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61 Cards in this Set
- Front
- Back
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bench terrace
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Nearly level land and vertical wall
(In us, used mainly in urban and suburban non-ag land) |
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broad-based terrace
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Small excavations with fill pushed DOWN-slope to form a ridge
Entire terrace area can be cultivated |
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steep-back slope terrace
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Small excavations with fill pushed UP-slope to form a ridge
Backslope planted with permanent vegetation Ridges can't be crossed by equipment. |
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What is the difference between a graded terrace system and a level terrace system?
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level: benches, flat
graded: carry runoff to a protected outlet- slows velocity, shortens slope and traps sediment |
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Narrow-based terrace
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ridges pushed uphill and steep on both sides
both sides of ridge with permanent vegetation Cheap to build, but equipment cannot cross |
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conservation bench terrace
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Level area behind ridge in which water can pond/infiltrate
Purpose: to increase water infiltration |
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Why aren't bench terraces used much in U.S. agriculture?
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labor intensive
hard to use with machinery |
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What are the advantages and disadvantages of steep-back slope terraces?
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Good: easy to farm, reduce slope of cropped area, can be used on land otherwise too steep to farm.
Bad: untillable backslopes, insects and burrowing pests can live in untilled backslope. Require great care because of equipment restrictions. |
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What are the advantages and disadvantages of broad-based terraces?
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bad: increase land slope, some sections too wet, bad for unproductive shallow soils
good: less damage to seeds/seedlings, erosion reduction |
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What determines how far apart terraces should be spaced?
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% slope
soil's resistance to erosion crop's resistance to erosion |
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How is the horizontal interval of terraces related to the vertical interval?
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(VI *100) / %slope
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What are the basic procedures in laying out farm terraces?
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Clear land, smoothing
can build with bulldozers or plows, parameters (VI&HI) according to the slope, crop and soil conditions |
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Diversion
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Ditch or channel with an accompanying ridge on the downhill side.
Purpose: to divert water away at a non-erosive velocity. |
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Which would you recommend draining terraces with, an underground outlet or a grass waterway? Why?
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Grass waterway in nrmal conditions, tile outlets when gully erosion is a risk (from excess water)
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What are the major purposes of earthen dams in conservation?
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trap sediment
stabilize drainage ways reduce erosion store excess water temporarily to reduce flooding can store water for other uses (irrigation, livestock, etc) |
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toe protector
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TOE: where gradient changes abruptly at waterline
toe protector: stones or other protective material placed at toe and spread by machine. |
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hardpoints
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stones or other protective material dropped at toe of slope (gradient change at waterline), but not spread is in "toe protectors"
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revetments
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continuous protective cover, such as a retaining wall made of stone, concrete,
also gabions: stone enclosed in wire mesh |
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woven mat barriers
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mats of woven plant material erected as barriers to wind erosion
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snow fence
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slats of wood fastened together by wire w/1" spacings that stop snow from drifting onto highways, runways or other critical areas.
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ID the variables in this equation for water flow through a terrace outlet orifice:
q=aC(2gh)^1/2 |
q: discharge (ft^3/sec)
a: XS area C: coefficient (usually 0.6) g: acceleration due to gravity (32 ft/sec^2) h: height of water ponded about orifice |
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Name the 3 zones of a fluvial system.
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Production (watershed)
Transfer (rivers & streams) Deposition (delta) |
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3 applications of Channel Stabilization?
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1. Maintain or alter channel bed elevation or gradient.
2. Modify sediment transport or deposition. 3. Manage surface water and ground water levels in floodplains, riparian areas, and wetlands |
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What are some ways to temporarily protect a stream bed during Channel stabilization measures?
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-Mulch (holds seeds, covers soil.)
-Bales of hay or silt fences. (trap sediment & slow the velocity of flowing water) |
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Gabions?
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riprap enclosed in wire mesh
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Riprap?
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Rocks large enough to be unmoved by the flowing water.
(Used on the bed of the channel as well as on the banks.) |
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Bio-engineering?
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Use of native vegetation for bank stabilization.
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What is channelization?
Some purposes of Channelization? |
All processes of river channel engineering.
For the purposes of: flood control drainage improvement maintenance of navigation reduction of bank erosion relocation for highway construction |
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Resectioning
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Increases the in-bank discharge capacity by enlarging cross-sectional area and/or elevating the slope.
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What is he purpose of stream Realignment?
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Increases flow velocity by reducing the natural sinuosity (meandering) or creating a straight alignment, thereby steepening the bed slope and increasing the energy gradient.
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Sinuosity?
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Meandering/curving in nature.
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Diversion Channels
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This approach aims to redirect flow away from a protected area.
*preferred method of flood protection in urban areas where spatial restrictions inhibit resectioning. |
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Why does construction activity often have such a negative effect on soil conservation?
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exposed soil & subsoil
uneven settling of materials soil compaction (from equipment) runoff |
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What are typical problems faced in reclaiming strip (surface) mining sites?
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soil layer mixing
unstable slopesclayey sils form anarobic blocks soil becomes sterile from salinity, sodicity or acidity & requires treatment |
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Discuss the problem occurring when iron pyrite is present in mine spoil.
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Iron pyrite= "fools gold"
pyrite oxidizes to form H2SO4 (sulfuric acid) which ruins land surfaces and water bodies killing plants and fish. |
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What are five recommended steps in reclaiming a gully?
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1. Divert water away from head
2. Smooth head and sides & straighten if needed 3. smooth channel 4. establish grassed waterway 5. fence out animals to protect while establishing vegetation Simply: control water, reshape & establish vegetation |
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What techniques can be used to stabilize coastal sand dunes? How about inland sand dunes?
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Plant salt-tolerant vegetation.
fertilize and mulch add more sand. |
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Define Pastureland
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Intensely MANAGED grazing area (in humid or irrigated area)
Planted, fertilized and irrigated in dry areas. |
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Define Rangeland
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unplowed areas with natural vegetation
(sometimes seeded to improve varieties, but NEVER plowed or irrigated) |
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Define Forestland
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>10% of land occupied by growing trees.
> 0.5 hectare |
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Another word for strip mining?
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surface mining
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What are several fertility considerations for pastures?
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soil productivity
liming plowing correct plant species animal stocking for optimum usage |
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Continuous grazing
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Placing livestock on a pasture and allowing them to graze there throughout the grazing season.
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Rotational grazing
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placing fences so the livestock can graze only part of the pasture at a time.
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Deferred grazing
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Delaying the start of grazing beyond the normal beginning of the grazing period. This permits species that are likely to be damaged or crowded out by grazing to become more vigorous.
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Selection Harvesting
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harvesting individual trees or small groups of trees as they mature.
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Shelterwood Harvesting
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removes all mature trees but in a series of harvest several years apart. There is always an understory to protect the site.
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Seed Tree Harvesting
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Seed tree – leaves only enough trees to bear seed for natural regeneration.
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Clearcutting
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Removes all trees from the harvested area.
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What are the 4 main harvesting methods for forestland described in class?
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selection
Shelterwood Seed tree Clearcutting |
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What % of the 307 million acres of publicly owned lands in the western US are grazed?
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85%
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most popular grazing regimen?
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continuous grazing
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AUM?
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Animal unit month
the approximate amount of forage a 100 lb cow w/calf eat in 1 month (standard by which ALL animals are measured) |
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What % of US land is forested?
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29%
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When does erosion occur in forestland?
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trees removed & forest litter disturbed
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How does forest land influence hydrology compared to row crop land?
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better groundwater recharge
less surface runoff low peak discharge |
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What are the 2 major influences forestland has on the environment at large?
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important in climate change and carbon sequestration
Preserves biodiversity on earth. |
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Purpose of the Taylor Grazing Act of 1943?
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prevent overgrazing & soil deterioration on public rangelands & stabilize the livestock industry
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BLM stands for...?
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Bureau of land management
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Purpose of federal land management act
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created policies authorizing 10 year permits for grazing on BLM administered public lands
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Major causes of erosion in mining sites?
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High Walls
& Steep slopes |
