control BMPs may be removed after final stabilization of the area above the BMP. The timing and/or installation of the perimeter control installations may be adjusted to accommodate short-term activities such as the passage of vehicles or to accommodate disturbing activities required to install the controls. Perimeter sediment control BMPs may include filter berms, filter socks, wattles, temporary earth diversion structures, vegetative filter strips, and silt fences.
c. On steep or lengthy slopes or for construction sites that show signs of concentrated flows, additional erosion and sediment control BMPs may be required. These practices may include silt fence, filter berms, filter socks, or other flow diversion and flow control BMPs to reduce the amount or velocity of flow a disturbed area receives. Follow the design considerations for a practice in SUDAS.
(3) Requirements for Treatment of Topsoil. The following requirements apply to all developments required to submit information on Erosion and Sediment Control in accordance with this Chapter where topsoil is stripped or otherwise disturbed and its removal and/or disturbance is not required for the function of the proposed project.
a. Practices to reduce compaction including reducing passes made over an area with heavy equipment and not using heavy equipment when soil is wet shall be used.
b. Topsoil that is removed but may be used for restoration after development activities cease shall be preserved on-site where possible. Topsoil shall be respread or restored to create a healthy soil profile following the methods for Soil Quality Management and Restoration in the Iowa Stormwater Management Manual or other professionally accepted methods.
(4) Construction Site Standards. The following requirements apply to all developments required to submit information on Erosion and Sediment Control in accordance with this Chapter where the site does not have an existing stabilized entrance or where a concrete truck will be used.
a. A stabilized entrance shall be designed to minimize tracking of sediment or other debris off the site and/or in the road right-of-way and shall be installed prior to land disturbing activities.
b. Concrete waste must be contained in washout areas installed following SUDAS or other professionally accepted design criteria.
C. Inspections and Responsibility.
(1) In no instance shall acceptance of the Erosion and Sediment Control plans and/or approval of the grading permit by Story County be construed as approval of the design, construction, or concurrence by Story County that all criteria have been satisfied. Story County shall not be liable for any damages resulting from erosion and sedimentation.
(2) An inspection for compliance with submitted erosion and sediment control plans and requirements of this Chapter shall be conducted by Planning and Development Staff as part of the required foundation location inspection for a zoning permit or if no development permits are applicable, as part of the grading permit and corresponding inspection after BMPs have been installed but prior to the commencement of land disturbing activities.
(3) Temporary erosion and sediment controls shall not be removed until the Planning and Development Staff have determined that the site has been permanently stabilized through a final inspection for a zoning permit, or if no zoning permit is required, an inspection once final stabilization is completed.
(4) The applicant or owner of the site agree to provide for access to the BMP and the land it serves at reasonable times for periodic inspection by County or County’s designee to ensure that the BMP is maintained in proper working condition to the requirements of this Chapter.
(5) Any amendments or changes to the submitted Grading Permit or Erosion and Sediment Control information shall be communicated to the Planning and Development Department and submitted prior to their implementation on-site. All amendments shall comply with the requirements for Erosion and Sediment Control in this Chapter.
(6) If a responsible party fails or refuses to meet the requirements of the approved plan or any provision of this ordinance or in the event that the erosion or sediment control BMP becomes a danger to public safety or public health, the County shall notify the party responsible for maintenance of the erosion or sediment control BMP in writing following the procedure for Notice of Violations in Chapter 93 of the Story County Land Development Regulations. Depending on the severity of the violation, the permitted timeframe to submit a compliance schedule may be reduced. If the violator does not correct/abate the violation or provide an acceptable schedule to correct/abate the violation or does not comply with the schedule, a citation for a County infraction may be issued in accordance with Chapter 93 of the Story County Land Development Regulations.
D. Exemptions. The following exemptions to the Erosion and Sediment Control requirements may apply; however, such uses shall not be exempt from adopted Floodplain Management Ordinance (codified in Chapter 80 of this Code of Ordinances) or other State or Federal requirements.
(1) Agricultural. Except to the extent required to implement Section 335.2, Code of Iowa, as amended, the grading permit application and Erosion and Sediment Control requirements shall not apply to development that is primarily adapted, by reason of nature or area, for use for agricultural purposes, while so used.
4. Post-Construction Stormwater Management. Stormwater runoff increases nonpoint source pollution, flooding, siltation, stream temperatures, and streambank erosion. The following requirements shall apply to development in Story County to ensure site design minimizes the generation of stormwater runoff and maximizes pervious areas, provide a single, consistent set of performance goals that apply to all developments, protect functional values of all types of natural watercourses, protect life and property from dangers associated with flooding, maintain existing flow patterns, and promote infiltration and recharge of groundwater.
A. Development that meets any of the following thresholds shall be required to submit a Stormwater Management Plan, in addition to other applicable development permit applications, prior to commencing development activities:
(1) Development, including common development, that disturbs an area one-acre or greater in size.
(2) Development that will result in the division of land into more than four development lots.
B. Criteria for Stormwater Management. Developments required to submit a Stormwater Management Plan shall be designed, constructed, and maintained to achieve the purposes of this Ordinance, as stated above, and to prevent flooding, minimize stream channel impacts, and protect water quality in accordance with the following criteria for stormwater management. See the Iowa Stormwater Management Manual for details on the calculation of the criteria. LID practices shall be used where possible to meet stormwater management criteria and in the design of a development.
(1) The site shall be designed to manage the water quality volume of a rainfall depth of 1.25 inches and to manage corresponding recharge volume through infiltration practices.
(2) To protect stream channels, the site shall be designed to provide 24-hours of extended detention of the channel protection volume determined for the 1 year, 24-hour storm.
(3) Stormwater management shall be provided to limit the post development rate of runoff from the site area during the 5-year through the 100-year, 24 hour storm events to the lesser of the following values: runoff rates equivalent to those from a storm event of the same intensity and duration based on pre-settlement conditions or runoff rates equivalent to those from the 5 year storm event based on conditions which exist as of the date of the proposed improvement plans (row crop agriculture cover, contoured in good condition and surface soil types as identified from County Soil Maps; unless otherwise approved).
(Ord. 310 – Oct. 23 Supp.)
C. Contents of the Stormwater Management Plan. The Stormwater Management Plan shall include a site plan, narrative, and other attachments necessary to illustrate how runoff and associated water quality impacts resulting from the development is proposed to be managed meeting the requirements of this Chapter and following the Iowa Stormwater Management Manual or other professionally accepted BMPs and/or through LID practices. It shall also:
(1) Be signed and certified by an Iowa licensed professional engineer (PE).
(2) Identify pre-development and post-development land use, including on and off-site features that may affect or be impacted by the stormwater management requirements for the development. Features may include:
a. Proposed and existing site improvements including lot divisions, building footprints, easements, and other impervious surfaces or areas of land disturbance.
b. Pre-developed land use and soil conditions including coverage, soil type, and Hydrologic Soil Group (HSG). If a geotechnical study of the site is used to determine HSG, provide boring logs and locations. If a soil survey is used to determine HSG, cite it and provide a copy of the area of interest map with HSGs.
c. Existing site topography with contours at two-foot intervals. Light Detection and Ranging (LIDAR) contour maps may be requested from the Story County Planning and Development Department or a survey of the site's topography may be completed and submitted to determine slopes.
d. Natural and artificial watercourses, wetlands, floodplains, lakes, existing stormwater storage facilities, woodlands, native vegetation, or other natural resources.
e. Proposed or existing drinking water wells, septic systems/drain fields, public wellheads and wellhead protection areas, hot spots, and areas with shallow bedrock.
(3) Identify the proposed stormwater management BMPs or LID practices selected for the site, their location, landscaping and stabilization to prevent their impairment, and any hydrologic and hydraulic design calculations and summaries/descriptions to show that the proposed BMPs are capable of achieving the criteria for stormwater management in Section 88.05(5)(B) and that they are designed in accordance with the Iowa Stormwater Management Manual. These may include, as applicable:
a. Impervious area (by area and percent of site)
b. Soil Curve Numbers or runoff coefficients
c. Times of concentration
d. Description of the design storm frequency, intensity and duration
e. Water quality volume and infiltration calculations
f. Channel protection volume calculations
g. Detention basin design calculations, runoff rates, volumes, water surface elevations, and data on the increase in rate and volume of runoff for the design storms referenced in the Iowa Stormwater Management Manual and stormwater management criteria
h. Peak runoff rates and total runoff volumes for each watershed area
i. Other design calculations for culverts, open channels, storm sewers, and intakes
j. Documentation of sources for all computation methods and field test results.
(4) Describe the maintenance procedures required for each selected practice and the party responsible for maintenance and their contact information if different from the property owner or permit applicant. Such maintenance procedures shall keep the stormwater management BMPs or LID practices functioning in an effective manner.
D. Inspections and Responsibility.
(1) In no instance shall the acceptance of the Stormwater Management Plan by Story County be construed as approval of the design, design methods, design calculations, detention facilities plan, construction, or concurrence by Story County that all design criteria have been satisfied. Story County shall not be liable for damages resulting from stormwater runoff or discharge of stormwater detention facilities.
(2) An inspection for compliance with submitted Stormwater Management Plan shall be conducted by Planning and Development Staff as part of the required final inspection for a zoning permit or if no zoning permit is required after BMPs have been installed.
(3) The applicant or owner of the site agree to provide for access to the BMP and the land it serves at reasonable times for periodic inspection by County or County's designee to ensure that the BMP is maintained in proper working condition to the requirements of this Chapter.
(4) Any amendments or changes to a Stormwater Management Plan shall be communicated to the Planning and Development and submitted as part of an amended plan to prior to their implementation on-site. All amendments shall comply with the requirements of this Chapter.
(5) If a responsible party fails or refuses to meet the requirements of the approved plan or any provision of this ordinance or in the event that the stormwater management BMP becomes a danger to public safety or public health, the County shall notify the party responsible for maintenance of the stormwater management BMP in writing following the procedure for Notice of Violations in Chapter 93 of the Story County Land Development Regulations. If the violator does not correct/abate the violation or provide an acceptable schedule to correct/abate the violation or does not comply with the schedule, a citation for a County infraction may be issued in accordance with Chapter 93 of the Story County Land Development Regulations.
E. Exemptions. The following exemptions to the Stormwater Management Plan requirement may apply; however, such uses shall not be exempt from adopted Floodplain Management Ordinance (codified in Chapter 80 of this Code of Ordinances) or other State or Federal requirements.
(1) Agricultural. Except to the extent required to implement Section 335.2, Code of Iowa, as amended, the Stormwater Management Plan requirement shall not apply to development that is primarily adapted, by reason of nature or area, for use for agricultural purposes, while so used.
(2) County, State, or Federal Government. County, state, or federal governments shall not be required to submit a Stormwater Management Plan for the maintenance and/or construction of county roads and public road right-of-way.
(3) Maintenance of Legally Established Development. The maintenance of development that has legally occurred prior to the adoption of this Ordinance (Ord. 285), shall not be counted towards the threshold for submitting a Stormwater Management Plan of one-acre disturbed or one-acre disturbed as part of a common development plan if the footprint of the maintenance work is within or the same area as that previously disturbed.
(4) When infiltration is infeasible due to the natural or existing physical characteristics of a site including, but not limited to, if the surface and underlying soils are NRCS Group D or have minimum infiltration rate less than .52 inch/hour, the measured groundwater elevation is less than four feet below the basin invert or infiltration surface, bedrock or impervious soils are less than four feet below the infiltration surface, recommended setbacks from site features (property lines, structures, septic systems, and wells) in the Iowa Stormwater Management Manual cannot be met, or where hotspots or contaminated soil make infiltration-oriented BMPs hazardous, the site shall be designed to provide water quality treatment for the runoff resulting from a rainfall depth of 1.25 inches and alternative practices such as a treatment train, constructed wetlands/wetland forebays, retention ponds/extended detention ponds, filters (sand-peat, underground sand, perimeter sand filter, organic sand, pocket sand filter, gravel, others), grassed/vegetated swales and channels, and vegetated filter strips shall be implemented to the maximum extent practical with the goal of an 80% reduction in of the annual average post-development total suspended soilds (TSS) load. The site limitations shall be identified in the Stormwater Management Plan.