Gg Power Point 13

Front 1

Running water in streams is among the most powerful erosional agents in Hawai‘i

Most major valleys were cut by streams

Back 1

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Front 2

Load

Back 2

is the actual material carried by a stream
a. Dissolved matter - from leaching out of soluble elements
b. Suspended – material in suspension
c. Bed load – material that rolls, slides, bounces along. Bed load is paramount in controlling the erosional power of streams

Front 3

Capacity

Back 3

refers to the total load a steam is able to carry; which depends on
a. Gradient
b. Velocity
c. Channel size and shape

Front 4

Streams are both depositional and erosional agents, depending on load vs. capacity.

Back 4

1.Streams can erode along one stretch and deposit along another, since gradient and channel shape/size vary along the stream's course.   
2. Streams can erode during periods of higher velocity or discharge (floods), and deposit during periods of lower velocity or discharge


Anything that alters the sediment load delivered to the channel, or that alters the stream's capacity to carry that load, will cause the stream to adjust its gradient or channel geometry (by erosion or deposition) to achieve a new equilibrium, a new balance between load and capacity

Front 5

Stream Load vs. Stream Capacity

Back 5

1. If capacity is less than load, the stream deposits part of it.  
2. If capacity exceeds load, the stream has excess energy (gravitational, potential energy) so it can erode more sediments

Front 6

Capacity varies with

Back 6

1. Gradient = elevation change over horizontal distance (slope). - Higher gradient = higher capacity
2. Velocity = rate of flow of water. Velocity varies with input (mainly rainfall). When streams flood, velocity and capacity increase dramatically
3. Channel size and shape

Front 7

Erosional power of streams

Back 7

Maximum discharge and velocity are associated with floods

More erosion can take place in a few hours of flooding than in decades of “normal” stream flow

Front 8

Hawaiian Stream Valleys
shapes and such

Back 8

1.V-shaped valleys, floored by alluvium

2.Amphitheater-headed valleys

3.Waterfalls

Front 9

Landscape evolution by coalescence of amphitheater-headed stream valleys

Back 9

Geomorphic development varies with age and location

Front 10

Waterfalls

Back 10

are the result of variable resistance to erosion

Most Hawaiian waterfalls occur at a resistant ledge (massive ‘a‘a lava flows, or intrusions)

With time, waterfalls migrate up-stream

Front 11

Stream development varies with rainfall and near surface permeability, which varies with age of the island.
- No permanent streams from Hilo to Pololū

Back 11

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