Exam 1 Flashcards

Question

How do you read a hydrograph?

Answer 1

X-axis: Time Y-axis: Discharge/ stage Line: The response of the stream to excess water

Answer 2

The height of water in a river relative to a defined zero point.

Answer 3

RI = (N+1)/M (N = number of years of data, M = rank of flood) Probability (P) = 1/RI (ex: a 100-year flood has a 1% chance annually).

Answer 4

X-axis: Flood recurrence interval Y-axis: River stage Higher stage = rarer, larger floods.

Answer 5

Transport-limited: Sediment available but slow transport. Supply-limited: Little sediment available despite high transport capacity.

Answer 6

Alluvial streams: Flow through loose sediment, constantly reshape. Bedrock streams: Flow over rock, erosion is slower.

Answer 7

They adjust width, depth, and slope to balance sediment transport and water discharge.

Answer 8

Resistant bedrock prevents easy erosion.

Answer 9

Steep slopes, powerful floods, high erosion forces, limited sediment storage.

Answer 10

Width & depth increase, gradient decreases, velocity stabilizes.

Answer 11

Driving: Discharge (Q), slope (So . Resisting: Sediment size, vegetation, channel boundary resistance.

Answer 12

Abrasion, plucking, hydraulic action.

Answer 13

Soft rock: Wide, meandering. Hard rock: Narrow, steep.

Answer 14

Smooth concave shape in alluvial streams. Energy In = Energy Out (balance between erosion & deposition).

Answer 15

Abrupt changes in slope (e.g., waterfalls), often due to rock type changes.

Answer 16

Force of water on the bed that moves sediment.

Answer 17

Discharge (Q), channel shape, slope, resistance from sediment.

Answer 18

Creates steep gradients, increasing erosion.

Answer 19

Harder materials slow erosion.

Answer 20

Dissolved load, suspended load, bedload.

Answer 21

Median grain size (50% of particles are smaller).

Answer 22

Driving: Slope, discharge. Resisting: Bedrock hardness, sediment cohesion.

Answer 23

Larger area = more water Larger grain size = harder to move.

Answer 24

Inputs: Precipitation, erosion. Outputs: Discharge, sediment transport

Answer 25

Entrainment, rolling, bouncing, suspension. Hjulstrom’s Curve shows sediment transport thresholds.

Answer 26

R = cross-sectional area / wetted perimeter. High R → easier transport.

Answer 27

Balance between erosion, transport, and deposition.

Answer 28

Predict soil behavior for construction, agriculture, etc.

Answer 29

Texture: Sand, silt, clay mix. Angle of repose: Maximum stable slope.

Answer 30

Increases weight, reduces friction, adds cohesion.

Answer 31

Stress = force/area, Strain = deformation.

Answer 32

Increased pore pressure weakens soil.

Answer 33

Well-graded (mixed sizes) is stronger than uniformly graded.

Answer 34

Define soil behavior at different moisture levels.

Answer 35

Gravity-driven downslope movement of earth materials.

Answer 36

Heavy rain, earthquakes, deforestation, overloading slopes.

Answer 37

Creep, slide, slump, earthflow, debris flow.

Answer 38

Drainage control, slope reinforcement, reforestation.

Answer 39

Increase runoff, disrupt natural drainage, trigger landslides.

Answer 40

Energy loss due to eddy viscosity is generally larger than that caused by innate (molecular) viscosity because turbulence at larger scales dissipates energy more efficiently than molecular interactions. Eddy viscosity dominates in high Reynolds number flows, while innate viscosity is significant in low Reynolds number flows.

Answer 41

Forces resisting entrainment include gravity, friction, and cohesion, while forces favoring entrainment include drag, lift, and buoyancy. Drag pushes grains downstream due to flow velocity, lift reduces normal forces through pressure differences, and buoyancy reduces the effective weight of the grain in water.

Answer 42

Shear stress is directly proportional to the rate of velocity change above the streambed, as described by the equation 𝜏= 𝜌𝑢∗^2, where 𝜏 (tau) is shear stress, 𝜌 (row) is fluid density, and 𝑢∗ is shear velocity. Greater velocity gradients near the bed result in higher shear stress, promoting sediment transport.

Answer 43

The Shields Diagram is used instead of Hjulstrom’s because it accounts for dimensionless variables that apply across different flow conditions and grain sizes. It relates the Shields parameter (𝜏∗) to the Reynolds number of the grain, considering factors like grain size, density, and shear stress for more accurate sediment transport predictions.

Answer 44

Floods entrain sediment when shear stress from flowing water overcomes resisting forces like gravity and cohesion, moving particles through rolling, saltation, or suspension. Hjulstrom’s Curve shows the velocities needed to erode, transport, and deposit different sediment sizes. Medium sand is the easiest to move because it lacks cohesion but is light enough to be lifted. Clays are hard to mobilize due to strong electrostatic cohesion, requiring higher velocities for erosion despite their small size.

Answer 45

Width (𝑤), depth (ℎ), and velocity (𝑢) are codependent because discharge (𝑄 = 𝑤 ⋅ ℎ ⋅ 𝑢) must remain balanced; when one variable changes, the others adjust to maintain equilibrium. For example, if depth decreases due to sediment deposition, velocity may increase to maintain discharge, preventing excessive widening or deepening of the stream.

Answer 46

Stress: Compression – Forces push inward, shortening and thickening the material. Tension – Forces pull outward, stretching and thinning the material. Shear – Forces act parallel but in opposite directions, causing distortion. Strain: Elastic strain – Temporary deformation that reverses when stress is removed. Plastic strain – Permanent deformation that does not return to the original shape. Fracture (brittle strain) – The material breaks under stress.

Answer 47

Shear strength is crucial because it determines the stability of slopes, foundations, and structures by resisting failure under stress. Understanding it helps engineers design safe embankments, retaining walls, and foundations to prevent landslides and collapses.

Answer 48

The yield point is the stress level at which a material transitions from elastic deformation to plastic deformation, meaning it will no longer return to its original shape when stress is removed. The rupture point is the stress level at which the material breaks or fractures, marking the failure of the material.

Answer 49

Stress axes s1, s2, and s3 represent the principal stresses in a material, with s1 being the maximum compressive stress, s2the intermediate stress, and s3 the minimum stress. These axes describe the orientation and magnitude of stress in a material, with each axis representing the direction in which the material experiences a specific stress (either compression, tension, or shear).

Answer 50

Shear stress develops in solid bodies when there is a combination of normal stresses (compressive or tensile) and differential stress (a difference between principal stresses). When two normal stresses are different in magnitude (shear stress is generated along planes oriented at 45° to the principal stress axes.

Answer 51

Normal stress (𝜎) is the force exerted per unit area perpendicular to a surface, either compressive (pushing inward) or tensile (pulling outward). It acts normal (or at a right angle) to the surface.

Answer 52

Soil is a naturally occurring, loose mixture of mineral particles, organic matter, water, and air, capable of supporting plant life and providing a habitat for organisms.

Answer 53

C: Climate L: Organisms (including plants and animals) O: Relief (topography) R: Parent material P: Time

Answer 54

Climate (C): Affects weathering rates, moisture, and temperature, influencing soil formation and properties. Organisms (L): Plants, animals, and microorganisms contribute organic matter and influence nutrient cycling. Relief (O): Slope and elevation affect water drainage, erosion, and accumulation of materials Parent material (R): The mineral composition of the original material from which soil forms affects soil texture and mineral content. Time (P): Soil formation takes time, with older soils often being more developed and having more horizons than younger soils.

Answer 55

O Horizon: Organic layer, composed mainly of decomposed plant material and organic matter. A Horizon: Topsoil, a mix of organic material and mineral particles, supporting plant life. E Horizon: Eluviation (leaching) layer, where materials like clay and minerals are washed out. B Horizon: Subsoil, where materials leached from the above layers accumulate (illuviation). C Horizon: Weathered parent material, consisting of partially disintegrated bedrock or unconsolidated material. R Horizon: Bedrock, the unweathered base material beneath the soil.

Answer 56

Saprolite is a weathered, soft, and partially disintegrated bedrock, often rich in clay minerals. It differs from soil because it lacks significant organic matter and has less biological activity. It differs from bedrock because it has undergone weathering but has not yet been broken down into fully formed soil.

Answer 57

Sand (0.05 – 2.0 mm) Silt (0.002 – 0.05 mm) Clay (less than 0.002 mm

Answer 58

Soils can be acidic due to the presence of hydrogen ions (H⁺), often resulting from the weathering of minerals, especially those containing calcium, potassium, or sodium. Acidic soils are also linked to organic acids from plant decay and microbial activity.

Answer 59

Clays are referred to as secondary minerals because they form as a result of weathering and alteration of primary minerals (like feldspar or granite) over time.

Answer 60

1:1 clays (e.g., kaolinite) have one tetrahedral layer and one octahedral layer. They are stable, non-expanding, and have low cation exchange capacity (CEC). 2:1 clays (e.g., smectite) have two tetrahedral layers and one octahedral layer. They can expand and contract, have higher CEC, and are more reactive.

Answer 61

Kaolinite does not expand or contract significantly when wetted and dried, remaining stable. Smectite expands when wetted and shrinks when dried, leading to changes in volume and structure.

Answer 62

Cations are attracted to clay surfaces due to the negatively charged sites on the clay particles (often from the isomorphous substitution of cations in the clay mineral structure), which attract positively charged ions like calcium (Ca²⁺).

Answer 63

Clay content: The higher the clay content, the greater the surface area for cation exchange. Organic matter: Organic particles, especially humus, have many negatively charged sites that increase cation exchange capacity.

Answer 64

Vertisols are clay-rich soils that expand when wet and shrink when dry, causing cracks to form. They typically form in areas with pronounced wet and dry seasons, where the alternating moisture content leads to swelling and shrinking of the clay particles.

Answer 65

Vertisols "churn" due to the expansion and contraction of clay minerals with moisture changes, causing the soil to shift and form small, uneven mounds and depressions. This is related to gilgai, which are small, irregular surface features (micro-relief) created by the swelling and shrinking of these soils.

Exam 1 Flashcards

Im anxious so a lot of the card definitions are taken from this quizlet: https://quizlet.com/187042100/geomorphology-3300-exam-1-flash-cards/?i=4a1e89&x=1jqt (89 cards)