1. A stream is a body of water that flows down-slope within a restricted passageway (channel) while transporting detrital particles and dissolved substances.

2. The sediment and dissolved matter transported by the stream is called its load.

3. The quantity of water passing a fixed point on the stream bank within a given interval of time is a measure of the stream's discharge.

(a) carry most of the water that go from land to sea

(b) transport billions of tons of sediment to oceans each year

(c) carry small amounts of soluble salts to the sea

(d) shape the surface of the earth

(a) 59% evaporates or is taken up by plants

(b) 1% infiltrates the ground

(c) 40% is runoff (overland flow + stream flow)

1. The size and shape of a channel cross section reflect the stream’s gradient, surrounding rock-type and discharge (volume of water the stream carries).

2. In general, small streams may be as deep as as they are wide whereas large streams usually have widths many times greater than their depths.

3. The gradient of a stream is a measure of the vertical distance that a stream channel falls between two points along its course.

gradient = vertical (altitude) change in channel (m) / distance between two points (km).

gradient = (h₁ – h₂) / l

h₁ = altitude of the stream at point #1

h₂ = altitude of the stream at point #2

l = horizontal distance between points #1 and #2

4. The average gradient of a river generally decreases downstream.

(a) gradient

(b) channel cross-sectional area (m²)

(c) average velocity of water flow (m/sec)

(d) discharge (m³/sec)

(e) load (kg/m³)

Q = A * V

Q = Discharge (m³/s)

A = Cross section area of channel (width * average depth) expressed as m²

V = Average velocity (m/s)

2. If discharge increases, then one or more of the factors on the right side of the equation must also change.

3. Figure 13.21: The discharge of a stream increases downstream as new tributaries join the main stream. This increase in discharge downstream is accompanied by increases in the width of the channel and stream velocity. The gradient of the stream, however, decreases downstream.

(a) discharge increases

(b) channel cross sectional area increases

(c) velocity increases slightly

1. Floods occur when a stream's discharge exceeds the capacity of the channel, causing the stream to overflow its banks.

2. Figure 13.15: A flood-frequency curve is used to predict future floods.

1. Straight Channel segments are rare and generally occur along brief stretches between channel curves. Highest water velocity is usually found near the surface in mid-channel.

2. Figure 13.11: Meandering Channels have many bends.

3. Figure 13.10: Wherever the water rounds a bend in a meandering channel, the highest velocity swings towards the outside of the channel. A decrease in water velocity within the inside of the channel bend results in sediments being deposited to form point bars. Meandering channels form where the gradients are low and the load is generally fine-grained.

4. Figure 13.10: Formation of an oxbow lake.

5. Figure 13.12: Water in Braided Channels repeatedly divides and reunites as it flows through two or more adjacent but interconnected channels. The channels are separated from one another by bars or islands. Braided patterns develop in streams with highly variable discharge and a large load to transport. The coarsest sediment is deposited as bars.

1. Figure 13.17: The limiting level below which a stream cannot erode the land is called the base level of the stream. The base level for most streams is global sea level.

(a) raindrops hitting the ground

(b) sheet erosion (overland flow during heavy rains)

(c) stream action

1. Figure 13.1a: Low velocity, parallel flow is called laminar flow and is usually confined along the bed and walls of the channel.

2. Figure 13.1b: Turbulent flow within a stream is erratic and complex and is typical of fast-moving waters.

1. Figure 13.2: The bed load consists of coarser particles that move (by rolling and sliding) along the streambed.

2. Figure 13.3: Saltation involves the progressive forward movement of a particle in a series of short, intermittent steps.

3. Figure 13.2: Finer particles are carried as the suspended load. Suspended load can be dropped to form alluvium.

4. Dissolved Load consists of dissolved chemical substances such as HCO^3-, Ca²⁺, SO₄²⁺, Cl^-, K⁺, Mg²⁺, Ca²⁺, etc.

5. Figure 13.4: For grains coarser than 2 mm in diameter (medium sand), a steady increase of water velocity is required to erode and transport larger and larger grains. Sediments less than 2mm, however, become more cohesive as grain sizes become smaller. As a result, the finer the cohesive particles, the greater the velocity required to erode them.

1.The grain sizes of sediment generally decrease downstream due to sorting and abrasion of the bed load

2. The composition of the steam load also changes downstream as sediments of different compositions are introduced.

3. The amount of sediment eroded from the land and carried by the stream is referred to as the sediment yield of the stream. Sediment yield is related to:

(a) Topography: High sediment yields occur in drainage basins near steep mountains.

(b) Climate: Highest yields are in tropical areas where ppt and chemical weathering are high. Vegetation, however, acts to reduce sediment yield. In temperate regions of extensive vegetation, erosion rates are lower. In drier regions with little vegetation, land is more vulnerable to erosion but precipitation. is less abundant.

(c) Rock Type. Clastic sedimentary rocks more easily eroded and therefore yield more sediment than hard igneous and metamorphic rocks.

(d) Structural factors such as jointing or fracturing which would make rocks more susceptible to erosion and thus increase sediment yield.

(e) Human activity such as clearing of forests, land cultivation, damming of streams, etc. affect sediment yields. The initial increase in sediment yields caused by land clearing could be reduced by subsequent construction of buildings, sidewalks, roads, etc.

1. The main features of a stream valley are:

(a) Figure 13.20a: Floodplain

(b) Figure 13.13: Natural Levees (built only during floods)

(c) Figure 13.20b: Terraces that mark former flood plains

1. Figure 13.21: Streams are generally divided by topographic rises that form a divide, a ridge of high ground along which all rainfall is shed as runoff into the streams.

2. Figure 13.21: All the divides that separate a stream and its tributaries from their neighbors define its drainage basin.

3. The size of drainage basins can range from small areas such as a ravine to large regions covering several states (Figure 13.22).

4. The pattern of connection among tributaries and the main stream define the drainage network. There are several types of drainage networks.

(a) Figure 13.23a: Dendritic drainage is characterized by a branching pattern which is characteristic of most streams and rivers.

(b) Figure 13.23b: Rectangular drainage is characterized by straight segments of streams taking on perpendicular directions and usually occurs in areas riddled with joints and fractures.

(c) Figure 13.23c: Trellis drainage forms when tributaries lie in the parallel valleys of steeply folded terrain.

(d) Figure 13.23d: Radial drainage occurs when streams flow in a radial pattern away from a central high point such as a dome or volcano.

1. Figure 13.19: In mountainous areas, a stream may deposit an alluvial fan when the channel undergoes a sudden decrease in slope (hence velocity).

1. Deltas form when a stream flows into a body of standing water such as a lake or ocean.

2. Figure 13.27: The main channel divides into distributaries.

3. Figure 13.28: The main stream channel can shift position over time to form a series of coalescing sub-deltas.

4. Some deltas have a triangular shape (e.g. Nile Delta).

5. Figure 13.26: The Mississippi Delta is an example of a bird-foot delta.