The Natural Environment

The Hydrologic Cycle

Hydrologic Processes

Precipitation Evapotranspiration Infiltration

Overland Flow 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 Sea1989 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

Geological Formations• Soil

– 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 RatesDarcy’s Law (1856) relates change in head and hydraulic conductivity to groundwater flow rates:

dLdhK

AQV

Seepage velocity (actual flow) is Darcy’s velocity divided by the porosity of the groundwater medium:

)(ndLdhK

nAQVs n = porosity

Porosity = vol void / total vol

dh/dL = change in headK = hydraulic conductivity = 10-2 cm/s (Sand) = 10-4 cm/s (Silt) = 10-7 cm/s (clay)

Climate ChangeGreenhouse 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

Above: IPCC projected global mean temperature change with different emission scenarios

Below: Global temperature profile with different GHG 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