Stormwater - General Flashcards
What is the hydrologic cycle?
the process of the earth’s water continuously moving and changing phases (between liquid, vapor, and ice) over millions of years.
(Module 2 / Page 4)
What percent of water on earth is “circulating in inland waterways, in the atmosphere or soil, or within organisms”?
Only 0.4%
94% of water is chemically bound in rocks. Of the remaining 6%, 97% of that water is in the oceans. Of the remaining 2.5%, 69.5% is in glaciers or permafrost, and 30% is in aquifers
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What is Stormwater Runoff?
Rain or snow that does not soak into the ground and flows overland to conveyance systems (natural or man-made)
(Module 2 / Page 3)
List some characteristics that influence stormwater discharge quantity and quality.
- Soil characteristics, topography, vegetation
- Weather patterns (rainfall intensity, frequency, duration)
- Channel lengths (long meandering vs. short straight)
- Channel characteristics (roughness, slope)
- Hydraulic Structrures, BMPs
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What negative impacts are associated with removal of vegetation with regards to stormwater?
Vegetation intercepts, slows, and returns rainfall to the air through evaporation and transpiration
(Module 2 / Page 9)
What negative impacts are associated with grading for development with regards to stormwater?
Grading flatten hilly terrain and fills in natural depressions that would normally slow and provide temporary storage for rainfall. Also, the remaining subsoil is compacted reducing the amount of infiltration.
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When runoff increases due the addition of impervious surfaces, in general what three things decrease”?
- Evapotranspiration
- Deep Infiltration
- Shallow Infiltration
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What are gutters, storm sewers, and smooth-lined channels designed to do?
Quickly carry runoff to rivers and streams
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What is time of concentration?
the time needed for water to flow from the most remote point in a watershed to the watershed outlet
What changes does land development have on stream hydrology?
- More runoff volume
- Higher Peak Discharge
- More Rapid Peak Discharge
- Lower Baseflow
(Module 2 / Page 12)
What percentage of streams and rivers in the United States in 2010 have seen significant changes in the amount of water flowing?
nearly 90% based on a study by the US Geological Survey.
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In general, what climate changes are occurring?
Temperatures are increasing and global precipitation regimes are shifting towards an increase in more intense rainfall events.
(Module 2 / Page 14)
Why would climate change cause more intense rainfall events?
A warmer atmosphere is capable of holding more water and that means more water would accumulate between rainfall events. When it does rain there is a greater likelihood of a heavy downpour.
(Module 2 / Page 14)
What are the two sources of water for streams?
- stormwater from overland flow after rain events
- baseflow supplied by groundwater
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What type of storm events are the primary channel forming event in streams and rivers?
-smaller bankfull and near bankfull events
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What effect will climate change and larger storm events have on existing best management practices?
The existing BMPs may prove to be undersized for the larger storms.
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What is Urban Stream Syndrome?
the consistently observed degraded ecological condition of streams draining urban areas.
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What are characteristics or urban streams that exhibit Urban Stream System?
- Increased flash flooding
- Elevated nutrient and pollutant levels
- Altered stream morphology
- Sedimentation from eroded stream banks
- Loss of biological diversity
(Module 2 / Page 22)
How do plant root systems relate to infiltration?
Root systems of plants provide pathways for downward movement of water into soil
(Module 2 / Page 25)
When water infiltrates into the soil what are the destinations of vertical flow and lateral flow?
- Vertical flow reaches the ground water table or aquifer
- Later flow often emerges as springs or seeps and provides base flow for streams)
(Module 2 / Page 25)
What is the difference between the hydrologic cycle in summer and winter?
Less evapotranspiration in the winter and more infiltration in the summer.
- summer, trees can transpire most of the precipitation that falls during rain showers.
- winter, more precipitation infiltrates and moves through the root zone and the groundwater level rises.
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What is the largest crop grown in the Chesapeake Bay Watershed? What percentage of the watershed is covered by this crop?
The most prevalent crop is “turf grass” and it covers 9.5% of the watershed
(Module 2 / Page 26)
What two things determine soil permeability?
- Porosity
- Pore interconnectedness
(Module 2 / Page 28)
What is the definition of Porosity?
The proportion of total volume occupied by pores or voids
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When less infiltration leads to reduced stream base flow, which areas show the most profound changes?
Wetlands and headwaters
-the reduced flow can stress or even eliminate the aquatic community
(Module 2 / Page 33)
What amount of impervious cover in a watershed causes ecological stresses to become apparent? What type of land use would exceed this amount?
Approximately 10 to 25 %
Typically low density residential has 20-40% impervious cover and would exceed this amount
(Module 2 / Page 34)
What is capable of negatively affecting stream biota (flora and fauna) even more than pollution?
-Altered stream flow
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What storm does Virginia (as well as most other states) consider to be the average “channel forming” storm?
The 1-year 24-hour storm event
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What storm generally forms an urban stream channel and what storm generally forms a rural stream channel?
The 0.9-year storm generally forms urban stream channels and the 1.5-year to 1.7-year storm generally forms rural areas.
(Module 2 / Page 38)
What is an “I-D-F” curve?
Intensity, Duration, Frequency curve
term used in (Module 2 / Page 39)
What is a stream’s “morphology”?
physical shape and character
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What are high-velocity bank-full flows capable of if they last long enough or occur often enough?
High-velocity flows can generate enough energy to scour soil from stream banks and transport sediment and rocks from the stream bottom.
(Module 2 / Page 40)
What occurs during larger flood events compared to bank-full flows?
- The flow spreads out
- Water velocity reduces
- Less impact on the shape of the stream
(Module 2 / Pages 40-41)
What is a long-term effect of increased occurrence of high-velocity bank-full flows in streams?
-Stream banks will gradually be undercut and slump into the channel and expose trees at the roots, making them more likely to be uprooted during major storms, further weakening bank structure
(Module 2 / Page 41)
What might be a downside of using a detention basin to hold water and prevent flooding?
Water will typically be released from detention basins at a rate that mimics bank-full flow, causing more erosion. Duration of erosive flows last longer and the stream bed and banks stay wet making them more susceptible to erosion
(Module 2 / Page 42)
Where is channel deterioration often most pronounced?
Downstream of detention basins or where similar stormwater management practices are placed as a result of land development
(Module 2 / Page 43)
What is a “riffle”?
The sections of a stream with shallower, faster flowing water. Also called “shoals”
(Module 2 / Page 46)
What is the importance of the “pool-riffle” structure of a stream?
Pools and riffles provide valuable varied aquatic habitat for fish and aquatic insects.
(Module 2 / Page 46)
List four reasons why stream temperature could increase in a more urban area as opposed to a forested area?
- runoff from warm impervious areas
- storage in impoundments
- loss of shading are trees topple over/are removed
- less water -> shallower channels -> warmer temps
(Module 2 / Page 47)
Why can increased stream temperatures be negative?
- Dissolved Oxygen levels are reduced and this disrupts the food chain
- certain aquatic species can only survive within a narrow temperature range
(Module 2 / Page 47)
What is nonpoint source (NPS) pollution?
Stormwater runoff that flows across the land surface and is not concentrated in a defined channel or pipe.
(Module 2 / Page 49)
What does CSO stand for? What does it mean?
Combined Sewer Overflow
A CSO occurs in older cities where sewer infrastructure also carries storm-water. Storm water causes excessive flow to waste-water treatment plants which exceed holding and treatment capacity causing the discharge of untreated waste-water into waterways.
(Module 2 / Page 51)
What land use activities are referred to as storm-water “hot-spots”?
- Commercial parking lots
- Vehicle service and maintenance facilities
- Fuel Stations
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What does the term “first-flush” refer to?
The first 1/2 inch of runoff from impervious surfaces during the first half hour of a storm.
(Module 2/ Page 54)
Why might capturing the first-flush (a previous Virginia storm-water management practice) not be effective enough?
The first flush typically only causes 20% of the annual runoff pollution load
(Module 2 / Page 54)
Why can sediment be a pollutant of concern?
-sediment suspended in the water can impact submerged aquatic vegetation, fish habitat, and can suffocate bottom-dwelling organisms. It can also carry oils, gasoline, nutrients, metals, and pathogens into the water and reduce the capacity of reservoirs
(Module 2 / Page 55)
Why can organic substances like grass clippings, leaves, animal waste, and street litter be a pollutant of concern?
These substances lead to depleted dissolved oxygen levels, impairments, and even fish kills.
(Module 2 / Page 55)
List reasons why urban storm-water typically contains elevated concentration of nitrogen and phosphorus.
- Lawn fertilizers
- Detergents
- Animal Waste
- Organic Matter
- Sewer Overflows and leaks
- Improperly Installed or Failing Septic Systems
(Module 2 / Page 56)
What do elevated nutrient concentrations cause?
- A growth in algae and decomposition by organisms that use up a waterbody’s dissolved oxygen leading to poor conditions for most existing aquatic organisms.
(Module 2 / Page 56)
What are pathogens?
Bacteria, viruses, and other microbes that can cause disease in humans
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What are considered “trace metals” and what are the potential sources?
- METALS:Copper, lead, zinc, mercury, cadmium, chromium, nickel, aluminum
- SOURCES: Normal wear of brakes, linings, and tires, automobile emissions and fluid leaks, metal roofs, and pipes
(Module 2 / Page 61)
What is rainwater harvesting?
Recycling or reusing stormwater
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List some benefits of rainwater harvesting?
- Reduction in water consumption
- Less stormwater runoff needing treatment
- Reduce erosion potential and reduce non-point source pollution
(Module 2 / Page 73)
What are some home uses for rainwater harvesting?
- Toilet flushing
- Laundry
- Fill Swimming Pools
- Vehicle and home power-washing
- Water lawns/gardens
(Module 2 / Page 73)
