NAT_RESOU Alluvial Channel Design and Stream Restoration Study Notes

Introduction to the topic of alluvial channel design as described in the United States Army Corps engineer's National Engineering Handbook.
Focus on understanding the distinctions between alluvial and colluvial channels.

Alluvial channel: A channel found in a valley characterized by a flatter stream.
- Typically observed in regions such as Alabama where large rocky or steep mountain landscapes are absent.
Colluvial channels: Not explicitly defined in the transcript, but generally refer to channels formed by sediment accumulation at the base of steep slopes.

Clarification that the materials discussed are published by the United States Department of Agriculture, specifically the Natural Resources Conservation Service, focusing on stream restoration design nationwide.

Understanding the functional processes of streams and methodologies for assessing those functions and processes.
- Emphasis on three critical roles of streams: transporting water, transporting sediment, and providing habitat/ecosystem diversity.

Discussion on the watershed and the interconnectedness of the water cycle.
- Emphasis on runoff as it pertains to streams.

Transporting Water: Streams are responsible for moving water from one point to another, contributing to the hydrological cycle.
Transporting Sediment: As water flows, it carries sediments eroded from the landscape, which is essential for various ecological processes.
Providing Ecosystem or Habitat: Streams offer diverse habitats for numerous animal species and contribute to the overall ecological balance of their surroundings.

Reference to geological processes:
- The ongoing effects of plate tectonics which uplift the earth and lead to erosion by water and streams.
- The East Coast mountains are noted as being ancient and having eroded over millions of years, with streams facilitating sediment transport from mountains to oceans.

Discussion of the causes of stream instability linked to human activities:
- Urbanization alters the landscape, impacting streams significantly.
Introduction to the field of stream restoration, a scientific and engineering discipline focused on correcting human-induced stream degradation.

Urbanization leads to alterations in land use that affect stream behaviors:
- Specific changes include:
1. Increased Runoff: Urban areas create impermeable surfaces, leading to greater volumes of water flow into streams.
2. Increased Peak Discharge: This denotes a rise in the maximum flow rate, resulting in more significant stream power.
Natural processes are disrupted leading to:
- Erosion of banks: The structural stability of banks is compromised due to increased stream power; they were initially not designed to handle urban peak discharges.
- Channel Incision: The erosive forces deepen the stream channel, leading to a phenomenon where the channel gets structurally altered and deeper over time.

Explanation of how streams are naturally designed to be connected to their floodplains:
- During significant events like a 25-year storm, water flows out of the channel into the floodplain. This process is biologically and hydrologically beneficial, allowing the water to disperse and slow down.
- However, if erosion and channel incision take place, the water is trapped within the channel rather than spilling into the floodplain, leading to increased erosion.

The cyclical nature of erosion and sediment transport underlines the importance of understanding stream dynamics to restore and maintain healthy stream ecosystems.