Stream - a body of water flowing downslope in a clearly defined natural passageway (a Channel)
 
 
 
 

River Systems ( or  Drainage Basins ) consist of
- a main channel and all streams that flow into it (tributaries).
 

 Water in the stream comes from Runoff and from Groundwater Discharge (opposite of infiltration)
 
 
 
 
 
 
 
 
 

- some Infiltrates and discharges into stream as GW.
- some flows overland and into stream as Runoff.

Spring - water flowing at surface from groundwater coming up.

Question: Why does the Kentucky River still flow even when it hasn't rained for a month?
 

Base Flow - low level of flow in streams between rainfall events due to slow discharge from GW.

- Rivers, Creeks, Cricks, Rivulets, Trickles
 
 

 Types of Material (Load) Carried by Streams:
1) Bed Load - particles moving along the bottom (bed) of the stream.  Sand, gravel, boulders, logs, dead bodies, etc.
 

- Smaller particles (sand) bounce along int the stream, larger particles (boulders) roll along.

2) Suspended Load - small particles too light to be deposited, carried along with the flow.  Clay particles and silt mostly.
 

3) Dissolved Load - ions in solution.  Varies from a few percent to as much as 50% of the total load.
- Where do the ions come from?
 

- Does a stream fed by groundwater or runoff have greater dissolved load?
 

- Mississippi: 750 mm tons/year: 500 mm uspended, 50 mm Bedload, 200 mm Dissolved load.
Stream Channel Types - Based on sinuosity (ratio of stream-length/straight-line-distance).
 
 
 
 
 

- Straight Streams: v. low sinuosity, highest gradient - carries much bedload.
 
 

- Braided Streams:  low sinuosity, intermediate gradient - carries much bedload, deposited in streambed during low flow (as “bars”) - bars break the stream up into smaller channels.
 
 

- Meandering Streams:  highly sinuous, lowest gradient - carries much suspended sediment.

 How do streams meander?  Erosion on outside of meanders (faster velocity, more erosive), and Deposition on inside of meander (point bars).
 
 
 
 
 

Stream Deposits: 
- Bars - bedload deposits - usually sandy or gravelly
 
 

- Levees and floodplains - suspended load deposits, usually fine-grained
 
 

- Terraces - abandoned floodplains at higher elevations than the present
 
 
 

Alluvial Fans - fan-shaped deposits formed where steep mountain streams hit a flat plain, dropping sediment
 
 

Deltas - river systems dumping into standing bodies of water
 
 

Flood - when a river's level exceeds the capacity of the channel.
- accompanied by more and faster water, more sediment, more strength (erosion!)
 

- Hundred Year Flood - level of a flood that can be expected to occur once/century.  May occur twice in a row.
 

 Case Study:  Add a dam to a happy river. (Nile River, Aswan Dam, Lake Nasser, Egypt)
 
 
 
 
 
 

- deposition at the reservoir head - fills up the reservoir.

- erosion below the dam - 500 bridges have washed out since 1953.  River is WIDER, FASTER, MEANDERING LIKE CRAZY.
Why?
 

- erosion of the Nile delta in the Mediterranean - little new sediment into system.

- no nutrients being added to the agricultural land of the delta, nor to the Mediterranean sea
- artificial fertilizer needed, fisheries are dying.