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Land Development
Question | Answer |
---|---|
Soil Erosion | Detachment and transport or sediment particles caused by wind, rain, ice, and gravity |
What do erosion rates directly compare to? | The percentage of bare soil on a site |
Sedimentation | The deposition of soil particles |
What are problems arising from construction related activities? | Degradation to downstream properties and waterways. Damage to new and existing infrastructure. Dust and mud tracked onto public streets. |
When is an E&SC Plan Needed? | Land disturbing activities > 10,000 ft&2 Legally enforced by localities with legislative backing (fines, bonds) |
What is a E&SC plan? | Used to show the location and size of the various E&SC practices |
What are the phases of the E&SC plan? | Phase I: Initial Planning Phase II: Finish grading and protection of site infrastructure |
What is a E&SC Narrative? | Provides supporting calculations, includes information often redundant to feasibility report |
What are factors that influence soil erosion? | Rainfall frequency and distribution type, soil properties, topography, vegetation |
What are the classes of sediment control measures? | Filtering, Prevention, Colleciton |
What are filtering measures? | Silt fence, straw bales, inlet protection |
What are prevention measures? | Construction entrances, slope drains, outlet protection, check dams, level spreaders, seeding |
What are collection measures? | Diversion dikes, sediment traps, sediment basins |
What are diversion dikes? | Used to direct flow away from vulnerable areas and into stabilized traps, basins, or channels |
What is a hydrograph? | a plot of discharge versus time |
What is a hyetograph? | a plot of rainfall intensity versus time |
What is duration? | how long the storm event lasts |
What is rain intensity? | the rate of rainfall in in/hr |
What is return frequency? | The average time between events of the same volume and duration |
What is the exceedance probability? | The probability that a storm of specified volume and duration will be observed or exceeded in a given year |
What is the rational method? | Drainage basins <200 acres, computes peak discharge, not a full hydrograph. Q=CiA |
What is NRCS TR-55? | It is used to compute a full hydrograph, used for detention basin size estimation |
What is the runoff coefficient? | C is a factor between 0 and 1, indicating the fraction |
What is time of concentration? | The time it takes the most hydraulically remote point in a watershed to contribute runoff to the point or analysis |
What is the drainage area? | The total acreage draining to a point of interest is delineated by examining topography and the presence of manmade infrastructure |
What are the three types of flow regimes? | Overland Flow, Shallow Concentrated Flow, Channel Flow |
What is overland flow? | Occurs over planar surfaces. Usually observed at the headwater of a given watershed. Restricted to 100 to 300 feet. |
What is shallow concentrated flow? | Occurs after sheet flow begins to accumulate enough depth and velocity to begin creating small flow channels |
What is concentrated flow/channel flow? | Occurs when there is a well defined conveyance channel. Use manning's equation. |
What is a contour? | a line connecting points of equal elevation above some datum |
What is a contour interval? | The vertical elevation difference between adjacent contour lines |
What is a TIN? | Triangulated Irregular Network. Surface model comprised of triangles. |
What are breaklines? | Linear surface features depicting an abrupt change in elevation |
Who regulates drinking water systems? | The Virginia Department of Health |
What influences average daily consumption? | Land-use and population |
What dictates Overall peak system requirements? | Fire Flow |
What are minor losses in pipes? | losses from valves, hydrants |
What is the typically pressure range in pipes? | 20 psi to 80 psi |
What is the most common material used in water supply pipes | Ductile Iron Pipe |
What is the typical range in diameter for water supply pipes? | 6" to 20" |
What are the most common joints in a water supply system? | Push on and mechanical joints |
What are the three types of valves in a water supply system? | Butterfly & Gate, Blowoff, Air Release |
What are blowoff valves? | Used to dewater lines for repairs and maintenance. Located at low points and ends of branches |
What is an air release valve? | Located at the high point of a water line to dissociate the air from the water |
Who regulates sanitary sewer requirements? | Virginia Department of Environmental Quality |
What is a sewer? | A conduit for conveying wasterwater |
What is a lateral? | the conduit connecting an individual building to a main sewer |
How much of a sewerage is comprised of water? | 99% |
What parameters define sewerage strength? | Biological Oxygen Demand, Composition of Suspended Solids |
What is BOD? | Biological Oxygen Demand is the measure of the amount of organic matter present |
What makes up suspended solids? | 80% organic matter including fecal matter, washwater particulates, kitchen waste |
What dictates wastewater system design flows? | Population and land use |
What are the required separations from drinking water lines to wastewater lines? | 10' horizontal and 18" vertical |
What is the most common sewer pipe SDR? | SDR-35 |
What is SDR? | The standard dimension ratio. Ratio of the external pipe diameter to wall thickness |
What is the most common material for waste water pipes? | PVC Pipe |
What is a manhole? | Provides an access point for inspection of the sewer system |
Where must a manhole be placed? | Terminal end of a line, every change in alignment, change in diameter, junctions |
What is the minimum flow velocity in a wastewater pipe? | 2 fps to prevent deposition |
What is the minimum pipe diameter for wasterwater pipes? | 8" but can less when fewer than 6 lots are served on a cul de sac. |