Chapter 4 Flashcards
soil series
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 soil series is 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 managemen
who provides soil maps?
Through the USDA, the NRCS (National Resources Conservation Service)
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
layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath.
defined by obvious physical features such as color and textur
Soil profile
vertical section of the soil through all its horizons and extending into the parent material
Sand
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
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
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.
why is soil texture important
important in determining a soil’s water-holding capacity, permeability and workability
influence upon the plant communities found in a soil class
friable soil
texture in which large clumps are easily broken apart by hand, but which cannot easily be broken apart into (undesirably) small particles
ideal for agriculture and for the growth of most plants
Porosity
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 (
Well-graded soil
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
contains various particle sizes, but in which gradation between sizes is broken by the absence of some particle sizes
Uniformly graded soil
soil that consists of a single range of particle size
Permeability
rate at which water moves through soil
Infiltration rate
rate at which water flows into soil through small pores
Percolation
the downward movement of water in a soil.
what to do when soils not draining
can be amended with sand and/or gravel to increase their permeability
to reduce soil permeability
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
characterized by being heavily saturated with water for prolonged periods of time
this prolonged saturation renders the soils anaerobic and generally results in the soils being bluish in color.
soils and septic systems in rural areas
Soils with a slow rate of percolation cannot accommodate septic systems
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
measure of a soil to decrease in volume under the pressure of a given weight
Angle of repose
maximum slope at which a loose material can be piled while remaining stable
Soil elasticity
ability of a soil to return to its original shape after being subjected to a load condition
Soil plasticity
ability of a soil to be deformed under pressure without breaking apart
Liquid limit
minimum moisture content at which a soil will flow under its own weight.
clay-heavy soils
a soil with a uniform particle size or those that shrink and expand through wetting and drying cycles
factors that effect erosion
precipitation patterns, topography (slope), soil disturbance and site location (e.g., coastal sites often experience erosion from storm events), natural disasters
hydrophobic soils
wildfires - the soil in burn areas exhibits water repellence. decreased, thereby increasing erosion
Soil erosion
not only 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)
Gully erosion
widening, deepening, and headcutting of small channels and waterways due to erosion
Rill erosion
removal of soil by running water with formation of shallow channels that can be smoothed out completely by normal cultivation.
Sheet erosion
removal of a fairly uniform layer of soil or materials from the land surface by the action of rainfall and runoff water.
soil fertility
Nitrogen (N)
Phosphorous (P)
Potassium (K)
Nitrogen (N)
supports plants’ rapid growth and encourages the healthy development of foliage and fruit
Phosphorous (P)
helps a plant convert other nutrients into usable building blocks with which to grow.
Potassium (K)
helps strengthen plants’ abilities to resist disease and plays an important role in increasing crop yields.
prime soils
require the fewest inputs for productive agriculture; less irrigation and fewer fertilizers and pesticides
pH
scale from 0-14
pH of 7 is considered neutral
pH affects the solubility of soil minerals and nutrient availability to plants
plants do best when the soil pH is between 5.5 and 7.
acidic soil
pH below 7
bogs—a type of wetland—are characterized by highly acidic soil
Ericaceae family (e.g. rhododendrons, azaleas, blueberries) are acid-loving
alkaline soil
pH above 7
alkaline soils and alkaline-tolerant plants are more common in the Western United States
how to amend soils
When soils are overly acidic, lime should be added.
When soils are overly alkaline, sulfur should be added
soils high in salt can be amended through the addition of gypsum
“iron chlorosis”
occurs 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
Spot elevations
highly accurate readings shown for specific points
more accurate than the information provided by contour lines
Contour lines
lines on a topographic map that establish the elevation at any point along that line
generally considered accurate to one half the contour interval given
Ridges
identified by contour lines that point downhill
drainage basin/watershed divides occur at ridges
Valleys/swales
identified by contour lines that point uphill
Geomorphology
is concerned with understanding the surface of the Earth and the processes by which it is shaped, both at the present as well as in the past.
character of slopes
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)
minimum slope for drainage
2% as the minimum slope necessary for a site to shed water and have proper drainage
slope analysis
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
slopes hottest in summer
western slopes
slopes receive cold winter winds
Northwestern
slope temperatures
North-facing slopes are colder than south-facing slopes
Southeastern slopes
offer the most desirable microclimates
receive the most sun in winter months
Southern slopes
Moraine
a mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges or extremity
Glacial Erratic
a glacially deposited rock (often a large boulder) differing from the type of rock native to the area in which it rests.
Karst
landscape underlain by limestone which has been eroded by dissolution, producing ridges, towers, fissures, sinkholes and other characteristic landforms
these impervious surfaces have had a direct and dramatic effect on hydrological systems
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
daylight
Daylighting is the opening up and restoration of a previously buried watercourse, one which had at some point been diverted below ground. Typically, the rationale behind returning the riparian environment of a stream, wash, or river to a more natural above-ground state is to reduce runoff, create habitat for species in need of it, or improve an area’s aesthetics.
Time of concentration
amount of time needed for water to flow from the most remote point in a watershed to the watershed outlet
what effects runoff
surface material
topography (affects the rate, direction and velocity)
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.
Watershed boundaries
occur along ridges, and water flows from these high points into valleys and other low points (such as rivers)
Q = ciA
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
interface between land and a river or stream
benefits of riparian zone or riparian area
- Groundwater recharge and discharge
- Sediment stabilization
- Flood attenuation
- Water quality maintenance
- Wildlife habitat
- Climate moderation
- Shoreline protection
First-order stream
primary drainage ways at the beginning of the hydrological system
Second-order streams
formed by the confluence of two first-order streams, and this naming convention continues as additional streams come together in a hydrological system
Ephemeral river
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
stream that flows continuously.
Floodplains
area of land adjoining a body of water that has been or may be covered by floodwater
Channel
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.
Freeboard
any portion of the flood in excess of the base flood elevation (measured in feet).
extents of floodplains can be determined by looking at four key variables
- Topography
- Soils
- Vegetation types
- Extent of past flood flows
flood hazards mitigation
expanding opportunities for stormwater infiltration,
minimizing the uses of impervious surfaces, decreasing the volume of runoff during storm events
through restricting development to areas outside of floodplains.
Point Source
single identifiable source of pollution from which pollutants are discharged (e.g. factory smokestack)
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
sediment
in sufficient concentrations—can dramatically reduce water quality
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
