Physiography What Can We Learn from Physiography When It Comes to Environmental Land‐Use Planning and Surface Water Conservation?

3/7/2017

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 • There are 10 general physiographic regions of the U.S.A. and Canada

• 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

Physiography ‐ Provinces

• Each region is then broken down into smaller parts, called provinces http://wmc.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

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

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Always think of the site in three dimensions

The site is a piece of real estate that extends above and below the land surface

This Not this

Site and Physiography The 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

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Allegheny Mountain Section • ridges decrease in elevation from south to north and the ridges have no topographic expression at the north end of the section • broad, rounded ridges separated by broad valleys

• ridges decrease in elevation from south to north and the ridges have no topographic expression at the north end of the section • broad, rounded ridges separated by broad valleys

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Watersheds as a planning unit

Recommended Watershed Terminology

• Region Subregion River Basin Subbasin Watershed Subwatershed Drainage Site

http://www.watershed.org/?q=node/187

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USGS Regions, Sub‐basins

USGS Regions (2 digit) USGS Sub‐regions (4 digit)

Hydrologic Unit Codes (HUC) USGS Sub‐basins (8 digit)

Basins as a Planning Unit http://www.portal.state.pa.us/portal/server.pt/community/state_water_plan/18721

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Watersheds as a Planning Unit http://www.dcnr.state.pa.us/brc/rivers/riversconservation/

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Map Scale • 1:100,000 = representative fraction or ratio

Streams ‐ Small vs. Large Scale representations in a GIS

1:100,000 1:24,000

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Watersheds

Definition: Area of land that drains water to a specific point or water body

Watershed boundary (surface water divide)

Drainage Area

Terminology: Watershed outlet (pour‐point) Catchment ‐ area of land receiving rainfall Watershed ‐ area of land draining water Sub‐watershed, Basin, Sub‐Basin, Regions…

WV Sub‐basins

USGS 8‐Digit sub‐basins in WV

1:250,000

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NRCS Watersheds

NRCS 10 and 12 watersheds in WV (5th and 6th level)

1:24,000

Watershed as a planning unit

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Watershed Attributes Other Topographic Attributes:

‐ Drainage Patterns ‐ Drainage Area ‐ Stream Length ‐ Average Slope ‐ Drainage Density ‐ Stream Order ‐ Shape factors

Help us understand the natural behavior of watersheds

Understand Geomorphology

• Geomorphology is the scientific study of the origin and evolution of topographic and bathymetric features created by physical or chemical processes operating at or near Earth's surface • (from Greek: γῆ, ge, "earth"; μορφή, morfé, "form"; and λόγος, logos, "study")

• Geomorphologists seek to understand why: • landscapes look the way they do (current) • to understand landform history and dynamics (past), and • to predict (future) changes through a combination of: 1. field observations, 2. physical experiments, and 3. numerical modeling

• Geomorphology is practiced within physical geography, environmental planning, geology, geodesy, engineering geology, archaeology, and geotechnical engineering

• This broad base of interests contributes to many research styles and interests within the field

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Watershed Formation •Climate and weather variations (e.g., rain, snow, wind, ice, temperature) are agents of erosion in a watershed.

•Erosional eﬀects of surface water create stream channels.

•As water carves it way through a watershed, it is responsible for most of the watershed’s “topographic identity.”

* Hills, valleys, and slopes of a topographic map.

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Upland &Divide

Divide is the location where two watersheds meet

Uplands connect the divide with the valley or lowland areas below

Large watershed tributaries form smaller watersheds called sub‐‐basins

Areas of the Watershed

•Aquatic areas include standing water (e.g., ponds, lakes, wetlands, bogs, streams and rivers)

•Riparian areas are those corridors of vegetaJon next to and inﬂuencing the aquaJc •Three Main Areas area. •1) Aquatc (water) •2) Riparian •3) Upland

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Watershed Area •The catchment area of a watershed inﬂuences the amount of water that ﬂows from the river or stream that drains it.

•Generally, large watersheds receive more precipitaJon than small ones in like climates.

•In moist climates, greater precipitaJon and runoﬀ may occur in smaller watersheds than in larger watersheds with arid climates.

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Watershed Shape and Slope

Shape and slope of a watershed and its drainage pabern inﬂuence surface runoﬀ and seepage in streams draining the watershed.

Steeper the slope, the greater the possibility for rapid runoﬀ and erosion.

Plant cover is more diﬃcult to establish and inﬁltraJon of surface water is reduced on steep slopes.

Great Lakes Drainage Basin

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Discharge of Major U.S. Rivers

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Orientation •Orientation of a watershed in relaJon to storm events impacts runoﬀ and peak ﬂows.

•A rainstorm moving up a watershed releases water in such a way that runoﬀ from the lower secJon has passed its peak before runoﬀ from the higher secJons has arrived.

•A storm starJng at the top of a watershed and moving down has an addiJve eﬀect on runoﬀ downstream.

Orientation •Watershed orientaJon relaJve to sun posiJon aﬀects temperature, evaporaJon, and transpiraJon.

•Soil moisture is more rapidly lost on steep slopes facing the sun.

•Watersheds sloping away from the sun are cooler, and evaporaJon and transpiraJon is less. *Note: OrientaJon to prevailing winds has similar eﬀects.

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Watershed Attributes

Drainage Patterns

http://maps.psiee.psu.edu/ImageryNavigator/

Dendritic Drainage Pattern

Dendritic drainage systems are the most common form of drainage system

• There are many contributing streams which are then joined together into the tributaries of the main river

• They develop where the river channel follows the slope of the terrain

• Dendritic systems form in V‐shaped valleys

• As a result, the rock types must be impervious and non‐porous

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Parallel Drainage Pattern

This system forms on uniformly sloping surfaces

• A parallel drainage system is a pattern of rivers caused by steep slopes with some relief

• Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction

• Tributary streams tend to stretch out in a parallel‐like fashion following the slope of the surface

• A parallel pattern sometimes indicates the presence of a major fault that cuts across an area of steeply folded bedrock

Trellis Drainage Pattern

Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America

• The geometry of a trellis drainage system is similar to that of a common garden trellis used to grow vines

• As the river flows along a strike valley, smaller tributaries feed into it from the steep slopes on the sides of mountains

• These tributaries enter the main river at approximately 90 degree angles, causing a trellis‐like appearance of the drainage system

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Radial Drainage Pattern

In a radial drainage system, the streams radiate outwards from a central high point

• Volcanoes usually display excellent radial drainage

• On these features the drainage may exhibit a combination of radial patterns

Valley Fill

http://blogs.wvgazette.com/coaltattoo/2009/03/25/epa-on-mountaintop-removal-whats-it-all-mean/

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Drainage Patterns

1:100,000 Streams

Drainage Patterns

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Drainage Patterns and Physiography

WV Physiographic Provinces

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Map Measurements

Area: example... ‐ 1 grid cell = 10 acres ‐ # cells x grid area = DA

http://www.pasda.psu.edu/default.asp

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Measurements

Area: example... ‐ 1 grid cell = 10 acres

40 cells = 400 acres

Watershed Shape Factor

Drainage Area (Main Channel Length)²

The size, shape and relief of the 1 basin are important controls. Water takes longer to reach the trunk 2 stream in a large, round basin than in does in a small, narrow one

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Basic Hydrograph

Hydrograph (or storm graph) plots discharge in cubic meters per second (cms) over time (could be hours or days

The shape of the graph varies dependent on the number of contributing features that influence flow

Base flow = ‘normal’ and is from groundwater seeping into the channel

Rising limb = indicates rapid increase due to rain event

Peak flow = when river reaches its maximum level

The time difference between peak of the rain event and peak discharge is the lag time (basin lag)

http://www.bbc.co.uk/scotland/education/int/geog/rivers/hydrographs/index.shtml

Influence of Steepness

Where gradients are steep, water runs off faster, reaches the river more quickly and causes a steep rising limb

Prolonged heavy rain causes more overland flow than light drizzly rain

http://www.bbc.co.uk/scotland/education/int/geog/rivers/hydrographs/index.shtml

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Runoﬀ Hydrograph (Recession Curve)

The hydrograph of a river can look similar to this example aher a brief but intense rainfall event.

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Hydrograph Shape •Main TWO factors inﬂuencing hydrograph shape are:

•1) Drainage characterisJcs: basin area, basin shape, basin slope, soil type, land use, drainage density, and drainage network topology.

**Note: Most changes to land cover/land use tend to increase runoﬀ.

•2) Rainfall characterisJcs: rainfall intensity, duraJon, and their spaJal and temporal distribuJon.

**Note: Storms moving downstream tend to produce larger peak ﬂows than storms moving upstream.

Hydrograph Shape

*Note: Also need to consider storm duration and spatial concentration.

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Stream Order

• Strahler Stream Order

“3rd order watershed”

Also Shreve, Horton

Stream Measurements

Flow length: ‐ Length of each stream reach

Avg. slope: ‐ΔElev./Flow length

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Streams ‐ Small vs. Large Scale representations in a GIS

1:100,000 1:24,000

Bifurcation Ratio

Bifurcation Ratio expresses the ratio of the number of streams of any giver order to the number in the next lower order or The slope of a line relating number of streams to stream order

#(n) order B.R.= #(n+1) order

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Bifurcation Ratio • If the bifurcation ratio of a river network is low, there is a higher chance of flooding

• The water will be concentrated in one channel rather than spread out, as a higher bifurcation ratio would indicate

• The bifurcation ratio can also show which parts of a drainage basin is more likely to flood, comparatively, by looking at the separate ratios

• The main stem of a river, typically found by following the branch with the highest Strahler number • Gleyzer et al. (2004) describe how to compute Strahler stream order values in a GIS application • This algorithm is implemented by RivEX, an ESRI ArcGIS 10.2.1 tool • The input to their algorithm is a network of the center lines of the bodies of water, represented as arcs (or edges) joined at nodes • Lake boundaries and river banks should not be used as arcs, as these will generally form a non‐ tree network with an incorrect topology

Drainage Density

Drainage density is simply a length per unit of area -Usually ranging from 1 to 1,000

Stream Length Drainage Density = Drainage Area

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Regional Curves

QaDA ()b

a, b = fitting coefficients DA = drainage area

Sherwood, J., Huitger, C, 2005. Bankfull Characteristics of Ohio Streams and Their Relation to Peak Streamflows, Scientific Investigations Report 2005‐5153

Hydrologic Response

• Watershed attributes influence runoff response, (along with landuse/landcover, soils…)

Response Type Characteristic (1) "Flashy" (2) "Sluggish" Area Small Large Drainage Density High Low Shape Equidimensional Elongated Slope Steep Flat Soils Thin Thick Vegetation Sparse Dense

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Slope What is slope? Why slope? Slope in the PA MPC Basic slope forms

What is slope? • Slope is used to describe the grade, steepness, incline or gradient of a straight line ∆y

• The slope of a line is defined as ∆x the ratio of the rise divided by the run between two points on the line ∆y m = • Slope is represented by ‘m’ in ∆x equations

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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 elevation X 100 distance

• 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 Cross Section View Profile View

Flow is coming toward you

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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 Area of primary forests in the United States • 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 http://www.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. Colored areas 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 the upper‐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, WV On 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, WV On 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 1728.com/gradient.htm http://www.

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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’s decision 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 unlawfully excluded 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 adverse environmental 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

September, 2006

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 along Route 65 site and three railroad tracks

Tribune Review February 7 2013 http://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 Hollow

Most common • Concave Nose

• S‐shaped

• Irregular

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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

= slope direction

Tilling should be done along the natural slope contour, not parallel with it…

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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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The angle of repose is the steepest angle at which a pile of unconsolidated Angle of Repose ‐ grains remains stable, and is controlled by the frictional contact between the grains

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

Thank you, http://www.tulane.edu/~sanelson

Angles of Repose

Angles of Repose Material (degrees) • These are general rules of thumb that a Planner can use for Sand (well drained) 33 assessment

Loam (well drained) 45 • If the project is active and Compact clay (well drained) 45 specific, consult the expertise of Sand or loam (forested) 50 a geotechnical expert or civil engineer Boulders and cobbles 35

Loess (well drained) 50 • Protect yourself and your ‘client’: Don’t work outside of your expertise! Loose clay (saturated) 15

Bedrock (consolidated) 65

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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. 1 • sand particles range in diameter from ⁄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

Soils and Land‐use Suitability

•Composition •Texture •Moisture and Drainage •Landforms and Topography

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Soil Composition

• Composition is the basic material that make up the soil • Four basic things: 1. Mineral particles 2. Organic material 3. Water (will discuss, but will return when we discuss groundwater) 4. Air

1. Mineral Particles –comprise about 50 – 80% of the volume of most soils and form the structural skeleton a. The structure enables the soil to support its own weight, the weight of water, and the weight of surface structures (such as buildings) • Sand and gravel –if packed solidly ‐ are generally the best at providing the best stability

Soil Composition

• Bearing Capacity –refers to the soil’s resistance to penetration from a weighted object • such as a structural foundation • Determining bearing capacity is a geo‐technical exercise and should be determined by a geo‐technical expert or civil/structural engineer

2. Organic Matter ‐ decaying plants and animals / living organisms / varies greatly in soils / example ‐ top soil • Positives of highly enriched organic soils: • Vital to fertility and hydrology of soils • Create moisture reservoirs for wetland vegetation • Points of entry for groundwater recharge

• Negatives of highly enriched organic soils: • Provide weak soil structural skeleton • Compresses and settles differentially • When dewatered, may experience volume loss, decomposition, and wind erosion

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Soil Texture • An easy way to help determine what type of soil you have is to simply feel it to determine texture and thus what the primary makeup of the soil is:

Grab a baseball size portion of the soil in your hands and wet the soil with water, working the moist soil with your hands

– The stickier it is, the more clay there is

– The soapier the soil feels the higher the silt content

– Grittiness is indicative of sand

The soil texture triangle shows the 12 major soil texture classes and what percent of each type soil makes them up

http://www.cmhc‐schl.gc.ca/en/co/maho/la/la_001.cfm

USDA Textural Classification of Soils ages/soiltriangle_large.jpg http://www.soilsensor.com/im Increasing sand

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USDA Textural Classification of Soils

Sticky Sticky ages/soiltriangle_large.jpg Gritty Soapy http://www.soilsensor.com/im

Feel test –  Thoroughly dry and crush a small amount of the soil by rubbing it with the Soil Texture forefinger in the palm of your other hand

 Then rub some of it between your thumb and fingers to measure the Testing Soil Texture Hand Field Test percentage of sand

 The grainier it feels, the higher the sand content

Moist cast test –  Compress moist soil by squeezing it in your hand*

 When you open your hand, if the soil holds together (that is, forms a cast), pass it from hand to hand

 The more durable the cast, the higher the percentage of clay

Ribbon test – Moist cast test Ribbon test  Roll a handful of moist soil is into a cigarette shape and squeeze it between your thumb and forefinger to form the longest and thinnest ribbon possible* *For these tests, the soil specimen should be gradually moistened and thoroughly  Soil with high silt content will form flakes or peel instead of forming a ribbon reshaped and kneaded to bring it to its maximum "plasticity" and to remove dry  The longer and thinner the ribbon, the higher the percentage of clay lumps.

Do not add too much water, as the sample will lose its cohesion.

http://www.cmhc‐schl.gc.ca/en/co/maho/la/la_001.cfm

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Field Tests for Soil Texture* Texture Feel Test Moist Cast Test Ribbon Test Soil Texture Sand Grainy, little floury material No cast Can't form a ribbon

Grainy with slight amount of Very weak cast, does Loamy sand Can't form a ribbon floury material not allow handling Testing Soil Texture Hand Field Test Silty sand Some floury material does not allow handling Can't form a ribbon

Grainy with a moderate Weak cast, allows Barely forms a ribbon —1.5 Sandy loam amount of floury material careful handling ‐2.5 cm (0.6 ‐1 in.) Fairly soft and smooth with Good cast, easily Thick and very short ‐ <2.5 Loam obvious graininess handled cm (1 in.) Weak cast, allows Makes flakes rather than a Silt loam Floury, slight graininess careful handling ribbon Weak cast, allows Makes flakes rather than a Silt Very floury careful handling ribbon Short and thick —2.5 ‐ 5 cm Sandy clay loam Very substantial graininess Moderate cast (1 ‐ 2 in.) Fairly thin, breaks easily, Strong cast clearly Clay loam Moderate graininess barely supports its own evident weight. Fairly thin, breaks easily, Ribbon test Silty clay loam Smooth, floury Strong cast barely supports its own Moist cast test weight.

Thin, fairly long, 5‐7.5 cm (2 Sandy clay Substantial graininess Strong cast ‐ 3 in.). Holds its own weight.

Thin and fairly long, 5 ‐ 7.5 Silty clay Smooth Very strong cast cm (2 ‐ 3 in.). Holds its own weight. Very thin and very long — Clay Smooth Very strong cast >7.5 cm (3 in.) *Table adapted from Denhom, K.A. and L.W. Schut, 1993. Field Manual for Describing Soils in Ontario. Centre for Soil Resource Evaluation. Guelph, Ont. http://www.cmhc‐schl.gc.ca/en/co/maho/la/la_001.cfm

USDA Textural Classification of Soils

Sticky Sticky ages/soiltriangle_large.jpg Gritty Soapy http://www.soilsensor.com/im

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USDA Textural Classification of Soils ages/soiltriangle_large.jpg http://www.soilsensor.com/im

Soil Moisture and Drainage ‐ Water content varies with particle size, drainage and topography ‐ Two principal forms of water occur in both mineral and organic soils: 1. Capillary water –a form of molecular water; called so because it is held in soil by the force of cohesion among water molecules • Under this force water molecules are mobile and move from moist to dry • During summer, most capillary water transfer is upward toward soil surface as water is lost to evaporation and transpiration • (more on these later too…)

2. Gravity water – liquid water that moves in response to the gravitational force • Movement is usually downward • Tends to accumulate in subsoil and bedrock to form groundwater • Groundwater completely fills inter‐particle spaces • Thus, below the water table, soil is largely devoid of air

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The angle of repose is the steepest angle at which a pile of unconsolidated Angle of Repose ‐ grains remains stable, and is controlled by the frictional contact between the grains

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

Thank you, http://www.tulane.edu/~sanelson

Soil Moisture Concepts

VVVtotal solid liquid  V vapor

V VVwater vapor  Porosity (n ) 100voids 100   VVtotal  total 

V Moisture Content ( ) = 100water Vtotal (or soil-water content)

Soil Particles Soil Water

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Porosity • Soil Porosity – is the percentage of total soil volume not occupied by soil particles and indicates its water‐ holding capacity

V VVwater vapor  Porosity (n ) 100voids 100   Or simply VVtotal  total  Porosity (n)

Specific Yield (Sy)

• Specific yield – the amount of water draining from the soil due to gravity (gravity water)

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Soil Moisture and Drainage

• Drainage – refers to gravity water and a soil’s ability to transfer water downward • Three terms are used to describe this process: 1. Infiltration capacity – the rate that water penetrates the soil surface

2. Permeability – the rate that water within the soil moves through a given volume of material

3. Percolation – the rate that water in a soil pit or pipe within the soil is taken up by the soil

Each of these will get more attention when we get to groundwater

Unsaturated (or Vadose) Zone

‘Vadose’ is Latin for ‘shallow’

Water table

Movement of water within the vadose zone is studied within soil physics and hydrology, particularly hydrogeology, and is of importance to agriculture, contaminant transport, and flood control

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USDA Textural Classification of Soils

Sticky Sticky ages/soiltriangle_large.jpg Gritty Soapy http://www.soilsensor.com/im

Soil Landforms and Topography • Parent material –the underlying geologic material in which soil horizons form Soil Horizon • Soil horizon ‐ a specific layer in the soil which measures parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath • Solum ‐ consists of the surface and subsoil layers that have undergone the same soil forming conditions

‐‐ The base is the relatively unweathered parent material (or substratum)

• Toposequence ‐ Predictable trends in soil makeup related to topographic gradients on individual landforms

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Common sources and settings of deposits in which soils form wetland ‐ slope ‐floodplain ‐ upland deposits

Relationship between soils and landforms in mountainous terrain

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Example of soil variation associated with toposequence on hillslope

Soil Landforms and Topography – Unified Soil‐Classification System

First Second Definition Criterion Definition Letter Letter well graded G gravel Texture W (diversified particle sizes) well graded w/ clay S sand Texture C fraction; binds soil together silt Texture / poorly graded M P (inorganic) composition (uniform particle sizes) clay Texture / low compressibility and C L (inorganic) composition low plasticity organic silts Texture / high compressibility and O H and clays composition high plasticity

P peat Composition

http://soilmap.psu.edu/code/mapindex.asp

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Soil Conservation

Soil conservation is a set of management strategies for prevention of soil being eroded from the earth’s surface or becoming chemically altered by overuse, salinization, acidification, or other chemical contamination

• The principal approaches these strategies take are: • choice of vegetative cover • erosion prevention • salinity management • acidity control • encouraging health of beneficial soil organisms • prevention and remediation of soil contamination • mineralization other ways include • no till farming • contour plowing • wind rows • crop rotation • the use of natural and man‐made fertilizer • resting the land

USDA State Soil Geographic Database (STATSGO) http://www.soilinfo.psu.edu/index.cgi?soil_data&conus

http://dbwww.essc.psu.edu/cgi-bin/geotree/list_datafiles.pl?1996-0021

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USDA NRCS Data Portal http://datagateway.nrcs.usda.gov/

http://soils.usda.gov/use/thematic/images/drought_1_gen_area_map.jpg

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http://soils.usda.gov/use/thematic/dv_soilmap_high.html