Rivers and StreamsRivers and Streams

The Hydrologic Cycle

Rivers and StreamsRivers and Streams

Drainage basin or watershed

Mill Creek Drainage BasinA River Drainage BasinA River Drainage Basin

Mill Creek Drainage BasinWalla Walla River Drainage BasinWalla Walla River Drainage Basin

FlowFlow

FlowFlow

Equilibrium and the longitudinal Equilibrium and the longitudinal profileprofile

GradientGradient

VelocityVelocity

DischargeDischarge Q = V x A ftQ = V x A ft33/sec (cfs) or m/sec (cfs) or m33/sec (cms)/sec (cms)

V = velocity V = velocity

A = Cross-sectional area = Width x mean depthA = Cross-sectional area = Width x mean depth

Base levelBase level (ultimate and local) (ultimate and local)GradientGradient

Load Load

Velocity VariationVelocity Variation

Variations Variations with with

Discharge Discharge

LoadLoad

Load:Load: Bed loadBed load (rolling, saltation) (rolling, saltation) Suspended load:Suspended load: silt and clay carried in suspension silt and clay carried in suspension

Dissolved load:Dissolved load: ions in solution ions in solution

HCOHCO33-- SO SO44

2-2- Ca Ca2+2+ Na Na++ Mg Mg2+2+ typically typically 90% of 90% of

dissolveddissolved

Competence:Competence: the amount of load that a particular stream the amount of load that a particular stream can carrycan carry

Load: Suspended LoadLoad: Suspended Load

Load: Bed-loadLoad: Bed-load

200

400

600

800

1000

1200

1400

1600

1800

2000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Maximum

Mean

Hydrograph for Mill Creek at Walla WallaAverages for 1942-1990

Dis

char

ge (

cfs)

Dis

char

ge (

cfs)

The Graded StreamThe Graded StreamThe Longitudinal ProfileThe Longitudinal Profile

Braided/MeanderingBraided/Meandering

Braided/MeanderingBraided/Meandering

Velocity VariationVelocity Variation

Meandering and FloodplainsMeandering and Floodplains

Point Bar – Cut BankPoint Bar – Cut Bank

Point Bar – Cut BankPoint Bar – Cut Bank

Point Bar – Cut BankPoint Bar – Cut Bank

Point Bar – Cut BankPoint Bar – Cut Bank

Meandering Meandering and and

FloodplainsFloodplains

Meandering and FloodplainsMeandering and Floodplains

Meandering and FloodplainsMeandering and Floodplains

Meandering and FloodplainsMeandering and Floodplains

Meandering and FloodplainsMeandering and Floodplains

Meandering and FloodplainsMeandering and Floodplains

Meandering and FloodplainsMeandering and Floodplains

DeltasDeltas

DeltasDeltas

DeltasDeltas

DeltasDeltas

DeltasDeltas

Alluvial FansAlluvial Fans

Floodplain TerracesFloodplain Terraces

Floodplain TerracesFloodplain Terraces

Stream Piracy

FloodingFlooding is dependent upon is dependent upon precipitation in drainage basinprecipitation in drainage basin precipitation rate/infiltration rateprecipitation rate/infiltration rate topographytopography

Flood DischargeFlood Discharge = channel discharge when a = channel discharge when a river overflows its banksriver overflows its banks

Flood MagnitudeFlood Magnitude = discharge above flood = discharge above flood dischargedischarge

Flood StageFlood Stage = elevation of water surface for a = elevation of water surface for a high-water condition likely to high-water condition likely to damage damage

Thus depends on Thus depends on useuse of floodplain of floodplain

Mill Creek Flows

0

500

1000

1500

2000

2500

3000

3500

0 5 10 15

Day in Feb, 1996

Dis

char

ge

(cfs

)

Hydrograph for Mill Creek flood, Feb, 1996Hydrograph for Mill Creek flood, Feb, 1996Measured at KooskooskieMeasured at Kooskooskie

(max. was 6000 cfs at Walla Walla)(max. was 6000 cfs at Walla Walla)

Recurrence IntervalRecurrence Interval

as flood indicatoras flood indicator

Rec. Int. = (Y-1)/RRec. Int. = (Y-1)/R

Y = # of years for dataY = # of years for data

R = rank of floodR = rank of flood

Natural LeveeNatural Levee

Response to Flood Hazards Physical barriers

Levees Flood walls with huge steel gates around

towns Retention reservoirs Channelization to handle increase

discharge Storm channel system (LA)

Levees protect area behind until Levees protect area behind until flood becomes too greatflood becomes too great

failed leveefailed levee

working leveeworking levee

levee damming water levee damming water behindbehind it it

Floodwalls on Mississippi in St. Louis and New OrleansFloodwalls on Mississippi in St. Louis and New Orleans

Flood Hazard MappingFlood Hazard Mapping

Satellite images

Upper = normal flow 1988

Lower = 1993 flooding

Landscape Evolution