Hydrology and Karst Geomorphology: Key Concepts and Formulas

Channel Discharge (Q)

velocity × cross-sectional area (Q = Av)

Wetted Perimeter

length of channel bed + banks in contact with water

Hydraulic Radius (R)

cross-sectional area ÷ wetted perimeter

Chezy Formula

v = C(Rs)^1/2

Manning's Formula

v = (1/n) R^(2/3) s^(1/2)

Laminar Flow

smooth, parallel flow (Re < 500)

Turbulent Flow

chaotic mixing flow (Re > 2000)

Reynolds Number

predicts flow type based on velocity, density, viscosity, hydraulic radius

Direct Precipitation

rainfall falling directly into streams

Interception

vegetation captures rainfall (through-fall + stemflow)

Infiltration

water entering soil; depends on texture and moisture

Runoff Equation

runoff = precipitation - interception - storage - infiltration

Runoff Channelization

sheetflow → rills → gullies → streams

Hydrograph

graph of stream discharge vs. time

Drainage Basin

area draining water to a stream, bounded by divides

Morphometry

quantitative analysis of drainage basin form

Fluvial Erosion Types

hydraulic action, abrasion, plucking, cavitation, corrosion

Hjulstrom Curve

velocity needed to erode, transport, or deposit sediment

Suspended Load

fine particles carried within water

Bed Load / Traction

coarse particles rolling/sliding along the bed

Dissolved Load

material carried in solution

Stream Competence

largest particle size a stream can transport

Stream Capacity

total amount of sediment a stream can transport

Meandering Stream

low gradient, fine sediment, produces meanders and oxbows

Sinuosity

stream length ÷ valley length

Thalweg

deepest and fastest part of a channel

Point Bar

deposition on inside of meander bend

Riffle-Pool Sequence

alternating shallow and deep channel segments

Braided Stream

multiple shifting channels with high sediment load

Anastomosing Stream

multiple stable, deep channels separated by cohesive sediment

Floodplain

flat surface beside river formed by flood deposition

Stream Terraces

old floodplains left above river after downcutting

Alluvial Fan

cone-shaped deposit where stream exits uplands

Delta

deposit formed where river enters standing water and velocity drops

Karst

terrain formed by dissolution of soluble rocks, usually limestone

Karst Characteristics

closed depressions, thin soils, lack of surface drainage, underground conduits

Karst Solution Chemistry

CaCO3 + H2O + CO2 ↔ Ca²⁺ + 2HCO3⁻

Karst Controls (Climate)

warm, humid climates promote dissolution

Karst Controls (Lithology)

thick, pure limestone dissolves most readily

Karst Controls (Structure)

joints, fractures, permeability, porosity enhance dissolution

Porosity

percent of void space in rock

Permeability

ease of water flow through rock

Sinkhole (Doline)

closed depression formed by solution or collapse

Solution Sinkhole

formed by dissolving rock

Collapse Sinkhole

formed when roof of subsurface cavity collapses

Uvala

large irregular closed depression formed by merging sinkholes

Cockpit Karst

star-shaped depressions, common in Jamaica

Tower Karst

steep limestone towers left after surrounding rock dissolves

Clints and Grikes

blocks (clints) and fissures (grikes) on limestone pavement

Swallow Hole

stream disappears underground

Dry Valley

valley lacking surface stream due to underground drainage

Stalactite

cave deposit hanging from ceiling

Stalagmite

cave deposit growing upward from floor

Extent of Glaciation (Current)

~10% of land surface

Extent of Glaciation (Ice Age Max)

~32% of land surface

Snow Density

0.1-0.2 g/cm³

Firn Density

0.4-0.8 g/cm³

Glacial Ice Density

>0.8 g/cm³

Mass Balance

accumulation minus ablation

Firn Line

boundary between accumulation zone and ablation zone

Bergschrund

crevasse at head of glacier

Plastic Flow

ice deformation when thickness > 40-60 m

Basal Sliding

glacier sliding over bed due to pressure melting and regelation

Wave Velocity

wavelength ÷ period (L/T)

Wave Energy

E = 1/8 (ρ g H²)

Wave Height Controls

wind strength, duration, fetch

Wave Shoaling

waves slow, shorten, and steepen in shallow water

Breaking Waves

form surf zone, swash, backwash

Wave Refraction

bending of waves focusing energy on headlands

Wave-Cut Platform

flat erosional bench at base of cliff

Sea Cave

wave-eroded opening in cliff

Sea Arch

opening through headland formed by erosion

Sea Stack

pillar left after collapse of sea arch

Sea Cliff

steep coastal slope formed by wave erosion