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Physiography
What can we learn from physiography when it comes to environmental land‐
use planning and surface water conservation?
Physiography ‐ Regions
• Physiographic regions are defined by the composite patterns of the main elements of landscape:
– Landforms
– Drainage features
– Soils
– Climate
– Vegetation
– Land‐use
• Describing physiographic regions is hierarchical, beginning usually with the major (geologic) structural divisions
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Physiography ‐ Regions
– Canadian Shield– Appalachian Mountains– Interior Highlands– Atlantic Coastal Plain– Interior Plains– Rocky Mountain Region– Intermontane Region– Pacific Mountain System– Arctic Coastal Plain– Alaska‐Yukon Plain
• There are 10 general physiographic regions of the U.S.A. and Canada
Physiography ‐ Provinces• Each region is then broken down into smaller parts, called provinces
http://w
mc.ar.nrcs.usda.gov/technical/images/phys.gif
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Physiography ‐ Provinces
• Let’s look at the Appalachian Province:
– Blue Ridge
– Piedmont
– Ridge and Valley
– Appalachian Plateaus
– Northern Appalachians
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Physiography ‐ Sections
• Physiographic provinces are further broke down into sections
• The physiographic sections of the Appalachian Plateaus Province are:
– Northwestern Glaciated Plateau
– High Plateau
– Pittsburgh Low Plateau
– Waynesburg Hills
– Allegheny Mountain
– Allegheny Front
– Deep Valleys
– Glaciated High Plateau
– Glaciated Low Plateau
– Glaciated Pocono Plateau
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Physiography ‐ Sections
• Each physiographic section is differentiated by particular ‘landscape level’ features (although I don’t like using that phrase…)
• Features include:
• Dominant topographic form
• Local relief
• Underlying rock type
• Geologic structure
• Approximate elevation (Min. and Max.)
• Drainage pattern
• Boundaries
• Origin
• Let’s look at the Pittsburgh Low Plateau and the Allegheny Mountain
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Site
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What is the ‘site’?
• What we call a ‘site’ is the specific piece of earth we are dealing with in the plan
• It can be:
– A parcel of land
– A municipality
– A stream corridor
– A watershed
Always think of the site in three dimensions
The site is a piece of real estate that extends above and below the land surface
ThisNot this
x x
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Site and PhysiographyThe very first step when assessing site is to determine physiography
and to think about the characteristics of the section
Pittsburgh Low Plateau Section Allegheny Mountain Section
Noticeable Variations
Pittsburgh low plateau section
• Smooth undulating upland
• cut by numerous, narrow, relatively shallow valleys
• Uplands are developed on rocks containing most of the bituminous coal in PA
• Elevations range from 660 to 1,700 feet
Allegheny mountain section
• Consists of broad, rounded ridges separated by broad valleys
• The ridges decrease in elevation from south to north and the ridges have no topographic expression at the north end of the section
• Elevations in the Section range from 775 to 3,213 feet
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Slope
What is slope?Why slope?
Slope in the PA MPCBasic slope forms
What is slope?
• Slope is used to describe the grade, steepness, incline or gradient of a straight line
• The slope of a line is defined as the ratio of the rise divided by the run between two points on the line
• Slope is represented by ‘m’ in equations
∆y
∆x
m = ∆y
∆x
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Slope units
• Slope is expressed sometimes in percentages and sometimes in degrees– These two are not the same
• 0% = 0°
• 100% = 45°
• When using a topographic map to determine slope:
Percent slope = Change in elevationdistance
X 100
• Degrees are usually used by engineers
• Percent is usually used by Planners
Grades in % and angles in °
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Slope applications
• Streams, railroads and roads are expressed in terms of the rise or fall of elevation over distance
– For example:
– ‘What is the slope of this section of stream?’
• a 1% grade would be a one‐foot rise or fall of elevation over a distance of 100 feet
Stream Views
Plan View
Flow is coming toward you
Cross Section View Profile View
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Why slope?
• Problems pertaining to slope usually arise due to disturbance
• Three general types of disturbance:
1. Mechanical cut‐and‐fill
2. Deforestation
3. Drainage alteration
Slope disturbances – cut and fill
• Modern (last 100 years)
• Caused primarily by heavy equipment
• Most often a result from:
– transportation development (roads), and
– surface mining
• Involves straightening and steeping of slopes
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The biggest mining dump truck in the world
Belaz 75710, capacity of 496t. The ultra‐heavy dump truck was launched by the Belarusian Company Belaz in October 2013 under an order from a Russian mining company.
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Slope disturbances – deforestation
• The major deforestation in the U.S.A. occurred in the late 1800s
• Lumbering, agriculture and urbanization drove this process
• Denuding hillsides of vegetation– reduces slope stability
– increases surface water runoff
– decreases groundwater recharge
Area of primary forests in the United States
http://w
ww.globalchange.umich.edu
Slope disturbances – drainage alteration
• Modification of water transport networks results in the alteration of water’s:
– direction
– velocity
– mass, and
– force
• This results in– Increased erosion and sediment load
– Undercutting of slopes
– Scouring of streambanks
All of which lead to decreased slope equilibrium and slope stability
(Slope movement is also known as ‘mass wasting’)
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Factors that influence slope stability• Gravity
– The main force responsible for mass wasting is gravity
– Perpendicular vs. tangential forces
• Water– Rainfall or snowmelt adds weight to slope
– Able to change angle of repose (the slope angle which is the stable angle for the slope)
• Material (soils)
– Composition and compaction
• Structural (geology)– Dipping bedding planes
– Weak layers
– Joints & Fractures
• Triggering Events
– Natural (seismic, rain, etc.)
– Anthropogenic (land‐use change, mining, construction, etc.)
Oso, Washington USA Mud Slide, 2014
NBC
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NYTimes
Shaded‐relief geomorphologic map of Oso Landslide of 2014 and adjacent areas. Oso is two miles west of this map, Hazel, one mile east. Coloredareas are older landslides, "D" being the oldest. Upper "A" is the March 2014 landslide, lower "A", Skaglund Hill. Topography shown is from 2006;red line is approximate location of the current head scarp. Red cross‐hatching is the runout area, now buried in mud and debris. Terrace on theupper‐left is Whitman Bench
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http://www.stopmountaintopremoval.org
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http://www.stopmountaintopremoval.org
The red is the area of the 10,000 acre Hobert MTR sites in Boone County, WVOn top of an aerial photo of Manhattan, NYC
http://ilovemountains.org/city-overlays
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The red is the area of the 10,000 acre Hobert MTR sites in Boone County, WVOn top of an aerial photo of Philadelphia
http://ilovemountains.org/city-overlays
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Remember: Slope Percent and Degree are different
• Degrees are usually used by engineers
• Percent is usually used by Planners
http
://w
ww
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m/g
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htm
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Slope in the PA MPC – Comp Plans• Article III – Comprehensive Plan
– Section 301. Preparation of Comprehensive Plan
• (6) 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. The plan shall be consistent with and may not exceed those requirements imposed under the following:
• (i) Act of June 22, 1937 (P.L.1987, No.394), known as “The Clean Streams Law”.• (ii) Act of May 31, 1945 (P.L.1198, No.418), known as the “Surface Mining Conservation and
Reclamation Act”.• (iii) Act of April 27, 1966 (1st SP.SESS., P.L.31, No.1), known as “The Bituminous Mine Subsidence and
Land Conservation Act”.• (iv) Act of September 24, 1968 (P.L.1040, No.318), known as the “Coal Refuse Disposal Control Act”.• (v) Act of December 19, 1984 (P.L.1140, No.223), known as the “Oil and Gas Act”.• (vi) Act of December 19, 1984 (P.L.1093, No.219), known as the “Noncoal Surface Mining
Conservation and Reclamation Act”.• (vii) Act of June 30, 1981 (P.L.128, No.43), known as the “Agricultural Area Security Law”.• (viii) Act of June 10, 1982 (P.L.454, No.133), entitled “An Act Protecting Agricultural Operations from
Nuisance Suits and Ordinances Under Certain Circumstances”.• (ix) Act of May 20, 1993 (P.L.12, No.6), known as the “Nutrient Management Act”, regardless of
whether any agricultural operation within the area to be affected by the plan is a concentrated animal operation as defined under the act.
Slope in the PA MPC – Zoning
• Article VI – Zoning• Section 605. Classifications. In any municipality, other than a county, which enacts a zoning
ordinance, no part of such municipality shall be left unzoned. The provisions of all zoning ordinances may be classified so that different provisions may be applied to different classes of situations, uses and structures and to such various districts of the municipality as shall be described by a map made part of the zoning ordinance. 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:
• (1) For the purpose of making transitional provisions at and near the boundaries of districts.• (1.1) For the purpose of regulating nonconforming uses and structures.• (2) For the regulation, restriction or prohibition of uses and structures at, along or near:• (i) major thoroughfares, their intersections and interchanges, transportation arteries and rail or
transit terminals;• (ii) natural or artificial bodies of water, boat docks and related facilities;• (iii) places of relatively steep slope or grade, or other areas of hazardous geological or topographic
features;• (iv) public buildings and public grounds;• (v) aircraft, helicopter, rocket, and spacecraft facilities;• (vi) places having unique historical, architectural or patriotic interest or value; or• (vii) flood plain areas, agricultural areas, sanitary landfills, and other places having a special character
or use affecting and affected by their surroundings.• As among several classes of zoning districts, the provisions for permitted uses may be mutually
exclusive, in whole or in part.
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Slope in the PA MPC – Zoning• Article VI – Zoning• Section 609.1. Procedure for Landowner Curative Amendments.
• (a) A landowner who desires to challenge on substantive grounds the validity of a zoning ordinance or map or any provision thereof, which prohibits or restricts the use or development of land in which he has an interest may submit a curative amendment to the governing body with a written request that his challenge and proposed amendment be heard and decided as provided in section 916.1. The governing body shall commence a hearing thereon within 60 days of the request as provided in section 916.1. The curative amendment and challenge shall be referred to the planning agency or agencies as provided in section 609 and notice of the hearing thereon shall be given as provided in section 610 and in section 916.1.
• (b) The hearing shall be conducted in accordance with section 908 and all references therein to the zoning hearing board shall, for purposes of this section be references to the governing body: provided, however, that the provisions of section 908 (1.2) and (9) shall not apply and the provisions of section 916.1 shall control. If a municipality does not accept a landowner’s curative amendment brought in accordance with this subsection and a court subsequently rules that the challenge has merit, the court’sdecision shall not result in a declaration of invalidity for the entire zoning ordinance and map, but only for those provisions which specifically relate to the landowner’s curative amendment and challenge.
• (c) The governing body of a municipality which has determined that a validity challenge has merit may accept a landowner’s curative amendment, with or without revision, or may adopt an alternative amendment which will cure the challenged defects. The governing body shall consider the curative amendments, plans and explanatory material submitted by the landowner and shall also consider:
• (1) the impact of the proposal upon roads, sewer facilities, water supplies, schools and other public service facilities;
• (2) if the proposal is for a residential use, the impact of the proposal upon regional housing needs and the effectiveness of the proposal in providing housing units of a type actually available to and affordable by classes of persons otherwise unlawfullyexcluded by the challenged provisions of the ordinance or map;
• (3) the suitability of the site for the intensity of use proposed by the site’s soils, slopes, woodlands, wetlands, flood plains, aquifers, natural resources and other natural features;
• (4) the impact of the proposed use on the site’s soils, slopes, woodlands, wetlands, flood plains, natural resources and natural features, the degree to which these are protected or destroyed, the tolerance of the resources to development and any adverseenvironmental impacts; and
• (5) the impact of the proposal on the preservation of agriculture and other land uses which are essential to public health and welfare.
Slope in the PA MPC – Zoning• Article IX ‐ Zoning Hearing Board and other Administrative
Proceedings• Section 916.1. Validity of Ordinance; Substantive Questions.
(a) A landowner who desires to challenge on substantive (5) Based upon the testimony presented at the hearing or hearings, the governing body or the zoning board, as the case may be, shall determine whether the challenged ordinance or map is defective, as alleged by the landowner. If a challenge heard by a governing body is found to have merit, the governing body shall proceed as provide in section 609.1. If a challenge heard by a zoning hearing board is found to have merit, the decision of the zoning hearing board shall include recommended amendments to the challenged ordinance which will cure the defects found. In reaching its decision, the zoning hearing board shall consider the amendments, plans and explanatory material submitted by the landowner and shall also consider:
• (i) the impact of the proposal upon roads, sewer facilities, water supplies, schools and other public service facilities;
• (ii) if the proposal is for a residential use, the impact of the proposal upon regional housing needs and the effectiveness of the proposal in providing housing units of a type actually available to and affordable by classes of persons otherwise unlawfully excluded by the challenged provisions of the ordinance or map;
• (iii) the suitability of the site for the intensity of use proposed by the site’s soils, slopes, woodlands, wetlands, flood plains, aquifers, natural resources and other natural features;
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General rules about slope:
• > 25° (just under 50%) is considered very steep
• 15 – 25° (roughly between below 30% and 50%) is considered steep
• 5 ‐ 15° (~10 and 25%) is considered moderate
• < 5° (10%) is considered gentle
• Structures are not generally built on slopes >25°– New construction technology, however, is allowing for increasing slopes
now suitable for structures
• Crops are not planted on slopes of more than 18 ‐ 20°
Kilbuck Twp., PA Wal‐Mart Construction
While excavating a huge tract of land to build a new Wal-Mart, Kilbuck properties failed to properly stabilize the site, which ultimately led to a massive landslide alongRoute 65 site and three railroad tracks
September, 2006
Tribune Review February 7 2013http://triblive.com/news/allegheny/3464526-74/wal-mart-site#axzz2LeZe9KwL
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Slope requirements for various land‐uses
Land‐use Maximum Minimum
House sites 20 ‐ 25% 0%
Playgrounds 2 ‐ 3% 0.05%
Public stairs 50% ‐
Lawns (mowed) 25% ‐
Septic drainfields 15%* 0%
Paved surfaces
Parking lots 3% 0.05%
Sidewalks 10% 0%
Streets and roads ‐
20 mph 12%
30 mph 10%
40 mph 8%
50 mph 7%
60 mph 5%
70 mph 4%
Industrial sites
Factory sites 3 ‐ 4% 0%
Lay down storage 3% 0.05%
Parking 3% 0.05%
*special drainfields are required at slopes above 10 ‐ 12 %
Basic Slope Forms
• Straight
• Convex
• Concave
• S‐shaped
• Irregular
Most commonNose
Hollow
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Slope and agriculture practices
A heavily eroded slope by discontinuous gullies
Largely due to poor land‐use practices, including plowing parallel with the slope rather than plowing along slope contours
County Conservation Districts assist farmers in these issues
Photograph Credit: Dr. Dan Balteanu
Contour Farming Technique
Tilling should be done along the natural slope contour, not parallel with it…
= slope direction
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Angle of Repose
• An engineering term that describes a property of granular materials
• The maximum at which any earth material can be safely inclined and beyond which it will fail
• AofR vary greatly with different materials, AND;– Water content (dry – saturated)
– Vegetative cover (grass – forested)
– Internal structure of particle mass
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Angle of Repose ‐
Generally, for dry materials the angle of repose increases
with increasing grain size, but usually lies between about 30 and 37o
Slightly wet unconsolidated materials exhibit a very high angle of repose because surface tension between the water and the grains tends to hold the grains in place
Material saturated with water reduces the angle of repose to a small value and the material tends to flow like
a fluid
The angle of repose is the steepest angle at which a pile of unconsolidated grains remains stable, and is controlled by the frictional contact between the grains
Thank you, http://www.tulane.edu/~sanelson
Angles of Repose
MaterialAngles of Repose
(degrees)
Sand (well drained) 33
Loam (well drained) 45
Compact clay (well drained) 45
Sand or loam (forested) 50
Boulders and cobbles 35
Loess (well drained) 50
Loose clay (saturated) 15
Bedrock (consolidated) 65
• These are general rules of thumb that a Planner can use for assessment
• If the project is active and specific, consult the expertise of a geotechnical expert or civil engineer
• Protect yourself and your ‘client’:Don’t work outside of your expertise!
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Materials
• Loam is soil composed of sand, silt, and clay in relatively even concentration (about 40‐40‐20% concentration respectively), considered ideal for gardening and agricultural uses
• Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine‐grained, silty, pale yellow or buff, windblown sediment
– A friable substance is any substance that can be reduced to fibres or finer particles by the action of comparatively little pressure or friction on its mass
– Loess is also highly erodible by water or wind, and soils underlain by loess tend to be excessively drained
Materials
• Clay is a naturally occurring material composed primarily of fine‐grained minerals, which show plasticity through a variable range of water content
• Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.– sand particles range in diameter from 1⁄16 mm to 2 millimeters.
– This is the size of a grain of sand
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Slope Stability Checklist
• Assess the characteristics of each of the criteria (at minimum) below– Steepness
– Composition
– History
– Vegetation
– Drainage
– Land‐use
• The method (‘how’) you assess these should be in compliance;First – with approval by engineer for local conditions
Second – in accordance with local planning ordinances