Strom: Storm Water Management Exam
Questions Correct Answers Current
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What is the primary consequence of surface changes? - Answers -✔✔ developed sites
lose much of their natural storm water storage capacity. The loss of vegetation, organic
litter, and changes in surface characteristics, such as roughness and perviousness,
result in the rapid conversion of rainfall to storm water runoff.
All storm water management practices must be what (3) things? - Answers -✔✔ - site
specific
- region specific
- climate specific
Define subsurface runoff - Answers -✔✔ is storm water that infiltrates and moves
through the soil both horizontally and vertically. The rate of movement is influenced by
soil permeability and usually occurs at a much slower rate than surface runoff.
When does surface runoff occur? - Answers -✔✔ For impervious surfaces, runoff
occurs immediately. For pervious surfaces, the intensity of precipitation must exceed
the infiltration rate, that is, the surface must be saturated before runoff can occur.
What are the environmental impacts from changes in storm water drainage patterns? -
Answers -✔✔ - increased flood potential due to increases in peak flow rates
- decreased groundwater supply caused by reduced infiltration
- increased soil erosion and sedimentation brought about by greater runoff volumes and
velocities
- increased petrochemical pollution from street and highway runoff
- contamination of winter runoff by salt and sand in colder regions
What changes in stream hydrology can result from development? - Answers -✔✔ -
peak discharges, which can be as much as two to five times the predevelopment rate,
generally increase the frequency and severity of flooding
- higher velocities coupled with increased imperviousness may also result in reduced
stream flow during extended dry periods caused by reduced infiltration. Groundwater
that would normally be recharged during wet periods and released slowly from soil
during dry periods is lost as surface runoff
- stream geometry also changes. Streams are widened due to increased volume and
velocity, which results in increased stream bank erosion.
- Usually the stream bank is undercut, destabilizing vegetation and, in turn,
exacerbating the erosion problem. Eroded material is deposited in stream channels as
sediment, which reduces stream flow capacity.
, - Flood elevations are raised; as noted, this phenomenon increases the extent of the
area at risk of flood damage
Where do contaminants come from? - Answers -✔✔ - pollutants are accumulated on
paved surfaces and are flushed from these surfaces during a rainstorm
- contaminants may be released through corrosion, decay, oil and fuel leaks, leaching or
wearing away of construction materials and coatings, brake linings, tires, and catalytic
converters.
- developed areas, as well as agricultural areas, contribute herbicides, pesticides,
fertilizers, which stimulate algal growth and reduce the availability of oxygen in water
- fallen leaves and animal poops that would normally decompose in underdeveloped or
low-density settings are more easily washed from paved surfaces, further increasing
nutrient and bacteria levels in streams, ponds, and lakes
Changes in stream hydrology and geometry, combined with reduced water quality,
decrease the value of what? - Answers -✔✔ aquatic, stream bank, and floodplain
habitats. Not only are stream channels and flows altered and pollution levels raised, but
these conditions are further exacerbated by low summer flows and higher water
temperatures.
How was storm water managed in the past and how is it different now? - Answers -✔✔
- Historically, the primary concern in dealing with storm water runoff was to remove it as
quickly as possible. Traditionally, this was accomplished by conveying runoff by storm
sewers, swales, gutters, and channels to the nearest water body, usually a stream or
river.
- more recently storm water management practices have recognized the need for
controlling off-site impacts caused by increased runoff. The objectives of these revised
practices are twofold:
1. to reduce downstream flooding through the use of detention facilities that store and
release runoff at a controlled rate.
2. to reduce flooding damage by restricting floodplain development. Most legislation at
either the state or local level states that the peak rate of runoff after development cannot
exceed the rate prior to development.
In the most recent philosophy, in addition to the volume and rate of runoff. One primary
management objective is what? - Answers -✔✔ deal with runoff on-site rather than
transporting the problem off-site!
a basic objective of any site design should be to minimize hydrologic problems by
preserving and maintaining the predevelopment drainage patterns to the greatest extent
possible. Combined with appropriate management techniques, including detention,
storage, and infiltration.
How do you reduce drainage system costs? - Answers -✔✔ Proposed drainage system
costs can be reduced by minimizing the need for piping and drainage structures
