Strom: Storm Water Management Questions & Answers 100% Correct!!
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Strom: Storm Water Management
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Strom: Storm Water Management
What is the primary consequence of surface changes? - ANSWERdeveloped 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 stor...
Strom: Storm Water Management
Questions & Answers 100% Correct!!
What is the primary consequence of surface changes? - ANSWERdeveloped 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? - ANSWER- site specific
- region specific
- climate specific
Define subsurface runoff - ANSWERis 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? - ANSWERFor 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? - ANSWER-
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? - ANSWER- 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? - ANSWER- 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? - ANSWERaquatic, 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? - ANSWER- 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.
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