Study Guide Ch. 4 Abiotic Systems Flashcards
Soil series
a group of soils originating from the same parent material and having similar soil horizons in the soil profile, with the primary difference between them being their soil texture
Each series named for a nearby geographic feature (e.g. town name)
divided into “phases” based upon their difference in texture, and the name of a soil phase indicates a feature that affects management
Through the USDA, the NRCS (National Resources Conservation Service) provides soil maps to the public that can be used to determine the soil series found at a specific site. If more detailed information (including soil chemistry) is required, the landscape architect can commission a soil survey for a site
Soil horizon
a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined by obvious physical features such as color and texture
Soil profile
a vertical section of the soil through all its horizons and extending into the parent material.
Soil Textures
All soils are composed of three components:
Sand
Silt
Clay
Soil textures vary according to the ratio of these three particles
As a general rule, there are equal parts sand and silt in a loam soil, and most sources list loam as being composed of 40% sand, 40% silt and 20% clay
Sand
The largest particle size, with soil particles between 0.05 and 2.0 millimeters in diameter
Silt
Fine soil particles between 0.05 and 0.002 millimeter in diameter that can be picked up by air or water and deposited as sediment
Clay
The smallest particle size, with soil particles smaller than 0.002 millimeters in diameter.
Loam
soil that is primarily composed of sand and silt, with a small amount of clay particles
Soil texture triangle
each side of the triangle represents one particle size, and the position along each axis determines the percentage of that particle in the soil. The intersection of the three sizes on the triangle gives the texture class
Texture is important in determining a soil’s
water-holding capacity
permeability and workability
and it also has a direct influence upon the plant communities found in a soil class
Friable soil
soil with a texture in which large clumps are easily broken apart by hand, but which cannot easily be broken apart into (undesirably) small particles.
As such, friable soils are ideal for agriculture and for the growth of most plants.
Porosity
describes the void size between particles within a soil and can be expressed as the percentage of void space in a soil
has a direct relationship with soil permeability
highly compacted soils generally have poor aeration and experience reduced infiltration because the void space between soil particles has been greatly reduced or eliminated, leaving little room for oxygen and water molecules. Conversely—due to the large particle size of sand—sandy soils are comparatively difficult to compact and therefore maintain their void space, allowing them to drain very quickly
Well-graded soil
a soil with a wide range and even distribution of soil particle sizes, in which the small soil particles fill the voids created by the larger grains
Gap-graded soil
a soil that contains various particle sizes, but in which gradation between sizes is broken by the absence of some particle sizes
Uniformly graded soil
a soil that consists of a single range of particle size
Permeability
is the rate at which water moves through soil
Infiltration rate
the rate at which water flows into soil through small pores
Percolation
the downward movement of water in a soil
highly permeable soils
contain large ratios of sand and/or larger material such as gravel, and—when soils are not draining well—they can be amended with sand and/or gravel to increase their permeability
Low permeable soils
Clay soils are well known for their low permeability, and adding clay to sandy soils can reduce permeability, as can the addition of peat moss or other highly absorbent organic materials
Hydric soils
Soils with low permeability in areas subject to regular moisture
are characterized by being heavily saturated with water for prolonged periods of time
and this prolonged saturation renders the soils anaerobic and generally results in the soils being bluish in color
Soil infiltration rates
are extremely important to the design of “green” stormwater management solutions such as bioswales
Infiltration of stormwater into the soil reduces the amount of water conveyed to “downstream” locations and—in aquifer recharge areas—infiltration can increase the amount of water present in an aquifer
Soil percolation
is particularly important to the design of septic systems in rural areas
Soils with a slow rate of percolation cannot accommodate septic systems, and these areas often preclude the development of housing or other uses that might require a septic system (where a municipal sewer system is not present).
Bearing capacity
can be defined as the measure of a soil to decrease in volume under the pressure of a given weight.
As such, knowing a soil’s bearing capacity can help determine where a foundation or roads can be constructed, given that soils with poor bearing capacity can lead to structural failures and other safety issues
Angle of repose
the maximum slope at which a loose material can be piled while remaining stable.
Soil elasticity
the ability of a soil to return to its original shape after being subjected to a load condition
Soil plasticity
the ability of a soil to be deformed under pressure without breaking apart
Liquid limit
the minimum moisture content at which a soil will flow under its own weight
best base course for roads and foundations
soils with a mix of particle sizes (i.e. a well-graded soil)
they offer greater stability and bearing capacity than a soil with a uniform particle size or those that shrink and expand through wetting and drying cycles (as is typical of clay-heavy soils).
factors that have a significant impact on erosion
precipitation patterns
topography (slope)
soil disturbance and site location (e.g. coastal sites often experience erosion from storm events).
Even natural disasters can impact erosion. For example, wildfires often result in hydrophobic soils, in which the soil in burn areas exhibits water repellence. Infiltration is decreased, thereby increasing erosion.
Soil erosion
removes fertile topsoil
it introduces high concentrations of sediment into watersheds, thereby reducing water quality and causing aggradation (the filling in of stream channels with sediment), among other issues
best practices to reduce soil erosion
- Preserve existing vegetation
- Reduce the total area of land disturbance
- Stabilize excavated areas with seeding, sodding, matting or mulching and divert runoff away from these areas
- Minimizing disturbance to steep slopes
- Schedule clearing and grading activities during the dry season and suspend them prior to and during precipitation events
- Locate non-point pollution sources (e.g. construction access roads) in areas that do not drain directly into water bodies
- Introduce erosion control fencing, blankets and stabilize drainage channels with erosion-resistant materials (e.g. riprap)
more common types of erosion
Gully
Rill
Sheet
Gully erosion
the widening, deepening, and headcutting of small channels and waterways due to erosion
Rill erosion
the removal of soil by running water with formation of shallow channels that can be smoothed out completely by normal cultivation
Sheet erosion
the removal of a fairly uniform layer of soil or materials from the land surface by the action of rainfall and runoff water
soil fertility
generally framed as an issue of NPK values
NPK values are always listed on a fertilizer and can be used to establish soil fertility. NPK values describe the ratio of:
Nitrogen (N)
Phosphorous (P)
Potassium (K)
Therefore, a fertilizer that is, for example, listed as 20-10-20 contains 20 parts N (nitrogen), 10 parts P (phosphorous) and 20 parts K (potassium)
Each of these elements plays a critical role in the development of healthy plants, and although each plant species has specific requirements for successful growth, we can make the following generalizations
Nitrogen supports plants' rapid growth and encourages the healthy development of foliage and fruit.
Phosphorous helps a plant convert other nutrients into usable building blocks with which to grow.
Potassium helps strengthen plants' abilities to resist disease and plays an important role in increasing crop yields.
Prime soils
a special USDA classification for highly fertile soils
these soils require the fewest inputs for productive agriculture.
Locations with prime soils require comparatively less irrigation and fewer fertilizers and pesticides than areas without prime soils.
soil pH
plays a critical role in plant health and in determining the presence of specific plant communities
pH is measured on a scale from 0-14. A pH of 7 is considered neutral, a pH below 7 is considered acidic (becoming more acidic as it approaches 0) and a pH above 7 is considered alkaline (becoming more alkaline as it approaches 14).
pH affects the solubility of soil minerals and nutrient availability to plants. Just as they prefer nutrient-rich, loam soils, most plants do best when the soil pH is between 5.5 and 7.5.
Note that alkaline soils and alkaline-tolerant plants are more common in the Western United States
bogs—a type of wetland—are characterized by highly acidic soils. Many plants in the Ericaceae family (e.g. rhododendrons, azaleas, blueberries) are acid-loving.
In situations where soil pH is not conducive to plants (e.g. weathered concrete releasing calcium carbonate into the soil, making it overly alkaline), amendments can be added.
When soils are overly acidic, lime should be added.
When soils are overly alkaline, sulfur should be added.
Note that soils high in salt can be amended through the addition of gypsum.
iron chlorosis
A condition occurring in plants where the pH is overly alkaline (and exacerbated by overwatering and a lack of aeration).
Chlorotic plants typically have yellowed leaves with green veins and browning along the leaf margin.
Topography
The physical features of a surface area, including relative elevations and the position of natural and artificial features
Comprising elevation, slope and aspect
topography is generally considered the most important variable when siting a new project
influences a wide variety of critical issues, including grading, development density, construction costs and the location of roads and other infrastructure
site planning and design should follow or otherwise relate to existing landforms not only to respect context, but also because grading causes significant site disturbance and is costly
Site elevations
impact drainage patterns and visibility
elevation both on a site and in the surrounding landscape determines the size and spatial configuration of local viewsheds.
Elevation data is generally shown in two different ways on topographic maps: spot elevations and contour lines.
Spot elevations
are highly accurate readings shown for specific points.
Often these are areas of importance to the designer (e.g. the finished floor elevation of a structure, the top or bottom of a wall) or to the understanding of a landform (e.g. the high point of a hill, the summit of a mountain).
Spot elevations are more accurate than the information provided by contour lines.
Contour lines
are lines on a topographic map that establish the elevation at any point along that line.
Contour intervals (the vertical distance between each contour line) will vary according to the accuracy of a map, but the elevational information provided by the contour line is generally considered accurate to one half the contour interval given.
For example, if a topographic map provides 2-foot contour intervals, that map would be considered accurate to one foot.
Note that some maps will use color (instead of contour lines) to convey elevational information, in which cooler colors depict low elevations and warmer colors depict higher elevations.
Under this system, the resultant color gradient values are computed by dividing the slope’s vertical change in elevation by its horizontal length, and—to limit the visual complexity—these maps typically limit themselves to between five and nine colors/classes of elevation.
Slope
Topographical information can be used to determine the intensity of a slope.
In general, contour lines that are closely spaced indicate a steep slope, whereas contour lines that are widely spaced indicate a gentle slope.
Contour lines can also indicate the “signature” of a landform.
Ridges are identified by contour lines that point downhill
Valleys/swales are identified by contour lines that point uphill
Note that it is important to be able to discern the difference between ridges and valleys on a topographical map because drainage basin/watershed divides occur at ridges.
the precise slope of a line can be measured from information provided on a topographical contour map. Slope is calculated as "rise over run", or the change in y (vertical) divided by change in x (horizontal).
Slopes are often expressed as a ratio (e.g. 2:1 slope) or as a percentage (e.g. a 2% slope). And although slope is calculated as rise divided by run, there are some debates as to how slope ratios should be expressed
general guide to the character of slopes (when expressed as a percentage)
0–3% (nearly level)
3–7% (gently sloping)
7–12% (moderately sloping)
12–25% (strongly sloping)
25–40% (steeply sloping)
40–70% (very steeply sloping)
70+% (extremely sloping)
Note that most sources identify 2% as the minimum slope necessary for a site to shed water and have proper drainage.
Slope analysis
is used to identify steep and unbuildable slopes and to identify the possible location for building sites and access (e.g. roads, walkways, etc.), as well as for stormwater management.
usually a graphic representation of slope shown in classes or ranges, with these ranges corresponding to (or precluding) specific site uses.
When mapped onto a site, slope percentages can be used to conduct a slope analysis
Aspect
or orientation
is the direction that the slope faces relative to the sun
is typically described by compass direction (e.g., a northerly aspect) and—along with slope—impacts the amount of solar radiation received at a given location on a site
orientation toward the sun may influence a building’s energy use and performance, and it helps determine what types of vegetation can be planted in specific areas (e.g. sun, part sun, shade)
relationships between slope aspect and microclimate
Southern slopes receive the most sun in winter months
Southeastern slopes offer the most desirable microclimates
North-facing slopes are colder than south-facing slopes
Northwestern slopes receive cold winter winds
Western slopes are hottest in the summer
Geology-specific site inventory and analysis is generally related to geomorphology and takes the following factors into consideration
Landforms
Seismic hazards
Depth to bedrock
geomorphology
the study of the physical features of the surface of the earth and their relation to its geological structures
Geologic map data generally shows
The age and distribution of rock layers, and the attributes of these rock layers.
Map data will also identify locations that are susceptible to earthquakes and landslides, and they will identify seismic fault lines.
These factors influence a site’s suitability for excavation and grading, wastewater disposal/infiltration and groundwater supply.
the cost of excavating a cubic yard of rock is many times greater than the cost of excavating the same volume of soil
Karst
landscape underlain by limestone which has been eroded by dissolution, producing ridges, towers, fissures, sinkholes and other characteristic landforms.
Glacial erratic
a glacially deposited rock (often a large boulder) differing from the type of rock native to the area in which it rests
Moraine
a mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges or extremity.
impervious surfaces have had a direct and dramatic effect on hydrological systems, including
- Increased rate and volume of stormwater runoff
- Increased frequency and severity of flooding
- Reduced water quality
- Reduced infiltration and diminished aquifer recharge
- Reduced stream flow during dry weather
- Ecological degradation
- Reduced recreational opportunities on the water
Site-disturbing activities such as construction increase the risks of
flooding
erosion
other ecological impacts to properties ‘‘downstream”
these problems are exacerbated by
the “channelizing” of hydrological resources into highly engineered, enclosed and impervious storm drain systems
purpose of these storm drain structures
to regulate the flow of rivers and streams and to mitigate flood risk
but these solutions effectively destroy any ecological or recreational benefits that these rivers/streams once had
With advances in sustainable design technologies and due to changing attitudes toward water resources, many municipalities are now looking to “daylight” hydrological systems that were once confined to underground storm drain systems.
Time of concentration
a term used in hydrology and other sciences to refer to the amount of time needed for water to flow from the most remote point in a watershed to the watershed outlet
note that “the most remote part of the drainage area” referenced in the definition of time of concentration is not necessarily the longest distance between two points in the drainage area, given that flow time is dependent on slope and surface. In other words, water may take much longer to flow over a small, flat grass field than a steeply sloped, impervious concrete parking lot
Impacts to runoff flow and concentration
surface types: water flows more quickly over concrete than over grass. Moreover, because concrete is impervious, the amount of water flowing across a concrete surface is not reduced by infiltration (whereas grass and other impervious surfaces allow for infiltration).
topography affects the rate, direction and velocity of runoff. infiltration is reduced as slope increases regardless of whether the surface of that slope is impervious or not. (water flowing over two identical grass surfaces will infiltrate at a lower rate on the surface with a greater slope)
Watershed boundaries occur along ridges, and water flows from these high points into valleys and other low points (such as rivers). Within the context of surface drainage on a site, water will flow from the site high point to the site low point following the prevailing site topography. If looking at a topographical map with contour lines, note that water always flows perpendicular to the direction of the contour line
Given that water flows downhill, stormwater retention and detention infrastructure should generally be located at the site’s low point, as it would allow all the stormwater draining on the site to travel to that location by gravity.
Rational Equation calculation
used to determine the rate of runoff and is as follows:
Q = ciA
you will be asked the purpose of this equation (i.e. determining the rate of runoff) or to identify each component of the equation. They are as follows:
Q = the peak discharge measured as cubic feet per second
c = the runoff coefficient (a value between 0 and 1). A measure of how permeable a surface or area is, with this number being a higher value for areas with low infiltration (e.g. pavement, steep slopes), and a lower value for areas with high infiltration (e.g. forest, flat land).
i = rainfall intensity measured as inches per hour
A = drainage area measured in acres
riparian zone or riparian area
the interface between land and a river or stream
Riparian zones generally provide the following benefits
Groundwater recharge and discharge
Sediment stabilization
Flood attenuation
Water quality maintenance
Wildlife habitat
Climate moderation
Shoreline protection
streams and rivers are classified as follows
First-order streams
Second-order streams
Ephemeral
Intermittent
Perennial
First-order streams
primary drainage ways at the beginning of the hydrological system.
Second-order streams
are formed by the confluence of two first-order streams, and this naming convention continues as additional streams come together in a hydrological system
Ephemeral
a stream that flows only in response to precipitation
Intermittent
a stream that flows only part of the time or through only part of its reach
Perennial
a stream that flows continuously
Floodplain
the area of land adjoining a body of water that has been or may be covered by floodwater
floodplains are differentiated by the frequency with which they are likely to flood in a 100-year period
the 100-year floodplain—in other words an area of land that has a 1% chance to flood in any given year
Floodplains are composed of three areas
Channel
Floodway
Flood Fringe
Channel
the portion of the floodplain where a stream/river flows under normal conditions
Floodway
the portion of the floodplain that is used to convey floodwaters during a 100-year flood.
Flood fringe
the portion of the floodplain outside the floodway that does not convey floodwaters and usually contains slow-moving or standing water.
Base flood elevation (BFE)
are whole-foot elevations of the 100-year floodplain that have been studied in detail at selected intervals. In areas where building has occurred within the 100-year floodplain, BFE calculations are often used to determine the height to which living spaces must be constructed to be safe from a 100-year flood.
Freeboard
any portion of the flood in excess of the base flood elevation (measured in feet)
Land uses inside the 100-year floodplain are strictly regulated
. For the purposes of the LARE Section 2, buildings cannot be erected inside the boundaries of the floodplain, although—in practice—flood-proof structures are sometimes allowed in the flood fringe. As such, if you encounter any questions related to proposed uses on sites within a floodplain, you should choose uses that do not require erecting any structures on site (e.g. golf courses, recreational uses, gardens, etc.).
Flood Insurance Rate Maps by FEMA
these maps document floodplains, as well as special hazard areas, throughout all of the United States
For the purposes of the Section 2 Exam, these maps should be considered the definitive resource for floodplain information,
Letter of Map Revision (LOMR)
Issued when flood insurance maps need to be amended or updated
Maps are updated for a variety of reasons, but increases to impervious surfaces from upstream uses contribute significantly to flood events in downstream areas.
In the absence of information provided by these FEMA maps, the extents of floodplains can be determined by looking at four key variables
Topography
Soils
Vegetation types
Extent of past flood flows
flood hazards can be mitigated through
expanding opportunities for stormwater infiltration
minimizing the uses of impervious surfaces
decreasing the volume of runoff during storm events
restricting development to areas outside of floodplains
Water quality impacts can originate from
erosion and sedimentation
chemicals
illegal dumping
microorganisms
pollution sources can be classified as either
Point
Non-point
Point source
any single identifiable source of pollution from which pollutants are discharged (e.g. factory smokestack)
from factories can contribute to acid rain and decrease the pH of water resources (i.e. make them more acidic).
Non-point source
pollution caused by rainfall or snowmelt moving over and through the ground, during which it absorbs and/or assimilates natural and human-made pollutants and deposits them into lakes, rivers, wetlands, groundwater and the ocean.
Surface water pollution associated with stormwater runoff not only impacts aquatic ecosystems, it reduces the aesthetic and recreational value of rivers, lakes, and other water bodies.
Groundwater pollution from septic tank effluent can limit an area’s suitability for wells.
Sediment can cause
Decline in water quality
Negative impacts to aquatic vegetation and animals
Negative impacts to aquatic recreation
Unwanted biological growth (e.g. algal blooms)
Increased turbidity
Decreased flow capacity in streams/rivers
Flooding in areas that never or rarely flooded in the past
processes of sedimentation and aggradation in rivers
As a river curves, erosive forces act against the outer bank of the river (i.e. the curve with the larger radius), carving into it over time and introducing a greater sediment load downstream. Sedimentation can be conceived of as the opposite of erosion, and the inner bank of the river (i.e. the curve with the smaller radius) is where sedimentation occurs. This process of sedimentation is also referred to as aggradation.
Water Tables
A high water table (also referred to as a “shallow” water table) can contribute to storm surges and flooding and—although it does not preclude excavation—it does make excavation more expensive given that any structure or foundation below the water table would need to be adequately waterproofed (thereby increasing the project budget).
A high water table can also impact on-site stormwater infiltration and the provision of septic systems.
Note also that groundwater pumping can lower the water table, thereby negatively impacting hydrological resources.
Aquifers and Aquifer Recharge Areas
Groundwater tables are falling as water demand exceeds aquifer recharge rates.
Excessive pumping of aquifer systems can result in land subsidence and related ground failures.
Aquifer recharge areas are particularly important locations to identify and protect from development. In Design With Nature, Ian McHarg specifically calls out the importance of protecting aquifers (and groundwater resources in general) from development pressures and pollution.
Climate has greatest impact on plant selection
Although often equated with temperature, climate is composed of numerous variables, including:
Temperature
Humidity
Wind
Precipitation (rain, snow)
Solar Radiation
USDA Plant Hardiness Zone Map
Consult to determine how climate interfaces with plant selection, and this map is numbered from Zone 1 (the coldest) to Zone 13 (the hottest).
Other sources exist with a higher granularity of information that take multiple climatic variables into consideration (e.g. Sunset Climate Zones), but the USDA map is the most commonly used resource in the profession of landscape architecture.
Albedo
is the measurement of an object’s reflectivity.
Specifically, it measures the fraction of solar energy reflected from a surface back into space.
Albedo varies between 0 and 1. Albedo commonly refers to the "whiteness" of a surface, with 0 meaning black and 1 meaning white. Therefore, an asphalt parking lot would have a low albedo (therefore absorbing a great deal of solar energy as heat), whereas a concrete surface painted white would have a high albedo (therefore reflecting much of the solar energy off its surface and not absorbing as much heat as the asphalt).
Angle of incidence
is the angle at which a ray of light (usually the sun) hits a surface.
Azimuth
the direction of a celestial object from the observer, expressed as the angular distance from the north or south point of the horizon to the point at which a vertical circle passing through the object intersects with the horizon.
Drainage wind
a wind that blows from a higher elevation to a lower elevation
Microclimate
differences in weather-related phenomena - such as humidity, temperature, rainfall and wind - over a relatively small geographical area. Microclimates are of great importance in the process of site analysis and site design.
has a particularly important effect on the energy consumption of buildings (i.e. heating and cooling costs), and the comfort of people in outdoor spaces.
Note, however, that both energy consumption and microclimate are influenced by the orientation and spatial organization of buildings, structures, and outdoor spaces.
Specific microclimate information relevant to the Section 2 exam includes
- Southern orientations receive the most sun in winter months
- Southeastern orientations offer the most desirable microclimates
- North-facing orientations are colder than those facing south
- Northwestern orientations receive cold winter winds
- Western orientations are hottest in the summer
Winter winds can be buffered
indbreaks, and land uses can be arranged to reduce the negative effects of winds on outdoor activities.
energy consumption for heating and cooling can be reduced through
both passive and active solar designs.
Climatic site inventory and site analysis therefore play a critical role in determining site design and provide information to the landscape architect that allows them to mitigate negative (micro)climate impacts through design choices.
For example, landscape architects will often conduct a sun/shade analysis to understand the impacts of solar radiation on a site design. In northern climates, it may be important to design outdoor spaces such that they receive a great deal of sun during the winter, not only to provide site users with “thermal comfort” (a balance between the body’s heat losses and heat gains), but also to prevent the formation of ice on pedestrian surfaces that could cause a safety issue. Conversely, outdoor spaces in desert regions may look to maximize shade opportunities to protect site users from excessive heat. Buildings, trees, walls, and other vertical elements cast shadows that influence site microclimate, and site elements such as fountains can cool the air in arid/dry environments (at the cost of using scarce water resources).
Thermal comfort
a balance between the body’s heat losses and heat gains
The color and character of surface materials also impacts microclimate
Dark-colored paving materials such as asphalt absorb solar radiation and raise the ambient air temperature in surrounding areas.
Metal surfaces and site elements (e.g. chairs) are much more reactive to temperature fluctuations and will become overly hot or cold, especially when compared to more thermally stable materials such as wood.
Existing and proposed vegetation can impact microclimate in several ways.
Large trees with a broad, dense canopy, for example, intercept the solar radiation that would otherwise heat hardscape surfaces.
Plants also tend to cool air temperatures through evapotranspiration (from their leaves), and plants can also improve air quality by removing certain chemical pollutants or capturing/screening dust pollution.
