GEOG201 Lecture Notes - Lecture 1: Flood, Anabranch, Drainage Density
14 Dec 2016
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Fluvial Geomorphology Exam Notes
Diversity of Form (factors that influence river processes)
- Climate (amount of water or snow in a system)
- Geology (sediment within a system)
- Vegetation cover (how much water gets processed)
- Topography (flatter plane = less energy = less work)
- Land use (changes in how water flows effect features)
There are two types of rivers; Perennial were water is always present because the water
table is located above the base level of the river and Ephemeral where water is only present
after a big storm and the water table has risen.
Channel substrate
- Bedrock channels are flow over igneous rock, strongly influenced by sediment, erosion is
a result of chemistry from bedrock materials
- Alluvial channels are flows over previously deposited sediment on valley floor, picked up
sediment is moved down stream
Diversity of River Channel forms
- Straight channels are few in nature where channel migration is limited, they are
normally engineered. Normally low energy and high bank strength
- Meandering channels occur in both bedrock and alluvial channels (or ice). They have
moderate stream power and meanders scale to the channel size.
- Braided channels are wide and shallow, flow is divided and rejoins around sediment
bars. Therefore, they require an abundant supply of sediment and unstable banks.
- Anabranching channels are relatively rate flow is divided into two or more separate
channels, each channel is called an anabranch.
- Bedrock channels are strongly influenced by the nature of their substrate. Geological
controls affect flow processes and river morphology
Scales in fluvial geomorphology
- Important when studying interactions both spatial and temporal
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Fluvial System Variables
- Variables are quantities whose values change with time, they are both internal and
external
- Internal Variables
o Drainage density
o Hill slope angle
o Soil type
o Discharge
o Sediment yield
o Channel pattern and depth
- External Variables
o Climate/Climate change
o Tectonics
o Base level
o Human activity
Concept of thresholds
- Internal threshold are changes that are possible independently within the system
(meanders or oxbow formations)
- External threshold are changes that are external factors in a system (small rain
triggering land slide)
Concept of feedback
- Feedback is a change in one variable that leads to a change in one or more variable,
feedback and be positive or negative
Independent variables that control changes in channel dimension and shape
- Discharge (Q)
- Sediment load (Qs)
- Size of bed material (D)
- Bank material
- Bank and floodplain vegetation
- Valley slope (Sv)
Variables used to define equilibrium for channel geometry
- Average bankfull channel width (w)
- Average bankfull depth (d)
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- Maximum depth (dm)
- Velocity (V)
- Height difference of Bedforms
- Wavelength of Bedforms
- Slope (S)
- Meander arc length (z)
- Sinuosity (P)
Watersheds
- All points enclosed within an area from which rain falling at these points will contribute
water to the outlet
Water collection and discharge
Precipitation (P) = Evapotranspiration (ET) + Streamflow (Q) +/- Difference in storage
Biochemical and Nutrient cycle
- Carbon, phosphorus and nitrogen cycles are liked to hydrological process that influence
the availability of nutrients affecting species (abundance and diversity)
Drainage basin area
- Area depicts: hydrologic design, volume of water from rainfall (depth is represented
equally over the entire watershed). Rainfall and drainage area is a required variable in
order to calculate maximum runoff volume
Maximum runoff volume = rainfall depth * drainage area
Watershed shape
- Different geomorphologic indices are used for the analysis of watershed shape. The
Gavelius’s Ide (Kg) is the relation between the perimeter of the watershed and that of
a circle having a surface equal to that of a watershed
Kg = [P / 2*SQROOT(PIE*A)] = [0.28 P/SQROOT(A)]
A = Watershed area (unit = km2)
P = Watershed perimeter (unit = km)
- The more the shape of a watershed resembles a circle the smaller the ratio for example
a very linear shaped watershed would have a Kg of 1:6 where as an oval shaped
watershed would have a Kg of 1:2
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Document Summary
Diversity of form (factors that influence river processes) Land use (changes in how water flows effect features) Climate (amount of water or snow in a system) Vegetation cover (how much water gets processed) Topography (flatter plane = less energy = less work) Bedrock channels are flow over igneous rock, strongly influenced by sediment, erosion is a result of chemistry from bedrock materials. Alluvial channels are flows over previously deposited sediment on valley floor, picked up sediment is moved down stream. Straight channels are few in nature where channel migration is limited, they are normally engineered. Meandering channels occur in both bedrock and alluvial channels (or ice). They have moderate stream power and meanders scale to the channel size. Braided channels are wide and shallow, flow is divided and rejoins around sediment bars. Therefore, they require an abundant supply of sediment and unstable banks.
