Unit 3: Rivers and Streams

Lotic Systems

Incredibly diverse, flowing water; heavily impacted by humans. 

4 dimensions of lotic systems…

Longitudinal, lateral, vertical, time. 

Longitudinal

Up/down stream

Pool

Deep/slow moving; weak currrent.

Runs/Glides

Smooth surface, fast-moving.

Riffles 

Shallow, turbulent, fast-moving. 

Rapids

Moderately steep, coarse substrates, fast moving.

Latteral

Across stream or river; left and right.

Wetted Channel

Contains water even during low flow. 

Active Channel

Actively modified by average stream discharges.

Riparian Zone

Transition between aquatic environment and upland terrestrial environment.

Floodplain 

Fluvial surface created by infrequent floods; humans have made floods more devastating.

Vertical

Up and down; top of water to bed.

Water Column

Water surface to benthic zone. 

Benthic Zone

The bottom.

Hyporheic Zone

Transition between surface water flow and the groundwater.

Phreatic Zone 

Below the hyporheic zone; contains groundwater. 

Time

Rivers vary across time and space, resulting in constant changes in shape, size, and content of the river; mutual interdependence between the river and the land.

Stream Types…

Depend on climate, closely related to precipitation and evaporation times.

Perennial/Permanent

Flow year round. 

Intermittent/Periodic

Flow most of the year.

Ephemeral/Episodic

Flow only after rainfall events.

Watersheds 

An area of land that intercepts and drains precipitation through a particular river system or group of river systems. 

Stream Order

Method of ordering the hierarchy of natural channels; 1st: nothing feeds into it. 2nd: 2 make one; etc.

Autochthonous

Organic matter originates within the stream.

Allochthonous

Organic matter originates outside of the stream. 

Types of organic matter…

Coarse, Fine, and Disolved.

Upper Reaches (Abiotic)

1st to 3rd order; strong influence of riparian vegetation; more respiration; dominated by allochthonous.

Upper Reaches (Biotic) 

Shredders and Collectors dominant invertebrates; fish require high O2 and low temps. 

Middle Reaches (Abiotic)

4th to 6th order, CPOM breaks down into FPOM; lots of algae and photosynthesis/high production; dominated by autochthonous.

Middle Reaches (Biotic)

Collectors and grazers are dominant invertebrate; fish tolerate higher temps and lower O2.

Lower Reaches (Abiotic) 

7th to 12th order; FROM dominates; turbidity 

Lower Reaches (Biotic)

Similar to lakes; higher planktonic organisms; dominant invertebrates are collectors; fish like higher temp and lower oxygen; plankton-feeding fish.

What is the “River Continuum Concept”

A model that predicts the characteristic changes from upstream to downstream; incorporates connections between watersheds, floodplains, and streams.

What is the human influence on floods? 

Rapid runoff into channelized streams increase flood frequency and enhance downstream peaks in flood hydrography. 

Impact of dams…

Modifies flow regime.

Overland Flow (Surface runoff)

Water running over land and directly into stream channel; precipitation rate exceeds soil infiltration rate;

What impacts overland flow?

When soils are saturated or have low permeability; strongly influenced by landform and land use.

Hydrograph

Plot of discharge vs. time; shows time it takes to rise from baseflow to maximum discharge to baseflow conditions.

What impacts hydrographs? 

Soil permeability, basin size and topography, forest cover, wetland storage, impervious surface. 

Hydrograph patterns…

High in early spring and fall; low in summer; rainfall causes spiky graph; smowmelt patterns cause smooth graph.

Flooding

Predictable and necessary occurrences; water will move to lowest point possible in urban settings.