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Steep Slope Ordinance

Zoning regulations for development on and disturbance of steep slopes can prevent erosion and reduce the risk of landslides that endanger lives, damage property and infrastructure, harm water quality, and degrade wildlife habitat. These regulations can also preserve the aesthetic character of visually prominent hillsides by discouraging vegetative clearing and excessive earthwork to accommodate development.


A Sensitive Feature

Steep slopes are among the most sensitive environmental features in our landscapes. They pose significant constraints to land development and resource extraction, being highly susceptible to erosion, land slippage, and subsidence if disturbed. Such disturbance can harm ecological values such as water quality, damage man-made structures, and present public safety risks. In many settings, steep slopes provide scenic views for neighboring areas, and extensive removal of vegetation, and extensive earthwork, can transform these intrinsic resources into visible eyesores. Considering all these factors, municipalities should pay close attention to steep slopes in their planning, conservation, and development permitting processes.

Tools to Regulate

The Municipalities Planning Code (MPC), Pennsylvania’s planning enabling legislation, specifically describes steep slopes and grades as natural features that qualify for municipal regulation. Tools employed at the municipal level to regulate steep slopes include the zoning ordinance and the subdivision and land development ordinance. Generally, the zoning ordinance provides greater protection of steep slopes by enabling a municipality to control the types of land uses located on or near steep slopes. And, unlike subdivision standards, zoning ordinance provisions are more difficult to vary from during a land development approval process. Zoning requirements must be met, or a formal zoning variance must be obtained. The subdivision and land development ordinance can certainly be designed to complement the steep slope provisions of a zoning ordinance by requiring a development applicant to submit for municipal review detailed topographic surveys, grading plans, and other site engineering details. These details will facilitate a careful municipal evaluation of any slope impacts of the proposed development. The development approval process within the subdivision and land development ordinance also requires applicants to demonstrate zoning ordinance compliance, and, in the case of steep slopes, show how the proposal avoids or minimizes impacts to steep slopes.

This guide focuses on use of the zoning ordinance as a tool to guide and restrict the use of steep slopes. Key discussion points include measuring and defining steep slopes, authority for and approaches to slope regulation, and implementation of steep slope regulations. Sample regulations are referenced throughout.

Defining Steep Slopes

Simply stated, slope is measured as rise over run. A stretch of land 100 feet long that rises three feet in elevation has a slope of three percent (3/100). Topographic maps, such as those prepared by the U.S. Geological Survey, and field surveys prepared by applicants’ surveyors during the subdivision and land development process, are the most common sources of slope information available to municipalities. County soil surveys, produced by the U.S. Department of Agriculture’s Natural Resource Conservation Service, also contain valuable topographic information. These surveys categorize soil types, in part, based on slope, with typical classifications occurring in the following ranges: zero to three percent, three to 8 percent, 8 to15 percent, 15 to 25 percent, and 25 to 50 percent.

Defining what constitutes “steep” for the purposes of slope regulation is at the discretion of each municipality, provided that the definition is reasonable. Some communities regulate slopes starting at 15 percent, which ties in neatly with soil survey slope classifications. Others start at 25 percent, another soil survey threshold and a clear benchmark for land use limitations. Others establish more than one minimum slope threshold based on use, e.g., 25 percent for residential uses, and 40 percent for non-residential uses. Some municipalities, particularly those in more hilly locations, regulate development of specific steeply sloping soil types. For example, Ferguson Township in Centre County, Pennsylvania specifically regulates the use of Colluvial soils – loose, unstable soils that gather in valleys – that pose tremendous environmental and safety hazards if inappropriately used.

Municipalities in southeastern Pennsylvania with fairly extensive slope features often use a two-tiered approach to slope regulation, with one set of restrictions tailored to slopes between 15 and 25 percent (a “moderate” or “moderately steep” slope) and another more prohibitive set of restrictions for slopes 25 percent and greater (a “steep” or “prohibitively steep” slope). A municipal ordinance could be drafted to establish more than two tiers, for example, by also restricting slopes in the 8 to 15 percent range. Generally, because slopes of 15 to 25 percent pose significant limitations to development, 15 percent is recommended as a minimum starting point for regulation. County soil surveys provide excellent summaries of such limitations.


A mapping inventory of steep slopes may help a municipality define and locate its steep slopes, although this mapping is not a pre-requisite of regulatory ordinance adoption. Today, through the use of Geographic Information System (GIS) technology, inventories of steep slopes within municipal boundaries are relatively easy for local governments and others to obtain through county, regional, or other government or non-profit sources. General slope categories should be coordinated between the municipality and the mapping agency prior to the GIS inventory. This slope mapping would be a valuable component of a municipality’s comprehensive plan or open space plan, or shown along with other natural and cultural resources on a Map of Primary and Secondary Conservation Lands prepared consistent with DCNR’s Growing Greener approach. If made part of a municipal, regional, or county plan, slope mapping should be accompanied by policies favoring slope protection and a discussion of one or more recommended slope protection implementation tools.

Authority to Plan and Regulate at the Municipal Level

Pennsylvania’s Municipalities Planning Code (MPC), Act 247 of 1968, as amended, clearly authorizes municipalities to plan and zone for steep slope protection.

Relevant Planning Provisions

§301(a)(6): The municipal… plan… shall include, but need not be limited to… a plan for the protection of natural and historic resources to the extent not preempted by federal or state law. This clause includes, but is not limited to, wetlands and aquifer recharge zones, woodlands, steep slopes, prime agricultural land, flood plains, unique natural areas and historic sites.

Relevant Provisions Regarding Zoning

§603(b)(5): Zoning ordinances… may permit, prohibit, regulate, restrict, and determine… protection and preservation of natural and historic resources and prime agricultural land and activities

§603(c)(7): Zoning ordinances may contain…provisions to promote and preserve prime agricultural land, environmentally sensitive areas and areas of historic significance.

§603(g)(2): Zoning ordinances shall provide for protection of natural and historic features and resources.

Section 605 of the MPC requires that, with few exceptions, zoning restrictions be uniform within discrete zoning districts. The exceptions, of which steep slopes are one, make possible the use of “overlay” zones:

§605(2)(iii): Where zoning districts are created, all provisions shall be uniform for each class of uses or structures, within each district, except that additional classifications may be made within any district…for the regulation, restriction or prohibition of uses and structures at, along or near…places of relatively steep slope or grade, or other areas of hazardous geological or topographic features.

Subdivision and Land Development

Other sections of the MPC enable municipalities to regulate subdivision and land development design as it relates to steep slopes and grades (Article V – Subdivision and Land Development). The Lehigh Valley Planning Commission’s Guide and Model Regulations for Steep Slopes discussed below provides a summary of these sections of the MPC and related provisions found in the Pennsylvania Constitution and federal statutes.

Cautionary Note

As with all land use regulations careful attention should be paid to issues of reasonableness and takings. Ordinances that are poorly defined or lack factually based purposes grounded in government policy may be subject to challenge.

Approaches to Protecting Steep Slopes through Zoning

Pennsylvania’s municipalities use a variety of approaches to regulate the use or disturbance of steep slopes. Some municipalities have started to increase their steep slope protection efforts by adding more than one set of zoning ordinance provisions that address the use or disturbance of steep slopes. Some also combine ordinance provisions with other conservation tools to increase protection of steep slopes. The following paragraphs describe a number of regulatory approaches to steep slope protection using the municipal zoning ordinance. This section also includes a review of select zoning ordinances from across the Commonwealth to illustrate the variety of approaches used.

Overlay Zones and Supplemental Regulations

The MPC allows the use of steep slopes to be regulated through a zoning overlay district. As steep slopes often occur throughout a municipality, the overlay approach enables their uniform regulation regardless of each municipality’s base zoning district provisions. Upper Salford Township, Montgomery County, employs this approach, which is typical of many municipalities across the Commonwealth. Its Overlay District comprises all areas of the Township with slopes greater than 15 percent. Four categories of slopes are differentially restricted, and a combination of disturbance (i.e., grading and vegetation removal) and lot size and design standards take precedence over the regulations of underlying districts.

Some municipalities, such as Kennett Township, Chester County, regulate steep slopes with supplemental regulations rather than using the overlay district approach. A separate article of Kennett’s zoning ordinance sets forth protection standards for a variety of natural resources, of which steep slopes are one. The Township classifies steep slopes in two tiers – “moderately steep” (15 to 25 percent) and “very steep” (25 percent and greater) – and limits the amount of disturbance within each slope tier as well as to other natural resources including floodplains, wetlands, and woodlands. Where steep slopes are present, detailed information related to grading and erosion and sediment control is required on development plans filed pursuant to the Township’s subdivision and land development ordinance. Other sections of the Township’s zoning ordinance require consideration of the same slope categories in determining, for example, minimum lot sizes and open space requirements.

In practice, overlay zones and supplemental regulations have the same effect in that they both augment the standards of base zoning districts. The decision to use one versus the other will largely depend on a zoning ordinance’s existing framework. Some municipalities use elements of both, with the overlay district more often controlling for use, and supplemental regulations often controlling for disturbance. For example, Ferguson Township, Centre County, has both “Slope Controls”, and a “Ridge Overlay District” designed to limit disturbance to Colluvial soils. According to this township’s zoning ordinance, Colluvial soils are rated by the Soil Survey of Centre County as having severe limitations for septic drainfields, roads and driveways, and buildings, and are characterized by one or more of the following physical constraints: seasonably high water table, fragipan, soil stability, steep slopes, slow permeability, large stones, and frost action. Similarly, Lycoming County’s county-wide zoning ordinance includes environmental protection standards for regulating the use and disturbance of steep slopes, and also development on or near ridges. This is particularly helpful given the increasing number of Marcellus Shale drilling sites in the County, and recent efforts by the County to regulate oil and gas industrial uses through its zoning ordinance.

Whether restricted by means of an overlay district or supplemental regulations, steep slopes need not be delineated on a municipality’s zoning map in order to qualify for regulation. While slope mapping at the municipal scale is invaluable for general land use planning purposes, the data used to do so is ineffective for evaluating the potential slope impacts of a proposed subdivision or land development. As a result, most municipal subdivision and land development ordinances include the requirement for development applicants to delineate steep slopes on development plans (preliminary and final subdivision plans) using detailed topographic information (see below).

Use Restrictions and Performance Standards

When drafting zoning ordinance provisions for steep slope protection, note that there is a difference between use and performance restrictions. Generally, restrictions on use limit the activities that may occur on steep slopes, while performance restrictions set forth the criteria and conditions under which steep slopes may be disturbed, regardless of use. Most municipalities employ elements of both, which these authors recommend.

The Lehigh Valley Planning Commission’s model steep slope regulations, discussed below, are primarily use-based in that each slope tier (15 to 25 percent and 25 percent and greater) has a series of permitted, prohibited, and conditional uses. For example, on-lot septic disposal systems are a conditional use on slopes of 15 to 25 percent and are prohibited on slopes greater than 25 percent. Performance-based standards are embedded in the model ordinance’s “General Provisions” section.

In contrast, Lehigh County’s Lower Milford Township takes a more performance-oriented approach to steep slope regulation. Within its four-tiered steep slope area, disturbance (i.e. grading, clearing, construction, etc…) is limited to a percentage of the land area occupied by each tier. Use restrictions – in addition to those imposed by the underlying zoning district – only apply to prohibitive slopes. As with Kennett Township, steep slopes are one of many natural resources Lower Milford regulates in a comprehensive natural resource protection ordinance that limits resource disturbance and requires the consideration of development-constrained land in the calculation of lot size and density.

Linking Lot Size to Slope

Some Pennsylvania municipalities use their zoning ordinance to protect steep slopes by linking the required minimum lot size within a base zoning district to the percentage of slope measured over the parcel proposed for subdivision. The minimum lot size requirement increases as percentage slope increases. For example, text may appear as:

“Every lot hereafter created by subdivision having an average slope of at least 15%, but not more than 25%, shall have the minimum lot area increased by a factor of 1.5….”

This approach assumes that a larger minimum lot size will allow for utilization of more unconstrained land within a building lot for construction without disturbing steep slopes. However, without additional zoning or subdivision and land development ordinance provisions that actually guide the placement of a proposed structure, or limit actual site disturbance, the increased lot size provision alone cannot guarantee steep slopes will be protected.

Complementary Regulatory Options

A steep slope overlay district (or set of supplemental regulations) alone may not accomplish the resource protection objectives desired by a municipality or yield development patterns appropriate for steeply sloping landscapes. Use of conservation-minded development options and, in special cases, landscape-specific zoning districts can augment standard steep slope regulations by preventing the fragmentation of large steeply sloping areas and ensuring hillside development has a minimal visual impact.

Conservation by Design and Planned Unit Development

The development options prescribed in base zoning districts have a major impact on the amount of steep slopes disturbed across a site. In contrast to conventional “cookie cutter” zoning restrictions, development options such as planned unit development and Conservation by Design can both require steep slope preservation and provide lot size, building setback, and other zoning flexibility to avoid steep slope disturbance. With these design approaches, preservation of steep slopes is attained through their mandatory set aside in open space areas and by means of smaller lot dimensions, which allow homes to be clustered in more suitable locations. An increasing number of municipalities now include some version of conservation subdivision design in their zoning ordinances.

Further Slope Protection through Resource “Net-outs”

Minimum net lot and tract area requirements, a related safeguard, may be used to ensure that lots or development sites have an adequate area of land for building excluding steep slopes and other sensitive environmental features. Use of this zoning technique would lessen the pressure to disturb steep slopes in the first place, though could also lead to a more disbursed development pattern. East Vincent Township, Chester County, excludes steep slopes, floodplains, and jurisdictional wetlands from its definition of “net tract area,” which is used to establish the maximum number of dwelling units permitted on a tract of land. Lower Milford Township, mentioned above, also requires all applicants for subdivision or land development approval to show building envelopes for all proposed lots that are free and clear of a property’s physical constraints, including steep slopes.

Use of Complimentary Performance or Design Standards

Certain landforms such as ridges, valleys, and hillsides may merit special protection beyond that afforded by traditional slope regulations. Ferguson Township’s Ridge Overlay District, mentioned previously, is one example of such special protection. Use and performance restrictions are combined with rigorous on-site soil investigation requirements and very specific conditional use criteria to maximize protection of the Township’ sensitive Colluvial soils. As noted earlier, Lycoming County’s county-wide zoning ordinance includes environmental protection standards for ridges, and requires the retention of a 100 feet “downslope” vegetated buffer when new homes are proposed on or near the tops of ridges. Where little downslope vegetation exists, homes must be set back from the steeply sloped sides of ridges and significant vegetative plantings are to be established within this setback. The City of Pittsburgh’s scenic hillsides play a major role in defining its visual character. In addition to a traditional steep slope overlay district, Pittsburgh has both a Hillside District and a View Protection Overlay District. The Hillside District is a base zoning district with unique hillside-appropriate site development standards. The View Protection Overlay District enables the City Planning Commission to create supplemental design guidelines for View Protection Districts, which may include hillsides.

Anatomy of a Basic Steep Slope Overlay District: LVPC’s Model

No municipality should be without zoning provisions that regulate the use of, and therefore the potential impacts to, steep slopes. While the special zoning districts and development options previously described may be unnecessary or inappropriate in certain locales (and are generally beyond the scope of this publication), use and disturbance limitations on slopes beginning at 15 percent provide essential and very reasonable safeguards to public health, safety, and general welfare.

For those municipalities that do not zone for steep slopes or have older slope regulations in need of updating, the Lehigh Valley Planning Commission’s (LVPC) Guide and Model Regulations for Steep Slopes provides a good starting point. As gleaned from this useful publication, the basic anatomy of a steep slope overlay district includes the following key elements.


All land use regulations should carefully articulate their purposes. Municipalities should clearly identify the purposes of their steep slope regulations, drawing closely from language from the MPC. The purposes recommended in LVPC’s model regulations cover several public benefits, including safety, protection of property and water resources, and land use compatibility. Consider tying purpose statements to comprehensive plan policies and to the zoning ordinance’s stated community development objectives (see Section 606 of the MPC).

Identification and Establishment

Zoning regulations for steep slopes should clearly identify the slopes subject to regulation in an overlay district or as a resource meriting supplemental regulation. LVPC’s recommended approach is to delineate steep slopes on a map incorporated by reference in the zoning ordinance, though supplemented with more detailed data whenever a subdivision or land development plan is submitted by an applicant for review and approval. In LVPC’s model, the steep slope overlay district is divided into two slope categories, 15 to 25 percent and 25 percent and greater. The municipal engineer determines the adequacy of steep slope mapping on subdivision and land development plans.

General Provisions

In a use-oriented steep slope overlay district, the general provisions section states the performance criteria for steep slope disturbance, including standards that must be met for cuts, fills, retaining walls, tree removal, site stabilization, roads, and driveways. In LVPC’s model, a minimum one-acre building lot exclusive of slopes 25 percent and greater – the net lot area approach mentioned above – is also required in this section. If not addressed elsewhere in the zoning ordinance, the general provisions may need to state the threshold at which steep slope disturbance is regulated by the zoning ordinance. In LVPC’s case, that threshold is 5,000 square feet of land disturbance to steep slopes.

Permitted, Prohibited, and Conditional Uses by Slope Classification

The core of LVPC’s model regulations is the listing of permitted, prohibited, and conditional uses by slope category. If not outright prohibited, most development-related uses are conditional uses, meaning a municipality’s elected officials (board of supervisors, borough or city council, etc…) may impose reasonable conditions on an applicant’s proposed disturbance of steep slopes. Use of the conditional use process has the advantage of giving a municipality significant discretion over steep slope permitting, though can require substantial board or council involvement in the public hearing and approval process. Such close involvement and discretion may indirectly act as a deterrent to slope development, or alternatively, may result in disastrously ineffective development restriction

On slopes between 15 and 25 percent, most non-disturbance related uses are permitted by right, provided that forestry, farming and related uses are done in compliance with “recognized natural resource and soil conservation practices.” The only prohibited uses in this slope category are waste disposal, outdoor storage, and the removal of topsoil except when related to an approved conditional use. Conditional uses include grading, vegetation removal, and virtually all physical improvements, such as roads, buildings, and utilities.

The regulations on slopes greater than 25 percent replicate the regulations for slopes in the 15 to 25 percent range with one significant exception—the conditional uses in the 15 to 25 percent range (e.g. roads, buildings, and utilities) are prohibited on slopes 25 percent and greater.

Conditional Use Standards and Criteria

Where the conditional use process is used to deny or permit steep slope disturbance, standards and criteria for the review of conditional use permits helps focus the local decision-makers’ attention on the conditions appropriate for and likely to be required of applicants. LVPC’s model regulations set forth eight such standards and criteria, such as the possible need for a woodlot management plan for wooded steep slope areas.


Capitalized terms unique to steep slope restrictions are defined in this section of LVPC’s model regulations, though many municipalities would simply add to or revise the existing definitions section of their zoning ordinances. Included in LVPC’s list of definitions is a fairly precise description of the basis on which steep slopes are measured, specifically, “five adjacent contour intervals of two feet each.” In other words, areas identified on a topographic map where five or more contour intervals (lines) are tightly clustered (i.e., two or less scale-feet apart), are characterized as steeply sloped. Topographic data of this detail would only be available following a site-level survey. Many of the municipalities mentioned previously require steep slopes to be delineated in this manner as part of the plan review process, which underscores the use of a municipality-wide steep slope map for general planning purposes only. If desired, municipalities may allow an applicant the use of publicly available topographic mapping (i.e., USGS) for the purposes of depicting critical slopes during an optional sketch plan submittal.


Adopt Clear and Effective Regulations

Successful implementation of zoning regulations for protecting steep slopes from indiscriminate disturbance starts with the adoption of clear and effective regulations. Review of the approaches, examples, and model regulations described in the previous sections – each with its pros and cons – by a task force comprised of elected and appointed officials, a municipal engineer and/or a municipal planner would be a valuable first step. Wholesale adoption of any particular model or example is not recommended, as each would require customization to mesh with a zoning ordinance’s existing provisions, definitions, and general framework. Consultation with professional planners, landscape architects, civil engineers, or geologists, and the municipality’s attorney would be essential for both drafting and ensuring that procedural requirements are met. Coordination with County planning staff (the MPC requires that County planning agencies be given the opportunity to comment on zoning ordinances before enactment) is also appropriate. Technical and financial assistance may be available through County planning departments, through state agencies such as The Governor's Center for Local Government Services, and often by contacting one of Pennsylvania’s regional land trusts, such as the Brandywine Conservancy, Natural Lands Trust, Berks Conservancy, or the Heritage Conservancy.

Procedures and Enforcement

Successful implementation also requires easily understood administrative procedures and a commitment to enforcement. The terms of the ordinance play a major role in setting the stage for both. For example, clear standards on mapping requirements ensure that the full extent of steep slopes is presented on submitted plans. Hard and fast standards on land disturbance within particular steep slope categories guarantees a minimum portion of steep slopes will be left undisturbed (at least as presented on submitted plans). To deviate from these quantitative, easily gauged standards would in most cases require a zoning variance, and demonstration of physical hardship.


Where discretion comes into play, as in the case of a conditional use approval, significant opportunity exists for limiting the disturbance of steep slopes. However, this opportunity depends largely on the rigor with which boards and councils, often based on recommendations from their appointed planning commissions and municipal consultants, impose protection-minded conditions on applicants. Discretion also leaves open the possibility for lax enforcement should officials or consultants not pay close enough attention to potential problems or err on the side of flexibility in favor of applicants. Many municipalities successfully blend quantitative standards and discretion, as in the case of Lower Milford Township, cited above, which in certain cases allows for “modifications” of steep slope and related natural features protection standards where applicants can demonstrate that such modifications will result in the same, if not better, resource protection.

Supplemental Tools

Conservation by Design, special zoning districts and other tools described at can play supportive or complimentary roles in regulating activities on steep slopes, especially in the context of their scenic values.  However, steep slope regulations, no matter their form, can be repealed or weakened at any time through simple majority vote of the governing board that enacted the regulations. Conservation easements, in contrast, can permanently protect steep slopes with proper monitoring and enforcement, regardless of how zoning changes. (Yet it generally makes little sense for a municipality to pursue conservation easements on steep slopes if it has not first enacted solid regulations.)

Case Study – Kilbuck Township Landslide

“The Protection of Steep Slopes Requires Effective and Meaningful Municipal Oversight” (An observation of the Pennsylvania Joint State Government Commission’s Investigation of a Massive Landslide in Kilbuck Township, Pennsylvania)

A major landslide in Kilbuck Township, Beaver County, Pennsylvania, in September of 2006, evidences disastrous consequences of failing to protect this municipality’s steep slopes from disturbance, even though appropriate municipal regulatory ordinances were in effect. Kilbuck Township’s Board of Supervisors was anxious to accommodate a retail developer’s super-store proposal, bringing property tax revenue and jobs to this community outside of Pittsburgh. The 75-acre site sits above the Ohio River, while Pennsylvania State Route 65 (Ohio River Boulevard), and a main east-west rail corridor operated by Norfolk Southern Corporation lay in-between the development site and shoreline. The site was once the location of the Dixmont State Hospital, and documents exist that portray at least part of the site experiencing significant slope failures, land subsidence, and dramatic uplifting of lands.

Kilbuck Properties, as the super-store applicant, proposed development plans that included a topographic survey showing slopes ranging from 25% to 50% in the area where the landslide occurred. Kilbuck Township’s zoning ordinance provisions regulating slopes of 25% or greater required subdivision and land development applicants planning to build on such slopes to notify the Township, and where determined appropriate by the zoning officer, submit geotechnical studies to the Township. The Township’s grading ordinance limited the stripping of vegetation or disturbance of slopes between 25% and 40% to 25% of the total area, and prohibited any development or disturbance of slopes exceeding 40%. The municipality’s engineer raised numerous concerns about ordinance compliance issues during initial development plan review, including several on-site grading concerns.

The Township Planning Commission recommended approval of the applicant’s development plan subject to appropriate resolution of the municipal engineer’s documented concerns. The township supervisors subsequently amended their grading ordinance, appointed their municipal engineer as the ordinance administrator, and gave the administrator the ability to grant modifications or waivers of ordinance provisions (outside of any public meeting or hearing process) when such provisions were found to be “impractical” to meet or achieve. Following these changes, Kilbuck Properties worked with this municipal engineer and was granted the necessary Township approvals and permits to allow the site construction to proceed. Necessary permits were also issued by PADOT and PADEP to allow the project, River Pointe Plaza, to move forward.

During the Township’s review and approval process, the Allegheny County Office of Economic Development submitted comments to Kilbuck Township warning of the former state hospital’s history with landslides and soil subsidence. The Township’s grading ordinance specifically referred to this Office as a credible source of soil stability information. Also, a citizens group comprised of residents, municipal officials, and small business owners of communities along the Ohio River corridor attended Kilbuck Township meetings and hearings, and offered qualified testimony in opposition of the River Pointe Plaza development. This group also filed numerous appeals of various township and state permits and approvals but were unsuccessful each time in halting the project.

In April of 2006, a small, but foreboding landslide occurred on the site without raising concern by local, county, or state approval authorities. PADOT inspected the site and landslide area in July of 2006. Then, in late September 2006, after a day of significant blasting, the entire hillside, estimated at 500,000 – 600,000 cubic yards of earthen material, flowed downward toward the Ohio River, covering the four lanes of the Ohio River Boulevard, and the three Norfolk Southern main lines, before stopping at the River’s edge.

The Norfolk Southern rail lines, which accommodated roughly 100 freight trains per day, were completely blocked for 24 hours, causing incredible tie-ups and re-routing challenges for Norfolk Southern, until the first set of tracks could open. After 36 hours, the second of the three rail lines was opened. Ohio River Boulevard, which accommodated roughly 22,000 vehicles per day, took far longer to open. The two southbound lanes were opened for traffic after 11 days of earthwork and cleaning, and one of the two northbound lanes opened after two weeks of earthwork and road repair. During this time, adjoining communities were ensnarled in traffic tie-ups and congestion, as through-traffic sought any alternative routes. It is estimated that two million dollars have been spent by the applicant/owner on site remediation, and an additional 75,000 per month on soil stability monitoring.

Wal-Mart Real Estate Trust, who initially owned a portion of the Kilbuck site, but then became the full owner of the 75-acre site after the landslide, had difficulty reaching agreement with PADEP on appropriate site restoration measures that would allow their super-center development to proceed. As a result, the Trust elected to drop their commercial development proposal, and restore the site to more natural topographic conditions and retain it in open space uses.

The Kilbuck Township landslide so significantly disrupted the flow of goods and people that it created a national security concern. The Pennsylvania House of Representatives directed the Joint State Government Commission to conduct an in-depth investigation into the landslide, including a thorough review of the applicable State and local permit and approval processes. A four-member legislative task force was created, and a 28 member advisory committee was also appointed. The investigation, findings, and recommendations of task force and advisory committee are a fascinating read.

As a result of the Commonwealth’s Kilbuck landslide investigation, Representative Petrone introduced legislation, the Geologically Hazardous Areas Act in the Pennsylvania House of Representatives to address the identification and delineation of geologically hazardous areas that are susceptible to mass earth movements, such as soil and rock slides, acid formation or sinkhole development. The legislature did not act on the proposal.

Although the task force and advisory committee found multiple causes and possible explanations for what contributed to the Kilbuck Township landslide, the disturbance of the site’s steep slopes more than likely played a major role, and the Township’s action, or lack thereof, in protecting its steep slopes through the appropriate enforcement of its own regulations regarding steep slopes, is highly suspect.



Kevin Anderson, AICP, Associate Planner, and John Theilacker, AICP, Associate Director, of the Brandywine Conservancy’s Environmental Management Center, are the primary authors. Andy Loza of the Pennsylvania Land Trust Association edited the guide.

The Lehigh Valley Planning Commission’s Guide and Model Regulations for Steep Slopes, the Delaware Valley Regional Planning Commission’s Sample Natural Resource Protection and Open Space Preservation Ordinances, and the Zoning for Landscape Protection guidelines developed by the firm Wallace, Roberts, and Todd for municipalities subject to the Pennsylvania Appalachian Trail Act provided excellent examples of steep slope zoning regulations, some of which are referenced here.

Roy Kraynyk of the Allegheny Land Trust was helpful in summarizing the events leading up to, and following, the Kilbuck Township landslide.


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Natural Lands Trust
(610) 353-5640 x230
Ann directs the statewide Growing Greener/ Conservation by Design conservation planning program. She is also is a Certified Planner and landscape architect.
Environmental Management Center, Brandywine Conservancy
(610) 388-8387
John has over 30 years of land use and environmental planning experience in southeast Pennsylvania, and is a frequent lecturer on topics of transferable development rights, historic preservation, and open space design.
Brandywine Conservancy
(610) 388-8389
John directs the Brandywine Conservancy’s Municipal Assistance Program. A Certified Planner, John has over 28 years of experience in land use and environmental planning.
Grim, Biehn & Thatcher
I have written, reviewed, and defended such ordinance provisions.

Featured Library Items

The Lehigh Valley Planning Commission’s model steep slope regulations are primarily use-based in that each slope tier (15 to 25 percent and 25 percent and greater) has a series of permitted, prohibited, and conditional uses. Performance-based standards are embedded in the model ordinance’s “Genera…
Ferguson Township, Centre County, PA zoning ordinance, which includes steep slope ordinance. The steep slope ordinance has both “Slope Controls” (page 405), and a “Ridge Overlay District (page 64)” designed to limit disturbance to Colluvial soils
Chapters 905 & 906 of Pittsburgh's zoning ordinances, which contain the city's steep slope ordinances. Pittsburgh's scenic hillsides play a major role in defining its visual character. In addition to a traditional steep slope overlay district, Pittsburgh has both a Hillside District, a base zonin…
The Delaware Valley Regional Planning Commission completed a survey of municipal natural resource protection tools in its service area in 2002, which was systematically updated in 2006. Outstanding examples of ordinances related to natural resources, including steep slopes, are posted on this webs…
Zoning ordinance for Lower Milford Township, Lehigh County, which include steep slope ordinances. Lower Milford Township takes a more performance-oriented approach to steep slope regulation; within its four-tiered steep slope area, disturbance (i.e. grading, clearing, construction, etc…) is limite…
A major landslide in Kilbuck Township, Beaver County, Pennsylvania, in September of 2006, demonstrates the disastrous consequences of failing to protect the municipality’s steep slopes from disturbance. This report presents the findings and recommendations of the Joint State Government Commission'…
The Pennsylvania Appalachian Trail Act requires Pennsylvania municipalities along the Appalachian National Scenic Trail to adequately protect it as a public natural resource. Planning and architecture firm Wallace, Roberts, and Todd was hired by a steering committee of municipalities subject to th…
The Munipalities Planning Code allows the use of steep slopes to be regulated through a zoning overlay district, which enables their uniform regulation regardless of each municipality’s base zoning district provisions. Upper Salford Township, Montgomery County, employs this approach, typical of ma…
Steep slope ordinance enacted by the City of Reading in 2017.
Guide to steep slopes in Centre County, including regulatory and non-regulatory protection strategies.
Amends the steep slope section of the zoning ordinance, eliminates steep slope conservation overlay district, and more.
Steep slope overlay district for Edgmont Township (Delaware County). Includes series of permitted, conditional, and prohibited uses for areas of "very steep slope" (greater than 25%) and "steep slope" (15–25%).
Section of Upper Providence Township (Delaware County) code about the township's steep slope conservation overlay district.
Steep slope overlay district for Whitemarsh Township (Montgomery County), which sets requirements for average lot area and maximum impervious ground cover based on steep slope ratio.
Section of Kennett Township (Chester County) zoning ordinance that includes supplemental regulations for natural resources such as steep slopes, floodplains, wetlands, woodlands, and riparian buffers.
Ordinance regulating stormwater management and steep slopes in Upper Dublin Township (Montgomery County). The minimum lot size requirement increases as the average slope increases.


Kevin Anderson, AICP, Associate Planner, and John Theilacker, AICP, Associate Director, of the Brandywine Conservancy’s Environmental Management Center, are the primary authors. Andy Loza of the Pennsylvania Land Trust Association edited the guide.


Nothing contained in this or any other document available at is intended to be relied upon as legal advice. The authors disclaim any attorney-client relationship with anyone to whom this document is furnished.

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