Section 3-Site Planning and Management Section 4-Predicting Soil Loss Flashcards
Resource Planning
on site/off site resources to protect and avoid during development
Erosion and sediment hazards
- large increase of soil exposed to erosion
- increased water runoff, soil movement, sediment accumulation and peak flows caused by:
a. removal of plant cover
b. decrease in area of soil with addition of impervious surface
c. change in drainage areas through grading, diversions, streets
d. change in volume and duration by altering steepness, distance, surface roughness
e. soil compaction
f. prolonged exposure of unprotected sites
- altering groundwater regime affecting drainage systems, slope stability, survival of existing vegetation and plant establishment
- exposing subsurface materials too rocky, acid, alkaline for plant establishment
- obstructing flow with new buildings, dikes, and fills
- improper timing and sequence of construction and development
- abandonment of site before completion
Factors that influence erosion- Soil erodibility
vulnerability of a soil to different erosion processes. Soil texture, structure, and percentage of organic matter. Most erodible contain silt and very fine sand. Clay and organic matter decreases erodibility. Clays are cohesive binding soil particles. Organic matter acts as an aggregate.
Factors that influence erosion-Vegetative Cover
protects soils from raindrop impact and runoff scour. Top growth shields soil while root mass holds soil in place. Moderates freeze/thaw, shrink/swell that causes detachment of bare soil and increases available transport by overland flow. Grass can act as sediment filter and slow velocity increasing infiltration capacity. Most important factor in minimizing erosion during development
Factors that influence erosion-Topography
slope length and steepness impact volume and velocity. Long slopes=more runoff to base of slopes. Steep slopes=increased runoff velocity. Slope roughness reduces both impacts
Factors that influence erosion-Climate
frequency, intensity, duration directly influence amount of runoff. Increased frequency, intensity, long duration=less chance to drain. Saturated soils increase runoff potential.
Factors that influence erosion-Season
temperature and rainfall. Soil thaw at surface with subsurface freeze creates runoff. Seasons of higher intensity, higher frequency storms=higher runoff.
Land Development Plans-Geography
land use, size, topo, drainage, geology, hydrology, soils, veg
Land Development Plans-Study of Soils
- descriptions, erodibility, limitations, capabilities
- engineering properties-grain size, plasticity index
- suitability for topsoil
- structural tolerances-buildings, roads, dams, veg
Erosion and sediment control plan-shows
existing topo, how and when it will be altered. Shows erosion and sediment control measures, how/when implemented/maintained. Phased schedule showing practices during construction
The Planning Process-Plan development that fits site
how it can be developed to minimize environmental damage through grading, avoiding sensitive areas, offsite impacts
The Planning Process-Determine limits of grading and clearing
minimize when possible. Staged clearing vs. mass clearing
The Planning Process-Divide site into natural drainage areas
define watersheds. Limit erosion at source rather than control sediment at perimeter
The Planning Process-Design Erosion and Sediment Control Practices
structural vs. vegetative. State/local handbooks to be used.
Design Erosion and Sediment Control Practices-Vegetative controls
best way. Temp seeding or mulching. Permanent stabilization as soon as possible. Control plans must contain provisions for permanent stabilization. Seed type, amendments, bed prep, and mulching should be described. Permanent veg include the following for each plant species:
a. establishment requirements
b. adaptability to site conditions
c. aesthetic and resource value
d. maintenance requirements
Design Erosion and Sediment Control Practices-Structural controls
when vegetative control cannot be promptly used
The Planning Process-Plan map details
- map of existing topo/grading
- Provisions for erosion/sediment control
- schedule of construction and erosion/sediment control activities
- maintenance phasing
The Planning Process-Implementation of Erosion/sediment control
good construction management,
- clear only what where under construction. Phase large projects.
- restablize asap
- divert off site run on and convey to stable areas
- physical demarcation of limits of disturbance
- educate workers
- establish person of responsible charge
- implement daily inspection program
The Planning Process-Planning Assistance
- streets at right angles create excessive grades
- utility plans include sediment control
- quality improved when open space, parks, etc incorporated into plan. Base upon soils, veg, topo, wildlife, aesthetics
- plant materials/mulch retain existing vegetation
- control measures installed asap after construction starts
- maintenance/installation of permanent BMPs promptly
Construction Sequences scheduling -Preconstruction actions
evaluate, mark, protect important trees, unique areas to be preserved, onsite septic fields, filter strip suitable veg
Construction Access
Entrances, routes, parking
Sediment barriers and traps types
basins, traps, silt fences, inlet protection
Runoff Control types
diversions, perimeter dikes, water bars, outlet protection. Install after sediment traps but before grading
Runoff conveyance system types
stabilized stream banks, storm drains, inlet and outlet protection, channels. Stabilize stream banks, install principle conveyance system. Install remainder after grading
Land clearing and grading mitigation
grading, drains, sediment traps, barriers, diversions, surface roughening
Surface Stabilization types
temporary and permanent seeding, mulching, sod, rip rap
Landscaping and final stabilization types
top soiling, plant materials, seeding, mulching, sodding, rip rap-remove temporary control measures and stabilize
Revised Universal Soil-Loss Equation (RUSLE)
Soil loss equations were developed to extrapolate limited erosion data that have not been directly represented in research
Erosion and sedimentation by water involve the processes of
detachment, transport and deposition of soil particles. Major forces are raindrop impact and water flowing over land surface.
Sediment Yield and erosion are/ are not the same
are not
Sediment yield
amount of eroded soil that is delivered to a point in the watershed that is remote from the original of the detached soil particles. It includes erosion from slopes, channels, and mass wasting, minus the sediment deposited after it is eroded but before it reaches the point of interest.
RUSLE does/ does not estimate sediment yield
does not estimate sediment yield. It computes the average annual erosion expected on field slopes. Designed to predict the longtime average annual soil loss (A) carried by runoff from specific slopes in specified management conditions