Lecture 13 Flashcards
What is the hydrologic cycle?
Circulation of Earth’s water supply, powered by sun, precipitation, evaporation, infiltration, runoff, and transpiration.
What controls infiltration capacity?
- Intensity and duration of rainfall
- Prior wetted condition of soil
- Soil texture
- Slope of land
- Nature of vegetative cover
How does water flow transition in the hydrologic cycle?
Saturated soil leads to sheet flow (thin, unconfined water layer).
Sheet flow becomes rills, which form gullies.
Gullies evolve into streams with defined channels.
What are the basic components of a stream?
- Head: Source area
- Course: Stream path
- Mouth: Where the stream ends in a water body
- Reach: Stream segment
- Bed: Bottom of the stream
- Banks: Sides of the stream
- Floodplain: Area subject to flooding
- Longitudinal profile: Gradient shown in side view
What are the two types of water flow in streams?
- Laminar flow: Water molecules move in straight, parallel paths
- Turbulent flow: Water moves chaotically with whirlpool-like eddies (fast, rough channel).
What factors determine a stream’s ability to erode and transport sediment?
Gradient (vertical drop over distance)
Channel shape, size, and roughness
Discharge (volume of water moving per second)
How does gradient affect stream velocity?
The steeper the gradient, the more gravitational energy is available for stream flow = higher velocity.
What is discharge, and how does it change downstream?
- vol. moving / time (m³/sec).
- Change: Discharge, channel width, depth, stream velocity increases.
How does flow change between headwaters and downstream?
- Headwaters: Flow turbulent.
- Downstream: Flow smoother/faster.
What is turbulent flow, and where does it commonly occur?
Turbulent flow is erratic water movement with whirlpool-like eddies, typically forming rapids in steep or rough channels.
What are the characteristics of a stream’s channel that influence its flow?
Shape: Cross-sectional profile affects water contact with the channel.
Size: Larger channels reduce friction, allowing smoother flow.
Roughness: Irregular surfaces (boulders, debris) increase turbulence
What is a longitudinal profile, and what does it show?
A longitudinal profile is a side view of a stream that displays its gradient from the head (source) to the mouth
What factors lead to increased discharge in a stream?
Increased precipitation or melting snow.
Contributing tributaries joining the main stream.
Reduced infiltration due to saturated ground.
How do headwater streams differ from downstream sections in terms of flow characteristics?
Headwaters: Narrow, turbulent, steep gradient.
Downstream: Wider channels, smoother flow, gentler gradient
