Fluvial Flashcards
What is the difference between geomorphology and hydrology?
Geomorphology is the science of how earth processes shape the landscape. Hydrology is the science of the distribution and movement of water.
What are some of the differences between headwater channels and lowland channels?
Headwater:
Channel - Bedrock = no movement of substrate
Drainage - subsurface and overland flow
Sediment transfer - steep slopes = mass movement which gives a variety of different sized materials.
Sediment size - mixed but generally larger
Water velocity = Slower
Regulations for development - less stringent
Landforms: Fans, nick points.
lowland: channels - Alluvial Drainage - channelled surface flow sediment transfer - more gentle slopes = fluvial Sediment size - sorted smaller Water velocity = higher more stringent regulations for development Landforms: Deltas and terraces.
How can looking at the sediment size and variability give an indication of the dominant sediment transport process?
Mixed = hill slope mass movement dominated
Sorted = fluvial
What are the 3 erosion processes in bedrock channels? (HAC)
Chemical weathering
- Solution and other chemical processes
Abrasion - Physical action of sediment moving over bedrock. Main one.
Hydraulic Action - Flowing water pushed and pulls on joints in bedrock blocks.
What are some common restoration problems that occur in bedrock channels?
1) In filled channels - typically happens when you divert streams.
2) Diversions of water either in or out. Leads to changed in channel bed material.
3) Chemical weathering leading to water quality issues
What are the two common ways that sediments enter a stream? What influences the transport of sediment?
Mass movement
Erosion - Sheet, rill, gully etc
Sediment size
Water discharge
Solubility of material
What are the definitions of Load and Capacity?
What are the 3 types of sediment transport?
What is sediment load?
Load is the amount of sediment that is moved at a given discharge.
1) Dissolved - occurs mostly in groundwater flow 60-80% of total load
2) Suspended - fine clays and silt. 90% of sediment load.
3) Bedload - 10% of sediment load.
Sediment load is suspended and bedload.
Capacity is the maximum amount of sediment that can be moved at a given discharge.
Why does discharge increase suspended load? Why does sediment peak before flow?
1) More water
2) Increased velocity
3) Increased turbulence intensity
4) Stored sediments on side of channel which are only picked up during high flow events.
Describe typical Alluvial and floodplain physical characteristics. How are floodplains created?
Broad, flat, composed of fine textured sediments, meanders, oxbow lakes, upper surface of floodplain is at peak water flow levels. Floods every 1-2 years. Implications for restoration. Natural levees.
Floodplains are created through the deposition of sediments on the inside of a meandering river. Not by flooding.
What are the 3 general channel patterns observed?
1) Straight - rare. Develop along tectonic or lithological boundaries. Stable channel with vertical banks. Little sediment transport.
2) Meandering - most common. Constantly erode and deposit material. Change channel coarse gradually.
3) Braided - high sediment load, floodplain occupied by channels, usually coarse sand and gravel.
What causes river incision?
Tectonic uplift
What are the main physical channel characteristics influenced by Stream Profile? What happens to these characteristics as you transition from headwaters to lowland channels?
Bed material - decreases Channel gradient - decreases Stream discharge - increases Stored alluvium - increases Channel width - increases Channel depth - increases Mean flow velocity - increases
What are the main controls of the profile? Think of waterfall creation or nick point.
What parameter do these factors influence?
Lithology
Tectonics
Flow discharge
Grain size
Base level - the theoretical level to which stream erosion is limited.
How are terraces formed?
Tectonics, bedrock, climate change, variations in base level, variations in flood magnitude
