MEMORANDUM
TO: Roger L. Stancil, Town Manager
FROM: J.B. Culpepper, Planning Director
Gene Poveromo, Development Manager
Sue Burke, Stormwater Engineer
SUBJECT: Land Use Management Ordinance Text Amendment – Consistency in Consideration of Gravel as Impervious Surface
DATE: April 15, 2009
INTRODUCTION
Tonight the Town Council continues the public hearing from January 26, 2009. Adoption of the attached ordinance would enact a proposed Land Use Management Ordinance text amendment regarding consideration of gravel as impervious surface both inside and outside the Town’s Watershed Protection District (WPD).
BACKGROUND
In 1993, the Town Council enacted watershed protection regulations, in accordance with a State mandate which limited the percentage of impervious surface on development sites located within the Jordan Lake Watershed Protection District (WPD). A map of the WPD within the Town’s planning jurisdiction is attached. In 1993, the State regulations considered gravel areas, within the Jordan Lake Watershed Protection District as built-upon area (impervious surface).
In 2003, the Land Use Management Ordinance was enacted, extending the 1993 State mandated impervious surface limits to that area of Town outside the Watershed Protection District. However, the 2003 Ordinance did not define gravel area outside the WPD as impervious surface area.
CURRENT LAND USE MANAGEMENT ORDINANCE
Table 3.8-1 in the Land Use Management Ordinance (LUMO) specifies a permitted percentage of impervious surface area for the Town’s planning jurisdiction. Associated with Table 3.8-1 is a section entitled “Rules for Interpretation of Table 3.8-1.” In this section of the Ordinance, text in Column (K) excludes gravel as impervious surface area for developments outside of the Watershed Protection District.
We note that Appendix A of the LUMO contains the following key definitions:
Built-upon area: that portion of a development project that is covered by impervious or partially impervious surfaces including buildings, pavement, gravel roads, recreation facilities (e.g. tennis courts), etc. (Note: slatted decks and the water area of a swimming pool are considered pervious.)
Impervious surface: a surface composed of any material that impedes or prevents natural infiltration of water into the soil.
The Land Use Management Ordinance Appendix A definitions of built-upon area (which identifies gravel as an impervious or partially impervious surface area) and impervious surface conflict with the view of gravel as permeable surface as reflected in another section of the Ordinance, the Rules for Interpretation for Table 3.8-1. We believe this conflict should be eliminated.
DISCUSSION
At the January 26, 2009 public hearing, the staff was asked to respond to three issues raised. Responses are provided below.
1. Relative Permeability of Different Paving Materials: A Council member asked about the different degrees of permeability of various paving materials.
Staff Response: Driving surfaces (roads, driveways, parking lots, etc.) are generally classified as impervious surfaces. The degree of imperviousness varies according to the composition of the paving material and the underlying soil type. Chapel Hill grit is similar to bare dirt and is less impervious than regular gravel. Please see Attachment #1, a chart on runoff curve numbers from the North Carolina Department of Environment and Natural Resources (DENR) Stormwater Best Management Practices (BMP) Manual.
The amount of water “infiltrated” by porous asphalt and concrete will depend on the void ratio of the mixture. The appropriateness of permeable pavements is generally limited to the Coastal Plain and Sandhills regions of the state (NC DENR Stormwater BMP Manual). Porous pavement as a Best Management Practice provides no water quality pollutant removal credit but may provide some peak rate and volume attenuation (NC DENR Stormwater BMP Manual).
2. Possible Unintended Consequence of Considering Asphalt and Gravel to have Same Permeability Characteristics: A Council member asked if considering these two materials to be equally impervious might encourage the use of more asphalt and discourage the use of gravel by developers, when gravel may actually allow more water infiltration.
Staff Response: Please see the response to #1 above. We do not believe that this change will have a significant impact on the type of surface utilized in development projects. The change is proposed to remove an inconsistency in the ordinance.
3. Request for Relief from Stormwater Management Requirements for Homeowners Managing Stormwater On Site: A citizen related that he had constructed an extensive gravel driveway and was required to pay into the Town’s stormwater utility system. It was his judgment that none of the runoff from his driveway contributed to the water flowing in the Town’s stormwater utility infrastructure. He asked if homeowners who manage stormwater within their property lines could be exempted from stormwater utility fees.
Staff Response: Runoff from developed property leaves the property as surface or groundwater flow. If the latter, it will eventually discharge to a manmade or natural drainage feature. It should be noted that during a large enough storm event, runoff from the resident’s yard will drain off onto adjacent properties and eventually discharge into a storm drain or directly into a stream.
The Town does not have a credit policy but, as part of the Town’s Stormwater Management Master Plan, Jewell Engineering Consultants, Inc. is evaluating credit policies and procedures associated with engineered stormwater management controls. A preliminary recommendation is expected in June, 2009.
PROPOSED LAND USE MANAGEMENT ORDINANCE TEXT AMENDMENT
The proposed text amendment would make consistent the interpretation of gravel area as impervious surface throughout the Ordinance. The amendment calls for removing the phrase “Gravel surfaces” from subsection (3) under Column K in the Rules for Interpretation of Table 3.8-1 section of the Land Use Management Ordinance, as shown below:
Gravel surfaces and l Lakes/ponds shall not be
considered to be impervious surfaces.
ZONING AMENDMENT
Article 4.4 of the Land Use Management Ordinance establishes the intent of Zoning Amendments (including both atlas and text amendments to the Ordinance) by stating that, “In order to establish and maintain sound, stable, and desirable development within the planning jurisdiction of the Town it is intended that this chapter shall not be amended except:
a) to correct a manifest error in the chapter; or
b) because of changed or changing conditions in a particular area or in the jurisdiction generally; or
c) to achieve the purposes of the Comprehensive Plan.
Article 4.4 further indicates:
It is further intended that, if amended, this chapter be amended only as reasonably necessary to the promotion of the public health, safety, or general welfare, and in conformance with the Comprehensive Plan.
A) An amendment to the Land Use Management Ordinance (text amendment) is necessary to correct a manifest error in the chapter.
Staff Comment: We believe the information in the record to date can be summarized as follows:
B) An amendment to the Land Use Management Ordinance (text amendment) is necessary because of changed or changing conditions in a particular area or in the jurisdiction generally.
Staff Comment: We believe the information in the record thus far can be summarized as follows:
C) An amendment to the Land Use Management Ordinance (text amendment) is justified to achieve the purposes of the Comprehensive Plan.
Staff Comment: We believe the information in the record thus far can be summarized as follows:
Each is briefly discussed below.
Participating in the regional planning process
Staff Comment: The proposed amendment would align the ordinance with the impervious surface definition in North Carolina Statutes as it pertains to protecting water quality.
Conserving and protecting the Town’s existing natural setting
Staff Comment: Gravel of the sizes typically used for driveways and walkways compacts over time, particularly with heavy traffic. Soil and plant debris also fill in the spaces between the gravel pieces. Both phenomena reduce or eliminate the initial semi- permeable characteristic of the gravel surface, preventing the infiltration of water to the subsoil.
Defining gravel as impervious surface area, whether inside or outside the Watershed Protection District, will result in greater stormwater management and water quality protection. We believe the proposed amendment would better meet the intent of the Town’s Watershed Protection District regulations to limit impervious surface area.
Providing quality facilities and services
Staff Comment: Because the Land Use Management Ordinance limits impervious surface area for newly developing sites throughout Town, regardless of whether the site is in or out of the Watershed Protection District, development applications require applicants to provide calculations of impervious surface area. We believe that the implementation of a unified impervious surface definition, that identifies all gravel surfaces throughout Town as impervious, will decrease confusion with respect to the implementation and enforcement of the Land Use Management Ordinance.
RECOMMENDATIONS
Planning Board Recommendation: The Planning Board met on January 6, 2009 to review the text amendment proposal and voted 7-1 to recommend the Town Council adopt the text amendment as written.
Staff Recommendation: We recommend that the Council enact the Ordinance to amend the Land Use Management Ordinance to provide consistency in the consideration of gravel as impervious surface.
ATTACHMENTS
[See also Manager’s Memorandum]
