Class 2-physical impacts of urbanization on watersheds

Question 1

where/when was the 1st planned sewers developed?

Answer 1

-1370, Paris, drained into the Seine river

Question 2

Explain the early SWM measures

Answer 2

-ditches & pipes, didnt care about fast hot and dirty, just get it off the roads.

Question 3

explain the paradigm shift in SWM

Answer 3

• now we care more about water quality, and we do SWM from a watershed approach.
• care more about sustainability (i.e. Healthy Cities) and now seeing SW as a resource

Question 4

What is the purpose of the water balance? what is the water balance equation?

Answer 4

-water balance is to estimate how much water we are working with, to quantify movement of water in the land phase of water cycle.
Precipitation= evapotraspiration+streamflow+change in storage

Question 5

How is the urban hydrologic system different from the natural one?

Answer 5

• there is an internal system and an external system
• internal system depends on piped water supply, no storage, only inputs an outputs
• water from internal and external system both count as runoff, so we dont just plan for the stormwater, we have to take care of sanitary sewers too.

Question 6

how does changes in pipe with & shape affect the water in the pipe?

Answer 6

-we can make the rising limb of the hydrograph less steep b/c the water would be slower, but the volume doenst change so really the peak is just extended

Question 7

What is the time of concentration?

Answer 7

time req’d for water to flow from most remote point of an area to the outlet once the soil has become saturated and minor depressions filled (when no more room to store in the soil, all water will be runoff)

Question 8

What are some factors within a watershed that affect runoff, and how?

Answer 8

• size/shape of watershed (narrow=faster into the river)
• topography (slope)
• geology
• soil type (clay=high runoff, sand=low runoff)
• land use

Question 9

What is the difference between Total imperv area and effective imperv area?

Answer 9

TIA: sum of all imperv surfaces in watershed as a percentage
EIA: portion of TIA that is connected to a storm sewer network, the actual % of runoff

Question 10

what happens to the stream as % impervious cover increases?

Answer 10

• changes in flow increase
• physical changes to channels (widening, sediment, temperature)
• contamination of water
• biological integrity decreases.