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Urbanwater > Effects Of Catchment Urbanisation > Flashcards

Effects Of Catchment Urbanisation Flashcards

1
Q

2 results of Catchment urbanization

A

Catchment imperviousness

Connection/drainage (dominated by extensive stormwater pipe net work)

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2
Q

Three features of peak discharge- average recurrence interval diagram
Imperviousness 20, 40, 60%

A
  1. Urbanization effect most significant for high-frequency events(ecology).
  2. 20% imperviousness sufficient to cause significant increase in frequency of bank full discharge.
  3. From Q5 to Q0.5 slope of flood frequency curve is flatter.
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3
Q

Drainage connection effects on catchment hydrology?

A

Increased hydraulic efficiency of drainage system accounts for between 80% and 90% of the increase in peak discharge.

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4
Q

Implications for receiving water?

A

Increase flow velocity and volume( habitat scour and erosion, reduced habitat diversity)
Sediment mobilization and deposition(habitat smothering, reduced habitat diversity)
Very efficient pollutant mobilization and transport

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5
Q

What effects urbanization has on direct habitat modification?

A

Streams channelized to increase hydraulic efficiency, thus increasing pollutant transport, scour and reducing diversity of habitat.

Loss of riparian zone values(shade, OM).

Isolation from floodplain.

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6
Q

Effects of 城市化 on stormwater pollution

A

Increased pollutant generation

Increased delivery efficiency

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7
Q

Types of pollutants

A

Sediments, organics( oxygen demand substances), nutrients, other contaminants, oil and grease, metals(copper, lead, zinc, etc), pathogens.

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8
Q

Urbanization impacts are exerted on?

A

Catchment hydrology
Water quality
Direct habitat modification( instream and riparian)

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9
Q

Gross pollutants and litter

A

Urban debris flushed from catchment
Visual impact, threat to aquatic ecosystem(physical impacts and contamination of water quality)
Public perceives it as major water quality issue. Reflect 公众对暴雨管理策略的感知

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10
Q

Gross pollutant impacts are?

A 
Aesthetic impacts, 
Aquatic habitat losses,
Marine debris impacts,
Clean-up costs,
Litter is one of many management issues.
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11
Q

Monitoring results of gross litter

A

Most litter from commercial areas
Highest concentrations early in the event
Highest loads during high discharge
Subsequent storms, in the same day, produce gross pollutant trends

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12
Q

What are the types of gross pollutant?

A

Vegetation-dominant; 75% of total gross pollutant load
The rest 25% is litter
Carries lower 两个magnitude nutrient load than found in urban stormwater, BOD 高

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13
Q

Causes of gross pollutant

A

Litter - dropping of rubbish, bin overflows (recycling), tip-escapes
Vegetation - deciduous trees, lawn clippings

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14
Q

What comprise sediment and Ss

A

Inorganic/organic materials

Erosion catchment or instream, related to I and v of flow
Construction activities
Catchment wash off of organic materials
Sewer overflow
Airborne particulate matter
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15
Q

Impacts of sediment and Ss

A

Saltation of waterways
Smothering of aquatic habitats, reduction in discharge capacity, turbidity( reduced light penetration and plant growth), transport of particulate-associated pollutants(phosphorus, metals)

Smaller particles-harder to remove

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16
Q

Concentration of sediment

A

Measure range for SS 0-30,000 mg/l
Event Mean Concentration 55-1000
Recommended EMC 140 (40-500)

17
Q

Nutrients sources

A 
Atmospheric deposition
Erosion
Septic tanks
Sewer overflow
Fertilizers
Kitchen wastes, detergents,
Nitrous oxide(vehicle emission, ash)
18
Q

Types of nutrients

A

Nitrogen ( nitrite, nitrate, ammonium, organic N)

Phosphorus -particulate and dissolved

19
Q

Impacts of nutrients

A

Wujibifan
Excess leads to eutrophication-excessive plant growth
Algae blooms- release of toxins, impacts on agriculture, reaction, fisheries.

20
Q

Micro-organisms involved in water quality influenced by stormwater?
Sources? Impacts?

A

Bacteria, viruses, fungi and Protozoa
Stormwater contains salmonella,
E. coli

Sources
Animal faeces, sewer overflows, ineffective septic systems, rural runoff.

Impacts - health, pathogens can cause hepatitis, gastroenteritis; closure of beaches, recreational waters.
- major public perception risk esp. For tourist areas

21
Q

Dissolved oxygen 2 features

A

Utilized by all organic material inn the process of biodegradation and chemical oxidation.
Important for aquatic organisms, fish etc

22
Q

BOD biochemical oxygen demand sources

A

Micro-organisms activities
Organic gross pollutants , leaf matter
Reduction of metals,
Microbial conversion of NH4 to NOx

23
Q

Impacts of BOD

A

Reduced DO levels- stress to aquatic community(cause death); release nutrients from sediment(desorption of phosphorus and metals from anaerobic sediment) ; contribution to eutrophication, algae bloom; offensive odors.

24
Q

Toxic organics and metals and their impacts

A

Excess of threshold will be toxic
Cd, Cr, Cu, Ni, Pb, Zn plus Hg, As

Impacts
Varied and complex-
interactions with water biophysical parameters( pH, temperature, redox potential)
Many metals found in particulate form ( transported with particles, not readily available for biological uptake )
Effects may be acute or chronic( bio accumulation , shellfish)
Cause of mutation which affect life cycle
Can influence other treatment process eg denitrification

25
Q

Oils and surfactants

A

Increase oxygen demand
Often toxic and cancerogenic
Affect respiration
Persistent and difficult to remove

Sources
Vehicle operation, cleaning, maintenance
Oil handling and disposal, road runoff, detergents

26
Q

What is the urban stream syndrome?

A 
Changed flow
Poor water quality
Simplified habitat
Reduced in-stream biodiversity
More algae growth
Less retention, more transport of pollutants
27
Q

Are impervious areas equal to each other? If not which is important.

A

No. What is important is the amount of impervious area directly connected to a stream.

28
Q

Effective imperviousness equation

A

EI = Total impervious area * connection %

Proportion of catchment which is impervious and directly connected to receiving water.

29
Q

How to break connection?

A

By retaining the first x mm of runoff.

  • permeable pavements.
  • rainwater tanks.
  • Swales.
  • ponds and storage tanks.
30
Q

Setting target for urban drainage

A

Environmental target, flow target, water quality target, concentration and loads

31
Q

Integrated targets for drainage

A 
Maintain pre-development ...
Runoff volume,
Runoff frequency,
Ratio of base flow
Pollutant concentration TSS, TP, TN, metals,
32
Q

impacts of urbanization

A 
Hydrology ( bigger floods, flashier) 
Water quality ( many types of pollutants, highly variable behavior)
Ecosystem health ( directly related to connected impervious area)

Target flow, water quality, ecosystem health

Urbanwater (5 decks)

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