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HomeMy WebLinkAboutSP200800058 Review Comments Special Use Permit 2008-11-18411A COUNTY OF ALBEMARLE Department of Engineering & Public Works MEMORANDUM TO: Applicants with disturbance of critical slopes FROM: Glenn Brooks, County Engineer DATE: 17 Nov 2008 RE: Critical slopes — a brief tutorial for applicants This memo is a basic primer on critical slopes disturbance requests for Albemarle County. It explains what a critical slope area is, what the applicable regulation says, and how to request permission to disturb such areas for development. Critical Slopes defined In the county definition, a critical slope is any slope that is 25% or steeper. In other words, a steepness of 4 horizontal feet to 1 foot of rise, or steeper, is protected. This is first defined in the Comprehensive Plan, Chapter 2, Natural Resources and Cultural Assets. It is referenced and codified in the Zoning Ordinance, Chapter 18, section 4.2. Critical slopes exist on most parcels in the county, and almost every development involves some disturbance of these areas. The county currently uses three sources to evaluate critical slopes; (1) Areas for preservation shown on Development Area Master Plans. (2) The Open Space Plan, from Chapter 2 of the Comprehensive Plan, (3) and current aerial topography. The Master Plans, and The Open Space Plan identify only broad areas of mountain ranges and stream and river valleys. They identify larger contiguous areas which require preservation or more careful treatment. They are not to be used to determine if critical slopes exist. They are a tool used by the County to assist in determining if the critical slopes constitute a significant resource. The current aerial topography is frequently used as the primary tool to determine if critical slopes exist on a property. The current aerial topography is available on the county website at http:// gisweb .albemarle.org/Welcome.aspx. Here is a sample of a parcel with critical slopes shown on the county's website; Critical Slopes Tutorial Page 2 of 6 ................. ch Zoom Out J J4 ................. J GDS r� v W v } v (ions: J 4 J In n... 1; r1�Lu a 8' -37 a k N qV Scale 1" = 197 W SOlIT11 Theme I Critical Resource Plan Email Map Clear Graphics Create Printable Mar) And here is the location shown on the Open Space Plan; Owner HARRIS, THOMAS Prop. Rddr. 6953 MARKWOOD Parcel ID 00800- 00- 00 -035A Overview Legend Target Click to recenter the main map draw a box to set the extent of T. ,.,.ti; I - rya � �• On this parcel there is a shaded band of critical slopes behind the residence, and to the side. These slopes are not contained in one of the larger systems shown on the open space plan. They Critical Slopes Tutorial Page 3 of 6 may even have been created by former building activity on the parcel. They may be man -made, rather than natural. However, they still are protected by ordinance, unless they are shown as graded areas on a site plan or subdivision plan previously approved by the county. Exemptions Exemptions to the critical slopes protections are according to section 18 -4.2.6 of the Zoning Ordinance. Exemptions are determined by staff in the Current Development Division of Community Development. Grandfathering provisions are provided for lots and structures in existence prior to 1980, for a first residence, provided no alternative locations out of critical slopes are available. Accessways and utilities, including stormwater management facilities and sewers may be exempt from the ordinance protections of critical slopes, provided that "the applicant demonstrates that no reasonable alternative location or alignment exists." (18- 4.2.6.c) This exemption is typically verified or determined by engineering staff in Current Development. An example might be the following parcel, where access is only available from the public road through the critical slopes. A request to disturb critical slopes for access would likely be granted for this parcel. If there is any doubt that an alterative location or access exists, an exemption will not be granted. Requests with the possibility of alternative locations or alignments, such as access from another road, or moving a sewer line up a hill, will be brought to the Planning Commission as waiver requests. As mentioned in the example given in the definition section, an exemption can also be granted by staff for slopes which were created with a plan previously approved by the county. Modifications and Waivers The Planning Commission is authorized to approve requests for modification or waivers to disturb critical slopes. Staff reviews these requests and makes recommendations to the Planning Commission. Requests for modifications or waivers to develop on critical slopes must be submitted in writing according to section 18 -4.2.5 of the Zoning Ordinance, and the format and Critical Slopes Tutorial Page 4 of 6 content should be as follows; Provide a plan or graphic representation of the parcel, existing topography, critical slope areas, and all proposed grades and development. The topography and critical slopes must match the county maps, as given above. If field run topography is provided, and more accurate than county topography, this can be used. Please provide sources and dates of field run topography. 2. Provide a letter from the owner requesting the waiver or modification, and containing the following information at a minimum: a) A description of the existing area, with photos if possible. b) A description of the intended disturbance, with plans if possible. c) The site area in acres. This is the acreage of the parcel, or a smaller acreage if only a small portion of the parcel is actually proposed for development. d) The acreage of critical slopes on the site, and the percentage (acres of critical slopes / site acres). e) The acreage of critical slopes proposed to be disturbed (acres of disturbed critical slopes/ acres of critical slopes). Items c) to e) typically are presented in the following table; Areas Acres Total site 0.6 acres approximately Critical slopes 0.3 50% of site Critical slopes disturbed 0.3 1 100% of critical slopes f) Address each of the five concerns of the Zoning Ordinance given in section 18- 4.2, as follows: (1) rapid and/or large -scale movement of soil and rock; Describe how disturbed and constructed slopes will be built, drained, and stabilized to prevent the possibility of soil or rock movement, or slope failure. (2) excessive stormwater run -off; Describe how stormwater runoff is treated, and how excessive runoff is prevented from running onto or off of slopes. (3) siltation of natural and man-made bodies of water; Critical Slopes Tutorial Page 5 of 6 Describe how erosion and sediment control will be achieved. Large slopes should have benches, diversions or extra stabilization measures, and the toe of the slope should be off -set from neighbors or property lines to allow the construction of sediment trapping measures. (4) loss of aesthetic resource; Provide photos. Indicate the visibility from neighbors or roadways. Describe any adjacent or on -site areas identified as resources or preservation areas in the Master Plan, if applicable, and the Open Space Plan. Describe any impacts to views from historic or cultural resources, such as Monticello. (5) and in the event of septic system failure, a greater travel distance of septic effluent. Describe measures taken to construct septic systems above and beyond traditional drainfield installation. Indicate the distance downhill to water features or neighboring property. Indicate the measures available to relocate drainfields, or prevent failure. If your site will receive public sewer, and this is not a concern, please state this. All information submitted will be forwarded to the Planning Commission and made available to the public. Staff will provide a recommendation based on the items outlined above. If staff recommends approval, an effort will be made to place these waivers on the Planning Commission's consent agenda. Violations and Unauthorized Land Disturbance In cases where critical slopes have already been disturbed, and a waiver is being requested after a zoning violation or unauthorized land disturbance, or for some other reason, the same procedure for waivers and modifications is used. Topography and critical slopes on the site before disturbance must be provided, with photographs if possible. The county has data for 2000 and 2007 online at http:// www .albemarle.org/department.asp ?department= ds�&relpage =9003. The University of Virginia Library Geostat Center has aerial photographs as far back as 1937, which can be of use for historical views of larger areas. The website is hqp://fisher.lib.virizinia.edu/collections/mqps/aerials/data/. In these cases, the Planning Commission may ask for the area to be restored, or approve the waiver with conditions, or some combination of these. Common Concerns In the Planning Commission's consideration of critical slopes waivers, engineering staff has been Critical Slopes Tutorial Page 6 of 6 asked to evaluate or suggest design solutions on sites with large areas of critical slope disturbance. Staff has also been asked to evaluate or suggest design alternatives where large constructed slopes are proposed. The following list will serve to clarify the different alternative solutions which have been suggested. (The use of one or more of these suggestions does not make a site design "adequate" or "approved ". That is a judgement to be made by the Planning Commission, with input from the applicant and county staff.) Reducing Critical Slope Disturbance: 1. The only way to reduce critical slope disturbance is to redesign the layout of the site, or reduce the extent of the development in these areas such that the slopes are left untouched. Improving Areas of Proposed Slopes to Be Constructed: 2. Change the site design so that it requires fewer and smaller areas of steep constructed slopes. 3. Change the building design so that it is split - level, or on footings which can change grade, rather than slabs, or make use of foundation retaining walls. 4. Use a 3:1 or flatter grade. County policy allows a 2:1 (50 %) maximum grade. Consequently, most designs use this as a default grading parameter, which is not always necessary. A slope of this grade is difficult to compact during construction, easily erodes, and cannot safely be mowed. 5. Use a ground cover or shrub which is more reliable than grass, and which is easier to maintain on a steep grade. (E &S regulation 3.29 states that mowed slopes should not be steeper than 3:1). 6. Provide for margins of error in topography and site boundaries, especially where the toe of the proposed slope is at a property line, stream or other limiting consideration. 7. Use small walls to accommodate some of the change in grade. 8. Collect and divert or pipe drainage away from slopes. 9. Provide "benches" or flat areas to break up continuous runs of slope, and to provide useable areas, and added stability. 10. Use off -sets or landings and plantings at the top and bottom of slopes to improve safety and access. Reducing Erosion and Impacts of Construction: 11. Reduce the time that slopes remain disturbed. Provide for phasing and vegetative stabilization as soon as final grades are reached, and specify a maximum number of days from start of disturbance to completion. 12. Use mats and fabric coverings along with slope drains during construction. 13. Use top -soil, sod, mulch and tree combinations to help more quickly stabilize slopes. 14. Leave room for silt traps and basins below steep slopes. Questions regarding the application of the ordinance sections, or other concerns, can be directed to the Chief of Current Development, the Senior Engineer in charge of plan review, or to the County Engineer.