Transcript Chapter 2 Presentati..

The Natural Environment
The Hydrologic Cycle
Hydrologic Processes
Precipitation
Evapotranspiration
Overland Flow
Infiltration
Groundwater Flow
Hydrologic Budget
• Change in storage = inflow – outflow
• ∆S = P – R – G – E – T
– Where:
•
•
•
•
•
•
P = Precipitation
R = Surface Runoff
G = Groundwater
E = Evapotranspiration
T = Transpiration
∆S = Change in storage over specified time
Aral Sea
1989
2008
Watersheds
• Area of land which
drains to a single outlet
point
• Characterized by
– Size, slope, shape, soil
type, storage capacity,
land use, channel
morphology
• Basin
– Large watershed
– i.e. Mississippi river
basin
Hydrology and Infrastructure
• Design infrastructure to
withstand precipitation of
specific reoccurrence
interval
• 100yr = 1% chance
• 10yr = 10% chance
• Expense increases as you
design to a less frequent
return period
• Location specific IDF
curves relate rainfall
intensity and duration to
probability
Rivers and Infrastructure
• flood probabilities not directly related to storm
probabilities
– 100yr storm does not necessarily equate to 100yr
flood
• Floodplain
– The land along a stream or river that is inundated
when the stream overtops its banks
• FEMA determines 100yr floodplain and updates it
accordingly with increasing development
– More impermeable surfaces = more runoff
– Most building codes prohibit construction in the 100yr
floodplain
The Woodlands
•Designed to handle 100yr flood by not altering the
natural floodplain
• Soil
Geological Formations
– Uppermost layer of
unconsolidated material
that lies above the
uppermost layer of rock
(consolidated material)
• Soil type and location of
bedrock have huge
influence in
construction
– Borings used to design
building foundation
– Location of consolidated
material varies even over
a short distances
Vertisols and Houston
Groundwater
• Water which fills
pores and fractures
of unconsolidated
material
• Aquifer
– Geologic formation
that stores water
• Supply in jeopardy
as demand
increases
Aquifer
Source: National Groundwater Association
Porosity, Head and GW Flow Rates
Darcy’s Law (1856) relates change in head and hydraulic conductivity
to groundwater flow rates:
Q
dh
V   K
A
dL
dh/dL = change in head
K = hydraulic conductivity
= 10-2 cm/s (Sand)
= 10-4 cm/s (Silt)
= 10-7 cm/s (clay)
Seepage velocity (actual flow) is Darcy’s velocity divided by
the porosity of the groundwater medium:
Q
dh
Vs 
 K
nA
dL(n)
n = porosity
Porosity = vol void / total vol
Climate Change
Greenhouse Gases:
•Trap heat radiating outward from Earth
•Increase Earth’s temperature to support life
• 30oC cooler w/o
•Increasing concentrations amplify such warming
•Five main greenhouse gases:
•Water Vapor (H2O) .004 – 4% (40–40000ppm)
• Carbon Dioxide (CO2) .0391% (391ppm)
• Methane (CH4) .00017% (1.7ppm)
• Nitrous Oxide (N2O) .000033% (.33ppm)
• Ozone (O3) .000005%
IPCC and Climate Change
•Intergovernmental panel on
climate change
•International body for the
assessment of climate change
• Found that climate change
is most likely anthropogenic
•Kyoto protocol created as a
result
•Calls for 5% global reduction
in greenhouse gas emissions
•US assigned 7% reduction
•US has not signed
Kyoto Countries
Climate Change Consequences
• Increased drought and
water shortages
• Extinction
• Coral reef loss
• Alterations to carbon
cycle
• Loss of habitat
• Changes in locations of
agricultural regions
• Increased flooding
• Increased malnutrition
and disease
• Increased frequency and
severity of storms
Climate Change Consequences
Downtown Boston 100 year floodplains: current (solid)
After “high level” greenhouse gas emission scenario (dashed)
Dealing With Climate Change
Below: Global temperature
profile with different GHG
emission scenarios
Above: IPCC projected global
mean temperature change with
different emission scenarios
Engineering for Climate Change
• Problem:
– Predicting the extent of
climate change is
challenging
– Two options:
• 1. design for current
day conditions and
risk failure
• 2. design for worst
case scenario and risk
extra expenditure
• Solution:
– Adaptive management
• Incorporate future
uncertainties into
design plan so that if
changes do occur,
strategy is in place to
handle them
• E.g. Design levee to
be readily modified
to accommodate
seawater increase
Conclusion
• Infrastructure has
impact on the
environment and
the environment
impacts
infrastructure
• Relationship must
be understood for
future sustainable
development