Module 5: Morphology, Facets, Ratios, and Stream Classification Iowa’s River Restoration Toolbox Level 1 / Base Training

Fluvial geomorphology Defines common forms of streams in plan, profile, and cross section Describes processes (driven by flow regimes, lithology, sediment supply, land-use change, etc.) that influence channels and floodplains. Fosters understanding that helps project work with, not against, the stream Morphology, more simply, refers to the shape of a river from three views: Plan, profile, and dimension

Valley Types Confined valleys result in lower sinuosity, step-pool channel formations, often with somewhat higher bed slopes. Unconfined valleys result in higher sinuosity, alluvial channel formation lower slopes Images from USDA Technical Supplement 3E, Rosgen Stream Classification Technique

Valley Length, Width, Slope Length is “Big Picture” or “Crow Flies” alignment, not including meanders. Width of the valley is where the stream’s boundaries occur, usually the edges of it’s meanders. These dimensions derive from geological factors, such as faults, bedrock, glaciation, ancient lakebeds, etc. They also derive from recent geomorphology history, such as abandonment of a terrace.

Stream Order Two of same order joined makes next highest order Density affected by annual rainfall and geology Affects applicability of reference reaches

Pattern measurements Point of Tangency (Pt) Belt Width (Wblt) Point of Curvature (Pc) Arc Length Channel Distance is on Centerline (Ch) Radius of Curvature (Rc) Amplitude (Am) Linear Wave Length (λ) Meander Length (Lm)

Sinuosity = Sinuosity Channel Distance Down Valley Length Channel is on Centerline (Ch) Down Valley Length Ratio value always greater than 1 Channel Distance = Sinuosity Down Valley Length

Thalweg Thalweg is the energy gradient water of the stream. Channel Distance is on Centerline (Ch) Thalweg is the energy gradient water of the stream. Survey the deepest point in the cross section. Do not use Thalweg for stationing! It’s inconsistent. Thalweg (Tw)

Facet Terminology Step-pool system Alluvial System Step (riffle) flow Step-pool system Step (riffle) Pool (scour pool) flow Alluvial System Point bar Riffle Run Glide Pool

Facets in the Longitudinal Profile Riffle Pool Glide Run Bankfull Slope Low Bank Height Degree of Incision Wedge

Slope… … is the ratio of fall over distance of stream Calculations are most accurate using water surface(WS) slope from facet to facet Bed slope (aka energy slope) goes from top of glide to top of glide BKF Slope=.00233 Elevation (feet) WS Slope=.00238 Bed slope = .00239 Distance (feet) Bankfull (BKF) slope is taken from field-observed calls All three slopes should be roughly parallel in a stable stream.

Cross sectional area Rivers and streams vary in width and depth. Pools tend to be deep and wide. The riffles tend to be the narrowest and shallowest. It is important to run hydrologic calculations at the riffle(s), because it is the “pinch point” for flow at bankfull. Pool (outside bend) Riffle (straightaway) Bankfull Typical riffle XS Typical pool XS

Cross sections Measured perpendicular to bankfull flow path / valley Defines the flow path, and cross sectional area of water at various depths Important for calculations, design, permitting Important for categorizing streams into “like” groupings Low terrace Low terrace Bankfull

The multi-stage channel Critical stages to investigate are: Base flow (depth maintained for habitat in draught) Inner berm (important for base depth and sediment transport) Bankfull floodplain (critical to dissipate shear stress through vegetation) Broad floodplain (for the “really big” floods, 50-year+)

Why all this focus on bankfull stage? Radically reduces shear stress per unit of discharge at a key moment for stability. Defines difference between “channel” and “floodplain” Consistent discharge at which to aggregate data (i.e. “normalizing factor” Useful bodies of work (regional curves, classifications, etc.) are already built around bankfull stage

Hydrologic models Can be useful to look in office prior to field work to calibrate. Iowa Flood Center’s IFIS tool has 2-year versus 50-year inundations maps for larger streams Upper Iowa River, Below Lower Dam

Inner berms In rain-driven systems (i.e. Iowa), sometimes confused with BKF because can form vegetated flats Iowa Flood Center’s IFIS tool has 2-year versus 50-year inundations maps for larger streams Bankfull Inner berm

Inner berms More prominent in lower drainage area streams (see Thomas Gardy paper) Shape has implications for sediment transport and base flow depths Note vegetated low flat well below Qbkf in this urban Des Moines stream

Why classify streams? To keep fewer numbers and words in your head at once To better understand stable ranges for a given type To study processes that lead to form To better apply design Better communication

Entrenchment ratio Width of River’s Floodprone Valley Width of Bankfull Channel at the Riffle Floodprone Width is the width of the valley at an elevation at double the Max BKF Depth Wfp is sometimes said to approximate the 50-yr flood stage, (i.e., A Really Big Flood)

Entrenchment ratio Mathematical expression of how much floodplain a stream can access. For example, the stream to the right does not access a floodplain at BKF discharge.

Width/Depth ratio Width of River’s Bankfull Channel at the Riffle Mean Bankfull Depth at the Riffle

Width/Depth ratio Expresses how shallow or deep a channel is at BKF discharge. Low ratio indicates a deeper, narrower channel. High ratio indicates a shallower, wider channel

BKF Width / Mean BKF Depth Classifying streams Classification A B C E DA D F G Entrenchment ratio* <1.4 1.4 -2.2 >2.2 >4.0 n/a FP width / BKF Width BKF Width / Mean BKF Depth W / D ratio* <12 >12 <40 >40 Typical sinuosity 1 -1.2 >1.2 >1.5 Not predictive Well-defined point bars Veg. islands Heavy veg. Both banks erode in wide dirt canyon Confined, u-shaped valley Often bedrock / log controlled Visual Cues Gully in soft materials Sed. islands Typical slope .04-.099 .02-.039 <.02 <.005 <.04 Typical stability Usually Stable Likely Unstable Classifications from Rosgen, 1996

“B” Channels “A” Channels Often somewhat steep U-shaped channel Skinny floodplains Tend to be riffle dominated “A” Channels Steep rocky channels Most often controlled by bedrock or logs

“C” Channels Broad floodplains Point bars on inside bends Moderately sinuous

“E” Channels Easy access to broad floodplains Tight, deep channel point bars on inside bends Extremely sinuous

“DA” Channels Steady high sediment supply Vegetated islands promote braided channels with power to transport sediment, leading to a steady- state Deltas into impoundments

“D” Channels High sediment supply Aggrading channel due to overwide conditions Braided channels through unvegetated islands

“F” Channels Widening channel Entrenched; no BKF floodplain connection Channel bottoms often very uniform fine sediments in Iowa

Photo from John Thomas, Hungry Canyons Alliance “G” Channels Gully channel Bed degrading, plainly seen by knick points / head cutting Highly entrenched Photo from John Thomas, Hungry Canyons Alliance

Categorize materials with pebble counts Randomly select a particle from a stream through a reach Measure medial diameter and record Repeat 99 more times Determine the size that 50 percent of the samples are small than. This is your “D50” Medial diameter is along the intermediate access. It is the limiting dimension preventing it from fitting through a sieve.

Classification with bed types Use pebble count to statistically determine D50 (meaning, 50 is percent finer than that width) Bed number is assigned, and combined with stream type to quickly convey channel shape, floodplain connectivity, and dominant materials Bed # Materials Category Diameter range (mm) 1 Bedrock N/A 2 Boulder 256-2048 3 Cobble 64-256 4 Gravel 2-64 5 Sand .062 to 2 6 Silt/Clay <.062

Examples of meanings inferred B3: Moderately entrenched step pool stream with cobble bed C4: High width/depth ratio stream with good access to floodplain, likely sinuous with point bars E6: A deep, narrow stream with a bed, cohesive silt-clay bed, plenty of access to a floodplain, probably heavily vegetated