Streams and Watersheds

Authors:Gene Surber, MSU ExtensionNatural Resources Specialist

Bob Ehrhart, Research Specialist,RWRP, Univ. of Montana

IntroductionRiparian AreasUplandsWatersheds

Importance of a Watershed

What happens in one part of the watershed – effects other partsRiparian areas – links between the uplands and the stream

Stream Classification1st order stream

starter stream

2nd order streamtwo or more 1st order

3rd order streamtwo or more 2nd order

Stream Classification, cont.

Perennial streamsIntermittent streamsEphemeral streams

Stream Classification, cont.

Gaining stream

Losing stream

Stream Classification, cont.

Channel Shape Method (Rosgen Classification)

SlopeSinuosityRatio (width to depth)EntrenchmentParticle size

Streams Reflect the Landscape

Steep, mountainous channelWide floodplain

Stream MechanicsStream hydrologyStream channels – “pipelines”

Average bankfull flowStable streams

Water/sediment IN = water/sediment OUT

Stream Mechanics, cont.“Out of Balance”

Water and sediment load changes

Stream Mechanics, cont.Energy = Mass x VelocityBiggest influence on a stream’s energy is speed

EnergyFriction slows waterSediment is depositedNo vegetation versus vegetated banks

Change is constantStreams are dynamicNatural versus man-made causes

StabilityDynamic UnstableStable streams change, but remain in equilibrium Unstable streams are “out of balance”

Nature has a different time scale

Stream InstabilityInstability:

Change in water flowElimination of streambank vegetationExcessive sediments

2 types:Lateral InstabilityVertical Instability

Stream Instability, cont.Vertical InstabilityDowncutting

More difficult to control than lateral cutting

Influences BOTH upstream & downstream

SummaryWhere we go from here…