Fluvial Geomorphology Ecological Perspective (1) Sediment size distribution (2) Channel Form X-sec Planform Basin Downstream changes Drainage pattern Channel size (3) Sediment movement Distance Elevation

Fluvial Geomorphology Definition: Fluvial --> “Of or found near a river” Geomorpholgy --> study of Earth’s physical features There is a dynamic balance between Flow regime (Q) Sediment regime (Qs) Maintains the shape of the channel What happens if Q >> Qs?? Depends on ‘transport capacity’ of channel (function of how steep channel slope is)

Fluvial Geomorphology Water moves sediment during higher flows Sediment gets stored during lower flows Movement and Storage From Ecological Perspective (1) Sediment size distribution (2) Channel Form (3) Sediment movement Habitat Structure Habitat Dynamics

(1) SEDIMENT SIZE Wentworth Scale (Table 3.1) Particle size names: Boulder, Cobble, Pebble, Gravel, Sand, Silt, Clay Phi (f) value is -log2 scale for particle size from Boulder (< -8) to silt > 5

(2) CHANNEL FORM or MORPHOLOGY 3 ways to view Channel Form Cross-section of stream (local or transect scale) Planform (reach scale) Longitudinal (whole basin) Controls on channel geometry Discharge Bed mobility Bank stability Can you think of factors that influence these?

(2) CHANNEL FORM or MORPHOLOGY A) View#1: Cross-section Channel geometry Width, average depth, wetted perimeter Channel occurs in valley Floodplain Terrace Hillslope

B) View #2: Planform Channel geometry: At “Reach Scale”: ~20 x channel width Channel geometry: average Width average Depth Gradient or Slope (S) S = Dy/ Dx = drop in elevation with distance Sinuosity = channel (thalweg) length / downvalley length [draw on board] number of channels, etc.

4 channel types defined at reach scale, based on 3 features Number of channels Channel stability Sinuosity photo: S. Hillebrand. U.S. Fish & Wildlife Service Digital Library System http://images.fws.gov/ single channel types Straight (Sinuosity << 1.5) Meandering (Sinuosity > 1.5)

multiple channel types Braided Qs >> Q … channels unstable, move during floods Anastomosing / Anabranching Cohesive banks. … channels stable, don’t move photo: © Michael Collier. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images, photo ixvt9i

How do meanders form? Differential erosion Cut off At a point in time Movement through time Cut off

Meander scaling laws

Sine curves (meanders) represent the most uniform distribution of change of energy dissipation along a curve. From Leopold (1994, A View of the River)

C) View#3: Whole Basin scale Perspective of Downstream Changes in … Discharge Stream gradient Sediment grain-size Influence of riparian Distance Elevation outlet max source High gradient Width Depth Velocity (why?) Low gradient

More scaling relations (Fig.3.3 text) Low order High order W What changes fastest downstream? D Is average velocity greater in large river than in small stream? U

Perspective of Drainage Pattern Reflect geology mostly

Channel Classification at whole basin scale 2 Classifications (Fig. 2.1 Knighton): Horton/Strahler (1945, 1952) - Stream Order Shreve (1967) - Link Order For point X, what is: stream order? link order? X

Scaling Relations (Fig. 2.1 Knighton)